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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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Vidal M, Gérard A, Floquet V, Forthomme J, Christensen JB, Almhagen E, Grusell E, Heymans V, Rossomme S, Dumas S, Trimaud R, Hérault J. Beam monitor chamber calibration of a synchro-cyclotron high dose rate per pulse pulsed scanned proton beam. Phys Med Biol 2024; 69:085016. [PMID: 38252970 DOI: 10.1088/1361-6560/ad2123] [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: 06/15/2022] [Accepted: 01/22/2024] [Indexed: 01/24/2024]
Abstract
Objective. Ionization chambers, mostly used for beam calibration and for reference dosimetry, can show high recombination effects in pulsed high dose rate proton beams. The aims of this paper are: first, to characterize the linearity response of newly designed asymmetrical beam monitor chambers (ABMC) in a 100-226 MeV pulsed high dose rate per pulse scanned proton beam; and secondly, to calibrate the ABMC with a PPC05 (IBA Dosimetry) plane parallel ionization chamber and compare to calibration with a home-made Faraday cup (FC).Approach. The ABMC response linearity was evaluated with both the FC and a PTW 60019 microDiamond detector. Regarding ionometry-based ABMC calibration, recombination factors were evaluated theoretically, then numerically, and finally experimentally measured in water for a plane parallel ionization chamber PPC05 (IBA Dosimetry) throughkssaturation curves. Finally, ABMC calibration was also achieved with FC and compared to the ionometry method for 7 energies.Main results. Linearity measurements showed that recombination losses in the new ABMC design were well taken into account for the whole range of the machine dose rates. The two-voltage-method was not suitable for recombination correction, but Jaffé's plots analysis was needed, emphasizing the current IAEA TRS-398 reference protocol limitations. Concerning ABMC calibration, FC based absorbed dose estimation and PPC05-based absorbed dose estimation differ by less than 6.3% for the investigated energies.Significance.So far, no update on reference dosimetry protocols is available to estimate the absorbed dose in ionization chambers for clinical high dose rate per pulse pulsed scanned proton beams. This work proposes a validation of the new ABMC design, a method to take into account the recombination effect for ionometry-based ABMC calibration and a comparison with FC dose estimation in this type of proton beams.
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Affiliation(s)
- Marie Vidal
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
| | - Anaïs Gérard
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
| | - Vincent Floquet
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
| | | | - Jeppe Brage Christensen
- DTU Health Tech, Technical University of Denmark, Roskilde, Denmark
- Department of Radiation Safety and Security, Paul Scherrer Institute, PSI Villigen, Switzerland
| | - Erik Almhagen
- Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Radiation Science-Skandion Clinics Uppsala, Sweden
| | - Erik Grusell
- Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Immunology, Genetics and Pathology, Medical Radiation Science-Skandion Clinics Uppsala, Sweden
| | | | | | - Serge Dumas
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
| | - Richard Trimaud
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
| | - Joël Hérault
- Institut Méditerranéen de Protonthérapie-Centre Antoine Lacassagne, Fédération Claude Lalanne, Nice, France
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Mahfirotin DA, Ferliano B, Handika AD, Asril YS, Fadli M, Ryangga D, Nelly N, Kurniawan E, Wibowo WE, Yadav P, Pawiro SA. A multicenter study of modified electron beam output calibration. J Appl Clin Med Phys 2024; 25:e14232. [PMID: 38088260 PMCID: PMC10795448 DOI: 10.1002/acm2.14232] [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: 02/28/2023] [Revised: 11/13/2023] [Accepted: 11/19/2023] [Indexed: 01/19/2024] Open
Abstract
PURPOSE This study aims to assess the accuracy of a modified electron beam calibration based on the IAEA TRS-398 and AAPM-TG-51 in multicenter radiotherapy. METHODS This study was performed using the Elekta and Varian Linear Accelerator electron beams with energies of 4-22 MeV under reference conditions using cylindrical (PTW 30013, IBA FC65-G, and IBA FC65-P) and parallel-plate (PTW 34045, PTW 34001, and IBA PPC-40) chambers. The modified calibration used a cylindrical chamber and an updatedk ' Q $k{^{\prime}}_Q$ based on Monte Carlo calculations, whereas TRS-398 and TG-51 used cylindrical and parallel-plate chambers for reference dosimetry. The dose ratio of the modified calibration procedure, TRS-398 and TG-51 were obtained by comparing the dose at the maximum depth of the modified calibration to TRS-398 and TG-51. RESULTS The study found that all cylindrical chambers' beam quality conversion factors determined with the modified calibration( k ' Q ) $( {{{k^{\prime}}}_Q} )$ to the TRS-398 and TG-51 vary from 0.994 to 1.003 and 1.000 to 1.010, respectively. The dose ratio of modified/TRS-398cyl and modified/TRS-398parallel-plate, the variation ranges were 0.980-1.014 and 0.981-1.019, while for the counterpart modified/TG-51cyl was found varying between 0.991 and 1.017 and the ratio of modified/TG-51parallel-plate varied in the range of 0.981-1.019. CONCLUSION This multi-institutional study analyzed a modified calibration procedure utilizing new data for electron beam calibrations at multiple institutions and evaluated existing calibration protocols. Based on observed variations, the current calibration protocols should be updated with detailed metrics on the stability of linac components.
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Affiliation(s)
- Dwi Aprilia Mahfirotin
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
- Department of Radiation OncologyMitra Keluarga Bekasi Timur Hospital, BekasiWest JavaIndonesia
| | - Brian Ferliano
- Department of Radiation OncologyGading Pluit HospitalJakartaIndonesia
| | - Andrian Dede Handika
- Department of Radiation OncologyPersahabatan Central General HospitalJakartaIndonesia
| | - Yosi Sudarsi Asril
- Department of Radiation OncologyMayapada Hospital Jakarta SelatanJakartaIndonesia
| | - Muhamad Fadli
- Department of Radiation OncologyMRCCC Siloam Hospital SemanggiJakartaIndonesia
| | - Dea Ryangga
- Department of Radiation OncologyPasar Minggu Regional HospitalJakartaIndonesia
| | - Nelly Nelly
- Department of Radiation OncologySiloam Hospital TB SimatupangJakartaIndonesia
| | - Eddy Kurniawan
- Department of Radiation OncologyTzu Chi HospitalJakartaIndonesia
| | - Wahyu Edy Wibowo
- Department of Radiation OncologyDr. Cipto Mangunkusumo National General Hospital CentralFaculty of MedicineUniversitas IndonesiaJakartaIndonesia
| | - Poonam Yadav
- Department of Radiation OncologyNorthwestern Memorial HospitalNorthwestern University Feinberg School of MedicineChicagoIllinoisUSA
| | - Supriyanto Ardjo Pawiro
- Department of PhysicsFaculty of Mathematics and Natural SciencesUniversitas Indonesia, DepokWest JavaIndonesia
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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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Saminathan S, Kannan M, Ganesh KM, Mazarello J, Fernandes R. Characteristics Performance of Newly Developed Parallel Plate Chamber in Electron Beams. J Med Phys 2023; 48:333-337. [PMID: 38223789 PMCID: PMC10783180 DOI: 10.4103/jmp.jmp_76_23] [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: 06/14/2023] [Revised: 09/26/2023] [Accepted: 09/30/2023] [Indexed: 01/16/2024] Open
Abstract
Background To investigate the dosimetric performance of newly developed parallel plate chamber in electron beams. Materials and Methods Rosalina Instruments India Private Limited (Mumbai, Maharashtra, India) has designed and fabricated PRATT2 parallel plate chamber. The various dosimetric characteristics, including pre- and post-irradiation leakage, stability, polarity effect, chamber response with bias voltage, dose linearity, dose rate effect, and chamber absorbed dose calibration, were performed for the developed chamber. The electron beam energies of 4, 6, 8, and 15MeV were used in this study. Results The pre- and post-irradiation leakage of the developed chamber was within the acceptable limit. The chamber shows good stability over the electron beams used in this study. The maximum error in polarity effect was 0.7% for the developed chamber. The chamber shows the good linear response with dose, and its response is independent of the dose rate for all electron beams. The beam quality correction factor (kQ, Q0) was determined for the all electron beam energies, which was used for determination absorbed dose in electron beams. Discussion The developed parallel plate chamber (PRATT2) is suitable for dosimetry of electron beams in radiotherapy. The chamber is cost effective and shows precise and reproducible response. The study carried out confirms that the newly designed and fabricated ion chamber can be used in the measurement of absorbed dose for therapeutic electron beams.
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Affiliation(s)
- Sathiyan Saminathan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - Mageshraja Kannan
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
| | - K. M. Ganesh
- Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India
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Hosseini Bojdani SM, Baghani HR, Robatjazi M, Andreoli S, Azadegan B. Comparison of derived correction factors for effects of ion recombination and photon beam quality index following TG-51 and TRS-398 dosimetry protocols. Appl Radiat Isot 2023; 197:110796. [PMID: 37037135 DOI: 10.1016/j.apradiso.2023.110796] [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: 09/14/2022] [Revised: 03/07/2023] [Accepted: 03/28/2023] [Indexed: 04/12/2023]
Abstract
In this study, ion recombination correction factor (kS) and beam quality conversion factor ( [Formula: see text] ) values were extracted following the recommendations of the TRS-398 and TG-51 dosimetry protocols for widely used cylindrical ionization chambers for high energy photon beam dosimetry to quantify the agreement between the instructions for these two protocols for absolute dosimetry inside water. Four different types of cylindrical ionization chambers comprising Farmer (TM30013), Semiflex 0.125 cm3 (TM31010), Semiflex 0.3 cm3 (TM31013), and PinPoint (TM31016) were considered, and kS and [Formula: see text] values were determined at photon energies of 6 MV and 15 MV. The maximum difference between the measured kS values according to the instructions in the TRS-398 and TG-51 protocols was 0.03%. The kS data measured with both protocols agreed well with those measured by using the Jaffe-plot approach, where the maximum difference was about 0.33%. The observed differences between the [Formula: see text] factors measured by using the TRS-398 and TG-51 dosimetry protocols at photon energies of 6 MV and 15 MV were 0.37% and 0.55%, respectively. The [Formula: see text] values measured using the TG-51 dosimetry protocols were slightly closer to those measured by a reference ionization chamber dosimeter. We conclude that the maximum differences were about 0.4% and 0.6% in the absorbed dose measurements according to the TRS-398 and TG-51 instructions at photon energies of 6 MV and 15 MV, respectively. The type of ionization chamber employed also affected the differences, where the maximum and minimum dose differences were found using the Farmer and PinPoint chambers, respectively.
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Affiliation(s)
| | | | - Mostafa Robatjazi
- Medical Physics and Radiological Sciences Department, Sabzevar University of Medical Sciences, Sabzevar, Iran
| | | | - Behnam Azadegan
- Physics Department, Hakim Sabzevari University, Sabzevar, Iran
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Muir B, Culberson W, Davis S, Kim GGY, Lee SW, Lowenstein J, Renaud J, Sarfehnia A, Siebers J, Tantôt L, Tolani N. AAPM WGTG51 Report 374: Guidance for TG-51 reference dosimetry. Med Phys 2022; 49:6739-6764. [PMID: 36000424 DOI: 10.1002/mp.15949] [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: 10/20/2021] [Revised: 07/21/2022] [Accepted: 07/27/2022] [Indexed: 12/13/2022] Open
Abstract
Practical guidelines that are not explicit in the TG-51 protocol and its Addendum for photon beam dosimetry are presented for the implementation of the TG-51 protocol for reference dosimetry of external high-energy photon and electron beams. These guidelines pertain to: (i) measurement of depth-ionization curves required to obtain beam quality specifiers for the selection of beam quality conversion factors, (ii) considerations for the dosimetry system and specifications of a reference-class ionization chamber, (iii) commissioning a dosimetry system and frequency of measurements, (iv) positioning/aligning the water tank and ionization chamber for depth ionization and reference dose measurements, (v) requirements for ancillary equipment needed to measure charge (triaxial cables and electrometers) and to correct for environmental conditions, and (vi) translation from dose at the reference depth to that at the depth required by the treatment planning system. Procedures are identified to achieve the most accurate results (errors up to 8% have been observed) and, where applicable, a commonly used simplified procedure is described and the impact on reference dosimetry measurements is discussed so that the medical physicist can be informed on where to allocate resources.
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Affiliation(s)
- Bryan Muir
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Wesley Culberson
- Department of Medical Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States
| | - Stephen Davis
- Radiation Oncology, Miami Cancer Institute, Miami, Florida, United States
| | - Grace Gwe-Ya Kim
- Department of Radiation Medicine and Applied Sciences, UC San Diego School of Medicine, La Jolla, California, United States
| | - Sung-Woo Lee
- Department of Radiation Oncology, University of Maryland School of Medicine, Columbia, Maryland, United States
| | - Jessica Lowenstein
- Department of Radiation Physics, UT M.D. Anderson Cancer Center, Houston, Texas, United States
| | - James Renaud
- Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada
| | - Arman Sarfehnia
- Department of Radiation Oncology, University of Toronto, Toronto, Ontario, Canada
| | - Jeffrey Siebers
- Department of Radiation Oncology, University of Virginia Health System, Charlottesville, Virginia, United States
| | - Laurent Tantôt
- Département de radio-oncologie, CIUSSS de l'Est-de-l'Île-de-Montréal - Hôpital Maisonneuve-Rosemont, Montreal, Quebec, Canada
| | - Naresh Tolani
- Department of Radiation Therapy, Michael E. DeBakey VA Medical Center, Houston, Texas, United States
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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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Konradsson E, Ceberg C, Lempart M, Blad B, Bäck S, Knöös T, Petersson K. Correction for Ion Recombination in a Built-in Monitor Chamber of a Clinical Linear Accelerator at Ultra-High Dose Rates. Radiat Res 2021; 194:580-586. [PMID: 33348371 DOI: 10.1667/rade-19-00012] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 04/29/2020] [Indexed: 11/03/2022]
Abstract
In the novel and promising radiotherapy technique known as FLASH, ultra-high dose-rate electron beams are used. As a step towards clinical trials, dosimetric advances will be required for accurate dose delivery of FLASH. The purpose of this study was to determine whether a built-in transmission chamber of a clinical linear accelerator can be used as a real-time dosimeter to monitor the delivery of ultra-high-dose-rate electron beams. This was done by modeling the drop-in ion-collection efficiency of the chamber with increasing dose-per-pulse values, so that the ion recombination effect could be considered. The raw transmission chamber signal was extracted from the linear accelerator and its response was measured using radiochromic film at different dose rates/dose-per-pulse values, at a source-to-surface distance of 100 cm. An increase of the polarizing voltage, applied over the transmission chamber, by a factor of 2 and 3, improved the ion-collection efficiency, with corresponding increased efficiency at the highest dose-per-pulse values by a factor 1.4 and 2.2, respectively. The drop-in ion-collection efficiency with increasing dose-per-pulse was accurately modeled using a logistic function fitted to the transmission chamber data. The performance of the model was compared to that of the general theoretical Boag models of ion recombination in ionization chambers. The logistic model was subsequently used to correct for ion recombination at dose rates ranging from conventional to ultra-high, making the transmission chamber useful as a real-time monitor for the dose delivery of FLASH electron beams in a clinical setup.
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Affiliation(s)
- Elise Konradsson
- Medical Radiation Physics, Department of Clinical Science, Lund University, Lund, Sweden
| | - Crister Ceberg
- Medical Radiation Physics, Department of Clinical Science, Lund University, Lund, Sweden
| | - Michael Lempart
- Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden
| | - Börje Blad
- Medical Radiation Physics, Department of Clinical Science, Lund University, Lund, Sweden.,Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden
| | - Sven Bäck
- Medical Radiation Physics, Department of Clinical Science, Lund University, Lund, Sweden.,Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden
| | - Tommy Knöös
- Medical Radiation Physics, Department of Clinical Science, Lund University, Lund, Sweden.,Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden
| | - Kristoffer Petersson
- Radiation Physics, Department of Hematology, Oncology and Radiation Physics, Skåne University Hospital, Lund, Sweden.,The CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, University of Oxford, Oxford, United Kingdom
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11
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Performance characteristics of some cylindrical ion chamber dosimeters in Megavoltage (MV) photon beam according to TRS-398 dosimetry protocol. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2020.109299] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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12
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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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13
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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: 114] [Impact Index Per Article: 28.5] [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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14
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Schönfeld AB, Schönfeld AA, Looe HK, Poppe B, de Wilde RL. Experimental determination of the recombination correction factor kS for SNC 125c, SNC 350p and SNC 600c ionization chambers in pulsed photon beams. Z Med Phys 2020; 30:300-304. [DOI: 10.1016/j.zemedi.2020.03.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 03/06/2020] [Accepted: 03/06/2020] [Indexed: 10/24/2022]
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15
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Baghani HR, Robatjazi M. Charge collection efficiency determination for a Farmer-type ion chamber through different recommended methods. Radiat Phys Chem Oxf Engl 1993 2020. [DOI: 10.1016/j.radphyschem.2020.108865] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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16
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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] [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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17
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Rossomme S, Delor A, Lorentini S, Vidal M, Brons S, Jäkel O, Cirrone GAP, Vynckier S, Palmans H. Three-voltage linear method to determine ion recombination in proton and light-ion beams. Phys Med Biol 2020; 65:045015. [PMID: 31365915 DOI: 10.1088/1361-6560/ab3779] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A new practical method to determine the ion recombination correction factor (k s ) for plane-parallel and Farmer-type cylindrical chambers in particle beams is investigated. Experimental data were acquired in passively scattered and scanned particle beams and compared with theoretical models developed by Boag and/or Jaffé. The new method, named the three-voltage linear method (3VL-method), is simple and consists of determining the saturation current using the current measured at three voltages in a linear region and dividing it by the current at the operating voltage (V) (even if it is not in the linear region) to obtain k s . For plane-parallel chambers, comparing k s -values obtained by model fits to values obtained using the 3VL-method, an excellent agreement is found. For cylindrical chambers, recombination is due to volume recombination only. At low voltages, volume recombination is too large and Boag's models are not applicable. However, for Farmer-type chambers (NE2571), using a smaller voltage range, limited down to 100 V, we observe a linear variation of k s with 1/V 2 or 1/V for continuous or pulsed beams, respectively. This linearity trend allows applying the 3VL-method to determine k s at any polarizing voltage. For the particle beams used, the 3VL-method gives an accurate determination of k s at any polarizing voltage. The choice of the three voltages must to be done with care to ensure to be in a linear region. For Roos-type or Markus-type chambers (i.e. chambers with an electrode spacing of 2 mm) and NE2571 chambers, the use of the 3VL-method with 300 V, 200 V and 150 V is adequate. A difference with the 2V-method and some 3V-methods in the literature is that in the 3VL-method the operational voltage does not have to be one of the three voltages. An advantage over a 2V-method is that the 3VL-method can inherently verify if the linearity condition is fulfilled.
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Affiliation(s)
- S Rossomme
- Molecular Imaging, Radiotherapy and Oncology, Institute for Experimental and Clinical Research, Université catholique de Louvain, Brussels, Belgium. Current email address. Author to whom any correspondence should be addressed
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18
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Avanzo M, Dassie A, Chandra Acharya P, Chiovati P, Pirrone G, Avigo C, Barresi L, Dang Quoc S, Fiagbedzi E, Navarria F, Palazzari E, Bertola G, De Paoli A, Stancanello J, Sartor G. Electron radiotherapy (IOERT) for applications outside of the breast: Dosimetry and influence of tissue inhomogeneities. Phys Med 2020; 69:82-89. [PMID: 31841774 DOI: 10.1016/j.ejmp.2019.12.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Revised: 11/17/2019] [Accepted: 12/04/2019] [Indexed: 12/12/2022] Open
Abstract
PURPOSE The purpose of study is to investigate the dosimetry of electron intraoperative radiotherapy (IOERT) of the Intraop Mobetron 2000 mobile LINAC in treatments outside of the breast. After commissioning and external validation of dosimetry, we report in vivo results of measurements for treatments outside the breast in a large patient cohort, and investigate if the presence of inhomogeneities can affect in vivo measurements. METHODS AND MATERIALS Applicator factors and profile curves were measured with a stereotactic diode. The applicators factors of the 6 cm flat and beveled applicators were also confirmed with radiochromic films, parallel-plate ion chamber and by an external audit performed with ThermoLuminescent Dosimeters (TLDs). The influence of bone on dose was investigated by using radiochromic films attached to an insert equivalent to cortical bone, immersed in the water phantom. In vivo dosimetry was performed on 126 patients treated with IOERT using metal oxide-silicon semiconductor field effect transistors (MOSFETs) placed on the tumor bed. RESULTS Relatively small differences were found among different detectors for measurements of applicator factors. In the external audit, the agreement with the TLD was mostly within ±0.2%. The largest increase of dose due to the presence of cortical bone insert was +6.0% with energy 12 MeV and 3 cm applicator. On average, in vivo dose was significantly (+3.1%) larger than prescribed dose. CONCLUSION IOERT in applications outside the breast results in low discrepancies between in vivo and prescribed doses, which can be also explained with the presence of tissue inhomogeneity.
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Affiliation(s)
- Michele Avanzo
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy.
| | - Andrea Dassie
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | | | - Paola Chiovati
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Giovanni Pirrone
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Cinzia Avigo
- Medical Physics, ULSS 1 Dolomiti- S. Martino Hospital, Medical Physics Department, Belluno, Italy
| | - Loredana Barresi
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Soai Dang Quoc
- Medicinal Supplies, Medical Physics Division, Hanoi Oncology Hospital, Hanoi, Vietnam
| | | | - Federico Navarria
- Radiation Oncology, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Elisa Palazzari
- Radiation Oncology, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Giulio Bertola
- Surgical Oncology, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | - Antonino De Paoli
- Radiation Oncology, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
| | | | - Giovanna Sartor
- Department of Medical Physics, Centro di Riferimento Oncologico di Aviano (CRO) IRCCS, 33081 Aviano, Italy
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19
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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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20
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Bourgouin A, Cojocaru C, Ross C, McEwen M. Determination of
W
air
in high‐energy electron beams using graphite detectors. Med Phys 2019; 46:5195-5208. [DOI: 10.1002/mp.13772] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2019] [Revised: 07/09/2019] [Accepted: 08/01/2019] [Indexed: 11/09/2022] Open
Affiliation(s)
- Alexandra Bourgouin
- Department of Physics Carleton University Ottawa ON K1S 5B6 Canada
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Claudiu Cojocaru
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Carl Ross
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
| | - Malcolm McEwen
- Ionizing Radiation Standards National Research Council of Canada Ottawa ON K1A 0R6Canada
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21
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Mirandola A, Magro G, Maestri D, Mairani A, Mastella E, Molinelli S, Russo S, Vai A, Ciocca M. Determination of ion recombination and polarity effect correction factors for a plane-parallel ionization Bragg peak chamber under proton and carbon ion pencil beams. Phys Med Biol 2019; 64:095010. [PMID: 30844771 DOI: 10.1088/1361-6560/ab0db4] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Within the dosimetric characterization of particle beams, laterally-integrated depth-dose-distributions (IDDs) are measured and provided to the treatment planning system (TPS) for beam modeling or used as a benchmark for Monte Carlo (MC) simulations. The purpose of this work is the evaluation, in terms of ion recombination and polarity effect, of the dosimetric correction to be applied to proton and carbon ion curves as a function of linear energy transfer (LET). LET was calculated with a MC code for selected IDDs. Several regions of Bragg peak (BP) curve were investigated. The charge was measured with the plane-parallel BP-ionization chamber mounted in the Peakfinder as a field detector, by delivering a fixed number of particles at the maximum flux. The dose rate dependence was evaluated for different flux levels. The chamber was connected to an electrometer and exposed to un-scanned pencil beams. For each measurement the chamber was supplied with {±400, +200, +100} V. Recombination and polarity correction factors were then calculated as a function of depth and LET in water. Three energies representative of the clinical range were investigated for both particle types. The corrected IDDs (IDD k s) were then compared against MC. Recombination correction factors were LET and energy dependent, ranging from 1.000 to 1.040 (±0.5%) for carbon ions, while nearly negligible for protons. Moreover, no corrections need to be applied due to polarity effect being <0.5% along the whole IDDs for both particle types. IDD k s showed a better agreement than uncorrected curves when compared to MC, with a reduction of the mean absolute variation from 1.2% to 0.9%. The aforementioned correction factors were estimated and applied along the IDDs, showing an improved agreement against MC. Results confirmed that corrections are not negligible for carbon ions, particularly around the BP region.
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Affiliation(s)
- A Mirandola
- Centro Nazionale di Adroterapia Oncologica (CNAO Foundation), I-27100 Pavia, Italy. Author to whom any correspondence should be addressed
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22
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Simulation and experimental validation of a prototype electron beam linear accelerator for preclinical studies. Phys Med 2019; 60:50-57. [DOI: 10.1016/j.ejmp.2019.03.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 03/12/2019] [Accepted: 03/17/2019] [Indexed: 11/24/2022] 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] [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 Physics, Medipol University Institute of Health Sciences, Istanbul, Turkey.,Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Gökhan Aydın
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Teuta Zoto Mustafayev
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
| | - Enis Özyar
- Department of Radiation Oncology, Acıbadem Mehmet Ali Aydınlar University School of Medicine, Istanbul, Turkey
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24
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Bruggmoser G, Saum R, Kranzer R. Determination of recombination and polarity correction factors, k S and k P , for small cylindrical ionization chambers PTW 31021 and PTW 31022 in pulsed filtered and unfiltered beams. Z Med Phys 2018; 28:247-253. [DOI: 10.1016/j.zemedi.2017.09.010] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2017] [Revised: 09/20/2017] [Accepted: 09/20/2017] [Indexed: 01/08/2023]
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de Prez L, de Pooter J, Jansen B, Perik T, Wittkämper F. Comparison of k Q factors measured with a water calorimeter in flattening filter free (FFF) and conventional flattening filter (cFF) photon beams. Phys Med Biol 2018; 63:045023. [PMID: 29461974 DOI: 10.1088/1361-6560/aaaa93] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recently flattening filter free (FFF) beams became available for application in modern radiotherapy. There are several advantages of FFF beams over conventional flattening filtered (cFF) beams, however differences in beam spectra at the point of interest in a phantom potentially affect the ion chamber response. Beams are also non-uniform over the length of a typical reference ion chamber and recombination is usually larger. Despite several studies describing FFF beam characteristics, only a limited number of studies investigated their effect on k Q factors. Some of those studies predicted significant discrepancies in k Q factors (0.4% up to 1.0%) if TPR20,10 based codes of practice (CoPs) were to be used. This study addresses the question to which extent k Q factors, based on a TPR20,10 CoP, can be applied in clinical reference dosimetry. It is the first study that compares k Q factors measured directly with an absorbed dose to water primary standard in FFF-cFF pairs of clinical photon beams. This was done with a transportable water calorimeter described elsewhere. The measurements corrected for recombination and beam radial non-uniformity were performed in FFF-cFF beam pairs at 6 MV and 10 MV of an Elekta Versa HD for a selection of three different Farmer-type ion chambers (eight serial numbers). The ratio of measured k Q factors of the FFF-cFF beam pairs were compared with the TPR20,10 CoPs of the NCS and IAEA and the %dd(10) x CoP of the AAPM. For the TPR20,10 based CoPs differences less than 0.23% were found in k Q factors between the corresponding FFF-cFF beams with standard uncertainties smaller than 0.35%, while for the %dd(10) x these differences were smaller than 0.46% and within the expanded uncertainty of the measurements. Based on the measurements made with the equipment described in this study the authors conclude that the k Q factors provided by the NCS-18 and IAEA TRS-398 codes of practice can be applied for flattening filter free beams without additional correction. However, existing codes of practice cannot be applied ignoring the significant volume averaging effect of the FFF beams over the ion chamber cavity. For this a corresponding volume averaging correction must be applied.
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Affiliation(s)
- Leon de Prez
- VSL-Dutch Metrology Institute, Delft, Netherlands
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Liszka M, Stolarczyk L, Kłodowska M, Kozera A, Krzempek D, Mojżeszek N, Pędracka A, Waligórski MPR, Olko P. Ion recombination and polarity correction factors for a plane-parallel ionization chamber in a proton scanning beam. Med Phys 2017; 45:391-401. [DOI: 10.1002/mp.12668] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Revised: 09/28/2017] [Accepted: 10/27/2017] [Indexed: 11/11/2022] Open
Affiliation(s)
- Małgorzata Liszka
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Liliana Stolarczyk
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
- Skandionkliniken; von Kraemers Allé 26 Uppsala 752 37 Sweden
| | - Magdalena Kłodowska
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Anna Kozera
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Dawid Krzempek
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Natalia Mojżeszek
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Anna Pędracka
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); The Bronowice Cyclotron Centre (CCB); Radzikowskiego 152 Krakow 31-342 Poland
| | - Michael Patrick Russell Waligórski
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); Division of Applied Physics; Proton Radiotherapy Group; Radzikowskiego 152 Krakow 31-342 Poland
- The Maria Skłodowska-Curie Memorial Centre of Oncology; Krakow Division; Garncarska 11 31-115 Krakow Poland
| | - Paweł Olko
- Institute of Nuclear Physics Polish Academy of Sciences in Krakow (IFJ PAN); Division of Applied Physics; Proton Radiotherapy Group; Radzikowskiego 152 Krakow 31-342 Poland
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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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Rossomme S, Horn J, Brons S, Jäkel O, Mairani A, Ciocca M, Floquet V, Romano F, Rodriguez Garcia D, Vynckier S, Palmans H. Ion recombination correction factor in scanned light-ion beams for absolute dose measurement using plane-parallel ionisation chambers. Phys Med Biol 2017; 62:5365-5382. [DOI: 10.1088/1361-6560/aa730f] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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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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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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Rossomme S, Hopfgartner J, Lee ND, Delor A, Thomas RAS, Romano F, Fukumura A, Vynckier S, Palmans H. Ion recombination correction in carbon ion beams. Med Phys 2016; 43:4198. [DOI: 10.1118/1.4953637] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Determination of the ion recombination correction factor for intraoperative electron beams. Z Med Phys 2016; 26:35-44. [DOI: 10.1016/j.zemedi.2015.06.011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Revised: 05/29/2015] [Accepted: 06/15/2015] [Indexed: 11/15/2022]
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McEwen M, DeWerd L, Ibbott G, Followill D, Rogers DWO, Seltzer S, Seuntjens J. Addendum to the AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon beams. Med Phys 2014; 41:041501. [PMID: 24694120 PMCID: PMC5148035 DOI: 10.1118/1.4866223] [Citation(s) in RCA: 200] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Revised: 02/03/2014] [Accepted: 02/06/2014] [Indexed: 11/07/2022] Open
Abstract
An addendum to the AAPM's TG-51 protocol for the determination of absorbed dose to water in megavoltage photon beams is presented. This addendum continues the procedure laid out in TG-51 but new kQ data for photon beams, based on Monte Carlo simulations, are presented and recommendations are given to improve the accuracy and consistency of the protocol's implementation. The components of the uncertainty budget in determining absorbed dose to water at the reference point are introduced and the magnitude of each component discussed. Finally, the consistency of experimental determination of ND,w coefficients is discussed. It is expected that the implementation of this addendum will be straightforward, assuming that the user is already familiar with TG-51. The changes introduced by this report are generally minor, although new recommendations could result in procedural changes for individual users. It is expected that the effort on the medical physicist's part to implement this addendum will not be significant and could be done as part of the annual linac calibration.
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Affiliation(s)
- Malcolm McEwen
- National Research Council, 1200 Montreal Road, Ottawa, Ontario, Canada
| | - Larry DeWerd
- University of Wisconsin, 1111 Highland Avenue, Madison, Wisconsin 53705
| | - Geoffrey Ibbott
- Department of Radiation Physics, M D Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030
| | - David Followill
- IROC Houston QA Center, Radiological Physics Center, 8060 El Rio Street, Houston, Texas 77054
| | - David W O Rogers
- Carleton Laboratory for Radiotherapy Physics, Physics Department, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada
| | - Stephen Seltzer
- National Institute of Standards and Technology, Gaithersburg, Maryland 20899
| | - Jan Seuntjens
- Medical Physics Unit, McGill University, 1650 Cedar Avenue, Montreal, Québec, Canada
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Kry SF, Popple R, Molineu A, Followill DS. Ion recombination correction factors (P(ion)) for Varian TrueBeam high-dose-rate therapy beams. J Appl Clin Med Phys 2012; 13:3803. [PMID: 23149774 PMCID: PMC5718527 DOI: 10.1120/jacmp.v13i6.3803] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2011] [Revised: 07/12/2012] [Accepted: 07/22/2012] [Indexed: 11/23/2022] Open
Abstract
Ion recombination is approximately corrected for in the Task Group 51 protocol by Pion, which is calculated by a two‐voltage measurement. This measurement approach may be a poor estimate of the true recombination, particularly if Pion is large (greater than 1.05). Concern exists that Pion in high‐dose‐per‐pulse beams, such as flattening filter free (FFF) beams, may be unacceptably high, rendering the two‐voltage measurement technique inappropriate. Therefore, Pion was measured for flattened beams of 6, 10, 15, and 18 MV and for FFF beams of 6 and 10 MV. The values for the FFF beams were verified with 1/V versus 1/Q curves (Jaffé plots). Pion was also measured for electron beams of 6, 12, 16, 18, and 20 MeV on a traditional accelerator, as well as on the high‐dose‐rate Varian TrueBeam accelerator. The measurements were made at a range of depths and with PTW, NEL, and Exradin Farmer‐type chambers. Consistent with the increased dose per pulse, Pion was higher for FFF beams than for flattening filter beams. However, for all beams, measurement locations, and chambers examined, Pion never exceeded 1.018. Additionally, Pion was always within 0.3% of the recombination calculated from the Jaffé plots. We conclude that ion recombination can be adequately accounted for in high‐dose‐rate FFF beams using Pion determined with the standard two‐voltage technique. PACS numbers: 87.56.‐v, 87.56.Da
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Affiliation(s)
- Stephen F Kry
- Department of Radiation Physics, Radiological Physics Center, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
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Andersson J, Kaiser FJ, Gómez F, Jäkel O, Pardo-Montero J, Tölli H. A comparison of different experimental methods for general recombination correction for liquid ionization chambers. Phys Med Biol 2012; 57:7161-75. [DOI: 10.1088/0031-9155/57/21/7161] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Zink K, Wulff J. Beam quality corrections for parallel-plate ion chambers in electron reference dosimetry. Phys Med Biol 2012; 57:1831-54. [DOI: 10.1088/0031-9155/57/7/1831] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Muir BR, McEwen MR, Rogers DWO. Beam quality conversion factors for parallel-plate ionization chambers in MV photon beams. Med Phys 2012; 39:1618-31. [DOI: 10.1118/1.3687864] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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40
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Karsch L, Richter C, Pawelke J. Experimentelle Untersuchung der Sättigungskorrektion einer PTW Roos-Ionisationskammer in gepulsten Strahlungsfeldern mit hoher Pulsdosis bei verschiedenen Pulsdauern. Z Med Phys 2011; 21:4-10. [DOI: 10.1016/j.zemedi.2010.10.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Revised: 10/22/2010] [Accepted: 10/25/2010] [Indexed: 10/18/2022]
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McEwen MR. Measurement of ionization chamber absorbed dose kQ factors in megavoltage photon beams. Med Phys 2010; 37:2179-93. [DOI: 10.1118/1.3375895] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Bass G, Thomas R, Pearce J. The calibration of parallel-plate electron ionization chambers at NPL for use with the IPEM 2003 code of practice: summary data. Phys Med Biol 2009; 54:N115-24. [DOI: 10.1088/0031-9155/54/8/n01] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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43
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Castro P, García-Vicente F, Mínguez C, Floriano A, Sevillano D, Pérez L, Torres JJ. Study of the uncertainty in the determination of the absorbed dose to water during external beam radiotherapy calibration. J Appl Clin Med Phys 2008; 9:70-86. [PMID: 18449162 PMCID: PMC5721533 DOI: 10.1120/jacmp.v9i1.2676] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2007] [Revised: 06/24/2007] [Accepted: 08/21/2007] [Indexed: 11/23/2022] Open
Abstract
To achieve a good clinical outcome in radiotherapy treatment, a certain accuracy in the dose delivered to the patient is required. Therefore, it is necessary to keep the uncertainty in each of the steps of the process inside some acceptable values, which implies as low a global uncertainty as possible. The work reported here focused on the uncertainty evaluation of absorbed dose to water in the routine calibration for clinical beams in the range of energies used in external‐beam radiotherapy. With this aim, we considered various uncertainty components (corrected electrometer reading, calibration factor, beam quality correction factor, and reference conditions) associated with beam calibration. Results show a typical uncertainty in the determination of absorbed dose to water during beam calibration of approximately 1.3% for photon beams and 1.5% for electron beams (k=1 in both cases) when the ND,w formalism is used and kQ,Q0 is calculated theoretically. These values may vary depending on the uncertainty provided by the standards laboratory for calibration factor, which is shown in the work. For primary standards based on clinical linear accelerator beam energies, the uncertainty in this step of the process could be placed close to 1.0%. We also discuss the possibility of an uncertainty reduction with the adoption of the absorbed dose to water formalism as compared with the air kerma formalism. PACS numbers: 87.53.Dq, 87.53.Hv
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Affiliation(s)
- Pablo Castro
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - Feliciano García-Vicente
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - Cristina Mínguez
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - Alejandro Floriano
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - David Sevillano
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - Leopoldo Pérez
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
| | - Juan J Torres
- Servicio de Oncología Radioterápica, Departamento de Radiofísica, Hospital Universitario "La Princesa", Madrid, Spain
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Bruggmoser G, Saum R, Schmachtenberg A, Schmid F, Schüle E. Determination of the recombination correction factorkSfor some specific plane-parallel and cylindrical ionization chambers in pulsed photon and electron beams. Phys Med Biol 2006; 52:N35-50. [PMID: 17202615 DOI: 10.1088/0031-9155/52/2/n01] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
It has been shown from an evaluation of the inverse reading of the dosemeter (1/M) against the inverse of the polarizing voltage (1/V), obtained with a number of commercially available ionization chambers, using dose per pulse values between 0.16 and 5 mGy, that a linear relationship between the recombination correction factor kS and dose per pulse (DPP) can be found. At dose per pulse values above 1 mGy the method of a general equation with coefficients dependent on the chamber type gives more accurate results than the Boag method. This method was already proposed by Burns and McEwen (1998, Phys. Med. Biol. 43 2033) and avoids comprehensive and time-consuming measurements of Jaffé plots which are a prerequisite for the application of the multi-voltage analysis (MVA) or the two-voltage analysis (TVA). We evaluated and verified the response of ionization chambers on the recombination effect in pulsed accelerator beams for both photons and electrons. Our main conclusions are: (1) The correction factor k(S) depends only on the DPP and the chamber type. There is no influence of radiation type and energy. (2) For all the chambers investigated there is a linear relationship between kS and DPP up to 5 mGy/pulse, and for two chambers we could show linearity up to 40 mGy/pulse. (3) A general formalism, such as that of Boag, characterizes chambers exclusively by the distance of the electrodes and gives a trend for the correction factor, and therefore (4) a general formalism has to reflect the influence of the chamber construction on the recombination by the introduction of chamber-type dependent coefficients.
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Affiliation(s)
- G Bruggmoser
- Univ.-Klinikum Freiburg, Klinik f Strahlenheilkunde, FB Med. Physik, Freiburg, Germany.
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45
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Pearce J, Thomas R, Dusautoy A. The characterization of the Advanced Markus ionization chamber for use in reference electron dosimetry in the UK. Phys Med Biol 2006; 51:473-83. [PMID: 16424576 DOI: 10.1088/0031-9155/51/3/001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The IPEM Code of Practice (IPEM 2003) for electron dosimetry for radiotherapy beams recommends design requirements for parallel-plate ionization chambers used to determine absorbed dose to water in an electron beam. The Classic Markus design has been found not to meet these requirements. The Advanced Markus ionization chamber has been designed to rectify the problems associated with the Classic Markus ionization chamber. The response of three Advanced Markus ionization chambers was investigated and compared to the designated chamber types. Absorbed dose to water calibration factors were derived at the National Physical Laboratory (NPL) for each ionization chamber at seven electron energies in the range nominally 4-19 MeV. Investigations were carried out into chamber settling, polarity effects, ion recombination and the chamber perturbation. The response of the ionization chambers in a clinical beam was also investigated. In general all three Advanced Markus ionization chambers showed the same energy response. The magnitude of the polarity effect was typically 5% at a nominal energy of 4 MeV. There was discrepancy between the polarity measurements made at the NPL and in the clinic. The recommendation of this study is that this chamber type is not suitable for reference dosimetry in electron beams.
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Affiliation(s)
- Julia Pearce
- Radiation Dosimetry Group, National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK.
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46
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Di Martino F, Giannelli M, Traino AC, Lazzeri M. Ion recombination correction for very high dose-per-pulse high-energy electron beams. Med Phys 2005; 32:2204-2210. [PMID: 16121574 DOI: 10.1118/1.1940167] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2004] [Accepted: 04/30/2005] [Indexed: 11/07/2022] Open
Abstract
The parallel-plate ionization chamber is the recommended tool for the absorbed dose measurement in pulsed high-energy electron beams. Typically, the electron beams used in radiotherapy have a dose-per-pulse value less then 0.1 cGy/pulse. In this range the factor to correct the response of an ionization chamber for the lack of complete charge collection due to ion recombination (ksat) can be properly evaluated with the standard "two voltage" method proposed by the international dosimetric reports. Very high dose-per-pulse electron beams are employed in some special Linac dedicated to the Intra-Operatory-Radiation-Therapy (IORT). The high dose-per-pulse values (3-13 cGy/pulse) characterizing the IORT electron beams allow to deliver the therapeutic dose (10-20 Gy) in less than a minute. This considerably reduces the IORT procedure time, but some dosimetric problems arise because the standard method to evaluate ksat overestimates its value by 20%. Moreover, if the dose-per-pulse value >1 cGy/pulse, the dependence of ksat on the dose-per-pulse value cannot be neglected for relative dosimetry. In this work the dependence of ksat on the dose-per-pulse value is derived, based on the general equation that describes the ion recombination in the Boag theory. A new equation for ksat, depending on known or measurable quantities, is presented. The new ksat equation is experimentally tested by comparing the absorbed doses to water measured with parallel-plate ionization chambers (Roos and Markus) to that measured using dose-per-pulse independent dosimeters, such as radiochromic films and chemical Fricke dosimeters. These measurements are performed in the high dose-per-pulse (3-13 cGy/pulse) electron beams of the IORT dedicated Linac Hitesys Novac7 (Aprilia-Latina, Italy). The dose measurements made using the parallel-plate chambers and those made using the dose-per-pulse independent dosimeters are in good agreement (<3%). This demonstrates the possibility of using the parallel-plate ionization chambers also for the very high dose-per-pulse (> 1 cGy/pulse) electron-beam dosimetry.
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Affiliation(s)
- F Di Martino
- UO Fisica Sanitaria, Sezione di Fisica Medica, Azienda Ospedaliera Universitaria Pisana, via Roma 67, 56126 Pisa, Italy.
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47
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Berg M, Noerrevang O. Recombination factors for the cylindrical FC65-G ionization chamber in pulsed photon beams and the plane-parallel Roos ionization chamber in pulsed electron beams. Phys Med Biol 2004; 49:5309-18. [PMID: 15656279 DOI: 10.1088/0031-9155/49/23/008] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The use of ionization chambers in linac radiotherapy dosimetry requires various corrections to the measured charges, one of these being the recombination correction. The recombination correction factor (k(s)) is generally estimated from the two-voltage analysis (TVA) for each beam quality. However, it is possible that the ionization chamber above some threshold polarizing voltage does not follow the accepted Boag theory very well. Secondly the TVA is time-consuming as the chamber needs to stabilize after each polarizing voltage change and since it must be performed for each beam quality. Another approach consists in using the fact that k(s) is predicted to depend linearly on dose per pulse by Boag theory: determining this relationship once and for all using a multi-voltage analysis (MVA), one also checks the range validity of the Boag theory for the chamber considered. This work presents a thorough analysis of k(s) dependence on dose per pulse of FC65-G (cylindrical) and Roos (plane-parallel) ionization chambers in pulsed photon and electron beams, respectively. Within the uncertainties, the recombination factors are found to be independent of beam quality, and no deviation from the Boag theory is observed within the tested range of polarizing voltages. Before adapting the equations given using the MVA other users should check that their ionization chambers show the same dose per pulse dependence using the TVA for a few beam qualities.
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Affiliation(s)
- Martin Berg
- Department of Medical Physics, Vejle Hospital, Kabbeltoft 25, DK-7100 Vejle, Denmark
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48
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Thwaites DI, DuSautoy AR, Jordan T, McEwen MR, Nisbet A, Nahum AE, Pitchford WG. The IPEM code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV based on an absorbed dose to water calibration. Phys Med Biol 2003; 48:2929-70. [PMID: 14529204 DOI: 10.1088/0031-9155/48/18/301] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This report contains the recommendations of the Electron Dosimetry Working Party of the UK Institute of Physics and Engineering in Medicine (IPEM). The recommendations consist of a code of practice for electron dosimetry for radiotherapy beams of initial energy from 4 to 25 MeV. The code is based on the absorbed dose to water calibration service for electron beams provided by the UK standards laboratory, the National Physical Laboratory (NPL). This supplies direct N(D,w) calibration factors, traceable to a calorimetric primary standard, at specified reference depths over a range of electron energies up to approximately 20 MeV. Electron beam quality is specified in terms of R(50,D), the depth in water along the beam central axis at which the dose is 50% of the maximum. The reference depth for any given beam at the NPL for chamber calibration and also for measurements for calibration of clinical beams is 0.6R(50.D) - 0.1 cm in water. Designated chambers are graphite-walled Farmer-type cylindrical chambers and the NACP- and Roos-type parallel-plate chambers. The practical code provides methods to determine the absorbed dose to water under reference conditions and also guidance on methods to transfer this dose to non-reference points and to other irradiation conditions. It also gives procedures and data for extending up to higher energies above the range where direct calibration factors are currently available. The practical procedures are supplemented by comprehensive appendices giving discussion of the background to the formalism and the sources and values of any data required. The electron dosimetry code improves consistency with the similar UK approach to megavoltage photon dosimetry, in use since 1990. It provides reduced uncertainties, approaching 1% standard uncertainty in optimal conditions, and a simpler formalism than previous air kerma calibration based recommendations for electron dosimetry.
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Affiliation(s)
- D I Thwaites
- Institute of Physics and Engineering in Medicine, Fairmount House, 230 Tadcaster Road, York YO24 1ES, UK
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Clift MA, Johnston PN, Webb DV. A temporal method of avoiding the Cerenkov radiation generated in organic scintillator dosimeters by pulsed mega-voltage electron and photon beams. Phys Med Biol 2002; 47:1421-33. [PMID: 12030564 DOI: 10.1088/0031-9155/47/8/313] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The output signal of an organic scintillator probe consists of a scintillation signal and Cerenkov and fluorescence radiation (CFR) signal when the probe is exposed to a mega-voltage photon or electron beam. The CFR signal is usually unwanted because it comes from both the scintillator and light guide and so it is not proportional to the absorbed dose in the scintillator. A new organic scintillator detector system has been constructed for absorbed dose measurement in pulsed mega-voltage electron and photon beams that are commonly used in radiotherapy treatment, eliminating most of the CFR signal. The new detector system uses a long decay constant BC-444G (Bicron, Newbury, OH, USA) scintillator which gives a signal that can be time resolved from the prompt CFR signal so that the measured contribution of prompt signal is negligible. The response of the new scintillator detector system was compared with the measurements from a plastic scintillator detector that were corrected for the signal contribution from the CFR, and to appropriately corrected ion chamber measurements showing agreement in the 16 MeV electron beam used.
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Affiliation(s)
- M A Clift
- Department of Applied Physics, Royal Melbourne Institute of Technology, Victoria, Australia.
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50
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Nohtomi A, Sakae T, Tsunashima Y, Kohno R. Dosimetry of pulsed clinical proton beams by a small ionization chamber. Med Phys 2001; 28:1431-5. [PMID: 11488575 DOI: 10.1118/1.1380435] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
Response of a micro volume (0.01 ml) ionization chamber has been studied with pulsed proton beams which are used for clinical purposes and has been compared with those of some JARP ionization chambers (0.6 ml). All chambers used had been calibrated by standard 60Co beams at the Electrotechnical Laboratory (ETL) and exposure calibration factors, Nx, were obtained on advance. Two methods are used to compensate the general recombination which occurs during pulsed beam irradiations: theoretical correction by a Boag's formulation and a modified two-voltage technique. An evaluation of absolute absorbed dose-to-water is performed on the basis of the protocol provided by ICRU report 59. The results imply that, to a first approximation, both chambers indicate the almost same result within 2% when unknown chamber-dependent parameters of the micro chamber are tentatively assumed to be identical to those of the JARP chamber for the calibration with 60Co beams. The about 1.5% discrepancy observed in the response of both chambers is not discussible due to presumably 1-2% uncertainty of the protocol of ICRU report 59 which does not include any chamber-dependent corrections for the perturbation effects in proton beams.
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Affiliation(s)
- A Nohtomi
- Proton Medical Research Center, University of Tsukuba, Japan.
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