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Fenwick JD, Kumar S, Pardo-Montero J. Collection efficiencies of cylindrical and plane parallel ionization chambers: analytical and numerical results and implications for experimentally determined correction factors. Phys Med Biol 2024; 69:155023. [PMID: 39013400 DOI: 10.1088/1361-6560/ad63ed] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 07/16/2024] [Indexed: 07/18/2024]
Abstract
Objectives.To derive a collection efficiency formula,fGauss, for cylindrical ionization chambers in pulsed radiation beams from a volume recombination model of Boaget al(1996Phys. Med. Biol.41885-97) including free electrons. To validatefGaussand a parallel plate chamber formulafexpusing an ion transport code and calculate changes in collection efficiencies caused by electric field charge screening at 0.1-100 mGy doses-per-pulse. And to determine collection efficienciesCE∞predicted at infinite voltage in the absence of avalanche effects by fitting scaled formulae to efficiencies computed for 100-400 V chamber voltages and 10 and 100 mGy doses-per-pulse.Approach.Calculations were performed for an idealized parallel plate chamber with 2 mm electrode separationd, and for an idealized cylindrical chamber with 0.5 and 2.333 mm inner and electrode radiirinandrout.Main results.fGaussandfexppredict the same collection efficiencies for cylindrical and parallel plate chambers satisfyingd2=(rout2-rin2)ln(rout/rin)/2, an equivalence condition met by the chambers studied. Without charge screening, efficiencies computed using the code equalledfGaussandfexp. With screening, efficiencies changed by ⩽0.03%, ⩽1.1% and ⩽21.3% at 1, 10 and 100 mGy doses-per-pulse, and differed between the chambers by ⩽0.9% and ⩽19.6% at ⩽10 and 100 mGy dose-per-pulse. For fits offexpandfGauss,CE∞values were ⩽1.2% and ⩽17.6% from unity at 10 and 100 mGy per pulse respectively, closer than for other formulae tested.Significance.Allowing for screening,fGaussandfexpdescribed computed collection efficiencies to within 0.03%, 1.1% and 21.3% at doses-per-pulse ⩽1, 10 and 100 mGy. Equivalence of the two chambers broke down at 100 mGy per pulse. Departures ofCE∞values from unity suggest that collection efficiencies determined experimentally by fittingfGaussorfexpto readings made at multiple voltages will be accurate to within 1.2% and 17.6% at 10 and 100 mGy per pulse respectively.
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Affiliation(s)
- John D Fenwick
- Department of Medical Physics and Bioengineering, 8th Floor, Malet Place Engineering Building, University College London, Gower Street, London WC1E 6BT, England, United Kingdom
| | - Sudhir Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CT & CRS Building, Anushaktinagar, Mumbai 400094, India
| | - Juan Pardo-Montero
- Group of Medical Physics and Biomathematics, Instituto de Investigación Sanitaria de Santiago (IDIS), 15706 Santiago de Compostela, Spain
- Department of Medical Physics, Complexo Hospitalario Universitario de Santiago de Compostela, 15706 Santiago de Compostela, Spain
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Subiel A, Bourgouin A, Kranzer R, Peier P, Frei F, Gomez F, Knyziak A, Fleta C, Bailat C, Schüller A. Metrology for advanced radiotherapy using particle beams with ultra-high dose rates. Phys Med Biol 2024; 69:14TR01. [PMID: 38830362 DOI: 10.1088/1361-6560/ad539d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 06/03/2024] [Indexed: 06/05/2024]
Abstract
Dosimetry of ultra-high dose rate beams is one of the critical components which is required for safe implementation of FLASH radiotherapy (RT) into clinical practice. In the past years several national and international programmes have emerged with the aim to address some of the needs that are required for translation of this modality to clinics. These involve the establishment of dosimetry standards as well as the validation of protocols and dosimetry procedures. This review provides an overview of recent developments in the field of dosimetry for FLASH RT, with particular focus on primary and secondary standard instruments, and provides a brief outlook on the future work which is required to enable clinical implementation of FLASH RT.
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Affiliation(s)
- Anna Subiel
- National Physical Laboratory, Hampton Road, Teddington TW11 0LW, United Kingdom
- University College London, Gower Street, London WC1E 6BT, United Kingdom
| | - Alexandra Bourgouin
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
- National Research Council of Canada (NRC), 1200 Montreal Road, Ottawa, ON, K1A0R6, Canada
| | | | - Peter Peier
- Federal Institute of Metrology METAS, Lindenweg 50, 3003 Bern-Wabern, Switzerland
| | - Franziska Frei
- Federal Institute of Metrology METAS, Lindenweg 50, 3003 Bern-Wabern, Switzerland
| | - Faustino Gomez
- University of Santiago de Compostela, 15782 Santiago de Compostela, Spain
| | - Adrian Knyziak
- Central Office of Measures (GUM), Elektoralna 2 Str., 00-139 Warsaw, Poland
| | - Celeste Fleta
- Instituto de Microelectrónica de Barcelona, Centro Nacional de Microelectrónica, IMB-CNM (CSIC), Barcelona, Spain
| | - Claude Bailat
- Institute of Radiation Physics, Lausanne University Hospital and University of Lausanne, Lausanne, Switzerland
| | - Andreas Schüller
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
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Claessens M, Vanreusel V, Gasparini A, Nascimento LDF, Yalvec B, Reniers B, Verellen D. Automated determination of the ion-recombination correction factor (k sat) in ultra-high dose rate electron radiation therapy. Med Phys 2024; 51:4536-4545. [PMID: 38639653 DOI: 10.1002/mp.17085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2023] [Revised: 03/06/2024] [Accepted: 03/13/2024] [Indexed: 04/20/2024] Open
Abstract
BACKGROUND Plane-parallel ionization chambers are the recommended secondary standard systems for clinical reference dosimetry of electrons. Dosimetry in high dose rate and dose-per-pulse (DPP) is challenging as ionization chambers are subject to ion recombination, especially when dose rate and/or DPP is increased beyond the range of conventional radiotherapy. The lack of universally accepted models for correction of ion recombination in UDHR is still an issue as it is, especially in FLASH-RT research, which is crucial in order to be able to accurately measure the dose for a wide range of dose rates and DPPs. PURPOSE The objective of this study was to show the feasibility of developing an Artificial Intelligence model to predict the ion-recombination factor-ksat for a plane-parallel Advanced Markus ionization chamber for conventional and ultra-high dose rate electron beams based on machine parameters. In addition, the predicted ksat of the AI model was compared with the current applied analytical models for this correction factor. METHODS A total number of 425 measurements was collected with a balanced variety in machine parameter settings. The specific ksat values were determined by dividing the output of the reference dosimeter (optically stimulated luminescence [OSL]) by the output of the AM chamber. Subsequently, a XGBoost regression model was trained, which used the different machine parameters as input features and the corresponding ksat value as output. The prediction accuracy of this regression model was characterized by R2-coefficient of determination, mean absolute error and root mean squared error. In addition, the model was compared with the Two-Voltage (TVA) method and empirical Petersson model for 19 different dose-per-pulse values ranging from conventional to UDHR regimes. The Akiake Information criterion (AIC) was calculated for the three different models. RESULTS The XGBoost regression model reached a R2-score of 0.94 on the independent test set with a MAE of 0.067 and RMSE of 0.106. For the additional 19 random data points, the ksat values predicted by the XGBoost model showed to be in agreement, within the uncertainties, with the ones determined by the Petersson model and better than the TVA method for doses per pulse >3.5 Gy with a maximum deviation from the ground truth of 14.2%, 16.7%, and -36.0%, respectively, for DPP >4 Gy. CONCLUSION The proposed method of using AI for ksat determination displays efficiency. For the investigated DPPs, the ksat values obtained with the XGBoost model were in concurrence with the ones obtained with the current available analytical models within the boundaries of uncertainty, certainly for the DPP characterizing UDHR. But the overall performance of the AI model, taking the number of free parameters into account, lacked efficiency. Future research should optimize the determination of the experimental ksat, and investigate the determination the ksat for DPPs higher than the ones investigated in this study, while also evaluating the prediction of the proposed XGBoost model for UDHR machines of different centers.
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Affiliation(s)
- Michaël Claessens
- Department of Radiation Oncology, Iridium Netwerk, Wilrijk, Antwerp, Belgium
- Centre for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Antwerp, Belgium
| | - Verdi Vanreusel
- Department of Radiation Oncology, Iridium Netwerk, Wilrijk, Antwerp, Belgium
- Centre for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Antwerp, Belgium
- Research in Dosimetric Applications (RDA), SCK CEN, Mol, Antwerp, Belgium
| | - Alessia Gasparini
- Department of Radiation Oncology, Iridium Netwerk, Wilrijk, Antwerp, Belgium
- Centre for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Antwerp, Belgium
| | | | - Burak Yalvec
- NuTeC, CMK, Hasselt University, Hasselt, Belgium
| | | | - Dirk Verellen
- Department of Radiation Oncology, Iridium Netwerk, Wilrijk, Antwerp, Belgium
- Centre for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp, Antwerp, Belgium
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Bancheri J, Seuntjens J. A semi-analytical procedure to determine the ion recombination correction factor in high dose-per-pulse beams. Med Phys 2024; 51:4458-4471. [PMID: 38446555 DOI: 10.1002/mp.17005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 02/08/2024] [Accepted: 02/13/2024] [Indexed: 03/08/2024] Open
Abstract
BACKGROUND The conventional theories and methods of determining the ion recombination correction factor, such as Boag theory and the related two voltage method and Jaffé plot extrapolation, do not seem to yield accurate results in FLASH /high dose per pulse (DPP) beams ( > $>$ 10 mGy DPP). This is due to the presence of a large free electron fraction that distorts the electric field inside the chamber sensitive volume. To understand the influence of these effects on the ion recombination correction factor and to develop new expressions for it, it is necessary to re-visit the underlying physics. PURPOSE To present a mathematical procedure to develop an analytical expression for the ion recombination correction factor. The expression is the basis for an extrapolation method so the correction factor can be determined in a clinical setting. METHODS A semi-analytical solution method, the homotopy perturbation method (HPM), is used to solve the partial differential equations (PDEs) describing the charge carrier physics, including space charge and free electrons. The electron velocity and attachment rate are modeled as functions of the electric field strength. An expression for the charge collection efficiency and ion recombination correction factor are developed. A fit procedure based on this expression is used to compare it to measured data from previously published articles. Another fit procedure using a general equation is also proposed and compared to the data. RESULTS The series obtained for the charge collection efficiency and the ion recombination correction factor are determined to be asymptotic series and the optimal truncation established. The ion recombination correction factor exhibits a1 / V 2 $1/V^2$ dependency due to the free electron presence. The fit using this expression agrees well with measured data as long as (1) the DPP is below 1 Gy for chambers with a 1 mm plate separation and (2) when the DPP is below 3 Gy for chambers with a 0.5 mm plate separation. In these DPP ranges, the deviation between measured and fit value did not exceed 6%. In both chamber cases the voltage range where the fit applies decreases as DPP increases. The general equation yielded comparable results. CONCLUSIONS The HPM was shown to be applicable to a complex system of PDEs and generate meaningful and novel solutions, as they include both space charge and free electrons. The HPM also lends itself to other chamber geometries. The fit procedure was also shown to yield accurate results for the ion recombination correction up to the 1 Gy DPP level.
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Affiliation(s)
- Julien Bancheri
- Department of Physics & Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | - Jan Seuntjens
- Princess Margaret Cancer Centre, Radiation Medicine Program, University Health Network, Department of Medical Biophysics, University of Toronto, Toronto, Canada
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Milluzzo G, De Napoli M, Di Martino F, Amato A, Del Sarto D, D'Oca MC, Marrale M, Masturzo L, Medina E, Okpuwe C, Pensavalle JH, Vignati A, Camarda M, Romano F. Comprehensive dosimetric characterization of novel silicon carbide detectors with UHDR electron beams for FLASH radiotherapy. Med Phys 2024. [PMID: 38772134 DOI: 10.1002/mp.17172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2023] [Revised: 04/26/2024] [Accepted: 04/27/2024] [Indexed: 05/23/2024] Open
Abstract
BACKGROUND The extremely fast delivery of doses with ultra high dose rate (UHDR) beams necessitates the investigation of novel approaches for real-time dosimetry and beam monitoring. This aspect is fundamental in the perspective of the clinical application of FLASH radiotherapy (FLASH-RT), as conventional dosimeters tend to saturate at such extreme dose rates. PURPOSE This study aims to experimentally characterize newly developed silicon carbide (SiC) detectors of various active volumes at UHDRs and systematically assesses their response to establish their suitability for dosimetry in FLASH-RT. METHODS SiC PiN junction detectors, recently realized and provided by STLab company, with different active areas (ranging from 4.5 to 10 mm2) and thicknesses (10-20 µm), were irradiated using 9 MeV UHDR pulsed electron beams accelerated by the ElectronFLASH linac at the Centro Pisano for FLASH Radiotherapy (CPFR). The linearity of the SiC response as a function of the delivered dose per pulse (DPP), which in turn corresponds to a specific instantaneous dose rate, was studied under various experimental conditions by measuring the produced charge within the SiC active layer with an electrometer. Due to the extremely high peak currents, an external customized electronic RC circuit was built and used in conjunction with the electrometer to avoid saturation. RESULTS The study revealed a linear response for the different SiC detectors employed up to 21 Gy/pulse for SiC detectors with 4.5 mm2/10 µm active area and thickness. These values correspond to a maximum instantaneous dose rate of 5.5 MGy/s and are indicative of the maximum achievable monitored DPP and instantaneous dose rate of the linac used during the measurements. CONCLUSIONS The results clearly demonstrate that the developed devices exhibit a dose-rate independent response even under extreme instantaneous dose rates and dose per pulse values. A systematic study of the SiC response was also performed as a function of the applied voltage bias, demonstrating the reliability of these dosimeters with UHDR also without any applied voltage. This demonstrates the great potential of SiC detectors for accurate dosimetry in the context of FLASH-RT.
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Affiliation(s)
- Giuliana Milluzzo
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
| | - Marzio De Napoli
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
| | - Fabio Di Martino
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Pisa, Italy
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, Pisa, Italy
- National Institute of Nuclear Physics (INFN), Pisa Division, Pisa, Italy
| | - Antonino Amato
- STLab srl, Catania, Italy
- National Institute of Nuclear Physics (INFN), Laboratori Nazionali del Sud, Catania, Italy
| | - Damiano Del Sarto
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Pisa, Italy
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, Pisa, Italy
| | - Maria Cristina D'Oca
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
- Department of Physics and Chemistry "Emilio Segrè", University of Palermo, Palermo, Italy
| | - Maurizio Marrale
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
- National Institute of Nuclear Physics (INFN), Laboratori Nazionali del Sud, Catania, Italy
| | - Luigi Masturzo
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Pisa, Italy
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, Pisa, Italy
- SIT-Sordina, Aprilia, Italy
| | - Elisabetta Medina
- Physics Department, University of Torino, Torino, Italy
- National Institute of Nuclear Physics (INFN), Torino Division, Torino, Italy
| | - Chinonso Okpuwe
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
- Physics Department, University of Catania, Catania, Italy
- Department of Physics, Federal University of Technology Owerri, Owerri, Nigeria
| | - Jake Harold Pensavalle
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Pisa, Italy
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, Pisa, Italy
- SIT-Sordina, Aprilia, Italy
| | - Anna Vignati
- Physics Department, University of Torino, Torino, Italy
- National Institute of Nuclear Physics (INFN), Torino Division, Torino, Italy
| | | | - Francesco Romano
- National Institute of Nuclear Physics (INFN), Catania Division, Catania, Italy
- Particle Therapy Research Center (PARTREC), Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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Oh K, Gallagher KJ, Hyun M, Schott D, Wisnoskie S, Lei Y, Hendley S, Wong J, Wang S, Graff B, Jenkins C, Rutar F, Ahmed M, McNeur J, Taylor J, Schmidt M, Senadheera L, Smith W, Umstadter D, Lele SM, Dai R, Jianghu (James) D, Yan Y, Su‐min Z. Initial experience with an electron FLASH research extension (FLEX) for the Clinac system. J Appl Clin Med Phys 2024; 25:e14159. [PMID: 37735808 PMCID: PMC10860433 DOI: 10.1002/acm2.14159] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 08/04/2023] [Accepted: 08/21/2023] [Indexed: 09/23/2023] Open
Abstract
PURPOSE Radiotherapy delivered at ultra-high-dose-rates (≥40 Gy/s), that is, FLASH, has the potential to effectively widen the therapeutic window and considerably improve the care of cancer patients. The underlying mechanism of the FLASH effect is not well understood, and commercial systems capable of delivering such dose rates are scarce. The purpose of this study was to perform the initial acceptance and commissioning tests of an electron FLASH research product for preclinical studies. METHODS A linear accelerator (Clinac 23EX) was modified to include a non-clinical FLASH research extension (the Clinac-FLEX system) by Varian, a Siemens Healthineers company (Palo Alto, CA) capable of delivering a 16 MeV electron beam with FLASH and conventional dose rates. The acceptance, commissioning, and dosimetric characterization of the FLEX system was performed using radiochromic film, optically stimulated luminescent dosimeters, and a plane-parallel ionization chamber. A radiation survey was conducted for which the shielding of the pre-existing vault was deemed sufficient. RESULTS The Clinac-FLEX system is capable of delivering a 16 MeV electron FLASH beam of approximately 1 Gy/pulse at isocenter and reached a maximum dose rate >3.8 Gy/pulse near the upper accessory mount on the linac gantry. The percent depth dose curves of the 16 MeV FLASH and conventional modes for the 10 × 10 cm2 applicator agreed within 0.5 mm at a range of 50% of the maximum dose. Their respective profiles agreed well in terms of flatness but deviated for field sizes >10 × 10 cm2 . The output stability of the FLASH system exhibited a dose deviation of <1%. Preliminary cell studies showed that the FLASH dose rate (180 Gy/s) had much less impact on the cell morphology of 76N breast normal cells compared to the non-FLASH dose rate (18 Gy/s), which induced large-size cells. CONCLUSION Our studies characterized the non-clinical Clinac-FLEX system as a viable solution to conduct FLASH research that could substantially increase access to ultra-high-dose-rate capabilities for scientists.
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Affiliation(s)
- Kyuhak Oh
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | | | - Megan Hyun
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | - Diane Schott
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | | | - Yu Lei
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | | | - Jeffrey Wong
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | - Shuo Wang
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | - Brendan Graff
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | | | - Frank Rutar
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | - Md Ahmed
- Varian Medical SystemsPalo AltoCaliforniaUSA
| | | | | | | | | | - Wendy Smith
- Varian Medical SystemsPalo AltoCaliforniaUSA
| | | | | | - Ran Dai
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | | | - Ying Yan
- University of Nebraska Medical CenterOmahaNebraskaUSA
| | - Zhou Su‐min
- University of Nebraska Medical CenterOmahaNebraskaUSA
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Liu K, Holmes S, Hooten B, Schüler E, Beddar S. Evaluation of ion chamber response for applications in electron FLASH radiotherapy. Med Phys 2024; 51:494-508. [PMID: 37696271 PMCID: PMC10840726 DOI: 10.1002/mp.16726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 08/08/2023] [Accepted: 08/23/2023] [Indexed: 09/13/2023] Open
Abstract
Ion chambers are required for calibration and reference dosimetry applications in radiation therapy (RT). However, exposure of ion chambers in ultra-high dose rate (UHDR) conditions pertinent to FLASH-RT leads to severe saturation and ion recombination, which limits their performance and usability. The purpose of this study was to comprehensively evaluate a set of commonly used commercially available ion chambers in RT, all with different design characteristics, and use this information to produce a prototype ion chamber with improved performance in UHDR conditions as a first step toward ion chambers specific for FLASH-RT. The Advanced Markus and Exradin A10, A26, and A20 ion chambers were evaluated. The chambers were placed in a water tank, at a depth of 2 cm, and exposed to an UHDR electron beam at different pulse repetition frequency (PRF), pulse width (PW), and pulse amplitude settings on an IntraOp Mobetron. Ion chamber responses were investigated for the various beam parameter settings to isolate their dependence on integrated dose, mean dose rate and instantaneous dose rate, dose-per-pulse (DPP), and their design features such as chamber type, bias voltage, and collection volume. Furthermore, a thin parallel-plate (TPP) prototype ion chamber with reduced collector plate separation and volume was constructed and equally evaluated as the other chambers. The charge collection efficiency of the investigated ion chambers decreased with increasing DPP, whereas the mean dose rate did not affect the response of the chambers (± 1%). The dependence of the chamber response on DPP was found to be solely related to the total dose within the pulse, and not on mean dose rate, PW, or instantaneous dose rate within the ranges investigated. The polarity correction factor (Ppol ) values of the TPP prototype, A10, and Advanced Markus chambers were found to be independent of DPP and dose rate (± 2%), while the A20 and A26 chambers yielded significantly larger variations and dependencies under the same conditions. Ion chamber performance evaluated under different irradiation conditions of an UHDR electron beam revealed a strong dependence on DPP and a negligible dependence on the mean and instantaneous dose rates. These results suggest that modifications to ion chambers design to improve their usability in UHDR beamlines should focus on minimizing DPP effects, with emphasis on optimizing the electric field strength, through the construction of smaller electrode separation and larger bias voltages. This was confirmed through the production and evaluation of a prototype ion chamber specifically designed with these characteristics.
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Affiliation(s)
- Kevin Liu
- Division of Radiation Oncology, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA
- Graduate School of Biomedical Sciences, The University of Texas, Houston, Texas, USA
| | | | | | - Emil Schüler
- Division of Radiation Oncology, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA
- Graduate School of Biomedical Sciences, The University of Texas, Houston, Texas, USA
| | - Sam Beddar
- Division of Radiation Oncology, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA
- Graduate School of Biomedical Sciences, The University of Texas, Houston, Texas, USA
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Bourgouin A, Paz-Martín J, Gedik YC, Frei F, Peier P, Rossomme S, Schönfeld AA, Schüller A, Rodriguez FG, Kapsch RP. Charge collection efficiency of commercially available parallel-plate ionisation chambers in ultra-high dose-per-pulse electron beams. Phys Med Biol 2023; 68:235002. [PMID: 37934049 DOI: 10.1088/1361-6560/ad0a58] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2023] [Accepted: 11/07/2023] [Indexed: 11/08/2023]
Abstract
Objective. This investigation aims to experimentally determine the charge collection efficiency (CCE) of six commercially available parallel-plate ionisation chamber (PPIC) models in ultra-high dose-per-pulse (UHDPP) electron beams.Approach. The CCE of 22 PPICs has been measured in UHDPP electron beams at the National Metrology Institution of Germany (PTB). The CCE was determined for a dose per pulse (DPP) range between 0.1 and 6.4 Gy (pulse duration of 2.5μs). The results obtained with the different PPICs were compared to evaluate the reproducibility, intra- and inter-model variation, and the performance of a CCE empirical model.Main results. The intra-model variation was, on average, 4.0%, which is more than three times the total combined relative standard uncertainty and was found to be greater at higher DPP (up to 20%). The inter-model variation for the PPIC with 2 mm electrode spacing, which was found to be, on average, 10%, was also significant compared to the relative uncertainty and the intra-model variation. The observed CCE variation could not be explained only by the expected deviation of the electrode spacing from the nominal value within the manufacturing tolerance. It should also be noted that a substantial polarity effect, between 0.914(5) and 1.201(3), was observed, and significant intra- and inter-model variation was observed on this effect.Significance. For research and pre-clinical study, the commercially available PPIC with a well-known CCE (directly measured for the specific chamber) and with a small electrode spacing could be used for relative and absolute dosimetry with a lower-limit uncertainty of 1.6% (k= 1) in the best case. However, to use a PPIC as a secondary standard in UHDPP electron beams for clinical purposes would require new model development to reduce the ion recombination, the polarity effect, and the total standard uncertainty on the dose measurement.
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Affiliation(s)
- Alexandra Bourgouin
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Jose Paz-Martín
- Departamento de Física de Partículas, Universidad de Santiago, Santiago de Compostela, Spain
| | - Yunus Can Gedik
- Nuclear Energy Research Institute (NÜKEN), Turkish Energy Nuclear and Mineral Research Agency (TENMAK), Ankara, Turkey
| | - Franziska Frei
- Eidgenössisches Institut für Metrologie (METAS), Bern-Wabern, Switzerland
| | - Peter Peier
- Eidgenössisches Institut für Metrologie (METAS), Bern-Wabern, Switzerland
| | | | - Andreas A Schönfeld
- Sun Nuclear, A Mirion Medical Company, Melbourne, FL, United States of America
| | - Andreas Schüller
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | | | - Ralf-Peter Kapsch
- Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
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Kojima H, Ishikawa M, Takigami M. Technical note: Point-by-point ion-recombination correction for accurate dose profile measurement in high dose-per-pulse irradiation field. Med Phys 2023; 50:7281-7293. [PMID: 37528637 DOI: 10.1002/mp.16641] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 07/13/2023] [Accepted: 07/14/2023] [Indexed: 08/03/2023] Open
Abstract
BACKGROUND Although flattening filter free (FFF) beams are commonly used in clinical treatment, the accuracy of dose measurements in FFF beams has been questioned. Higher dose per pulse (DPP) such as FFF beams from a linear accelerator may cause problems in dose profile measurements using an ionization chamber due to the change of the charge collection efficiency. Ionization chambers are commonly used for percent depth dose (PDD) measurements. Changes of DPP due to chamber movement during PDD measurement can vary the ion collection efficiency of ionization chambers. In the case of FF beams, the DPP fluctuation is negligible, but in the case of the FFF beams, the DPP is 2.5 ∼ 4 times larger than that of the FF beam, and the change in ion collection efficiency is larger than that of the FF beam. PDD profile normalized by maximum dose depth, 10 cm depth for example, may therefore be affected by the ion collection efficiency. PURPOSE In this study, we investigate the characteristics of the ion collection efficiency change depending on the DPP of each ionization chamber in the FFF beam. We furthermore propose a method to obtain the chamber- independent PDD by applying a DPP-dependent ion recombination correction. METHODS Prior to investigating the relationship between DPP and charge collection efficiency, Jaffe-plots were generated with different DPP settings to investigate the linearity between the applied voltage and collected charge. The absolute dose measurement using eight ionization chambers under the irradiation settings of 0.148, 0.087, and 0.008 cGy/pulse were performed. Applied voltages for the Jaffe-plots were 100, 125, 150, 200, 250, and 300 V. The ion recombination correction factor Pion was calculated by the two-voltage analysis (TVA) method at the applied voltages of 300 and 100 V. The DPP dependency of the charge collection efficiency for each ionization chamber were evaluated from the DPP- Pion plot. PDD profiles for the 10 MV FFF beam were measured using Farmer type chambers (TN30013, FC65-P, and FC65-G) and mini-type chambers (TN31010, TN31021, CC13, CC04, and FC23-C). The PDD profiles were corrected with ion recombination correction at negative and positive polar applied voltages of 100 and 300 V. RESULTS From the DPP-Pion relation for each ionization chamber with DPP ranging from 0.008 cGy/pulse to 0.148 cGy/pulse, all Farmer and mini-type chambers satisfied the requirements described in AAPM TG-51 addendum. However, Pion for the CC13 was most affected by DPP among tested chambers. The maximum deviation among PDDs using eight ionization chambers for 10 MV FFF was about 1%, but the deviation was suppressed to about 0.5% by applying ion recombination correction at each depth. CONCLUSIONS In this study, the deviation of PDD profile among the ionization chambers was reduced by the ion recombination coefficient including the DPP dependency, especially for high DPP beams such as FFF beams. The present method is particularly effective for CC13, where the ion collection efficiency is highly DPP dependent.
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Affiliation(s)
- Hideki Kojima
- Department of Radiation Oncology, Sapporo Higashi Tokushukai Hospital, Sapporo, Hokkaido, Japan
| | - Masayori Ishikawa
- Faculty of Health Sciences, Hokkaido University, Sapporo, Hokkaido, Japan
| | - Makoto Takigami
- Department of Radiation Technology, KKR Sapporo Medical Center, Sapporo, Hokkaido, Japan
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10
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Absolute dosimetry for FLASH proton pencil beam scanning radiotherapy. Sci Rep 2023; 13:2054. [PMID: 36739297 PMCID: PMC9899251 DOI: 10.1038/s41598-023-28192-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2022] [Accepted: 01/13/2023] [Indexed: 02/05/2023] Open
Abstract
A paradigm shift is occurring in clinical oncology exploiting the recent discovery that short pulses of ultra-high dose rate (UHDR) radiation-FLASH radiotherapy-can significantly spare healthy tissues whilst still being at least as effective in curing cancer as radiotherapy at conventional dose rates. These properties promise reduced post-treatment complications, whilst improving patient access to proton beam radiotherapy and reducing costs. However, accurate dosimetry at UHDR is extremely complicated. This work presents measurements performed with a primary-standard proton calorimeter and derivation of the required correction factors needed to determine absolute dose for FLASH proton beam radiotherapy with an uncertainty of 0.9% (1[Formula: see text]), in line with that of conventional treatments. The establishment of a primary standard for FLASH proton radiotherapy improves accuracy and consistency of the dose delivered and is crucial for the safe implementation of clinical trials, and beyond, for this new treatment modality.
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11
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Ion recombination correction factors and detector comparison in a very-high dose rate proton scanning beam. Phys Med 2023; 106:102518. [PMID: 36638707 DOI: 10.1016/j.ejmp.2022.102518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/30/2022] [Revised: 12/09/2022] [Accepted: 12/27/2022] [Indexed: 01/13/2023] Open
Abstract
PURPOSE Accurate dosimetry is paramount to study the FLASH biological effect since dose and dose rate are critical dosimetric parameters governing its underlying mechanisms. With the goal of assessing the suitability of standard clinical dosimeters in a very-high dose rate (VHDR) experimental setup, we evaluated the ion collection efficiency of several commercially available air-vented ionization chambers (IC) in conventional and VHDR proton irradiation conditions. METHODS A cyclotron at the Orsay Proton Therapy Center was used to deliver VHDR pencil beam scanning irradiation. Ion recombination correction factors (ks) were determined for several detectors (Advanced Markus, PPC05, Nano Razor, CC01) at the entrance of the plateau and at the Bragg peak, using the Niatel model, the Two-voltage method and Boag's analytical formula for continuous beams. RESULTS Mean dose rates ranged from 4 Gy/s to 385 Gy/s, and instantaneous dose rates up to 1000 Gy/s were obtained with the experimental set-up. Recombination correction factors below 2 % were obtained for all chambers, except for the Nano Razor, at VHDRs with variations among detectors, while ks values were significantly smaller (0.8 %) for conventional dose rates. CONCLUSIONS While the collection efficiency of the probed ICs in scanned VHDR proton therapy is comparable to those in the conventional regime with recombination coefficiens smaller than 1 % for mean dose rates up to 177 Gy/s, the reduction in collection efficiency for higher dose rates cannot be ignored when measuring the absorbed dose in pre-clinical proton scanned FLASH experiments and clinical trials.
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Pettinato S, Girolami M, Stravato A, Serpente V, Musio D, Rossi MC, Trucchi DM, Olivieri R, Salvatori S. A Highly Versatile X-ray and Electron Beam Diamond Dosimeter for Radiation Therapy and Protection. MATERIALS (BASEL, SWITZERLAND) 2023; 16:824. [PMID: 36676560 PMCID: PMC9861322 DOI: 10.3390/ma16020824] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/18/2022] [Revised: 01/11/2023] [Accepted: 01/12/2023] [Indexed: 06/17/2023]
Abstract
Radiotherapy is now recognized as a pillar in the fight against cancer. Two different types are currently used in clinical practice: (1) external beam radiotherapy, using high-energy X-rays or electron beams, both in the MeV-range, and (2) intraoperative radiotherapy, using low-energy X-rays (up to 50 keV) and MeV-range electron beams. Versatile detectors able to measure the radiation dose independently from the radiation nature and energy are therefore extremely appealing to medical physicists. In this work, a dosimeter based on a high-quality single-crystal synthetic diamond sample was designed, fabricated and characterized under low-energy X-rays, as well as under high-energy pulsed X-rays and electron beams, demonstrating excellent linearity with radiation dose and dose-rate. Detector sensitivity was measured to be 0.299 ± 0.002 µC/Gy under 6 MeV X-ray photons, and 0.298 ± 0.004 µC/Gy under 6 MeV electrons, highlighting that the response of the diamond dosimeter is independent of the radiation nature. Moreover, in the case of low-energy X-rays, an extremely low limit of detection (23 nGy/s) was evaluated, pointing out the suitability of the device to radiation protection dosimetry.
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Affiliation(s)
- Sara Pettinato
- Engineering Faculty, Niccolò Cusano University, Via Don Carlo Gnocchi 3, 00166 Rome, Italy
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), DiaTHEMA Lab, Strada Provinciale 35D, 9, Montelibretti, 00010 Rome, Italy
| | - Marco Girolami
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), DiaTHEMA Lab, Strada Provinciale 35D, 9, Montelibretti, 00010 Rome, Italy
| | - Antonella Stravato
- Azienda Ospedaliera “San Giovanni–Addolorata”, Via dell’Amba Aradam, 8, 00184 Rome, Italy
| | - Valerio Serpente
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), DiaTHEMA Lab, Strada Provinciale 35D, 9, Montelibretti, 00010 Rome, Italy
| | - Daniela Musio
- Azienda Ospedaliera “San Giovanni–Addolorata”, Via dell’Amba Aradam, 8, 00184 Rome, Italy
| | - Maria C. Rossi
- Department of Industrial, Electronic and Mechanical Engineering, Università degli Studi Roma Tre, Via Vito Volterra 62, 00146 Rome, Italy
| | - Daniele M. Trucchi
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), DiaTHEMA Lab, Strada Provinciale 35D, 9, Montelibretti, 00010 Rome, Italy
| | - Riccardo Olivieri
- Azienda Ospedaliera “San Giovanni–Addolorata”, Via dell’Amba Aradam, 8, 00184 Rome, Italy
| | - Stefano Salvatori
- Engineering Faculty, Niccolò Cusano University, Via Don Carlo Gnocchi 3, 00166 Rome, Italy
- Istituto di Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), DiaTHEMA Lab, Strada Provinciale 35D, 9, Montelibretti, 00010 Rome, Italy
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13
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Fenwick JD, Kumar S. Collection efficiencies of ionization chambers in pulsed radiation beams: an exact solution of an ion recombination model including free electron effects. Phys Med Biol 2022; 68:015016. [PMID: 36571457 DOI: 10.1088/1361-6560/aca74e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 11/29/2022] [Indexed: 12/05/2022]
Abstract
Objective.Boaget al(1996) formulated a key model of collection efficiency for ionization chambers in pulsed radiation beams, in which some free electrons form negatively charged ions with a density that initially varies exponentially across the chamber. This non-uniform density complicates ion recombination calculations, in comparison with Boag's 1950 work in which a collection efficiency formula,f, was straightforwardly obtained assuming a uniform negative ion cloud. Boaget al(1996) therefore derived collection efficiency formulaef',f″ andf'″ based on three approximate descriptions of the exponentially-varying negative ion cloud, each uniform within a region. Collection efficiencies calculated by Boaget al(1996) using these formulae differed by a maximum of 5.1% relative (at 144 mGy dose-per-pulse with 212 V applied over a 1 mm electrode separation) and all three formulae are often used together. Here an exact solution of the exponentially-varying model is obtained.Approach.The exact solution was derived from a differential equation relating the number of negative ions collected from within some distance of the anode to numbers of ions initially located within that region. Using the resulting formula,fexp, collection efficiencies were calculated for a range of ionization chamber properties and doses-per-pulse, and compared withf,f',f″ andf″' values and results from an ion transport code.Main results.fexpvalues agreed to 5 decimal places with ion transport code results. The maximum relative difference betweenfexpandf″', which was often closest tofexp, was 0.78% for the chamber properties and doses-per-pulse studied by Boaget al(1996), rising to 6.1% at 1 Gy dose-per-pulse and 2 mm electrode separation.Significance.Use offexpshould reduce ambiguities in collection efficiencies calculated using the approximate formulae, although like themfexpdoes not account for electric field distortion, which becomes substantial at doses-per-pulse ≥100 mGy.
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Affiliation(s)
- John D Fenwick
- Department of Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, The Sherrington Building, Ashton Street, Liverpool L69 3BX, United Kingdom
| | - Sudhir Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CT & CRS Building, Anushaktinagar, Mumbai-400094, India
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14
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Ultra-high dose rate FLASH irradiator at the radiological research accelerator facility. Sci Rep 2022; 12:22149. [PMID: 36550150 PMCID: PMC9780319 DOI: 10.1038/s41598-022-19211-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 08/25/2022] [Indexed: 12/24/2022] Open
Abstract
The Radiological Research Accelerator Facility has modified a decommissioned Varian Clinac to deliver ultra-high dose rates: operating in 9 MeV electron mode (FLASH mode), samples can be irradiated at a Source-Surface Distance (SSD) of 20 cm at average dose rates of up to 600 Gy/s (3.3 Gy per 0.13 µs pulse, 180 pulses per second). In this mode multiple pulses are required for most irradiations. By modulating pulse repetition rate and irradiating at SSD = 171 cm, dose rates below 1 Gy/min can be achieved, allowing comparison of FLASH and conventional irradiations with the same beam. Operating in 6 MV photon mode, with the conversion target removed (SuperFLASH mode), samples are irradiated at higher dose rates (0.2-150 Gy per 5 µs pulse, 360 pulses per second) and most irradiations can be performed with a single very high dose rate pulse. In both modes we have seen the expected inverse relation between dose rate and irradiated area, with the highest dose rates obtained for beams with a FWHM of about 2 cm and ± 10% uniformity over 1 cm diameter. As an example of operation of the ultra-high dose rate FLASH irradiator, we present dose rate dependence of dicentric chromosome yields.
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15
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Mastella E, Szilagyi KE, De Guglielmo E, Fabbri S, Calderoni F, Stefanelli A, Di Domenico G, Turra A. Dosimetric characterization of a mobile accelerator dedicated for intraoperative radiation therapy: Monte Carlo simulations and experimental validation. Phys Med 2022; 104:167-173. [PMID: 36463581 DOI: 10.1016/j.ejmp.2022.11.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 10/12/2022] [Accepted: 11/25/2022] [Indexed: 12/03/2022] Open
Abstract
PURPOSE This Technical Note validates previously published data about the dosimetry of the electron beams produced by a mobile accelerator dedicated for intraoperative radiation therapy (IORT). The evaluation of the directional response of a PTW microDiamond detector is presented together with a detailed analysis of the output factors (OFs) for bevelled applicators. METHODS The OFs of the 6, 8, 10 and 12 MeV electron beams produced by a light intraoperative accelerator (LIAC, SIT, Italy) were measured in a commercial water phantom using the microDiamond. A set of flat and bevelled applicators with sizes ranging from 4 to 10 cm was characterized. For bevelled applicators, a correction for the angular dependence of the microDiamond was calculated using a home-made spherical phantom. Correction factors were obtained through measurements performed rotating the accelerator treatment head at 0°, 15°, 30° and 45°. RESULTS For flat applicators, the average deviation between measured and simulated OFs was (-1.1 ± 0.7)%. The microDiamond showed a higher angular dependence for the 6 MeV beam (∼8% for angles up to 45°, range 92 % ÷ 100 %), while the variations for 8, 10 and 12 MeV beams were ∼ 4 % (range 97 % ÷ 101 %). Correcting for this dependence, the average deviation of the OFs for bevelled applicators was (-0.9 ± 1.6)%. CONCLUSIONS The presented results were in very good agreement with those reported in literature. Very similar deviations were found between flat and bevelled applicators confirming the suitability of our method to determine the angular dependence correction factors of the microDiamond detector.
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Affiliation(s)
- Edoardo Mastella
- Struttura Complessa di Fisica Medica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy.
| | - Klarisa E Szilagyi
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, via Saragat 1, I-44122 Ferrara, Italy
| | - Eleonora De Guglielmo
- Struttura Complessa di Fisica Medica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy
| | - Sara Fabbri
- Struttura Complessa di Fisica Medica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy
| | - Francesca Calderoni
- Struttura Complessa di Fisica Medica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy
| | - Antonio Stefanelli
- Struttura Complessa di Radioterapia Oncologica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy
| | - Giovanni Di Domenico
- Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, via Saragat 1, I-44122 Ferrara, Italy
| | - Alessandro Turra
- Struttura Complessa di Fisica Medica, Azienda Ospedaliero-Universitaria di Ferrara, via A. Moro 8, I-44124 Cona (Ferrara), Italy
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Baack L, Schuy C, Brons S, Horst F, Voss B, Zink K, Haberer T, Durante M, Weber U. Reduction of recombination effects in large plane parallel beam monitors for FLASH radiotherapy with scanned ion beams. Phys Med 2022; 104:136-144. [PMID: 36403543 DOI: 10.1016/j.ejmp.2022.10.029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 10/12/2022] [Accepted: 10/31/2022] [Indexed: 11/18/2022] Open
Abstract
PURPOSE Radiotherapy escalating dose rates above 50Gys-1, might offer a great potential in treating tumours while further sparing healthy tissue. However, these ultra-high intensities of FLASH-RT lead to new challenges with regard to dosimetry and beam monitoring. FLASH experiments at HIT (Heidelberg Ion Beam Therapy Center) and at GSI (GSI Helmholtz Centre for Heavy Ion Research) have shown a significant loss of signal in the beam monitoring system due to recombination effects. To enable accurate beam monitoring, this work investigates the recombination loss of different fill gases in the plane parallel ionisation chambers (ICs). METHODS Therefore, saturation curves at high intensities were measured for the currently used fill gases Ar/CO2 (80/20) and pure He and also for He/CO2 mixtures as alternative fill gases. Furthermore, breakdown voltages and ion mobilities were measured in ICs filled with He/CO2 mixtures. A numerical model for volume recombination in plane parallel ionisation chambers was developed and implemented in Python. This includes a novel simulation method of the space charge effect from the charge carriers in the detector volume and predicts a significant effect on the electric field for high intensity beams. RESULTS Even at high intensities the He/CO2 mixtures allow operation of the ICs at an electric field strength of 2 kVcm-1 or more which reduces recombination to negligible levels at intensities larger than 3 × 101012C-ions per second. Our measurements show that added fractions of CO2 to He decrease the ion mobility in the fill gas but significantly increase the breakdown voltage in the ICs compared to pure He.
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Affiliation(s)
- Leon Baack
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany; Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstraße 8, 64289 Darmstadt, Germany
| | - Christoph Schuy
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany
| | - Stephan Brons
- Heidelberg Ion-Beam Therapy Center (HIT), Department of Radiation Oncology, Heidelberg University Hospital, 69120 Heidelberg, Germany
| | - Felix Horst
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany
| | - Bernd Voss
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Sciences, Giessen, Germany; Department of Radiation Oncology, Philipps-University, Marburg, Germany
| | - Thomas Haberer
- Heidelberg Ion-Beam Therapy Center (HIT), Department of Radiation Oncology, Heidelberg University Hospital, 69120 Heidelberg, Germany
| | - Marco Durante
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany; Institut für Festkörperphysik, Technische Universität Darmstadt, Hochschulstraße 8, 64289 Darmstadt, Germany
| | - Uli Weber
- Biophysics Department, GSI Helmholtzzentrum für Schwerionenforschung, Planckstraße 1, 64291 Darmstadt, Germany.
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Di Martino F, Del Sarto D, Barone S, Giuseppina Bisogni M, Capaccioli S, Galante F, Gasparini A, Mariani G, Masturzo L, Montefiori M, Pacitti M, Paiar F, Harold Pensavalle J, Romano F, Ursino S, Vanreusel V, Verellen D, Felici G. A new calculation method for the free electron fraction of an ionization chamber in the ultra-high-dose-per-pulse regimen. Phys Med 2022; 103:175-180. [DOI: 10.1016/j.ejmp.2022.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2022] [Revised: 10/27/2022] [Accepted: 11/01/2022] [Indexed: 11/11/2022] Open
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18
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Di Martino F, Del Sarto D, Giuseppina Bisogni M, Capaccioli S, Galante F, Gasperini A, Linsalata S, Mariani G, Pacitti M, Paiar F, Ursino S, Vanreusel V, Verellen D, Felici G. A new solution for UHDP and UHDR (Flash) measurements: Theory and conceptual design of ALLS chamber. Phys Med 2022; 102:9-18. [PMID: 36030665 DOI: 10.1016/j.ejmp.2022.08.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 07/27/2022] [Accepted: 08/10/2022] [Indexed: 10/15/2022] Open
Abstract
Ultra-High dose-per-pulse regimens (UHDP), necessary to trigger the "FLASH" effect, still pose serious challenges to dosimetry. Dosimetry plays a crucial role, both to significantly improve the accuracy of the radiobiological experiments necessary to fully understand the mechanisms underlying the effect and its dependencies on the beam parameters, and to be able to translate such effect into clinical practice. The standard ionization chamber in UHDP region is significantly affected by the effects of the electric field generated by the enormous density of charges produced by the dose pulse. This work describes the theory and the conceptual design of a gas chamber (the ALLS chamber) which overcomes the above-mentioned problems.
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Affiliation(s)
- Fabio Di Martino
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, ed.18 via Roma 67, Pisa, Italy; Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy; INFN, Sezione di Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy.
| | - Damiano Del Sarto
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy
| | - Maria Giuseppina Bisogni
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy; Department of Physics, University of Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy; INFN, Sezione di Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy
| | - Simone Capaccioli
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy; Department of Physics, University of Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy
| | | | - Alessia Gasperini
- Iridium Kankernetwerk, 2610 Antwerp, Belgium; Antwerp University, Faculty of Medicine and Health Sciences, 2610 Antwerp, Belgium
| | - Stefania Linsalata
- Fisica Sanitaria, Azienda Ospedaliero Universitaria Pisa AOUP, ed.18 via Roma 67, Pisa, Italy
| | | | | | - Fabiola Paiar
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy; INFN, Sezione di Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy; Radiation Oncology Unit, Department of Translational Research, University of Pisa, Pisa, Italy
| | - Stefano Ursino
- Centro Pisano ricerca e implementazione clinica Flash Radiotherapy (CPFR@CISUP), Presidio S. Chiara, ed. 18 via Roma 67, Pisa, Italy; INFN, Sezione di Pisa, Largo B. Pontecorvo 3, I-57127 Pisa, Italy; Radiation Oncology Unit, Department of Translational Research, University of Pisa, Pisa, Italy
| | - Verdi Vanreusel
- Iridium Kankernetwerk, 2610 Antwerp, Belgium; Antwerp University, Faculty of Medicine and Health Sciences, 2610 Antwerp, Belgium
| | - Dirk Verellen
- Iridium Kankernetwerk, 2610 Antwerp, Belgium; Antwerp University, Faculty of Medicine and Health Sciences, 2610 Antwerp, Belgium
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Bourgouin A, Keszti F, Schönfeld AA, Hackel T, Kozelka J, Hildreth J, Simon W, Schüller A, Kapsch RP, Renaud J. The probe-format graphite calorimeter, Aerrow, for absolute dosimetry in ultra-high pulse dose rate electron beams. Med Phys 2022; 49:6635-6645. [PMID: 35912973 DOI: 10.1002/mp.15899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 07/02/2022] [Accepted: 07/22/2022] [Indexed: 11/12/2022] Open
Abstract
PURPOSE The purpose of this investigation is to evaluate the use of a probe-format graphite calorimeter, Aerrow, as an absolute and relative dosimeter of high-energy pulse dose rate (UHPDR) electron beams for in-water reference and depth-dose type measurements, respectively. METHODS In this paper, the calorimeter system is used to investigate the potential influence of dose per pulses delivered up to 5.6 Gy, the number of pulses delivered per measurement and its potential for relative measurement (depth dose curve measurement). The calorimeter system is directly compared against an Advanced Markus ion chamber. The finite element method was used to calculate heat transfer corrections along the percentage depth dose of a 20 MeV electron beam. Monte Carlo-calculated dose conversion factors necessary to calculate absorbed dose to-water at a point from the measured dose-to-graphite are also presented. RESULTS The comparison of Aerrow against a fully calibrated Advanced Markus chamber, corrected for the saturation effect, has shown consistent results in terms of dose to water determination. The measured reference depth is within 0.5 mm from the expected value from Monte Carlo simulation. The relative standard uncertainty estimated for Aerrow was 1.06%, which is larger compared to alanine dosimetry (McEwen et al. https://doi.org/10.1088/0026-1394/52/2/272) but has the advantage of being a real time detector. CONCLUSION In this investigation, it was demonstrated that the Aerrow probe-type graphite calorimeter can be used for relative and absolute dosimetry in water in an UHPDR electron beam. To the author's knowledge, this is the first reported use of an absorbed dose calorimeter for an in-water percentage depth dose curve measurement. The use of the Aerrow in quasi-adiabatic mode has greatly simplified the signal readout, compared to isothermal mode, as the resistance was directly measured with a high-stability Digital-Multimetre (DMM). This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Alexandra Bourgouin
- Dosimetry for radiation therapy and diagnostic radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Federico Keszti
- Medical Physics Unit, McGill University, Montreal, Quebec, Canada
| | | | - Thomas Hackel
- Dosimetry for radiation therapy and diagnostic radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Jakub Kozelka
- Research, Sun Nuclear, A Mirion Medical Company, Melbourne, Florida, USA
| | - Jeff Hildreth
- Research, Sun Nuclear, A Mirion Medical Company, Melbourne, Florida, USA
| | - William Simon
- Research, Sun Nuclear, A Mirion Medical Company, Melbourne, Florida, USA
| | - Andreas Schüller
- Dosimetry for radiation therapy and diagnostic radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Ralf-Peter Kapsch
- Dosimetry for radiation therapy and diagnostic radiology, Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - James Renaud
- Medical and Industrial Dosimetry, National Research Council of Canada (NRC), Ottawa, Ontario, Canada
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20
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Cavallone M, Jorge PG, Moeckli R, Bailat C, Flacco A, Prezado Y, Delorme R. Determination of the ion collection efficiency of the Razor Nano Chamber for ultra-high dose-rate electron beams. Med Phys 2022; 49:4731-4742. [PMID: 35441716 PMCID: PMC9539950 DOI: 10.1002/mp.15675] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 04/07/2022] [Accepted: 04/12/2022] [Indexed: 11/10/2022] Open
Abstract
Background Ultra‐high dose‐rate (UHDR) irradiations (>40 Gy/s) have recently garnered interest in radiotherapy (RT) as they can trigger the so‐called “FLASH” effect, namely a higher tolerance of normal tissues in comparison with conventional dose rates when a sufficiently high dose is delivered to the tissue. To transfer this to clinical RT treatments, adapted methods and practical tools for online dosimetry need to be developed. Ionization chambers remain the gold standards in RT but the charge recombination effects may be very significant at such high dose rates, limiting the use of some of these dosimeters. The reduction of the sensitive volume size can be an interesting characteristic to reduce such effects. Purpose In that context, we have investigated the charge collection behavior of the recent IBA Razor™ Nano Chamber (RNC) in UHDR pulses to evaluate its potential interest for FLASH RT. Methods In order to quantify the RNC ion collection efficiency (ICE), simultaneous dose measurements were performed under UHDR electron beams with dose‐rate‐independent Gafchromic™ EBT3 films that were used as the dose reference. A dose‐per‐pulse range from 0.01 to 30 Gy was investigated, varying the source‐to‐surface distance, the pulse duration (1 and 3 μs investigated) and the LINAC gun grid tension as irradiation parameters. In addition, the RNC measurements were corrected from the inherent beam shot‐to‐shot variations using an independent current transformer. An empirical logistic model was used to fit the RNC collection efficiency measurements and the results were compared with the Advanced Markus plane parallel ion chamber. Results The RNC ICE was found to decrease as the dose‐per‐pulse increases, starting from doses above 0.2 Gy/pulse and down to 40% of efficiency at 30 Gy/pulse. The RNC resulted in a higher ICE for a given dose‐per‐pulse in comparison with the Markus chamber, with a measured efficiency found higher than 85 and 55% for 1 and 10 Gy/pulse, respectively, whereas the Markus ICE was of 60 and 25% for the same doses. However, the RNC shows a higher sensitivity to the pulse duration than the Advanced Markus chamber, with a lower efficiency found at 1 μs than at 3 μs, suggesting that this chamber could be more sensitive to the dose rate within the pulse. Conclusions The results confirmed that the small sensitive volume of the RNC ensures higher ICE compared with larger chambers. The RNC was thus found to be a promising online dosimetry tool for FLASH RT and we proposed an ion recombination model to correct its response up to extreme dose‐per‐pulses of 30 Gy.
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Affiliation(s)
- Marco Cavallone
- Institut Curie, PSL Research University, Radiation Oncology Department, Proton Therapy Centre, Centre Universitaire, Orsay, 91898, France.,Laboratoire d'Optique Appliquée, ENSTA Paris, École Polytechnique, CNRS-UMR7639, Institut Polytechnique de Paris, Palaiseau Cedex, 91762, France
| | | | - Raphaël Moeckli
- Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland
| | - Claude Bailat
- Institute of Radiation Physics, Lausanne University Hospital, Lausanne, Switzerland
| | - Alessandro Flacco
- Laboratoire d'Optique Appliquée, ENSTA Paris, École Polytechnique, CNRS-UMR7639, Institut Polytechnique de Paris, Palaiseau Cedex, 91762, France
| | - Yolanda Prezado
- Institut Curie, Université PSL, CNRS UMR3347, Inserm U1021, Signalisation Radiobiologie et Cancer, Orsay, 91400, France.,Université Paris-Saclay, CNRS UMR3347, Inserm U1021, Signalisation Radiobiologie et Cancer, Orsay, 91400, France
| | - Rachel Delorme
- University of Grenoble Alpes, CNRS, Grenoble INP, LPSC-IN2P3, Grenoble, 38000, France.,Imagerie et Modélisation en Neurobiologie et Cancérologie (IMNC), CNRS Univ Paris-Sud, Université Paris-Saclay, Orsay, F-91400, France
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21
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Rodríguez FG, Gonzalez-Castaño DM, Fernández NG, Pardo-Montero J, Schüller A, Gasparini A, Vanreusel V, Verellen D, Felici G, Kranzer R, Paz-Martín J. Development of an ultra-thin parallel plate ionization chamber for dosimetry in flash radiotherapy. Med Phys 2022; 49:4705-4714. [PMID: 35416306 PMCID: PMC9545838 DOI: 10.1002/mp.15668] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Revised: 03/29/2022] [Accepted: 03/30/2022] [Indexed: 11/29/2022] Open
Abstract
Background Conventional air ionization chambers (ICs) exhibit ion recombination correction factors that deviate substantially from unity when irradiated with dose per pulse magnitudes higher than those used in conventional radiotherapy. This fact makes these devices unsuitable for the dosimetric characterization of beams in ultra‐high dose per pulse as used for FLASH radiotherapy. Purpose We present the design, development, and characterization of an ultra‐thin parallel plate IC that can be used in ultra‐high dose rate (UHDR) deliveries with minimal recombination. Methods The charge collection efficiency (CCE) of parallel plate ICs was modeled through a numerical solution of the coupled differential equations governing the transport of charged carriers produced by ionizing radiation. It was used to find out the optimal parameters for the purpose of designing an IC capable of exhibiting a linear response with dose (deviation less than 1%) up to 10 Gy per pulse at 4
μs pulse duration. As a proof of concept, two vented parallel plate IC prototypes have been built and tested in different ultra‐high pulse dose rate electron beams. Results It has been found that by reducing the distance between electrodes to a value of 0.25 mm it is possible to extend the dose rate operating range of parallel plate ICs to ultra‐high dose per pulse range, at standard voltage of clinical grade electrometers, well into several Gy per pulse. The two IC prototypes exhibit behavior as predicted by the numerical simulation. One of the so‐called ultra‐thin parallel plate ionization chamber (UTIC) prototypes was able to measure up to 10 Gy per pulse, 4
μs pulse duration, operated at 300 V with no significant deviation from linearity within the uncertainties (ElectronFlash Linac, SIT). The other prototype was tested up to 5.4 Gy per pulse, 2.5
μs pulse duration, operated at 250 V with CCE higher than 98.6% (Metrological Electron Accelerator Facility, MELAF at Physikalisch‐Technische Bundesanstalt, PTB). Conclusions This work demonstrates the ability to extend the dose rate operating range of ICs to ultra‐high dose per pulse range by reducing the spacing between electrodes. The results show that UTICs are suitable for measurement in UHDR electron beams.
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Affiliation(s)
- Faustino Gómez Rodríguez
- Department of Particle Physics, University of Santiago, Santiago de Compostela, Spain.,Radiation Physics Laboratory, University of Santiago, Santiago de Compostela, Spain
| | | | | | - Juan Pardo-Montero
- Group of Medical Physics and Biomathematics, Instituto de Investigación Sanitaria de Santiago (IDIS), Santiago de Compostela, Spain.,Department of Medical Physics, Complexo Hospitalario Universitario de Santiago de Compostela, Spain
| | - Andreas Schüller
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
| | - Alessia Gasparini
- Department of Radiotherapy, Iridium Network, Belgium.,Faculty of Medicine and Health sciences, University of Antwerp, Belgium.,SCK CEN, Research in dosimetric applications, Mol, Belgium
| | - Verdi Vanreusel
- Department of Radiotherapy, Iridium Network, Belgium.,Faculty of Medicine and Health sciences, University of Antwerp, Belgium.,SCK CEN, Research in dosimetric applications, Mol, Belgium
| | - Dirk Verellen
- Department of Radiotherapy, Iridium Network, Belgium.,Faculty of Medicine and Health sciences, University of Antwerp, Belgium
| | | | - Rafael Kranzer
- PTW, Freiburg, Germany.,University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University Oldenburg, Germany
| | - Jose Paz-Martín
- Department of Particle Physics, University of Santiago, Santiago de Compostela, Spain
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22
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Romano F, Bailat C, Jorge PG, Lerch MLF, Darafsheh A. Ultra‐high dose rate dosimetry: challenges and opportunities for FLASH radiation therapy. Med Phys 2022; 49:4912-4932. [PMID: 35404484 PMCID: PMC9544810 DOI: 10.1002/mp.15649] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 02/03/2022] [Accepted: 02/20/2022] [Indexed: 11/11/2022] Open
Affiliation(s)
- Francesco Romano
- Istituto Nazionale di Fisica Nucleare Sezione di Catania Catania Italy
| | - Claude Bailat
- Institute of Radiation Physics Lausanne University Hospital Lausanne University Switzerland
| | - Patrik Gonçalves Jorge
- Institute of Radiation Physics Lausanne University Hospital Lausanne University Switzerland
- Department of Radiation Oncology Lausanne University Hospital Lausanne Switzerland
- Radio‐Oncology Laboratory DO/CHUV Lausanne University Hospital Lausanne Switzerland
| | | | - Arash Darafsheh
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
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23
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Experimental Setup for Irradiation of Cell Cultures at L2A2. QUANTUM BEAM SCIENCE 2022. [DOI: 10.3390/qubs6010010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Laser–plasma proton sources and their applications to preclinical research has become a very active field of research in recent years. In addition to their small dimensions as compared to classical ion accelerators, they offer the possibility to study the biological effects of ultra-short particle bunches and the correspondingly high dose rates. We report on the design of an experimental setup for the irradiation of cell cultures at the L2A2 laboratory at the University of Santiago de Compostela, making use of a 1.2 J Ti: Sapphire laser with a 10 Hz repetition rate. Our setup comprises a proton energy separator consisting of two antiparallel magnetic fields realized by a set of permanent magnets. It allows for selecting a narrow energy window around an adaptable design value of 5 MeV out of the initially broad spectrum typical for Target Normal Sheath Acceleration (TNSA). At the same time, unwanted electrons and X-rays are segregated from the protons. This part of the setup is located inside the target vessel of the L2A2 laser. A subsequent vacuum flange sealed with a thin kapton window allows for particle passage to external sample irradiation. A combination of passive detector materials and real-time monitors is applied for measurement of the deposited radiation dose. A critical point of this interdisciplinary project is the manipulation of biological samples under well-controlled, sterile conditions. Cell cultures are prepared in sealed flasks with an ultra-thin entrance window and analysed at the nearby Fundación Pública Galega Medicina Xenómica and IDIS. The first trials will be centred at the quantification of DNA double-strand breaks as a function of radiation dose.
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24
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Jeong DH, Lee M, Lim H, Kang SK, Lee K, Lee SJ, Kim H, Han WK, Kang TW, Jang KW. Optical Filter-Embedded Fiber-Optic Radiation Sensor for Ultra-High Dose Rate Electron Beam Dosimetry. SENSORS (BASEL, SWITZERLAND) 2021; 21:5840. [PMID: 34502730 PMCID: PMC8434457 DOI: 10.3390/s21175840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 08/19/2021] [Accepted: 08/24/2021] [Indexed: 11/24/2022]
Abstract
FLASH radiotherapy is an emerging radiotherapy technique used to spare normal tissues. It employs ultra-high dose rate radiation beams over 40 Gy/s, which is significantly higher than those of conventional radiotherapy. In this study, a fiber-optic radiation sensor (FORS) was fabricated using a plastic scintillator, an optical filter, and a plastic optical fiber to measure the ultra-high dose rate electron beams over 40 Gy/s used in FLASH radiotherapy. The radiation-induced emissions, such as Cherenkov radiation and fluorescence generated in a transmitting optical fiber, were spectrally discriminated from the light outputs of the FORS. To evaluate the linearity and dose rate dependence of the FORS, the outputs of the fiber-optic radiation sensor were measured according to distances from an electron scattering device, and the results were compared with those of an ionization chamber and radiochromic films. Finally, the percentage depth doses were obtained using the FORS as a function of depth in a water phantom. This study found that ultra-high dose rate electron beams over 40 Gy/s could be measured in real time using a FORS.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | - Kyoung-Won Jang
- Research Center, Dongnam Institute of Radiological and Medical Sciences, Busan 46033, Korea; (D.-H.J.); (M.L.); (H.L.); (S.-K.K.); (K.L.); (S.-J.L.); (H.K.); (W.-K.H.); (T.-W.K.)
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25
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Szpala S, Huang V, Zhao Y, Kyle A, Minchinton A, Karan T, Kohli K. Dosimetry with a clinical linac adapted to FLASH electron beams. J Appl Clin Med Phys 2021; 22:50-59. [PMID: 34028969 PMCID: PMC8200504 DOI: 10.1002/acm2.13270] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 03/03/2021] [Accepted: 04/10/2021] [Indexed: 11/21/2022] Open
Abstract
PURPOSE To assess dosimetric properties and identify required updates to commonly used protocols (including use of film and ionization chamber) pertaining to a clinical linac configured into FLASH (ultra-high dose rate) electron mode. METHODS An 18MV photon beam of a Varian iX linac was converted to FLASH electron beam by replacing the target and the flattening filter with an electron scattering foil. The dose was prescribed by entering the MUs through the console. Fundamental beam properties, including energy, dose rate, dose reproducibility, field size, and dose rate dependence on the SAD, were examined in preparation for radiobiological experiments. Gafchromic EBT-XD film was evaluated for usability in measurements at ultra-high dose rates by comparing the measured dose to the inverse square model. Selected previously reported models of chamber efficiencies were fitted to measurements in a broad range of dose rates. RESULTS The performance of the modified linac was found adequate for FLASH radiobiological experiments. With exception of the increase in the dose per MU on increase in the repetition rate, all fundamental beam properties proved to be in line with expectations developed with conventional linacs. The field size followed the theorem of similar triangles. The highest average dose rate (2 × 104 Gy/s) was found next to the internal monitor chamber, with the field size of FWHM = 1.5 cm. Independence of the dose readings on the dose rate (up to 2 × 104 Gy/s) was demonstrated for the EBT-XD film. A model of recombination in an ionization chamber was identified that provided good agreement with the measured chamber efficiencies for the average dose rates up to at least 2 × 103 Gy/s. CONCLUSION Dosimetric measurements were performed to characterize a linac converted to FLASH dose rates. Gafchromic EBT-XD film and dose rate-corrected cc13 ionization chamber were demonstrated usable at FLASH dose rates.
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26
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Kranzer R, Poppinga D, Weidner J, Schüller A, Hackel T, Looe HK, Poppe B. Ion collection efficiency of ionization chambers in ultra-high dose-per-pulse electron beams. Med Phys 2021; 48:819-830. [PMID: 33251606 DOI: 10.1002/mp.14620] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 09/30/2020] [Accepted: 11/18/2020] [Indexed: 02/03/2023] Open
Abstract
PURPOSE The ion collection efficiency of vented ionization chambers has been investigated in an ultra-high dose-per-pulse (DPP) electron beam. The role of the chamber design and the electric field strength in the sensitive air volume have been evaluated. METHODS An advanced Markus chamber and three specially designed parallel plate air-filled ionization chambers (EWC: End Window Chamber) with varying electrode distance of 0.5, 1, and 2 mm have been investigated. Their ion collection efficiencies were determined experimentally using two methods: extrapolation of Jaffé plots and comparison against a DPP-independent reference detector. The latter was achieved by calibrating a current transformer against alanine dosimeters. All measurements were performed in a 24 MeV electron beam with DPP values between 0.01 and 3 Gy. Additionally, the numerical approach introduced by Gotz et al. was implemented taking into account space charge effects at these ultra-high DPPs. The method has been extended to obtain time-resolved and position-dependent electric field distortions within the air cavity. RESULTS The ion collection efficiency of the investigated ionization chambers drops significantly in the ultra-high DPP range. The extent of this drop is dependent on the electrode distance, the applied chamber voltage and thus the field strength in the sensitive air volume. For the Advanced Markus chamber, a good agreement between the experimental, numerical and the results of Petersson et al. could be shown. Using the three EWCs with different electrode spacing, an improvement of the ion collection efficiency and a reduction of the polarity effect with decreasing electrode distance could be demonstrated. Furthermore, the results revealed that the determination of the ion collection efficiency from the Jaffé plots and therefore also from two-voltage method typically underestimate the ion collection efficiency in the region of high dose-per-pulse (3 to 130 mGy) and overestimate the ion collection efficiency at ultra-high dose-per-pulse (>1 Gy per pulse). CONCLUSIONS In this work, the ion collection efficiency determined with different methods and ionization chambers have been compared and discussed. As expected, an increase of the electric field in the ionization chamber, either by applying a higher bias voltage or a reduction of the electrode distance, improves the ion collection efficiency and also reduces the polarity effect. For the Advanced Markus chamber, the experimental results obtained by comparison against a reference agree well with the numerical solution. Based on these results, it seems possible to keep the recombination loss less than or equal to 5% up to a dose-per-pulse of 3 Gy with an appropriately designed ionization chamber, which corresponds to the level accepted in conventional radiotherapy dosimetry protocols.
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Affiliation(s)
- Rafael Kranzer
- PTW-Freiburg, Freiburg, 79115, Germany.,University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, 26121, Germany
| | | | | | - Andreas Schüller
- Physikalisch-Technische Bundesanstalt, Braunschweig, 38116, Germany
| | - Thomas Hackel
- Physikalisch-Technische Bundesanstalt, Braunschweig, 38116, Germany
| | - Hui Khee Looe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, 26121, Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics, Medical Campus Pius Hospital, Carl von Ossietzky University, Oldenburg, 26121, Germany
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Esplen N, Mendonca MS, Bazalova-Carter M. Physics and biology of ultrahigh dose-rate (FLASH) radiotherapy: a topical review. Phys Med Biol 2020; 65:23TR03. [PMID: 32721941 DOI: 10.1088/1361-6560/abaa28] [Citation(s) in RCA: 117] [Impact Index Per Article: 29.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Ultrahigh dose-rate radiotherapy (RT), or 'FLASH' therapy, has gained significant momentum following various in vivo studies published since 2014 which have demonstrated a reduction in normal tissue toxicity and similar tumor control for FLASH-RT when compared with conventional dose-rate RT. Subsequent studies have sought to investigate the potential for FLASH normal tissue protection and the literature has been since been inundated with publications on FLASH therapies. Today, FLASH-RT is considered by some as having the potential to 'revolutionize radiotherapy'. FLASH-RT is considered by some as having the potential to 'revolutionize radiotherapy'. The goal of this review article is to present the current state of this intriguing RT technique and to review existing publications on FLASH-RT in terms of its physical and biological aspects. In the physics section, the current landscape of ultrahigh dose-rate radiation delivery and dosimetry is presented. Specifically, electron, photon and proton radiation sources capable of delivering ultrahigh dose-rates along with their beam delivery parameters are thoroughly discussed. Additionally, the benefits and drawbacks of radiation detectors suitable for dosimetry in FLASH-RT are presented. The biology section comprises a summary of pioneering in vitro ultrahigh dose-rate studies performed in the 1960s and early 1970s and continues with a summary of the recent literature investigating normal and tumor tissue responses in electron, photon and proton beams. The section is concluded with possible mechanistic explanations of the FLASH normal-tissue protection effect (FLASH effect). Finally, challenges associated with clinical translation of FLASH-RT and its future prospects are critically discussed; specifically, proposed treatment machines and publications on treatment planning for FLASH-RT are reviewed.
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Affiliation(s)
- Nolan Esplen
- Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada
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28
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Schüller A, Heinrich S, Fouillade C, Subiel A, De Marzi L, Romano F, Peier P, Trachsel M, Fleta C, Kranzer R, Caresana M, Salvador S, Busold S, Schönfeld A, McEwen M, Gomez F, Solc J, Bailat C, Linhart V, Jakubek J, Pawelke J, Borghesi M, Kapsch RP, Knyziak A, Boso A, Olsovcova V, Kottler C, Poppinga D, Ambrozova I, Schmitzer CS, Rossomme S, Vozenin MC. The European Joint Research Project UHDpulse – Metrology for advanced radiotherapy using particle beams with ultra-high pulse dose rates. Phys Med 2020; 80:134-150. [DOI: 10.1016/j.ejmp.2020.09.020] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 08/17/2020] [Accepted: 09/23/2020] [Indexed: 02/08/2023] Open
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29
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Lashkari S, Baghani HR, Tavakoli MB, Mahdavi SR. An inter-comparison between accuracy of EGSnrc and MCNPX Monte Carlo codes in dosimetric characterization of intraoperative electron beam. Comput Biol Med 2020; 128:104113. [PMID: 33197735 DOI: 10.1016/j.compbiomed.2020.104113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 10/20/2020] [Accepted: 11/05/2020] [Indexed: 10/23/2022]
Abstract
BACKGROUND Ionometric dosimetry in IOERT is a complicated process, due to the sophisticated beam setup and the necessity for dedicated protocols for ion chamber response correction. On the other hand, the Monte Carlo (MC) technique can easily overcome such limitations and be considered as an alternative dosimetry approach. This paper presents a comparative analysis of two widely used MC codes, EGSnrc and MCNPX, for intraoperative electron beam dosimetry. METHOD The head of LIAC12, a dedicated IOERT accelerator, was modeled by both mentioned MC codes. Then, the percentage depth dose (PDD) curves, transverse dose profiles (TDPs), and output factor (OF) values were accordingly calculated within the water phantom. To realize the accuracy of MC codes in dosimetric characterization of intraoperative electron beam, their results were finally compared with those measured by corresponding ionometric dosimetry for all forms of electron energy/applicator size. RESULTS A good agreement was observed between the simulated and measured PDDs/TDPs for both considered MC codes, such that the calculated gamma index values were always lower than unity for both considered MC codes. Nevertheless, the lower gamma index values were found in the case of the EGSnrc code. The maximum difference between the measured and calculated OF was obtained as 2.3% and 3.1% for EGSnrc and MCNPX code, respectively. CONCLUSIONS Although both studied MC codes showed compatible results with the measured ones, EGSnrc code has superior accuracy in this regard and can be considered as a more reliable toolkit in Monte Carlo-based commissioning of dedicated IOERT accelerators.
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Affiliation(s)
- Sara Lashkari
- Department of Medical Physics and Medical Engineering, Isfahan University of Medical Sciences, Isfahan, Iran
| | | | - Mohammad Bagher Tavakoli
- Department of Medical Physics and Medical Engineering, Isfahan University of Medical Sciences, Isfahan, Iran.
| | - Seyed Rabi Mahdavi
- Medical Physics Department, Iran University of Medical Sciences, Tehran, Iran
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30
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Technical challenges for FLASH proton therapy. Phys Med 2020; 78:71-82. [PMID: 32947086 DOI: 10.1016/j.ejmp.2020.08.005] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Revised: 08/03/2020] [Accepted: 08/04/2020] [Indexed: 12/21/2022] Open
Abstract
There is growing interest in the radiotherapy community in the application of FLASH radiotherapy, wherein the dose is delivered to the entire treatment volume in less than a second. Early pre-clinical evidence suggests that these extremely high dose rates provide significant sparing of healthy tissue compared to conventional radiotherapy without reducing the damage to cancerous cells. This interest has been reflected in the proton therapy community, with early tests indicating that the FLASH effect is also present with high dose rate proton irradiation. In order to deliver clinically relevant doses at FLASH dose rates significant technical hurdles must be overcome in the accelerator technology before FLASH proton therapy can be realised. Of these challenges, increasing the average current from the present clinical range of 1-10 nA to in excess of 100 nA is at least feasible with existing technology, while the necessity for rapid energy adjustment on the order of a few milliseconds is much more challenging, particularly for synchrotron-based systems. However, the greatest challenge is to implement full pencil beam scanning, where scanning speeds 2 orders of magnitude faster than the existing state-of-the-art will be necessary, along with similar improvements in the speed and accuracy of associated dosimetry. Hybrid systems utilising 3D-printed patient specific range modulators present the most likely route to clinical delivery. However, to correctly adapt and develop existing technology to meet the challenges of FLASH, more pre-clinical studies are needed to properly establish the beam parameters that are necessary to produce the FLASH effect.
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31
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Darafsheh A, Hao Y, Zwart T, Wagner M, Catanzano D, Williamson JF, Knutson N, Sun B, Mutic S, Zhao T. Feasibility of proton FLASH irradiation using a synchrocyclotron for preclinical studies. Med Phys 2020; 47:4348-4355. [DOI: 10.1002/mp.14253] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 05/15/2020] [Accepted: 05/15/2020] [Indexed: 11/12/2022] Open
Affiliation(s)
- Arash Darafsheh
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Yao Hao
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Townsend Zwart
- Mevion Medical Systems 300 Foster St. Littleton MA 01460 USA
| | - Miles Wagner
- Mevion Medical Systems 300 Foster St. Littleton MA 01460 USA
| | | | - Jeffrey F. Williamson
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Nels Knutson
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Baozhou Sun
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Sasa Mutic
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
| | - Tianyu Zhao
- Department of Radiation Oncology Washington University School of Medicine St. Louis MO 63110 USA
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McManus M, Romano F, Lee ND, Farabolini W, Gilardi A, Royle G, Palmans H, Subiel A. The challenge of ionisation chamber dosimetry in ultra-short pulsed high dose-rate Very High Energy Electron beams. Sci Rep 2020; 10:9089. [PMID: 32493952 PMCID: PMC7270129 DOI: 10.1038/s41598-020-65819-y] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 03/16/2020] [Indexed: 12/04/2022] Open
Abstract
High dose-rate radiotherapy, known as FLASH, has been shown to increase the differential response between healthy and tumour tissue. Moreover, Very High Energy Electrons (VHEEs) provide more favourable dose distributions than conventional radiotherapy electron and photon beams. Plane-parallel ionisation chambers are the recommended secondary standard systems for clinical reference dosimetry of electrons, therefore chamber response to these high energy and high dose-per-pulse beams must be well understood. Graphite calorimetry, the UK primary standard, has been employed to measure the dose delivered from a 200 MeV pulsed electron beam. This was compared to the charge measurements of a plane-parallel ionisation chamber to determine the absolute collection efficiency and infer the ion recombination factor. The dose-per-pulse measured by the calorimeter ranged between 0.03 Gy/pulse and 5.26 Gy/pulse, corresponding to collection efficiencies between 97% and 4%, respectively. Multiple recombination models currently available have been compared with experimental results. This work is directly applicable to the development of standard dosimetry protocols for VHEE radiotherapy, FLASH radiotherapy and other high dose-rate modalities. However, the use of secondary standard ionisation chambers for the dosimetry of high dose-per-pulse VHEEs has been shown to require large corrections for charge collection inefficiency.
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Affiliation(s)
- M McManus
- Medical Radiation Science, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom.
- Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT, United Kingdom.
| | - F Romano
- Medical Radiation Science, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom
- Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Catania, Via S Sofia 64, I-95123, Catania, Italy
| | - N D Lee
- Medical Radiation Science, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom
| | - W Farabolini
- CERN, Geneva, 1217, Switzerland
- CEA-Saclay, IRFU, 91191, Gif-sur-Yvette, France
| | | | - G Royle
- Medical Physics and Biomedical Engineering, University College London, Gower Street, London, WC1E 6BT, United Kingdom
| | - H Palmans
- Medical Radiation Science, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom
- MedAustron, Marie Curie-Strasse 5, 2700, Wiener Neustadt, Austria
| | - A Subiel
- Medical Radiation Science, National Physical Laboratory, Hampton Road, Teddington, Middlesex, TW11 0LW, United Kingdom.
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D'Arienzo M, Andreoli S, Pimpinella M. Evaluation of the uncertainty associated with the ion recombination correction in high dose-per-pulse electron beam dosimetry: an MC approach. Phys Med Biol 2020; 65:09NT01. [PMID: 32097891 DOI: 10.1088/1361-6560/ab79c2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The high dose and dose-per-pulse rates (up to 130 mGy/pulse) produced by some intraoperative radiation therapy (IORT) accelerators pose specific dosimetric problems due to the high density of electric charge per pulse produced in the ionization chamber cavity. In particular, the correction factor for ion recombination, ks , calculated with the traditional two-voltage method is significantly overestimated and three alternative models have been proposed in the literature allowing for the presence of a free-electron component. However, at present there is no general consensus on the best model to assess the ion recombination correction and controversy remains on the uncertainty associated with k s . In the present work we adopted a Monte Carlo (MC) approach to assess the uncertainty associated with the ion recombination correction in plane-parallel chambers used in high dose-per-pulse electron beam dosimetry. The uncertainty associated with k s was calculated for the following plane-parallel ionization chambers: Scanditronix/Wellhofer Parallel Plate Chamber PPC05 and PPC40, PTW Advanced Markus Model 34 045 and PTW Roos Model 34 001. Input variables for MC calculations were derived from experimental data at 28 and 73 mGy/pulse. Taken together, the results of this study indicate that ks values calculated according to the three ion recombination models do not overlap within their standard uncertainties, suggesting that an additional type-B uncertainty component would be necessary to take into account possible differences between the models. Our results indicate that the combined relative standard uncertainty in k s should be calculated as the sum in quadrature of a (type-A) MC-based uncertainty component and a (type-B) uncertainty contribution evaluated assuming a uniform distribution between k s values obtained from the two extreme models.
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Affiliation(s)
- Marco D'Arienzo
- ENEA, National Institute of Ionizing Radiation Metrology, Rome, Italy
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Characterization of Fricke-gelatin dosimeters for intraoperative Radiation Therapy dosimetry. Radiat Phys Chem Oxf Engl 1993 2020. [DOI: 10.1016/j.radphyschem.2019.108629] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Martin-Martin G, Aguilar PB, Barbés B, Guibelalde E. Assessment of ion recombination correction and polarity effects for specific ionization chambers in flattening-filter-free photon beams. Phys Med 2019; 67:176-184. [PMID: 31734555 DOI: 10.1016/j.ejmp.2019.07.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 07/23/2019] [Accepted: 07/24/2019] [Indexed: 11/17/2022] Open
Abstract
PURPOSE To investigate ion recombination correction and polarity effects in four ion chamber models in flattening-filter-free (FFF) beams to (1) evaluate their suitability for reference dosimetry; (2) assess the accuracy of the two-voltage technique (TVA) against the Bruggmoser formalism; and (3) examine the influence of the accelerator type on the recombination correction. METHODS Jaffé plots were created for a variety of microchambers, small-volume and Farmer-type chambers to obtain kS, the recombination correction factor, using two different types of accelerators. These values were plotted against dose-per-pulse and Jaffé plots for opposite polarities were created to determine which chambers meet the AAPM TG-51 addendum recombination and polarity specifications. RESULTS Nearly all small-volume chambers exhibited reference-class behavior with respect to ion recombination and polarity effects. The microchambers exhibited anomalous recombination and polarity effects, precluding their use for reference dosimetry in FFF beams. For the reference-class chambers, agreement between TVA-determined kS values and Jaffé and Bruggmoser formalisms-determined kS values was within 0.1%. No significant differences were found between the kS values obtained with the two different accelerators used in this work. CONCLUSIONS This study stresses the need to characterize ion recombination correction and polarity effects for small-volume chambers and microchambers on an individual chamber basis and with the more rigorous criteria of the AAPM TG-51 addendum. Furthermore, the study demonstrated the suitability of the TVA method for chambers that exhibit reference-class behavior in FFF beams. Finally, this work has shown that the recombination correction does not depend on the type of accelerator but on its dose-per-pulse.
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Affiliation(s)
- Guadalupe Martin-Martin
- Medical Physics and Radiation Protection Service, Hospital Universitario de Fuenlabrada, C/ Camino del Molino 2, 28492 Fuenlabrada, Madrid, Spain.
| | - Pedro Borja Aguilar
- Clínica Universidad de Navarra, Department of Radiation Physics, Avenida Pío XII, 31080 Pamplona, Navarra, Spain
| | - Benigno Barbés
- Clínica Universidad de Navarra, Department of Radiation Physics, Avenida Pío XII, 31080 Pamplona, Navarra, Spain
| | - Eduardo Guibelalde
- Medical Physics Group, Department of Radiology, University Complutense of Madrid, 28040 Madrid, Spain
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Gotz M, Ka L, Tölli H, Pawelke J. Correction for volume recombination in liquid ionization chambers at high dose-per-pulse. Med Phys 2019; 46:3692-3699. [PMID: 31102553 DOI: 10.1002/mp.13600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 05/13/2019] [Accepted: 05/13/2019] [Indexed: 11/09/2022] Open
Abstract
PURPOSE To determine the volume recombination at high dose-per-pulse in liquid ionization chambers (LIC) and to ascertain whether existing calculation methods verified in air-filled chambers may be used to calculate a correction factor. METHODS Two LICs, one filled with 2,2,4-trimethylpentane (isooctane) the other with tetramethylsilane (TMS), were irradiated in a pulsed, 20 MeV electron beam. Via reference measurements with a Faraday cup, the saturation correction for volume recombination was determined for dose-per-pulse values ranging from about 5 mGy to 1 Gy for both chambers at a pulse duration of 693 ns. In addition, the isooctane chamber was irradiated with pulses of varying duration, ranging from 5 ps to 10 ms, at a dose-per-pulse of about 76.5 mGy. The dose-per-pulse-dependent measurements were compared to calculations based on Boag's models (with and without a free electron fraction), the two-dose-rate method, and a numerical calculation. The pulse duration dependent measurements were compared only to a numerical calculation that iteratively calculates the charge transport and loss in a 1D model of an ionization chamber. RESULTS In TMS only Boag's model with a free electron fraction and the numerical calculation are in good agreement with the experimental data. However, in isooctane, good agreement is observed between the experimental data, the numerical calculation as well as the two-dose-rate method, and Boag's model including a free electron fraction. Only Boag's model without a free electron fraction shows a good agreement with lesser extend. Furthermore, the pulse duration-dependent data for isooctane are well described by the numerical model. CONCLUSION With isooctane as an active medium, a LIC could be directly used in a field with high dose-per-pulse utilizing the well-established two-dose-rate method to correct the volume recombination. In addition, pulsed fields with variable pulse duration are easily modeled for this medium using a numerical calculation. Other media, as exemplified by the TMS-filled chamber, might require additional considerations, such as including a fraction of free electrons in the consideration of volume recombination.
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Affiliation(s)
- Malte Gotz
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany
| | - Leonhard Ka
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany.,Institute of Radiooncology - OncoRay, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
| | - Heikki Tölli
- Department of Radiation Sciences, Radiation Physics, Umeå University, SE- 901 87, Umeå, Sweden
| | - Jörg Pawelke
- OncoRay - National Center for Radiation Research in Oncology, Faculty of Medicine and University Hospital Carl Gustav Carus, Technische Universität Dresden, Helmholtz-Zentrum Dresden - Rossendorf, Fetscherstr. 74, PF 41, 01307, Dresden, Germany.,Institute of Radiooncology - OncoRay, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstr. 400, 01328, Dresden, Germany
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Pimpinella M, Andreoli S, De Angelis C, Della Monaca S, D'Arienzo M, Menegotti L. Output factor measurement in high dose-per-pulse IORT electron beams. Phys Med 2019; 61:94-102. [DOI: 10.1016/j.ejmp.2019.04.021] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 04/18/2019] [Accepted: 04/24/2019] [Indexed: 12/14/2022] Open
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Baghani HR, Robatjazi M, Mahdavi SR, Hosseini Aghdam SR. Evaluating the performance characteristics of some ion chamber dosimeters in high dose per pulse intraoperative electron beam radiation therapy. Phys Med 2019; 58:81-89. [DOI: 10.1016/j.ejmp.2019.01.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/09/2018] [Revised: 01/29/2019] [Accepted: 01/30/2019] [Indexed: 10/27/2022] Open
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Güngör G, Aydın G, Mustafayev TZ, Özyar E. Output factors of ionization chambers and solid state detectors for mobile intraoperative radiotherapy (IORT) accelerator electron beams. J Appl Clin Med Phys 2019; 20:13-23. [PMID: 30632271 PMCID: PMC6370992 DOI: 10.1002/acm2.12522] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 12/06/2018] [Accepted: 12/09/2018] [Indexed: 11/11/2022] Open
Abstract
PURPOSE The electron energy characteristics of mobile intraoperative radiotherapy (IORT) accelerator LIAC® differ from commonly used linear accelerators, thus some of the frequently used detectors can give less accurate results. The aim of this study is to evaluate the output factors (OFs) of several ionization chambers (IC) and solid state detectors (SS) for electron beam energies generated by LIAC® and compare with the output factor of Monte Carlo model (MC) in order to determine the adequate detectors for LIAC® . METHODS The OFs were measured for 6, 8, 10, and 12 MeV electron energies with PTW 23343 Markus, PTW 34045 Advanced Markus, PTW 34001 Roos, IBA PPC05, IBA PPC40, IBA NACP-02, PTW 31010 Semiflex, PTW 31021 Semiflex 3D, PTW 31014 Pinpoint, PTW 60017 Diode E, PTW 60018 Diode SRS, SNC Diode EDGE, and PTW 60019 micro Diamond detectors. Ion recombination factors (ksat ) of IC were measured for all applicator sizes and OFs were corrected according to ksat . The measured OFs were compared with Monte Carlo output factors (OFMC ). RESULTS The measured OFs of IBA PPC05, PTW Advanced Markus, PTW Pinpoint, PTW microDiamond, and PTW Diode E detectors are in good agreement with OFMC . The maximum deviations of IBA PPC05 OFs to OFMC are -1.6%, +1.5%, +1.5%, and +2.0%; for PTW Advanced Markus +1.0%, +1.5%, +2.0%, and +2.0%; for PTW Pinpoint +2.0%, +1.6%, +4.0%, and +2.0%; for PTW microDiamond -1.6%, +2%, +1.1%, and +1.0%; and for PTW Diode E -+1.7%, +1.7%, +1.3%, and +2.5% for 6, 8, 10, and 12 MeV, respectively. PTW Roos, PTW Markus, IBA PPC40, PTW Semiflex, PTW Semiflex 3D, SNC Diode Edge measured OFs with a maximum deviation of +5.6%, +4.5%, +5.6%, +8.1%, +4.8%, and +9.6% with respect to OFMC , while PTW Diode SRS and IBA NACP-02 were the least accurate (with highest deviations -37.1% and -18.0%, respectively). CONCLUSION The OFs results of solid state detectors PTW microDiamond and PTW Diode E as well as the ICs with small electrode spacing distance such as IBA PPC05, PTW Advanced Markus and PTW Pinpoint are in excellent agreement with OFMC . The measurements of the other detectors evaluated in this study are less accurate, thus they should be used with caution. Particularly, PTW Diode SRS and IBA NACP-02 are not suitable and their use should be avoided in relative dosimetry measurements under high dose per pulsed (DPP) electron beams.
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Affiliation(s)
- Görkem Güngör
- Department of Medical PhysicsMedipol University Institute of Health SciencesIstanbulTurkey
- Department of Radiation OncologyAcıbadem Mehmet Ali Aydınlar University School of MedicineIstanbulTurkey
| | - Gökhan Aydın
- Department of Radiation OncologyAcıbadem Mehmet Ali Aydınlar University School of MedicineIstanbulTurkey
| | - Teuta Zoto Mustafayev
- Department of Radiation OncologyAcıbadem Mehmet Ali Aydınlar University School of MedicineIstanbulTurkey
| | - Enis Özyar
- Department of Radiation OncologyAcıbadem Mehmet Ali Aydınlar University School of MedicineIstanbulTurkey
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Robatjazi M, Tanha K, Mahdavi SR, Baghani HR, Mirzaei HR, Mousavi M, Nafissi N, Akbari E. Monte Carlo Simulation of Electron Beams produced by LIAC Intraoperative Radiation Therapy Accelerator. J Biomed Phys Eng 2018; 8:43-52. [PMID: 29732339 PMCID: PMC5928310] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 07/08/2016] [Indexed: 12/04/2022]
Abstract
Background One of the main problems of dedicated IORT accelerators is to determine dosimetric characteristics of the electron beams. Monte Carlo simulation of IORT accelerator head and produced beam will be useful to improve the accuracy of beam dosimetry. Materials and Methods Liac accelerator head was modeled using the BEAMnrcMonte Carlo simulation system. Phase-space files were generated at the bottom of the applicators. These phase-space files were used as an input source in DOSXYZnrc and BEAMDP codes for dose calculation and analysis of the characteristic of the electron beams in all applicators and energies. Results The results of Monte Carlo calculations are in very close agreement with the measurements. There is a decrease in the peak of the initial spectrum when electrons come from the end of accelerator wave guide to the end of applicator. By decreasing the applicator diameter, the mean energy of electron beam decreased. Using applicators and increasing their size, X-ray contamination will increase. The percentage of X-ray contamination increases by applicator diameter. This is related to the increase of the mean energy of electron beams. Conclusion Application of PMMA collimator leads to, although well below accepted level, the production of bremsstrahlung. The results of this study showed that special design of LIAC head accompanying by PMMA collimator system cause to produce an electron beam with an individual dosimetric characteristic making it a useful tool for intraoperative radiotherapy purposes.
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Affiliation(s)
- M Robatjazi
- Medical Physics and Radiological Sciences Department, Sabzevar University of Medical Sciences, Sabzevar, Iran
| | - K Tanha
- Persian Gulf Nuclear Medicine Research Center, Bushehr University of Medical Sciences, Bushehr, Iran
| | - S R Mahdavi
- Medical Physics Department, Iran University of Medical Sciences, Tehran, Iran
| | - H R Baghani
- Physics Department, School of Sciences, Hakim Sabzevari University, Sabzevar, Iran
| | - H R Mirzaei
- Radiation Therapy Department, Shahid Beheshti University of Medical Sciences, Tehran, Iran
| | - M Mousavi
- Medical Physics and Radiological Sciences Department, Sabzevar University of Medical Sciences, Sabzevar, Iran
| | - N Nafissi
- Surgery Department, Iran University of Medical Sciences, Tehran, Iran
| | - E Akbari
- Oncological Surgery Department, Shahid Beheshti University of Medical Sciences, Tehran, Iran
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Gotz M, Karsch L, Pawelke J. A new model for volume recombination in plane-parallel chambers in pulsed fields of high dose-per-pulse. ACTA ACUST UNITED AC 2017; 62:8634-8654. [DOI: 10.1088/1361-6560/aa8985] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Heidarloo N, Baghani HR, Aghamiri SMR, Mahdavi SR, Akbari ME. Commissioning of beam shaper applicator for conformal intraoperative electron radiotherapy. Appl Radiat Isot 2017; 123:69-81. [DOI: 10.1016/j.apradiso.2017.02.039] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 02/04/2017] [Accepted: 02/23/2017] [Indexed: 11/27/2022]
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Petersson K, Jaccard M, Germond JF, Buchillier T, Bochud F, Bourhis J, Vozenin MC, Bailat C. High dose-per-pulse electron beam dosimetry - A model to correct for the ion recombination in the Advanced Markus ionization chamber. Med Phys 2017; 44:1157-1167. [PMID: 28094853 DOI: 10.1002/mp.12111] [Citation(s) in RCA: 117] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Revised: 01/11/2017] [Accepted: 01/11/2017] [Indexed: 11/12/2022] Open
Abstract
PURPOSE The purpose of this work was to establish an empirical model of the ion recombination in the Advanced Markus ionization chamber for measurements in high dose rate/dose-per-pulse electron beams. In addition, we compared the observed ion recombination to calculations using the standard Boag two-voltage-analysis method, the more general theoretical Boag models, and the semiempirical general equation presented by Burns and McEwen. METHODS Two independent methods were used to investigate the ion recombination: (a) Varying the grid tension of the linear accelerator (linac) gun (controls the linac output) and measuring the relative effect the grid tension has on the chamber response at different source-to-surface distances (SSD). (b) Performing simultaneous dose measurements and comparing the dose-response, in beams with varying dose rate/dose-per-pulse, with the chamber together with dose rate/dose-per-pulse independent Gafchromic™ EBT3 film. Three individual Advanced Markus chambers were used for the measurements with both methods. All measurements were performed in electron beams with varying mean dose rate, dose rate within pulse, and dose-per-pulse (10-2 ≤ mean dose rate ≤ 103 Gy/s, 102 ≤ mean dose rate within pulse ≤ 107 Gy/s, 10-4 ≤ dose-per-pulse ≤ 101 Gy), which was achieved by independently varying the linac gun grid tension, and the SSD. RESULTS The results demonstrate how the ion collection efficiency of the chamber decreased as the dose-per-pulse increased, and that the ion recombination was dependent on the dose-per-pulse rather than the dose rate, a behavior predicted by Boag theory. The general theoretical Boag models agreed well with the data over the entire investigated dose-per-pulse range, but only for a low polarizing chamber voltage (50 V). However, the two-voltage-analysis method and the Burns & McEwen equation only agreed with the data at low dose-per-pulse values (≤ 10-2 and ≤ 10-1 Gy, respectively). An empirical model of the ion recombination in the chamber was found by fitting a logistic function to the data. CONCLUSIONS The ion collection efficiency of the Advanced Markus ionization chamber decreases for measurements in electron beams with increasingly higher dose-per-pulse. However, this chamber is still functional for dose measurements in beams with dose-per-pulse values up toward and above 10 Gy, if the ion recombination is taken into account. Our results show that existing models give a less-than-accurate description of the observed ion recombination. This motivates the use of the presented empirical model for measurements with the Advanced Markus chamber in high dose-per-pulse electron beams, as it enables accurate absorbed dose measurements (uncertainty estimation: 2.8-4.0%, k = 1). The model depends on the dose-per-pulse in the beam, and it is also influenced by the polarizing chamber voltage, with increasing ion recombination with a lowering of the voltage.
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Affiliation(s)
- Kristoffer Petersson
- CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland
| | - Maud Jaccard
- CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland
| | | | - Thierry Buchillier
- CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland
| | - François Bochud
- CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland
| | - Jean Bourhis
- CHUV, Service de Radio-Oncologie, Rue du Bugnon 46, CH - 1011, Lausanne, Switzerland
| | | | - Claude Bailat
- CHUV, Institut de Radiophysique, Rue du Grand-Pré 1, CH-1007, Lausanne, Switzerland
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Jaccard M, Petersson K, Buchillier T, Germond JF, Durán MT, Vozenin MC, Bourhis J, Bochud FO, Bailat C. High dose-per-pulse electron beam dosimetry: Usability and dose-rate independence of EBT3 Gafchromic films. Med Phys 2017; 44:725-735. [PMID: 28019660 DOI: 10.1002/mp.12066] [Citation(s) in RCA: 96] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Revised: 12/02/2016] [Accepted: 12/07/2016] [Indexed: 11/09/2022] Open
Abstract
PURPOSE The aim of this study was to assess the suitability of Gafchromic EBT3 films for reference dose measurements in the beam of a prototype high dose-per-pulse linear accelerator (linac), capable of delivering electron beams with a mean dose-rate (Ḋm ) ranging from 0.07 to 3000 Gy/s and a dose-rate in pulse (Ḋp ) of up to 8 × 106 Gy/s. To do this, we evaluated the overall uncertainties in EBT3 film dosimetry as well as the energy and dose-rate dependence of their response. MATERIAL AND METHODS Our dosimetric system was composed of EBT3 Gafchromic films in combination with a flatbed scanner and was calibrated against an ionization chamber traceable to primary standard. All sources of uncertainties in EBT3 dosimetry were carefully analyzed using irradiations at a clinical radiotherapy linac. Energy dependence was investigated with the same machine by acquiring and comparing calibration curves for three different beam energies (4, 8 and 12 MeV), for doses between 0.25 and 30 Gy. Ḋm dependence was studied at the clinical linac by changing the pulse repetition frequency (f) of the beam in order to vary Ḋm between 0.55 and 4.40 Gy/min, while Ḋp dependence was probed at the prototype machine for Ḋp ranging from 7 × 103 to 8 × 106 Gy/s. Ḋp dependence was first determined by studying the correlation between the dose measured by films and the charge of electrons measured at the exit of the machine by an induction torus. Furthermore, we compared doses from the films to independently calibrated thermo-luminescent dosimeters (TLD) that have been reported as being dose-rate independent up to such high dose-rates. RESULTS We report that uncertainty below 4% (k = 2) can be achieved in the dose range between 3 and 17 Gy. Results also demonstrated that EBT3 films did not display any detectable energy dependence for electron beam energies between 4 and 12 MeV. No Ḋm dependence was found either. In addition, we obtained excellent consistency between films and TLDs over the entire Ḋp range attainable at the prototype linac confirming the absence of any dose-rate dependence within the investigated range (7 × 103 to 8 × 106 Gy/s). This aspect was further corroborated by the linear relationship between the dose-per-pulse (Dp ) measured by films and the charge per pulse (Cp ) measured at the prototype linac exit. CONCLUSION Our study shows that the use of EBT3 Gafchromic films can be extended to reference dosimetry in pulsed electron beams with a very high dose rate. The measurement results are associated with an overall uncertainty below 4% (k = 2) and are dose-rate and energy independent.
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Affiliation(s)
- Maud Jaccard
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Kristoffer Petersson
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Thierry Buchillier
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Jean-François Germond
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Maria Teresa Durán
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Marie-Catherine Vozenin
- Department of Radiation Oncology, Lausanne University Hospital, Lausanne, Switzerland.,Radio-Oncology Laboratory, DO/CHUV, Lausanne University Hospital Lausanne, Lausanne, Switzerland
| | - Jean Bourhis
- Department of Radiation Oncology, Lausanne University Hospital, Lausanne, Switzerland.,Radio-Oncology Laboratory, DO/CHUV, Lausanne University Hospital Lausanne, Lausanne, Switzerland
| | - François O Bochud
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
| | - Claude Bailat
- Institute of Radiation Physics (IRA), Lausanne University Hospital, Lausanne, Switzerland
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Hyun MA, Miller JR, Micka JA, DeWerd LA. Ion recombination and polarity corrections for small-volume ionization chambers in high-dose-rate, flattening-filter-free pulsed photon beams. Med Phys 2017; 44:618-627. [PMID: 28001291 DOI: 10.1002/mp.12053] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2016] [Revised: 10/25/2016] [Accepted: 11/16/2016] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To investigate ion recombination and polarity effects in scanning and microionization chambers when used with digital electrometers and high-dose-rate linac beams such as flattening-filter-free (FFF) fields, and to compare results against conventional pulsed and continuous photon beams. METHODS Saturation curves were obtained for one Farmer-type ionization chamber and eight small-volume chamber models with volumes ranging from 0.01 to 0.13 cm3 using a Varian TrueBeam™ STx with FFF capability. Three beam modes (6 MV, 6 MV FFF, and 10 MV FFF) were investigated, with nominal dose-per-pulse values of 0.0278, 0.0648, and 0.111 cGy/pulse, respectively, at dmax . Saturation curves obtained using the Theratronics T1000 60 Co unit at the UWADCL and a conventional linear accelerator (Varian Clinac iX) were used to establish baseline behavior. Jaffé plots were fitted to obtain Pion , accounting for exponential effects such as charge multiplication. These values were compared with the two-voltage technique recommended in TG-51, and were plotted as a function of dose-per-pulse to assess the ability of small-volume chambers to meet reference-class criteria in FFF beams. RESULTS Jaffé- and two-voltage-determined Pion values measured for high-dose-rate beams agreed within 0.1% for the Farmer-type chamber and 1% for scanning and microionization chambers, with the exception of the CC01 which agreed within 2%. With respect to ion recombination and polarity effects, the Farmer-type chamber, scanning chambers and the Exradin A26 microchamber exhibited reference-class behavior in all beams investigated, with the exception of the IBA CC04 scanning chamber, which had an initial recombination correction that varied by 0.2% with polarity. All microchambers investigated, with the exception of the A26, exhibited anomalous polarity and ion recombination behaviors that make them unsuitable for reference dosimetry in conventional and high-dose-rate photon beams. CONCLUSIONS The results of this work demonstrate that recombination and polarity behaviors seen in conventional pulsed and continuous photon beams trend accordingly in high-dose-rate FFF linac beams. Several models of small-volume ionization chambers used with a digital electrometer have been shown to meet reference-class requirements with respect to ion recombination and polarity, even in the high-dose-rate environment. For such chambers, a two-voltage technique agreed well with more rigorous methods of determining Pion . However, the results emphasize the need for careful reference detector selection, and indicate that ionization chambers ought to be extensively tested in each beam of interest prior to their use for reference dosimetry.
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Affiliation(s)
- Megan A Hyun
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Jessica R Miller
- Department of Human Oncology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53792, USA
| | - John A Micka
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI, 53705, USA
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Abstract
Literature was reviewed to assess the physical aspects governing the present and emerging technologies used in intraoperative radiation therapy (IORT). Three major technologies were identified: treatment with electrons, treatment with external generators of kV X-rays and electronic brachytherapy. Although also used in IORT, literature on brachytherapy with radioactive sources is not systematically reviewed since an extensive own body of specialized literature and reviews exists in this field. A comparison with radioactive sources is made in the use of balloon catheters for partial breast irradiation where these are applied in almost an identical applicator technique as used with kV X-ray sources. The physical constraints of adaption of the dose distribution to the extended target in breast IORT are compared. Concerning further physical issues, the literature on radiation protection, commissioning, calibration, quality assurance (QA) and in-vivo dosimetry of the three technologies was reviewed. Several issues were found in the calibration and the use of dosimetry detectors and phantoms for low energy X-rays which require further investigation. The uncertainties in the different steps of dose determination were estimated, leading to an estimated total uncertainty of around 10-15% for IORT procedures. The dose inhomogeneity caused by the prescription of electrons at 90% and by the steep dose gradient of kV X-rays causes additional deviations from prescription dose which must be considered in the assessment of dose response in IORT.
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Affiliation(s)
- Frank W Hensley
- Department of Radiation Oncology, University Hospital of Heidelberg, Im Neuenheimer Feld 400, 69120, Heidelberg, Germany.
- , Present address: Birkenweg 35, 69221, Dossenheim, Germany.
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Scalchi P, Ciccotelli A, Felici G, Petrucci A, Massafra R, Piazzi V, D'Avenia P, Cavagnetto F, Cattani F, Romagnoli R, Soriani A. Use of parallel-plate ionization chambers in reference dosimetry of NOVAC and LIAC®mobile electron linear accelerators for intraoperative radiotherapy: a multi-center survey. Med Phys 2017; 44:321-332. [DOI: 10.1002/mp.12020] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 11/06/2016] [Accepted: 11/11/2016] [Indexed: 11/12/2022] Open
Affiliation(s)
- Paolo Scalchi
- Department of Medical Physics; Azienda U.L.S.S. 8; Vicenza 36100 Italy
| | | | | | - Assunta Petrucci
- Department of Medical Physics; S. Filippo Neri Hospital; Rome 00135 Italy
| | - Raffaella Massafra
- Department of Medical Physics; I.R.C.C.S. Institute of Oncology Giovanni Paolo II; Bari 70124 Italy
| | - Valeria Piazzi
- Department of Radiotherapy; Multimedica Hospital; Castellanza 21053 Italy
| | - Paola D'Avenia
- Department of Medical Physics; ASUR MARCHE AV3; Macerata 62100 Italy
| | | | - Federica Cattani
- Department of Medical Physics; European Institute of Oncology; Milan 20141 Italy
| | | | - Antonella Soriani
- Laboratory of Medical Physics and Expert Systems; Regina Elena National Cancer Institute; Rome 00144 Italy
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Saminathan S, Godson HF, Ponmalar R, Manickam R, Mazarello J, Fernandes R. Dosimetric Performance of Newly Developed Farmer-Type Ionization Chamber in Radiotherapy Practice. Technol Cancer Res Treat 2016; 15:NP113-NP120. [PMID: 26682769 DOI: 10.1177/1533034615621635] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 11/03/2015] [Accepted: 11/10/2015] [Indexed: 11/17/2022] Open
Abstract
Dose measurement with ionization chamber is essential to deliver accurate dose to the tumor in radiotherapy. The cylindrical Farmer-type ionization chamber is recommended by various dosimetry protocols for dose measurement of radiotherapy beams. The air-equivalent graphite wall Farmer-type ionization chamber (FAR 65 GB) of active volume 0.65 cm3 with aluminum as the central electrode material was fabricated. Various dosimetric parameters were studied for the newly developed ionization chamber in cobalt-60, 6 and 18 MV photon beams. The preirradiation and postirradiation leakage of the chamber was within 0.08%. The long-term stability and the stem effect of the chamber were within 0.07% and 0.3%, respectively. The sensitivity of the ionization chamber was found to be 22.15 nC/Gy. The chamber shows linear response with dose for cobalt-60, 6 and 18 MV photon beams. The ion recombination correction factor increases with increase in bias voltage. For all energies and field sizes, the polarity correction factor is almost closer to unity. The ion recombination and polarity correction measurements show that the polarizing potential and polarity recommended during the calibration of ionization chamber should be used for routine measurement to avoid the uncertainty. The chamber response is independent of dose rate and energy. The chamber is cost-effective and shows precise and reproducible response. The study carried out confirms that the newly fabricated ion chamber can be used in the measurement of absolute dose for high-energy photon beams.
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Affiliation(s)
- Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India
| | - Henry Finlay Godson
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India
| | - Retna Ponmalar
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India
| | - Ravikumar Manickam
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India
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Karsch L. Derivation of formulas to calculate the saturation correction of ionization chambers in pulsed beams of short, nonvanishing pulse durations. Med Phys 2016; 43:6154. [DOI: 10.1118/1.4965808] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Karsch L. Derivation of a formula describing the saturation correction of plane-parallel ionization chambers in pulsed fields with arbitrary repetition rate. Phys Med Biol 2016; 61:3222-36. [DOI: 10.1088/0031-9155/61/8/3222] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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