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Das IJ, Francescon P, Moran JM, Ahnesjö A, Aspradakis MM, Cheng CW, Ding GX, Fenwick JD, Saiful Huq M, Oldham M, Reft CS, Sauer OA. Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non-equilibrium conditions. Med Phys 2021; 48:e886-e921. [PMID: 34101836 DOI: 10.1002/mp.15030] [Citation(s) in RCA: 53] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Revised: 05/06/2021] [Accepted: 06/02/2021] [Indexed: 12/14/2022] Open
Abstract
Small-field dosimetry used in advance treatment technologies poses challenges due to loss of lateral charged particle equilibrium (LCPE), occlusion of the primary photon source, and the limited choice of suitable radiation detectors. These challenges greatly influence dosimetric accuracy. Many high-profile radiation incidents have demonstrated a poor understanding of appropriate methodology for small-field dosimetry. These incidents are a cause for concern because the use of small fields in various specialized radiation treatment techniques continues to grow rapidly. Reference and relative dosimetry in small and composite fields are the subject of the International Atomic Energy Agency (IAEA) dosimetry code of practice that has been published as TRS-483 and an AAPM summary publication (IAEA TRS 483; Dosimetry of small static fields used in external beam radiotherapy: An IAEA/AAPM International Code of Practice for reference and relative dose determination, Technical Report Series No. 483; Palmans et al., Med Phys 45(11):e1123, 2018). The charge of AAPM task group 155 (TG-155) is to summarize current knowledge on small-field dosimetry and to provide recommendations of best practices for relative dose determination in small megavoltage photon beams. An overview of the issue of LCPE and the changes in photon beam perturbations with decreasing field size is provided. Recommendations are included on appropriate detector systems and measurement methodologies. Existing published data on dosimetric parameters in small photon fields (e.g., percentage depth dose, tissue phantom ratio/tissue maximum ratio, off-axis ratios, and field output factors) together with the necessary perturbation corrections for various detectors are reviewed. A discussion on errors and an uncertainty analysis in measurements is provided. The design of beam models in treatment planning systems to simulate small fields necessitates special attention on the influence of the primary beam source and collimating devices in the computation of energy fluence and dose. The general requirements for fluence and dose calculation engines suitable for modeling dose in small fields are reviewed. Implementations in commercial treatment planning systems vary widely, and the aims of this report are to provide insight for the medical physicist and guidance to developers of beams models for radiotherapy treatment planning systems.
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Affiliation(s)
- Indra J Das
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL, USA
| | - Paolo Francescon
- Department of Radiation Oncology, Ospedale Di Vicenza, Vicenza, Italy
| | - Jean M Moran
- Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
| | - Anders Ahnesjö
- Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - Maria M Aspradakis
- Institute of Radiation Oncology, Cantonal Hospital of Graubünden, Chur, Switzerland
| | - Chee-Wai Cheng
- Department of Radiation Oncology, University Hospitals Cleveland Medical Center, Cleveland, OH, USA
| | - George X Ding
- Department of Radiation Oncology, Vanderbilt University School of Medicine, Nashville, TN, USA
| | - John D Fenwick
- Molecular and Clinical Cancer Medicine, Institute of Systems, Molecular and Integrative Biology, University of Liverpool, Liverpool, UK
| | - M Saiful Huq
- Department of Radiation Oncology, University of Pittsburgh, School of Medicine and UPMC Hillman Cancer Center, Pittsburgh, PA, USA
| | - Mark Oldham
- Department of Radiation Oncology, Duke University Medical Center, Durham, NC, USA
| | - Chester S Reft
- Department of Radiation Oncology, University of Chicago, Chicago, IL, USA
| | - Otto A Sauer
- Department of Radiation Oncology, Klinik fur Strahlentherapie, University of Würzburg, Würzburg, Germany
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Wagner A, Brou Boni K, Rault E, Crop F, Lacornerie T, Van Gestel D, Reynaert N. Integration of the M6 Cyberknife in the Moderato Monte Carlo platform and prediction of beam parameters using machine learning. Phys Med 2020; 70:123-132. [PMID: 32007601 DOI: 10.1016/j.ejmp.2020.01.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Revised: 12/27/2019] [Accepted: 01/20/2020] [Indexed: 11/18/2022] Open
Abstract
PURPOSE This work describes the integration of the M6 Cyberknife in the Moderato Monte Carlo platform, and introduces a machine learning method to accelerate the modelling of a linac. METHODS The MLC-equipped M6 Cyberknife was modelled and integrated in Moderato, our in-house platform offering independent verification of radiotherapy dose distributions. The model was validated by comparing TPS dose distributions with Moderato and by film measurements. Using this model, a machine learning algorithm was trained to find electron beam parameters for other M6 devices, by simulating dose curves with varying spot size and energy. The algorithm was optimized using cross-validation and tested with measurements from other institutions equipped with a M6 Cyberknife. RESULTS Optimal agreement in the Monte Carlo model was reached for a monoenergetic electron beam of 6.75 MeV with Gaussian spatial distribution of 2.4 mm FWHM. Clinical plan dose distributions from Moderato agreed within 2% with the TPS, and film measurements confirmed the accuracy of the model. Cross-validation of the prediction algorithm produced mean absolute errors of 0.1 MeV and 0.3 mm for beam energy and spot size respectively. Prediction-based simulated dose curves for other centres agreed within 3% with measurements, except for one device where differences up to 6% were detected. CONCLUSIONS The M6 Cyberknife was integrated in Moderato and validated through dose re-calculations and film measurements. The prediction algorithm was successfully applied to obtain electron beam parameters for other M6 devices. This method would prove useful to speed up modelling of new machines in Monte Carlo systems.
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Affiliation(s)
- A Wagner
- Department of Medical Physics, Centre Oscar Lambret, Lille, France; Faculty of Biomedical Sciences, University of Brussels ULB, Belgium.
| | - K Brou Boni
- Department of Medical Physics, Centre Oscar Lambret, Lille, France; University of Lille, CNRS, CRIStAL, Centrale Lille, France
| | - E Rault
- Department of Medical Physics, Centre Oscar Lambret, Lille, France
| | - F Crop
- Department of Medical Physics, Centre Oscar Lambret, Lille, France
| | - T Lacornerie
- Department of Medical Physics, Centre Oscar Lambret, Lille, France
| | - D Van Gestel
- Faculty of Biomedical Sciences, University of Brussels ULB, Belgium; Department of Radiation Therapy, Institut Jules Bordet, Brussels, Belgium
| | - N Reynaert
- Department of Medical Physics, Centre Oscar Lambret, Lille, France; Faculty of Biomedical Sciences, University of Brussels ULB, Belgium; Department of Medical Physics, Institut Jules Bordet, Brussels, Belgium
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Kakade NR, Kumar R, Sharma SD, Mittal V, Datta D. Pretreatment Dose Verification in Volumetric Modulated Arc Therapy Using Liquid Ionization Chamber. J Med Phys 2019; 44:9-15. [PMID: 30983765 PMCID: PMC6438046 DOI: 10.4103/jmp.jmp_108_18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Purpose: The purpose of the present study was to evaluate the practicability of liquid ionization chamber (LIC) for pretreatment dose verification of the advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT). Materials and Methods: The dosimetric characteristics of LIC such as repeatability, sensitivity, monitor unit linearity, dose rate dependence, angular dependence, voltage-current response, and output factors were investigated in 6 MV therapeutic X-ray beams. The LIC was cross-calibrated against 0.125-cc air-filled thimble ionization chamber. A dedicated dosimetry insert made up of Perspex to incorporate the LIC at proper location in the intensity-modulated radiation therapy thorax phantom was locally fabricated. The collection efficiency and ion recombination correction factor was determined using the two-dose rate method. Pretreatment dose verification measurement of VMAT treatment plans were carried out using the liquid ionization chamber as well as small volume (0.125 cc) air-filled thimble ionization chamber. The measured dose values by the two dosimeters and TPS calculated dose at a given point were compared. Results: The relative percentage differences between the TPS calculated and measured doses were within ± 1.57% for LIC and ± 2.21% for 0.125 cc ionization chamber, respectively. Conclusions: The measured dose values by the two dosimeters and TPS calculated dose at a given point were found comparable suggesting that the LIC could be a good choice of dosimeter for pretreatment dose verification in VMAT.
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Affiliation(s)
- Nitin R Kakade
- Radiological Physics and Advisory Division, Bhabha Atomic Research Center, Anushaktinagar, Mumbai, Maharashtra, India.,Homi Bhabha National Institute, Anushaktinagar, Mumbai, Maharashtra, India
| | - Rajesh Kumar
- Radiological Physics and Advisory Division, Bhabha Atomic Research Center, Anushaktinagar, Mumbai, Maharashtra, India
| | - Sunil Dutt Sharma
- Radiological Physics and Advisory Division, Bhabha Atomic Research Center, Anushaktinagar, Mumbai, Maharashtra, India.,Homi Bhabha National Institute, Anushaktinagar, Mumbai, Maharashtra, India
| | - Vikram Mittal
- Department of Radiotherapy, P. D. Hinduja National Hospital, Mumbai, Maharashtra, India
| | - D Datta
- Radiological Physics and Advisory Division, Bhabha Atomic Research Center, Anushaktinagar, Mumbai, Maharashtra, India.,Homi Bhabha National Institute, Anushaktinagar, Mumbai, Maharashtra, India
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Reynaert N, Crop F, Sterpin E, Kawrakow I, Palmans H. On the conversion of dose to bone to dose to water in radiotherapy treatment planning systems. PHYSICS & IMAGING IN RADIATION ONCOLOGY 2018; 5:26-30. [PMID: 33458365 PMCID: PMC7807555 DOI: 10.1016/j.phro.2018.01.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/22/2017] [Revised: 12/21/2017] [Accepted: 01/17/2018] [Indexed: 11/16/2022]
Abstract
Background and purpose Conversion factors between dose to medium (Dm,m) and dose to water (Dw,w) provided by treatment planning systems that model the patient as water with variable electron density are currently based on stopping power ratios. In the current paper it will be illustrated that this conversion method is not correct. Materials and methods Monte Carlo calculations were performed in a phantom consisting of a 2 cm bone layer surrounded by water. Dw,w was obtained by modelling the bone layer as water with the electron density of bone. Conversion factors between Dw,w and Dm,m were obtained and compared to stopping power ratios and ratios of mass-energy absorption coefficients in regions of electronic equilibrium and interfaces. Calculations were performed for 6 MV and 20 MV photon beams. Results In the region of electronic equilibrium the stopping power ratio of water to bone (1.11) largely overestimates the conversion obtained using the Monte Carlo calculations (1.06). In that region the MC dose conversion corresponds to the ratio of mass energy absorption coefficients. Near the water to bone interface, the MC ratio cannot be determined from stopping powers or mass energy absorption coefficients. Conclusion Stopping power ratios cannot be used for conversion from Dm,m to Dw,w provided by treatment planning systems that model the patient as water with variable electron density, either in regions of electronic equilibrium or near interfaces. In regions of electronic equilibrium mass energy absorption coefficient ratios should be used. Conversions at interfaces require detailed MC calculations.
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Affiliation(s)
- Nick Reynaert
- Institut Jules Bordet, Belgium.,Centre Oscar Lambret, Lille, France
| | | | - Edmond Sterpin
- Katholieke Universiteit Leuven, Department of Oncology, Laboratory of Experimental Radiotherapy, Leuven, Belgium.,Université catholique de Louvain, Institut de Recherche expérimentale et Clinique, Center of Molecular Imaging, Radiotherapy and Oncology, Brussels, Belgium
| | - Iwan Kawrakow
- Viewray, 2 Thermo Fisher Way, Oakwood Village, OH 44146, USA
| | - Hugo Palmans
- National Physics Laboratory, Acoustics and Ionising Radiation Division, Teddington, TW 11 0LW, UK.,EBG MedAustron GmbH, Medical Physics Department, Wiener Neustadt A-2700, Austria
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Lebredonchel S, Lacornerie T, Rault E, Wagner A, Reynaert N, Crop F. About the non-consistency of PTV-based prescription in lung. Phys Med 2017; 44:177-187. [DOI: 10.1016/j.ejmp.2017.03.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2016] [Revised: 03/16/2017] [Accepted: 03/18/2017] [Indexed: 12/31/2022] Open
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Wagner A, Crop F, Mirabel X, Tailly C, Reynaert N. Use of an in-house Monte Carlo platform to assess the clinical impact of algorithm-related dose differences on DVH constraints. Phys Med 2017; 42:319-326. [PMID: 28662849 DOI: 10.1016/j.ejmp.2017.05.062] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 04/18/2017] [Accepted: 05/18/2017] [Indexed: 10/19/2022] Open
Abstract
PURPOSE The aim of the present work is to evaluate a semi-automatic prescription and validation system of treatment plans for complex delivery techniques, integrated in a Monte Carlo platform, and to investigate the clinical impact of dose differences due to the calculation algorithms, by assessing the changes in DVH constraints. METHODS A new prescription module was implemented into the Moderato system, an in-house Monte Carlo platform, with corresponding dose constraints generated depending on the anatomical region and fractionation scheme considered. The platform was tested on 83 cases treated with Cyberknife and Tomotherapy machines, to assess whether dose variations between the re-calculated dose and the Treatment Planning System might impact the dose constraints on the sensitive structures. RESULTS Dose differences were small (within 3%) between calculation algorithms in most of the thoracic, pelvic and abdominal cases, both for the Cyberknife and Tomotherapy machines. On the other hand, spinal and head and neck treatments presented a few significant dose deviations for constraints on small volumes, such as the optic pathways and the spinal cord. These differences range from -11% to +6%, inducing constraint violations of up to 8% over the dose limit. CONCLUSIONS The Moderato platform offers an interesting tool for plan quality validation, with a prescription module highlighting crucial features in the structures list, and a Monte Carlo dose re-calculation for complex modern techniques. Due to the high number of warnings appearing in some situations, display optimization is required in practice.
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Affiliation(s)
- A Wagner
- Department of Medical Physics, Centre Oscar Lambret and University Lille 1, France
| | - F Crop
- Department of Medical Physics, Centre Oscar Lambret and University Lille 1, France
| | - X Mirabel
- Academic Department of Radiation Oncology, Centre Oscar Lambret and University Lille 2, France
| | - C Tailly
- Department of Medical Physics, Centre Oscar Lambret and University Lille 1, France
| | - N Reynaert
- Department of Medical Physics, Centre Oscar Lambret and University Lille 1, France
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Benmakhlouf H, Andreo P. Spectral distribution of particle fluence in small field detectors and its implication on small field dosimetry. Med Phys 2017; 44:713-724. [DOI: 10.1002/mp.12042] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2016] [Revised: 11/14/2016] [Accepted: 11/27/2016] [Indexed: 11/07/2022] Open
Affiliation(s)
- Hamza Benmakhlouf
- Department of Medical Radiation Physics and Nuclear Medicine; Karolinska University Hospital; SE-17176 Stockholm Sweden
| | - Pedro Andreo
- Department of Medical Radiation Physics and Nuclear Medicine; Karolinska University Hospital; SE-17176 Stockholm Sweden
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Sutton JD, Littler JP. Accounting for the ion recombination factor in relative dosimetry of flattening filter free photon radiation. Biomed Phys Eng Express 2017. [DOI: 10.1088/2057-1976/aa5493] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Reynaert N, Demol B, Charoy M, Bouchoucha S, Crop F, Wagner A, Lacornerie T, Dubus F, Rault E, Comte P, Cayez R, Boydev C, Pasquier D, Mirabel X, Lartigau E, Sarrazin T. Clinical implementation of a Monte Carlo based treatment plan QA platform for validation of Cyberknife and Tomotherapy treatments. Phys Med 2016; 32:1225-1237. [DOI: 10.1016/j.ejmp.2016.09.009] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 09/12/2016] [Accepted: 09/13/2016] [Indexed: 10/21/2022] Open
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Godson HF, Ravikumar M, Ganesh K, Sathiyan S, Ponmalar YR. Small field output factors: Comparison of measurements with various detectors and effects of detector orientation with primary jaw setting. RADIAT MEAS 2016. [DOI: 10.1016/j.radmeas.2015.12.038] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Brualla-González L, Gómez F, Pombar M, Pardo-Montero J. Dose rate dependence of the PTW 60019 microDiamond detector in high dose-per-pulse pulsed beams. Phys Med Biol 2015; 61:N11-9. [PMID: 26625177 DOI: 10.1088/0031-9155/61/1/n11] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Recombination effects can affect the detectors used for the dosimetry of radiotherapy fields. They are important when using ionization chambers, especially in liquid-filled ionization chambers, and should be corrected for. The introduction of flattening-filter-free accelerators increases the typical dose-per-pulse used in radiotherapy beams, which leads to more important recombination effects. Diamond detectors provide a good solution for the dosimetry and quality assurance of small radiotherapy fields, due to their low energy dependence and small volume. The group of Università di Roma Tor Vergata has developed a synthetic diamond detector, which is commercialized by PTW as microDiamond detector type 60019. In this work we present an experimental characterization of the collection efficiency of the microDiamond detector, focusing on high dose-per-pulse FFF beams. The collection efficiency decreases with dose-per-pulse, down to 0.978 at 2.2 mGy/pulse, following a Fowler-Attix-like curve. On the other hand, we have found no significant dependence of the collection efficiency on the pulse repetition frequency (or pulse period).
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Affiliation(s)
- Luis Brualla-González
- Servicio de Radiofísica, ERESA, Hospital General Universitario de Valencia, 46014 València, Spain
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Demol B, Viard R, Reynaert N. Monte Carlo calculation based on hydrogen composition of the tissue for MV photon radiotherapy. J Appl Clin Med Phys 2015; 16:117–130. [PMID: 26699320 PMCID: PMC5690166 DOI: 10.1120/jacmp.v16i5.5586] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 04/14/2015] [Accepted: 04/09/2015] [Indexed: 12/04/2022] Open
Abstract
The purpose of this study was to demonstrate that Monte Carlo treatment planning systems require tissue characterization (density and composition) as a function of CT number. A discrete set of tissue classes with a specific composition is introduced. In the current work we demonstrate that, for megavoltage photon radiotherapy, only the hydrogen content of the different tissues is of interest. This conclusion might have an impact on MRI‐based dose calculations and on MVCT calibration using tissue substitutes. A stoichiometric calibration was performed, grouping tissues with similar atomic composition into 15 dosimetrically equivalent subsets. To demonstrate the importance of hydrogen, a new scheme was derived, with correct hydrogen content, complemented by oxygen (all elements differing from hydrogen are replaced by oxygen). Mass attenuation coefficients and mass stopping powers for this scheme were calculated and compared to the original scheme. Twenty‐five CyberKnife treatment plans were recalculated by an in‐house developed Monte Carlo system using tissue density and hydrogen content derived from the CT images. The results were compared to Monte Carlo simulations using the original stoichiometric calibration. Between 300 keV and 3 MeV, the relative difference of mass attenuation coefficients is under 1% within all subsets. Between 10 keV and 20 MeV, the relative difference of mass stopping powers goes up to 5% in hard bone and remains below 2% for all other tissue subsets. Dose‐volume histograms (DVHs) of the treatment plans present no visual difference between the two schemes. Relative differences of dose indexes D98,D95,D50,D05,D02, and Dmean were analyzed and a distribution centered around zero and of standard deviation below 2% (3σ) was established. On the other hand, once the hydrogen content is slightly modified, important dose differences are obtained. Monte Carlo dose planning in the field of megavoltage photon radiotherapy is fully achievable using only hydrogen content of tissues, a conclusion that might impact MRI dose calculation, but can also help selecting the optimal tissue substitutes when calibrating MVCT devices. PACS numbers: 87.55.D‐, 87.55.dk, 87.55.K‐, 87.57.Q‐
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Tanny S, Sperling N, Parsai EI. Correction factor measurements for multiple detectors used in small field dosimetry on the Varian Edge radiosurgery system. Med Phys 2015; 42:5370-6. [DOI: 10.1118/1.4928602] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Petasecca M, Newall MK, Booth JT, Duncan M, Aldosari AH, Fuduli I, Espinoza AA, Porumb CS, Guatelli S, Metcalfe P, Colvill E, Cammarano D, Carolan M, Oborn B, Lerch MLF, Perevertaylo V, Keall PJ, Rosenfeld AB. MagicPlate-512: A 2D silicon detector array for quality assurance of stereotactic motion adaptive radiotherapy. Med Phys 2015; 42:2992-3004. [DOI: 10.1118/1.4921126] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Benmakhlouf H, Johansson J, Paddick I, Andreo P. Monte Carlo calculated and experimentally determined output correction factors for small field detectors in Leksell Gamma Knife Perfexion beams. Phys Med Biol 2015; 60:3959-73. [DOI: 10.1088/0031-9155/60/10/3959] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Francescon P, Beddar S, Satariano N, Das IJ. Variation of kQclin,Qmsr (fclin,fmsr) for the small-field dosimetric parameters percentage depth dose, tissue-maximum ratio, and off-axis ratio. Med Phys 2014; 41:101708. [PMID: 25281947 PMCID: PMC5175987 DOI: 10.1118/1.4895978] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2014] [Revised: 08/25/2014] [Accepted: 08/31/2014] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Evaluate the ability of different dosimeters to correctly measure the dosimetric parameters percentage depth dose (PDD), tissue-maximum ratio (TMR), and off-axis ratio (OAR) in water for small fields. METHODS Monte Carlo (MC) simulations were used to estimate the variation of kQclin,Qmsr (fclin,fmsr) for several types of microdetectors as a function of depth and distance from the central axis for PDD, TMR, and OAR measurements. The variation of kQclin,Qmsr (fclin,fmsr) enables one to evaluate the ability of a detector to reproduce the PDD, TMR, and OAR in water and consequently determine whether it is necessary to apply correction factors. The correctness of the simulations was verified by assessing the ratios between the PDDs and OARs of 5- and 25-mm circular collimators used with a linear accelerator measured with two different types of dosimeters (the PTW 60012 diode and PTW PinPoint 31014 microchamber) and the PDDs and the OARs measured with the Exradin W1 plastic scintillator detector (PSD) and comparing those ratios with the corresponding ratios predicted by the MC simulations. RESULTS MC simulations reproduced results with acceptable accuracy compared to the experimental results; therefore, MC simulations can be used to successfully predict the behavior of different dosimeters in small fields. The Exradin W1 PSD was the only dosimeter that reproduced the PDDs, TMRs, and OARs in water with high accuracy. With the exception of the EDGE diode, the stereotactic diodes reproduced the PDDs and the TMRs in water with a systematic error of less than 2% at depths of up to 25 cm; however, they produced OAR values that were significantly different from those in water, especially in the tail region (lower than 20% in some cases). The microchambers could be used for PDD measurements for fields greater than those produced using a 10-mm collimator. However, with the detector stem parallel to the beam axis, the microchambers could be used for TMR measurements for all field sizes. The microchambers could not be used for OAR measurements for small fields. CONCLUSIONS Compared with MC simulation, the Exradin W1 PSD can reproduce the PDDs, TMRs, and OARs in water with a high degree of accuracy; thus, the correction used for converting dose is very close to unity. The stereotactic diode is a viable alternative because it shows an acceptable systematic error in the measurement of PDDs and TMRs and a significant underestimation in only the tail region of the OAR measurements, where the dose is low and differences in dose may not be therapeutically meaningful.
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Affiliation(s)
- Paolo Francescon
- Department of Radiation Oncology, Ospedale Di Vicenza, Viale Rodolfi, Vicenza 36100, Italy
| | - Sam Beddar
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77005
| | - Ninfa Satariano
- Department of Radiation Oncology, Ospedale Di Vicenza, Viale Rodolfi, Vicenza 36100, Italy
| | - Indra J Das
- Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, Indiana 46202
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Papaconstadopoulos P, Tessier F, Seuntjens J. On the correction, perturbation and modification of small field detectors in relative dosimetry. Phys Med Biol 2014; 59:5937-52. [DOI: 10.1088/0031-9155/59/19/5937] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Wagner A, Crop F, Lacornerie T, Reynaert N. Characterization of recombination effects in a liquid ionization chamber used for the dosimetry of a radiosurgical accelerator. J Vis Exp 2014. [PMID: 24835586 PMCID: PMC4174048 DOI: 10.3791/51296] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Most modern radiation therapy devices allow the use of very small fields, either through beamlets in Intensity-Modulated Radiation Therapy (IMRT) or via stereotactic radiotherapy where positioning accuracy allows delivering very high doses per fraction in a small volume of the patient. Dosimetric measurements on medical accelerators are conventionally realized using air-filled ionization chambers. However, in small beams these are subject to nonnegligible perturbation effects. This study focuses on liquid ionization chambers, which offer advantages in terms of spatial resolution and low fluence perturbation. Ion recombination effects are investigated for the microLion detector (PTW) used with the Cyberknife system (Accuray). The method consists of performing a series of water tank measurements at different source-surface distances, and applying corrections to the liquid detector readings based on simultaneous gaseous detector measurements. This approach facilitates isolating the recombination effects arising from the high density of the liquid sensitive medium and obtaining correction factors to apply to the detector readings. The main difficulty resides in achieving a sufficient level of accuracy in the setup to be able to detect small changes in the chamber response.
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Benmakhlouf H, Sempau J, Andreo P. Output correction factors for nine small field detectors in 6 MV radiation therapy photon beams: A PENELOPE Monte Carlo study. Med Phys 2014; 41:041711. [DOI: 10.1118/1.4868695] [Citation(s) in RCA: 108] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Chalkley A, Heyes G. Evaluation of a synthetic single-crystal diamond detector for relative dosimetry measurements on a CyberKnife. Br J Radiol 2014; 87:20130768. [PMID: 24588671 PMCID: PMC4064610 DOI: 10.1259/bjr.20130768] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 01/07/2014] [Accepted: 01/08/2014] [Indexed: 11/05/2022] Open
Abstract
OBJECTIVE To evaluate a new commercial PTW-60019 microDiamond (PTW, Freiburg, Germany) synthetic single-crystal diamond detector for relative dosimetry measurements on a clinical CyberKnife™ VSI (Accuray Inc., Sunnyvale, CA) system. METHODS Relative output factors (ROFs) were measured for collimator diameters from 5 to 60 mm, and compared with diode [PTW-60017, PTW-60018 and IBA Dosimetry (Schwarzenbruck, Germany) SFD] and ionization chamber (PTW-31014 PinPoint and PTW-31010 Semiflex) measurements. Beam profiles were measured at a range of depths, and collimator sizes, with the detector stem oriented both parallel and perpendicular to the central axis (CAX). Percentage depth-dose (PDD) curves were obtained for the 60-mm collimator and compared with natural Diamond Detector (PTW-60003) and ionization chamber curves to evaluate energy dependence. RESULTS Penumbral broadening was noted on profile measurements made with the microDiamond oriented with the stem parallel to the CAX, in comparison with diodes. Oriented perpendicular to the CAX, the profile penumbra was sharper, but stem effects could not be ruled out. The PDD measurements were within 0.5% of ionization chamber measurements, indicating insignificant dose-rate dependence. The ROF for the microDiamond fell between diode and ionization chamber results. Published Monte Carlo-derived CyberKnife-specific factors were applied to the PTW-60017, PTW-60018 and PTW-31014 ROFs, and the microDiamond factors agreed within 2.0% of the mean of these. CONCLUSION Over a range of small field relative dosimetry measurements, the microDiamond detector shows excellent spatial resolution, dose-rate independence and water equivalence. ADVANCES IN KNOWLEDGE The microDiamond is a suitable tool for commissioning stereotactic systems.
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Affiliation(s)
- A Chalkley
- Radiotherapy Physics and Cancer Centre, Hall-Edwards Radiotherapy Research Group, Queen Elizabeth Hospital Birmingham, Edgbaston, Birmingham, UK
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