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Episkopakis A, Margaroni V, Kanellopoulou S, Marinos N, Koutsouveli E, Karaiskos P, Pappas EP. Dose-response dependencies of OSL dosimeters in conventional linacs and 1.5T MR-linacs: an experimental and Monte Carlo study. Phys Med Biol 2023; 68:225002. [PMID: 37857285 DOI: 10.1088/1361-6560/ad051e] [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: 08/13/2023] [Accepted: 10/19/2023] [Indexed: 10/21/2023]
Abstract
Objective. This work focuses on the optically stimulated luminescence dosimetry (OSLD) dose-response characterization, with emphasis on 1.5T MR-Linacs.Approach. Throughout this study, the nanoDots OSLDs (Landauer, USA) were considered. In groups of three, the mean OSLD response was measured in a conventional linac and an MR-Linac under various irradiation conditions to investigate (i) dose-response linearity with and without the 1.5T magnetic field, (ii) signal fading rate and its dependencies, (iii) beam quality, detector orientation and dose rate dependencies in a conventional linac, (iii) potential MR imaging related effects on OSLD response and (iv) detector orientation dependence in an MR-Linac. Monte Carlo calculations were performed to further quantify angular dependence after rotating the detector around its central axis parallel to the magnetic field, and determine the magnetic field correction factors,kB,Q,for all cardinal detector orientations.Main results. OSLD dose-response supralinearity in an MR-Linac setting was found to agree within uncertainties with the corresponding one in a conventional linac, for the axial detector orientation investigated. Signal fading rate does not depend on irradiation conditions for the range of 3-30 d considered. OSLD angular (orientation) dependence is more pronounced under the presence of a magnetic field. OSLDs irradiated with and without real-time T2w MR imaging enabled during irradiation yielded the same response within uncertainties.kB,Qvalues were determined for all three cardinal orientations. Corrections needed reached up to 6.4%. However, if OSLDs are calibrated in the axial orientation and then irradiated in an MR-Linac placed again in the axial orientation (perpendicular to the magnetic field), then simulations suggest thatkB,Qcan be considered unity within uncertainties, irrespective of the incident beam angle.Significance. This work contributes towards OSLD dose-response characterization and relevant correction factors availability. OSLDs are suitable for QA checks in MR-based beam gating applications andin vivodosimetry in MR-Linacs.
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Affiliation(s)
- Anastasios Episkopakis
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
- Global Clinical Operations, Elekta Ltd., Fleming way, RH10 99RR Crawley, West Sussex, United Kingdom
| | - Vasiliki Margaroni
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
| | | | - Nikolas Marinos
- Global Clinical Operations, Elekta Ltd., Fleming way, RH10 99RR Crawley, West Sussex, United Kingdom
| | - Efi Koutsouveli
- Medical Physics Department, Hygeia Hospital, Kifissias Avenue & 4 Erythrou Stavrou, Marousi, 151 23 Athens, Greece
| | - Pantelis Karaiskos
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
| | - Eleftherios P Pappas
- Medical Physics Laboratory, Medical School, National and Kapodistrian University of Athens, 75 Mikras Asias, 115 27 Athens, Greece
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2
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Patterson E, Stokes P, Cutajar D, Rosenfeld A, Baines J, Metcalfe P, Powers M. High-resolution entry and exit surface dosimetry in a 1.5 T MR-linac. Phys Eng Sci Med 2023; 46:787-800. [PMID: 36988905 DOI: 10.1007/s13246-023-01251-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Accepted: 03/21/2023] [Indexed: 03/30/2023]
Abstract
The magnetic field of a transverse MR-linac alters electron trajectories as the photon beam transits through materials, causing lower doses at flat entry surfaces and increased doses at flat beam-exiting surfaces. This study investigated the response of a MOSFET detector, known as the MOSkin™, for high-resolution surface and near-surface percentage depth dose measurements on an Elekta Unity. Simulations with Geant4 and the Monaco treatment planning system (TPS), and EBT-3 film measurements, were also performed for comparison. Measured MOSkin™ entry surface doses, relative to Dmax, were (9.9 ± 0.2)%, (10.1 ± 0.3)%, (11.3 ± 0.6)%, (12.9 ± 1.0)%, and (13.4 ± 1.0)% for 1 × 1 cm2, 3 × 3 cm2, 5 × 5 cm2, 10 × 10 cm2, and 22 × 22 cm2 fields, respectively. For the investigated fields, the maximum percent differences of Geant4, TPS, and film doses extrapolated and interpolated to a depth suitable for skin dose assessment at the beam entry, relative to MOSkin™ measurements at an equivalent depth were 1.0%, 2.8%, and 14.3%, respectively, and at a WED of 199.67 mm at the beam exit, 3.2%, 3.7% and 5.7%, respectively. The largest measured increase in exit dose, due to the electron return effect, was 15.4% for the 10 × 10 cm2 field size using the MOSkin™ and 17.9% for the 22 × 22 cm2 field size, using Geant4 calculations. The results presented in the study validate the suitability of the MOSkin™ detector for transverse MR-linac surface dosimetry.
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Affiliation(s)
- E Patterson
- Centre of Medical and Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.
| | - P Stokes
- Townsville Cancer Centre, Townsville Hospital and Health Service, Townsville, QLD, Australia
| | - D Cutajar
- Centre of Medical and Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
| | - A Rosenfeld
- Centre of Medical and Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
- Illawarra Health Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia
| | - J Baines
- Townsville Cancer Centre, Townsville Hospital and Health Service, Townsville, QLD, Australia
- College of Science and Engineering, James Cook University, Townsville, QLD, Australia
| | - P Metcalfe
- Centre of Medical and Radiation Physics, University of Wollongong, Wollongong, NSW, Australia
- Illawarra Health Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia
- Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
| | - M Powers
- Townsville Cancer Centre, Townsville Hospital and Health Service, Townsville, QLD, Australia
- College of Science and Engineering, James Cook University, Townsville, QLD, Australia
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Abu Mhanna HY, Omar AF, Radzi YM, Akhdar HF, Al Ewaidat H. Expired EBT3 Films’ Sensitivity for the Measurement of X-ray and UV Radiation: An Optical Analysis. MATERIALS 2022; 15:ma15082903. [PMID: 35454597 PMCID: PMC9027090 DOI: 10.3390/ma15082903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/23/2022] [Revised: 03/15/2022] [Accepted: 04/13/2022] [Indexed: 11/25/2022]
Abstract
The aim of this study is to compare the optical responses of external beam therapy 3 (EBT3) films exposed to X-rays and solar ultraviolet rays (SUV-rays), as a dose control technique in the clinical sector for various radiation types, energies, and absorbed doses up to 4 Gy. In this study, EBT3 films with three different expiry dates were prepared and cut into pieces of size 2 by 2 cm2. The first group was exposed to 90 kVp X-rays, while the second group was exposed to the SUV-rays at noon. The analysis was performed using a visible Jaz spectrometer and an EPSON Perfection V370 Photo scanner to obtain the absorbance, the net reflective optical density (ROD) and the red-green-blue (RGB) values of the samples. The results have shown that spectroscopic measurements of the exposed expired EBT3 films with these radiation sources are able to produce primary peaks and secondary peaks at λ = 641.74 nm and λ = 585.98 nm for X-rays, and at λ = 637.93 nm and λ = 584.45 nm for SUV-rays, respectively. According to these findings, compared to 2021 films that expired shortly before the trial start date; 2018 films responded better to the absorbed dose than 2016 films when exposed to both X-ray and SUV-rays. In terms of energy dependence, the expired EBT3 2018 had the largest net ROD value. Using L*a*b* indices extracted from the RGB data, and despite that EBT3 films have expiry dates according to the manufacturer; all the films exhibited a substantial colour change, indicating that these films are still usable for clinical and research purposes.
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Affiliation(s)
- Hamad Yahia Abu Mhanna
- School of Physics, Universiti Sains Malaysia, Penang 11800, Malaysia;
- Correspondence: (H.Y.A.M.); (A.F.O.); (H.F.A.)
| | - Ahmad Fairuz Omar
- School of Physics, Universiti Sains Malaysia, Penang 11800, Malaysia;
- Correspondence: (H.Y.A.M.); (A.F.O.); (H.F.A.)
| | - Yasmin Md Radzi
- School of Physics, Universiti Sains Malaysia, Penang 11800, Malaysia;
| | - Hanan Fawaz Akhdar
- Physics Department, College of Science, Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh 13318, Saudi Arabia
- Correspondence: (H.Y.A.M.); (A.F.O.); (H.F.A.)
| | - Haytham Al Ewaidat
- Department of Allied Medical Sciences-Radiologic Technology, Faculty of Applied Medical Sciences, Jordan University of Science and Technology, Irbid 22110, Jordan;
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Patterson E, Oborn BM, Cutajar D, Jelen U, Liney G, Rosenfeld AB, Metcalfe PE. Characterizing magnetically focused contamination electrons by off-axis irradiation on an inline MRI-Linac. J Appl Clin Med Phys 2022; 23:e13591. [PMID: 35333000 PMCID: PMC9195023 DOI: 10.1002/acm2.13591] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 12/10/2021] [Accepted: 03/02/2022] [Indexed: 11/18/2022] Open
Abstract
Purpose The aim of this study is to investigate off‐axis irradiation on the Australian MRI‐Linac using experiments and Monte Carlo simulations. Simulations are used to verify experimental measurements and to determine the minimum offset distance required to separate electron contamination from the photon field. Methods Dosimetric measurements were performed using a microDiamond detector, Gafchromic® EBT3 film, and MOSkinTM. Three field sizes were investigated including 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm2. Each field was offset a maximum distance, approximately 10 cm, from the central magnetic axis (isocenter). Percentage depth doses (PDDs) were collected at a source‐to‐surface distance (SSD) of 1.8 m for fields collimated centrally and off‐axis. PDD measurements were also acquired at isocenter for each off‐axis field to measure electron contamination. Monte Carlo simulations were used to verify experimental measurements, determine the minimum field offset distance, and demonstrate the use of a spoiler to absorb electron contamination. Results Off‐axis irradiation separates the majority of electron contamination from an x‐ray beam and was found to significantly reduce in‐field surface dose. For the 1.9 × 1.9, 5.8 × 5.8, and 9.7 × 9.6 cm2 field, surface dose was reduced from 120.9% to 24.9%, 229.7% to 39.2%, and 355.3% to 47.3%, respectively. Monte Carlo simulations generally were within experimental error to MOSkinTM and microDiamond, and used to determine the minimum offset distance, 2.1 cm, from the field edge to isocenter. A water spoiler 2 cm thick was shown to reduce electron contamination dose to near zero. Conclusions Experimental and simulation data were acquired for a range of field sizes to investigate off‐axis irradiation on an inline MRI‐Linac. The skin sparing effect was observed with off‐axis irradiation, a feature that cannot be achieved to the same extent with other methods, such as bolusing, for beams at isocenter.
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Affiliation(s)
| | - Bradley M Oborn
- Centre for Medical Radiation Physics, Wollongong, NSW, Australia.,Illawarra Cancer Care Centre, Wollongong Hospital, Wollongong, NSW, Australia
| | - Dean Cutajar
- Centre for Medical Radiation Physics, Wollongong, NSW, Australia
| | - Urszula Jelen
- Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
| | - Gary Liney
- Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
| | - Anatoly B Rosenfeld
- Centre for Medical Radiation Physics, Wollongong, NSW, Australia.,Illawarra Health Medical Research Institute, University of Wollongong, Wollongong, NSW, Australia
| | - Peter E Metcalfe
- Centre for Medical Radiation Physics, Wollongong, NSW, Australia.,Ingham Institute for Applied Medical Research, Liverpool, NSW, Australia
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Boh Lim S, Tyagi N, Subashi E, Liang J, Chan M. An evaluation of the use of EBT-XD film for SRS/SBRT commissioning of a 1.5 Tesla MR-Linac system. Phys Med 2022; 96:9-17. [PMID: 35189431 PMCID: PMC9396448 DOI: 10.1016/j.ejmp.2022.02.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 02/06/2022] [Accepted: 02/12/2022] [Indexed: 11/26/2022] Open
Abstract
Purpose: The goal of this study was to evaluate the use of EBT-XD film for SRS/SBRT commissioning in a 1.5T hybrid MR-Linac (MRL). Method: The output factors (St), from 1x1, 2x2, 3x3 cm2, were measured with film in solid water. The results were compared with (1) the measurements by a PTW diamond detector (CVD) and an Exradin® A26MR ion chamber in 3D water phantom; (2) Monte Carlo calculation by Monaco TPS (MTPS) in water. The inline (IN) and crossline (CR) profiles, measured by films and the CVD, were also compared. An SRS plan with two targets was created in MTPS and was measured with EBT-XD film in a StereoPHAN™ phantom serving as an end-to-end test. The 3x3 cm2 was used for film calibration with doses ranging from 0 to 28 Gy. Water was added to the phantom-film-phantom interface to reduce the electron-return-effect (ERE). Films were calibrated with One-scan-dosimetry protocol. Results: The film St were within 1.2% and 2.2% compared to other detectors and MTPS respectively. At the central B-field induced asymmetric region, films were within 0.6% between the CVD and the MTPS, but 5–8% differences were observed in the 40%-5% gradient region in CR due to ERE. The differences in localization and dose were found to be 0.6 mm and 3.3%. The γ(3%/2mm), γ (5%/2mm), γ (5%/1mm) were 97.7%, 99.3%, 94.6%. Conclusions: Films can provide accurate dosimetric results under ERE and are valuable for commissioning MRL. Using the One-scan-dosimetry protocol with EBT-XD film for MRL increases accuracy and efficiency in commissioning and QA of SRS/SBRT.
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Affiliation(s)
- Seng Boh Lim
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States.
| | - Neelam Tyagi
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States.
| | - Ergys Subashi
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States.
| | - Jiayi Liang
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States.
| | - Maria Chan
- Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, NY 10065, United States.
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6
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Silvestre Patallo I, Carter R, Maughan D, Nisbet A, Schettino G, Subiel A. Evaluation of a micro ionization chamber for dosimetric measurements in image-guided preclinical irradiation platforms. Phys Med Biol 2021; 66. [PMID: 34794132 DOI: 10.1088/1361-6560/ac3b35] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 11/18/2021] [Indexed: 11/12/2022]
Abstract
Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5 to 4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector's orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform "user's" quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.
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Affiliation(s)
- Ileana Silvestre Patallo
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Rebecca Carter
- Cancer Institute, University College London, London, London, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - David Maughan
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Andrew Nisbet
- Department of Medical Physics & Biomedical Engineering, University College London, London, London, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Giuseppe Schettino
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, Middlesex, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Anna Subiel
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
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Yang B, Tang KK, Huang CY, Geng H, Lam WW, Wong YS, Tse MY, Lau KK, Cheung KY, Yu SK. Out-of-field dose and its constituent components for a 1.5 T MR-Linac. Phys Med Biol 2021; 66. [PMID: 34700308 DOI: 10.1088/1361-6560/ac3346] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2021] [Accepted: 10/26/2021] [Indexed: 11/11/2022]
Abstract
This study aims to quantify the relative contributions of phantom scatter, collimator scatter and head leakage to the out-of-field doses (OFDs) of both static fields and clinical intensity-modulated radiation therapy (IMRT) treatments in a 1.5 T MR-Linac. The OFDs of static fields were measured at increasing distances from the field edge in an MR-conditional water phantom. Inline scans at depths of dmax (14 mm), 50 and 100 mm were performed for static fields of 5 × 5, 10 × 10 and 15 × 15 cm2under three different conditions: full scatter, with phantom scatter prevented, and head leakage only. Crossline scans at isocenter and offset positions were performed in full scatter condition. EBT3 radiochromic films were placed at 100 mm depth of solid water phantom to measure the OFD of clinical IMRT plans. All water tank data were normalized to Dmax of a 10 × 10 cm2field and the film results were presented as a fraction of the target mean dose.The OFD in the inline direction varied from 3.5% (15 × 15 cm2, 100 mm depth, 50 mm distance) to 0.014% (5 × 5 cm2, dmax, 400 mm distance). For all static fields, the collimator scatter was higher than the phantom scatter and head leakage at a distance of 100-400 mm. Head leakage remained the smallest among the three components, except at long distances (>375 mm) with small field size. Compared to the inline scans, the crossline scans at the isocenter showed higher doses at distances longer than 80 mm. All crossline profiles at longitudinal offset positions showed a cone shape with laterally shifted maxima. The OFD of IMRT deliveries varied with different target size. For prostate stereotactic body radiation therapy (SBRT) treatment, the OFD decreased from 2% to 0.03% at a distance of 50-500 mm. The OFDs have been measured for a 1.5 T MR-Linac. The presented dosimetric data are valuable for radiation safety assessments on patients treated with the MR-Linac, such as evaluating carcinogenic risk and radiation exposure to cardiac implantable electronic devices.
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Affiliation(s)
- Bin Yang
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Ka Keung Tang
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Chen-Yu Huang
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Hui Geng
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Wai Wang Lam
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Yeung Sum Wong
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Mei Yan Tse
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Ka Ki Lau
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Kin Yin Cheung
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
| | - Siu Ki Yu
- Medical Physics Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong, People's Republic of China
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8
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Billas I, Bouchard H, Oelfke U, Duane S. Traceable reference dosimetry in MRI guided radiotherapy using alanine: calibration and magnetic field correction factors of ionisation chambers. Phys Med Biol 2021; 66. [PMID: 34049290 DOI: 10.1088/1361-6560/ac0680] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 05/28/2021] [Indexed: 12/27/2022]
Abstract
Magnetic resonance imaging (MRI)-guided radiotherapy (RT) (MRIgRT) falls outside the scope of existing high energy photon therapy dosimetry protocols, because those protocols do not consider the effects of the magnetic field on detector response and on absorbed dose to water. The aim of this study is to evaluate and demonstrate the traceable measurement of absorbed dose in MRIgRT systems using alanine, made possible by the characterisation of alanine sensitivity to magnetic fields reported previously by Billaset al(2020Phys. Med. Biol.65115001), in a way which is compatible with existing standards and calibrations available for conventional RT. In this study, alanine is used to transfer absorbed dose to water to MRIgRT systems from a conventional linac. This offers an alternative route for the traceable measurement of absorbed dose to water, one which is independent of the transfer using ionisation chambers. The alanine dosimetry is analysed in combination with measurements with several Farmer-type chambers, PTW 30013 and IBA FC65-G, at six different centres and two different MRIgRT systems (Elekta Unity™ and ViewRay MRIdian™). The results are analysed in terms of the magnetic field correction factors, and in terms of the absorbed dose calibration coefficients for the chambers, determined at each centre. This approach to reference dosimetry in MRIgRT produces good consistency in the results, across the centres visited, at the level of 0.4% (standard deviation). Farmer-type ionisation chamber magnetic field correction factors were determined directly, by comparing calibrations in some MRIgRT systems with and without the magnetic field ramped up, and indirectly, by comparing calibrations in all the MRIgRT systems with calibrations in a conventional linac. Calibration coefficients in the MRIgRT systems were obtained with a standard uncertainty of 1.1% (Elekta Unity™) and 0.9% (ViewRay MRIdian™), for three different chamber orientations with respect to the magnetic field. The values obtained for the magnetic field correction factor in this investigation are consistent with those presented in the summary by de Pooteret al(2021Phys. Med. Biol.6605TR02), and would tend to support the adoption of a magnetic field correction factor which depends on the chamber type, PTW 30013 or IBA FC65-G.
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Affiliation(s)
- Ilias Billas
- National Physical Laboratory, Teddington, United Kingdom.,Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
| | - Hugo Bouchard
- Université de Montréal, Département de Physique, Montréal, Canada and Centre Hospitalier de l'Université de Montréal, Montréal, Canada and Centre de recherche du CHUM, Montréal, Canada
| | - Uwe Oelfke
- Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
| | - Simon Duane
- National Physical Laboratory, Teddington, United Kingdom
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9
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Xhaferllari I, Kim JP, Liyanage R, Liu C, Du D, Doemer A, Chetty IJ, Wen N. Clinical utility of Gafchromic film in an MRI-guided linear accelerator. Radiat Oncol 2021; 16:117. [PMID: 34174932 PMCID: PMC8236160 DOI: 10.1186/s13014-021-01844-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2021] [Accepted: 06/15/2021] [Indexed: 11/18/2022] Open
Abstract
Background The purpose of this study is to comprehensively evaluate the suitability of Gafchromic EBT3 and EBT-XD film for dosimetric quality assurance in 0.35 T MR-guided radiotherapy. Methods A 0.35 T magnetic field strength was utilized to evaluate magnetic field effects on EBT3 and EBT-XD Gafchromic films by studying the effect of film exposure time within the magnetic field using two timing sequences and film not exposed to MR, the effect of magnetic field exposure on the crystalline structure of the film, and the effect of orientation of the film with respect to the bore within the magnetic field. The orientation of the monomer crystal was qualitatively evaluated using scanning electron microscopy (SEM) compared to unirradiated film. Additionally, dosimetric impact was evaluated through measurements of a series of open field irradiations (0.83 × 0.83-cm2 to 19.92 × 19.92-cm2) and patient specific quality assurance measurements. Open fields were compared to planned dose and an independent dosimeter. Film dosimetry was applied to twenty conventional and twenty stereotactic body radiotherapy (SBRT) patient specific quality assurance cases. Results No visual changes in crystal orientation were observed in any evaluated SEM images nor were any optical density differences observed between films irradiated inside or outside the magnetic field for both EBT3 and EBT-XD film. At small field sizes, the average difference along dose profiles measured in film compared to the same points measured using an independent dosimeter and to predicted treatment planning system values was 1.23% and 1.56%, respectively. For large field sizes, the average differences were 1.91% and 1.21%, respectively. In open field tests, the average gamma pass rates were 99.8% and 97.2%, for 3%/3 mm and 3%/1 mm, respectively. The median (interquartile range) 3%/3 mm gamma pass rates in conventional QA cases were 98.4% (96.3 to 99.2%), and 3%/1 mm in SBRT QA cases were 95.8% (95.0 to 97.3%). Conclusions MR exposure at 0.35 T had negligible effects on EBT3 and EBT-XD Gafchromic film. Dosimetric film results were comparable to planned dose, ion chamber and diode measurements.
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Affiliation(s)
- Ilma Xhaferllari
- Department of Radiation Oncology, Beaumont Health, Troy, MI, USA
| | - Joshua P Kim
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA
| | - Ruchira Liyanage
- Department of Chemical Engineering and Material Science, Wayne State University, Detroit, MI, USA
| | - Chang Liu
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA
| | - Dongsu Du
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA
| | - Anthony Doemer
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA
| | - Indrin J Chetty
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA
| | - Ning Wen
- Department of Radiation Oncology, Henry Ford Health System, 2799 West Grand Blvd, Detroit, MI, USA.
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Yang B, Wong YS, Lam WW, Geng H, Huang CY, Tang KK, Law WK, Ho CC, Nam PH, Cheung KY, Yu SK. Initial clinical experience of patient-specific QA of treatment delivery in online adaptive radiotherapy using a 1.5 T MR-Linac. Biomed Phys Eng Express 2021; 7. [PMID: 33882471 DOI: 10.1088/2057-1976/abfa80] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Accepted: 04/21/2021] [Indexed: 11/11/2022]
Abstract
Purpose. This study aims to evaluate the performance of a commercial 1.5 T MR-Linac by analyzing its patient-specific quality assurance (QA) data collected during one full year of clinical operation.Methods and Materials. The patient-specific QA system consisted of offline delivery QA (DQA) and online calculation-based QA. Offline DQA was based on ArcCHECK-MR combined with an ionization chamber. Online QA was performed using RadCalc that calculated and compared the point dose calculation with the treatment planning system (TPS). A total of 24 patients with 189 treatment fractions were enrolled in this study. Gamma analysis was performed and the threshold that encompassed 95% of QA results (T95) was reported. The plan complexity metric was calculated for each plan and compared with the dose measurements to determine whether any correlation existed.Results. All point dose measurements were within 5% deviation. The mean gamma passing rates of the group data were found to be 96.8 ± 4.0% and 99.6 ± 0.7% with criteria of 2%/2mm and 3%/3mm, respectively. T95 of 87.4% and 98.2% was reported for the overall group with the two passing criteria, respectively. No statistically significant difference was found between adaptive treatments with adapt-to-position (ATP) and adapt-to-shape (ATS), whilst the category of pelvis data showed a better passing rate than other sites. Online QA gave a mean deviation of 0.2 ± 2.2%. The plan complexity metric was positively correlated with the mean dose difference whilst the complexity of the ATS cohort had larger variations than the ATP cohort.Conclusions. A patient-specific QA system based on ArcCHECK-MR, solid phantom and ionization chamber has been well established and implemented for validation of treatment delivery of a 1.5 T MR-Linac. Our QA data obtained over one year confirms that good agreement between TPS calculation and treatment delivery was achieved.
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Affiliation(s)
- B Yang
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - Y S Wong
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - W W Lam
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - H Geng
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - C Y Huang
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - K K Tang
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - W K Law
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - C C Ho
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - P H Nam
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - K Y Cheung
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
| | - S K Yu
- Medical Physics and Research Department, Hong Kong Sanatorium & Hospital, 2 Village Road, Happy Valley, Hong Kong
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11
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Huang CY, Yang B, Lam WW, Tang KK, Li TC, Law WK, Cheung KY, Yu SK. Effects on skin dose from unwanted air gaps under bolus in an MR-guided linear accelerator (MR-linac) system. Phys Med Biol 2021; 66:065021. [PMID: 33607641 DOI: 10.1088/1361-6560/abe837] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Bolus is commonly used in MV photon radiotherapy to increase superficial dose and improve dose uniformity for treating shallow lesions. However, irregular patient body contours can cause unwanted air gaps between a bolus and patient skin. The resulting dosimetric errors could be exacerbated in MR-Linac treatments, as secondary electrons generated by photons are affected by the magnetic field. This study aimed to quantify the dosimetric effect of unwanted gaps between bolus and skin surface in an MR-Linac. A parallel-plate ionization chamber and EBT3 films were utilized to evaluate the surface dose under bolus with various gantry angles, field sizes, and different air gaps. The results of surface dose measurements were then compared to Monaco 5.40 Treatment Planning System (TPS) calculations. The suitability of using a parallel-plate chamber in MR-Linac measurement was validated by benchmarking the percentage depth dose and output factors with the microDiamond detector and air-filled ionization chamber measurements in water. A non-symmetric response of the parallel-plate chamber to oblique beams in the magnetic field was characterized. Unwanted air gaps significantly reduced the skin dose. For a frontal beam, skin dose was halved when there was a 5 mm gap, a much larger difference than in a conventional linac. Skin dose manifested a non-symmetric pattern in terms of gantry angle and gap size. The TPS overestimated skin dose in general, but shared the same trend with measurement when there was no air gap, or the gap size was larger than 5 mm. However, the calculated and measured results had a large discrepancy when the bolus-skin gap was below 5 mm. When treating superficial lesions, unwanted air gaps under the bolus will compromise the dosimetric goals. Our results highlight the importance of avoiding air gaps between bolus and skin when treating superficial lesions using an MR-Linac system.
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Axford A, Dikaios N, Roberts DA, Clark CH, Evans PM. An end-to-end assessment on the accuracy of adaptive radiotherapy in an MR-linac. Phys Med Biol 2021; 66:055021. [PMID: 33503604 DOI: 10.1088/1361-6560/abe053] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
PURPOSE To develop and demonstrate an end-to-end assessment procedure for adaptive radiotherapy (ART) within an MR-guided system. METHODS AND MATERIALS A 3D printed pelvic phantom was designed and constructed for use in this study. The phantom was put through the complete radiotherapy treatment chain, with planned internal changes made to model prostate translations and shape changes, allowing an investigation into three ART techniques commonly used. Absolute dosimetry measurements were made within the phantom using both gafchromic film and alanine. Comparisons between treatment planning system (TPS) calculations and measured dose values were made using the gamma evaluation with criteria of 3 mm/3% and 2 mm/2%. RESULTS Gamma analysis evaluations for each type of treatment plan adaptation investigated showed a very high agreement with pass rates for each experiment ranging from 98.10% to 99.70% and 92.60% to 97.55%, for criteria of 3%/3 mm and 2%/2 mm respectively. These pass rates were consistent for both shape and position changes. Alanine measurements further supported the results, showing an average difference of 1.98% from the TPS. CONCLUSION The end-to-end assessment procedure provided demanding challenges for treatment plan adaptations to demonstrate the capabilities and achieved high consistency in all findings.
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Affiliation(s)
- A Axford
- The Centre for Vision Speech and Signal Processing (CVSSP), University of Surrey, Guildford, Surrey, United Kingdom. Metrology for Medical Physics (MEMPHYS), National Physical Laboratory, Teddington, United Kingdom
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13
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Bernchou U, Christiansen RL, Bertelsen A, Tilly D, Riis HL, Jensen HR, Mahmood F, Hansen CR, Hansen VN, Schytte T, Brink C. End-to-end validation of the geometric dose delivery performance of MR linac adaptive radiotherapy. Phys Med Biol 2021; 66:045034. [PMID: 33321475 DOI: 10.1088/1361-6560/abd3ed] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The clinical introduction of hybrid magnetic resonance (MR) guided radiotherapy (RT) delivery systems has led to the need to validate the end-to-end dose delivery performance on such machines. In the current study, an MR visible phantom was developed and used to test the spatial deviation between planned and delivered dose at two 1.5 T MR linear accelerator (MR linac) systems, including pre-treatment imaging, dose planning, online imaging, image registration, plan adaptation, and dose delivery. The phantom consisted of 3D printed plastic and MR visible silicone rubber. It was designed to minimise air gaps close to the radiochromic film used as a dosimeter. Furthermore, the phantom was designed to allow submillimetre, reproducible positioning of the film in the phantom. At both MR linac systems, 54 complete adaptive, MR guided RT workflow sessions were performed. To test the dose delivery performance of the MR linac systems in various adaptive RT (ART) scenarios, the sessions comprised a range of systematic positional shifts of the phantom and imaging or plan adaptation conditions. In each workflow session, the positional translation between the film and the adaptive planned dose was determined. The results showed that the accuracy of the MR linac systems was between 0.1 and 0.9 mm depending on direction. The highest mean deviance observed was in the posterior-anterior direction, and the direction of the error was consistent between centres. The precision of the systems was related to whether the workflow utilized the internal image registration algorithm of the MR linac. Workflows using the internal registration algorithm led to a worse precision (0.2-0.7 mm) compared to workflows where the algorithm was decoupled (0.2 mm). In summary, the spatial deviation between planned and delivered dose of MR-guided ART at the two MR linac systems was well below 1 mm and thus acceptable for clinical use.
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Affiliation(s)
- Uffe Bernchou
- Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Odense, Denmark. Department of Clinical Research, University of Southern Denmark, Odense, Denmark
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14
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Cervantes Y, Billas I, Shipley D, Duane S, Bouchard H. Small-cavity chamber dose response in megavoltage photon beams coupled to magnetic fields. Phys Med Biol 2020; 65:245008. [PMID: 32674077 DOI: 10.1088/1361-6560/aba6d6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In MRgRT, dosimetry measurements are performed in the presence of magnetic fields. For high-resolution measurements, small-cavity ionization chambers are required. While Monte Carlo simulations are essential to determine dosimetry correction factors, models of small-chambers require careful validation with experimental measurements. The aim of this study is to characterize small-cavity chamber response coupled to magnetic fields. Small-cavity chambers (PTW31010, PTW31016, PTW31021 and PTW3022) are irradiated by a 6 MV photon beam for 9 magnetic field strengths between -1.5 T and +1.5 T. The chamber axis is orientated either parallel or perpendicular to the irradiation beam, with the magnetic field always perpendicular to the beam. MC simulations are performed in EGSnrc. The sensitive volume of the chambers is reduced to account for the inefficiency adjacent to the guard electrode (dead volume) based on COMSOL calculations of electric potentials. The magnetic field affects the chamber response by up to 4.1% and 4.5% in the parallel and perpendicular orientations, respectively, compared to no magnetic field. The maximal difference in dose response between experiments and simulations is up to 6.1% and 4.5% for parallel and perpendicular orientation, respectively. When the dead volume is removed, which accounts for the 15%-23% of the nominal volume, the difference, in most cases, is within the stated uncertainties. Nevertheless, for a particular chamber, the reduced nominal volume barely improved the agreement between the experimental and calculated relative response (4.53% to 4.13%). This disagreement may be due to the imperfect chamber geometry model, as was found from microCT images. A detailed uncertainty analysis is presented. The characterization of small-cavity ion chamber response coupled to magnetic fields is complex. Small differences between real and model chamber geometry that normally would be insignificant become an issue in the presence of magnetic fields. Accurate characterization of the nominal volume is essential for small-cavity ion chamber modelling.
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Affiliation(s)
- Yunuen Cervantes
- Département de physique, Université de Montréal, Complexe des sciences, 1375 Avenue Thérèse-Lavoie-Roux, Montréal, Québec H2V 0B3, Canada. Centre de recherche du Centre hospitalier de l'Université de Montréal, 900 Rue Saint-Denis, Montréal, Québec, H2X 0A9, Canada
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Cusumano D, Placidi L, D'Agostino E, Boldrini L, Menna S, Valentini V, De Spirito M, Azario L. Characterization of an inorganic scintillator for small-field dosimetry in MR-guided radiotherapy. J Appl Clin Med Phys 2020; 21:244-251. [PMID: 32841500 PMCID: PMC7497936 DOI: 10.1002/acm2.13012] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Revised: 04/04/2020] [Accepted: 07/27/2020] [Indexed: 11/11/2022] Open
Abstract
INTRODUCTION Aim of this study is to dosimetrically characterize a new inorganic scintillator designed for magnetic resonance-guided radiotherapy (MRgRT) in the presence of 0.35 tesla magnetic field (B). METHODS The detector was characterized in terms of signal to noise ratio (SNR), reproducibility, dose linearity, angular response, and dependence by energy, field size, and B orientation using a 6 MV magnetic resonance (MR)-Linac and a water tank. Field size dependence was investigated by measuring the output factor (OF) at 1.5 cm. The results were compared with those measured using other detectors (ion chamber and synthetic diamond) and those calculated using a Monte Carlo (MC) algorithm. Energy dependence was investigated by acquiring a percentage depth dose (PDD) curve at two field sizes (3.32 × 3.32 and 9.96 × 9.96 cm2 ) and repeating the OF measurements at 5 and 10 cm depths. RESULTS The mean SNR was 116.3 ± 0.6. Detector repeatability was within 1%, angular dependence was <2% and its response variation based on the orientation with respect to the B lines was <1%. The detector has a temporal resolution of 10 Hz and it showed a linear response (R2 = 1) in the dose range investigated. All the OF values measured at 1.5 cm depth using the scintillator are in accordance within 1% with those measured with other detectors and are calculated using the MC algorithm. PDD values are in accordance with MC algorithm only for 3.32 × 3.32 cm2 field. Numerical models can be applied to compensate for energy dependence in case of larger fields. CONCLUSION The inorganic scintillator in the present form can represent a valuable detector for small-field dosimetry and periodic quality controls at MR-Linacs such as dose stability, OFs, and dose linearity. In particular, the detector can be effectively used for small-field dosimetry at 1.5 cm depth and for PDD measurements if the field dimension of 3.32 × 3.32 cm2 is not exceeded.
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Affiliation(s)
- Davide Cusumano
- Fondazione Policlinico Universitario A. Gemelli IRCCSRomeItaly
| | - Lorenzo Placidi
- Fondazione Policlinico Universitario A. Gemelli IRCCSRomeItaly
| | | | - Luca Boldrini
- Fondazione Policlinico Universitario A. Gemelli IRCCSRomeItaly
| | | | | | | | - Luigi Azario
- Fondazione Policlinico Universitario A. Gemelli IRCCSRomeItaly
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Darafsheh A, Hao Y, Maraghechi B, Cammin J, Reynoso FJ, Khan R. Influence of 0.35 T magnetic field on the response of EBT3 and EBT-XD radiochromic films. Med Phys 2020; 47:4543-4552. [PMID: 32502280 DOI: 10.1002/mp.14313] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Revised: 05/26/2020] [Accepted: 05/27/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To investigate the inconsistency of recent literature on the effect of magnetic field on the response of radiochromic films, we studied the influence of 0.35 T magnetic field on dosimetric response of EBT3 and EBT-XD GafchromicTM films. METHODS Two different models of radiochromic films, EBT3 and EBT-XD, were investigated. Pieces of films samples from two different batches for each model were irradiated at different dose levels ranging from 1 to 20 Gy using 6 MV flattening filter free (FFF) x-rays generated by a clinical MR-guided radiotherapy system (B = 0.35 T). Film samples from the same batch were irradiated at corresponding dose levels using 6 MV FFF beam from a conventional linac (B = 0) for comparison. The net optical density was measured 48 h postirradiation using a flatbed scanner. The absorbance spectra were also measured over 500-700 nm wavelength range using a fiber-coupled spectrometer with 2.5 nm resolution. To study the effect of fractionated dose delivery to EBT3 (/EBT-XD) films, 8 (/16) Gy dose was delivered in four 2 (/4) Gy fractions with 24 h interval between fractions. RESULTS No significant difference was found in the net optical density and net absorbance of the films irradiated with or without the presence of magnetic field. No dependency on the orientation of the film during irradiation with respect to the magnetic field was observed. The fractionated dose delivery resulted in the same optical density as delivering the whole dose in a single fraction. CONCLUSIONS The 0.35 T magnetic field employed in the ViewRay® MR-guided radiotherapy system did not show any significant influence on the response of EBT3 and EBT-XD GafchromicTM films.
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Affiliation(s)
- Arash Darafsheh
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Yao Hao
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Borna Maraghechi
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Jochen Cammin
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Francisco J Reynoso
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
| | - Rao Khan
- Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO, 63110, USA
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Shortall J, Vasquez Osorio E, Aitkenhead A, Berresford J, Agnew J, Budgell G, Chuter R, McWilliam A, Kirkby K, Mackay R, van Herk M. Experimental verification the electron return effect around spherical air cavities for the MR-Linac using Monte Carlo calculation. Med Phys 2020; 47:2506-2515. [PMID: 32145087 DOI: 10.1002/mp.14123] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 02/28/2020] [Accepted: 02/28/2020] [Indexed: 11/10/2022] Open
Abstract
PURPOSE Dose deposition around unplanned air cavities during magnetic resonance-guided radiotherapy (MRgRT) is influenced by the electron return effect (ERE). This is clinically relevant for gas forming close to or inside organs at risk (OARs) that lie in the path of a single beam, for example, intestinal track during pelvic treatment. This work aims to verify Monte Carlo calculations that predict the dosimetric effects of ERE around air cavities. For this, we use GafChromic EBT3 film inside poly-methyl methacrylate (PMMA) -air phantoms. METHOD Four PMMA phantoms were produced. Three of the phantoms contained centrally located spherical air cavities (0.5, 3.5, 7.5 cm diameter), and one phantom contained no air. The phantoms were split to sandwich GafChromic EBT3 film in the center. The phantoms were irradiated on an Elekta Unity system using a single 10 × 10 cm2 7-MV photon beam under the influence of a 1.5-T transverse magnetic field. The measurements were replicated using the Elekta Monaco treatment planning system (TPS). Gamma analysis with pass criteria 3%/3 mm was used to compare the measured and calculated dose distributions. We also consider 3%/2 mm, 2%/3 mm, and 2%/2 mm pass criteria for interest. RESULTS The gamma analysis showed that >95% of the points agreed between the TPS-calculated and measured dose distributions, using 3%/3 mm criteria. The phantom containing the largest air cavity had the lowest agreement, with most of the disagreeing points lying inside the air cavity (dose to air region). CONCLUSIONS The dose effects due to ERE around spherical air cavities are being calculated in the TPS with sufficient accuracy for clinical use.
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Affiliation(s)
- J Shortall
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
| | - E Vasquez Osorio
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
| | - A Aitkenhead
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - J Berresford
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - J Agnew
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - G Budgell
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - R Chuter
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - A McWilliam
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - K Kirkby
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - R Mackay
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
| | - M van Herk
- Department of Cancer Sciences, The University of Manchester, Manchester, UK
- Department of Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK
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Ito S, Araki F, Ohno T. Impact of transverse magnetic fields on dose response of a radiophotoluminescent glass dosimeter in megavoltage photon beams. Med Phys 2020; 47:1995-2004. [DOI: 10.1002/mp.14054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2019] [Revised: 01/13/2020] [Accepted: 01/20/2020] [Indexed: 11/10/2022] Open
Affiliation(s)
- Shotaro Ito
- Graduate school of Health Sciences Kumamoto University 4‐24‐1 Kuhonji, Chuo‐ku Kumamoto 862‐0976Japan
| | - Fujio Araki
- Department of Health Sciences Faculty of Life Sciences Kumamoto University 4‐24‐1 Kuhonji, Chuo‐ku Kumamoto 862‐0976Japan
| | - Takeshi Ohno
- Department of Health Sciences Faculty of Life Sciences Kumamoto University 4‐24‐1 Kuhonji, Chuo‐ku Kumamoto 862‐0976Japan
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Pappas E, Kalaitzakis G, Boursianis T, Zoros E, Zourari K, Pappas EP, Makris D, Seimenis I, Efstathopoulos E, Maris TG. Dosimetric performance of the Elekta Unity MR-linac system: 2D and 3D dosimetry in anthropomorphic inhomogeneous geometry. ACTA ACUST UNITED AC 2019; 64:225009. [DOI: 10.1088/1361-6560/ab52ce] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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