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Chea M, Croisé M, Huet C, Bassinet C, Benadjaoud MA, Jenny C. MR compatible detectors assessment for a 0.35 T MR-linac commissioning. Radiat Oncol 2024; 19:40. [PMID: 38509543 PMCID: PMC10956263 DOI: 10.1186/s13014-024-02431-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Accepted: 03/11/2024] [Indexed: 03/22/2024] Open
Abstract
PURPOSE To assess a large panel of MR compatible detectors on the full range of measurements required for a 0.35 T MR-linac commissioning by using a specific statistical method represented as a continuum of comparison with the Monte Carlo (MC) TPS calculations. This study also describes the commissioning tests and the secondary MC dose calculation validation. MATERIAL AND METHODS Plans were created on the Viewray TPS to generate MC reference data. Absolute dose points, PDD, profiles and output factors were extracted and compared to measurements performed with ten different detectors: PTW 31010, 31021, 31022, Markus 34045 and Exradin A28 MR ionization chambers, SN Edge shielded diode, PTW 60019 microdiamond, PTW 60023 unshielded diode, EBT3 radiochromic films and LiF µcubes. Three commissioning steps consisted in comparison between calculated and measured dose: the beam model validation, the output calibration verification in four different phantoms and the commissioning tests recommended by the IAEA-TECDOC-1583. MAIN RESULTS The symmetry for the high resolution detectors was higher than the TPS data of about 1%. The angular responses of the PTW 60023 and the SN Edge were - 6.6 and - 11.9% compared to the PTW 31010 at 60°. The X/Y-left and the Y-right penumbras measured by the high resolution detectors were in good agreement with the TPS values except for the PTW 60023 for large field sizes. For the 0.84 × 0.83 cm2 field size, the mean deviation to the TPS of the uncorrected OF was - 1.7 ± 1.6% against - 4.0 ± 0.6% for the corrected OF whereas we found - 4.8 ± 0.8% for passive dosimeters. The mean absolute dose deviations to the TPS in different phantoms were 0 ± 0.4%, - 1.2 ± 0.6% and 0.5 ± 1.1% for the PTW 31010, PTW 31021 and Exradin A28 MR respectively. CONCLUSIONS The magnetic field effects on the measurements are considerably reduced at low magnetic field. The PTW 31010 ionization chamber can be used with confidence in different phantoms for commissioning and QA tests requiring absolute dose verifications. For relative measurements, the PTW 60019 presented the best agreement for the full range of field size. For the profile assessment, shielded diodes had a behaviour similar to the PTW 60019 and 60023 while the ionization chambers were the most suitable detectors for the symmetry. The output correction factors published by the IAEA TRS 483 seem to be applicable at low magnetic field pending the publication of new MR specific values.
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Affiliation(s)
- Michel Chea
- Medical Physics Department, Pitié-Salpêtrière Hospital, AP-HP Sorbonne University, 47-83 Boulevard de l'Hôpital, 75651, Paris Cedex 13, France.
| | - Mathilde Croisé
- Medical Physics Department, Pitié-Salpêtrière Hospital, AP-HP Sorbonne University, 47-83 Boulevard de l'Hôpital, 75651, Paris Cedex 13, France
| | - Christelle Huet
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SDOS/LDRI, 92260, Fontenay-aux-Roses, France
| | - Céline Bassinet
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SDOS/LDRI, 92260, Fontenay-aux-Roses, France
| | - Mohamed-Amine Benadjaoud
- Institut de Radioprotection et Sûreté Nucléaire (IRSN), PSE-SANTE/SERAMED, 92260, Fontenay-aux-Roses, France
| | - Catherine Jenny
- Medical Physics Department, Pitié-Salpêtrière Hospital, AP-HP Sorbonne University, 47-83 Boulevard de l'Hôpital, 75651, Paris Cedex 13, France
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Ullah Khan A, DeWerd LA, Yadav P. Beam quality correction factors for ionization chambers in a 0.35 T magnetic resonance (MR)-linac - A Monte Carlo study. Phys Med 2024; 119:103314. [PMID: 38335742 DOI: 10.1016/j.ejmp.2024.103314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Revised: 01/29/2024] [Accepted: 02/04/2024] [Indexed: 02/12/2024] Open
Abstract
PURPOSE The purpose of this study was to directly calculate [Formula: see text] correction factors for four cylindrical ICs for a 0.35 T MR-linac using the Monte Carlo (MC) method. METHODS A previously-validated TOPAS/GEANT4 MC head model of the 0.35 T MR-linac was employed. The MR-compatible Exradin A12, A1SL, A26, and A28 cylindrical ICs were modeled considering the dead volume in the air cavity. The [Formula: see text] correction factor was determined for initial electron energies of 5-7 MeV. The correction factor was calculated for all four angular orientations in the lateral plane. The impact of the 0.35 T magnetic field on the IC response was also investigated. RESULTS The maximum beam quality dependence in the [Formula: see text] exhibited by the A12, A1SL, A26, and A28 ICs was 1.10 %, 2.17 %, 0.81 %, and 1.75 %, respectively, considering all angular orientations. The magnetic field dependence was < 1 % and the maximum [Formula: see text] correction was < 2 % when the detector was aligned along the direction of the magnetic field at 0° and 180° angles. The A12 IC over-responded up to 5.40 % for the orthogonal orientation. An asymmetry in the response of up to 8.30 % was noted for the A28 IC aligned at 90° and 270° angles. CONCLUSIONS A parallel orientation for the IC, with respect to the magnetic field, is recommended for reference dosimetry in MRgRT. Both over and under-response in the IC signal was noted for the orthogonal orientations, which is highly dependent on the cavity diameter, cavity length, and the dead volume.
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Affiliation(s)
- Ahtesham Ullah Khan
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, USA; Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, USA
| | - Poonam Yadav
- Department of Radiation Oncology, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
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Frick S, Schneider M, Kapsch RP, Thorwarth D. Experimental characterization of four ionization chamber types in magnetic fields including intra-type variation. Phys Imaging Radiat Oncol 2024; 29:100561. [PMID: 38463218 PMCID: PMC10924196 DOI: 10.1016/j.phro.2024.100561] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2023] [Revised: 02/16/2024] [Accepted: 02/20/2024] [Indexed: 03/12/2024] Open
Abstract
Background and purpose For dosimetry in magnetic resonance (MR) guided radiotherapy, assessing the magnetic field correction factors of air-vented ionization chambers is crucial. Novel MR-optimized chambers reduce MR-imaging artefacts, enhancing their quality assurance utility. This study aimed to characterize two new MR-optimized ionization chambers with sensitive volumes of 0.07 and 0.016 cm3 regarding magnetic field correction factors and intra-type variation and compare them to their conventional counterparts. Material and methods Five chambers of each type were evaluated in a water phantom, using a clinical linear accelerator and an electromagnet, as well as a 1.5 T MR-linac system. The magnetic field correction factor k B → , Q , addressing the change of response caused by a magnetic field, was assessed together with its intra-type variation. MR-optimized and conventional chambers were compared using a Mann-Whitney U-Test. Results Considering 1.5 T and a perpendicular chamber orientation, we observed significant differences in the magnetic field-induced change in chamber reading between the two 0.016 cm3 chamber versions (p = 0.03). For a 7 MV beam, MR-optimized chambers (0.016/0.07 cm3) showed k B → , Q values of 1.0426(66) and 1.0463(44), compared to 1.0319(53) and 1.0480(41) of their conventional counterparts. In anti-parallel orientation, k B → , Q was 1.0012(69) and 0.9863(49) for the MR-optimized chambers. The average intra-type variation of k B → , Q over all chamber types was 0.3%. Conclusion Magnetic field correction factors were successfully determined for four ionization chamber types, including two new MR-optimized versions, allowing their use in MR-linac absolute dosimetry. Evaluation of the intra-type variation enabled the assessment of their contribution to the uncertainty of tabulated k B → , Q .
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Affiliation(s)
- Stephan Frick
- Physikalisch-Technische Bundesanstalt, Braunschweig, Germany
| | - Moritz Schneider
- Section for Biomedical Physics, Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany
| | | | - Daniela Thorwarth
- Section for Biomedical Physics, Department of Radiation Oncology, University Hospital Tübingen, Tübingen, Germany
- German Cancer Consortium (DKTK), Partner site Tübingen, A Partnership between DKFZ and University Hospital Tübingen, Germany
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Begg J, Jelen U, Moutrie Z, Oliver C, Holloway L, Brown R. ACPSEM position paper: dosimetry for magnetic resonance imaging linear accelerators. Phys Eng Sci Med 2023; 46:1-17. [PMID: 36806156 PMCID: PMC10030536 DOI: 10.1007/s13246-023-01223-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/19/2023] [Indexed: 02/23/2023]
Abstract
Consistency and clear guidelines on dosimetry are essential for accurate and precise dosimetry, to ensure the best patient outcomes and to allow direct dose comparison across different centres. Magnetic Resonance Imaging Linac (MRI-linac) systems have recently been introduced to Australasian clinics. This report provides recommendations on reference dosimetry measurements for MRI-linacs on behalf of the Australiasian College of Physical Scientists and Engineers in Medicine (ACPSEM) MRI-linac working group. There are two configurations considered for MRI-linacs, perpendicular and parallel, referring to the relative direction of the magnetic field and radiation beam, with different impacts on dose deposition in a medium. These recommendations focus on ion chambers which are most commonly used in the clinic for reference dosimetry. Water phantoms must be MR safe or conditional and practical limitations on phantom set-up must be considered. Solid phantoms are not advised for reference dosimetry. For reference dosimetry, IAEA TRS-398 recommendations cannot be followed completely due to physical differences between conventional linac and MRI-linac systems. Manufacturers' advice on reference conditions should be followed. Beam quality specification of TPR20,10 is recommended. The configuration of the central axis of the ion chamber relative to the magnetic field and radiation beam impacts the chamber response and must be considered carefully. Recommended corrections to delivered dose are [Formula: see text], a correction for beam quality and [Formula: see text], for the impact of the magnetic field on dosimeter response in the magnetic field. Literature based values for [Formula: see text] are given. It is important to note that this is a developing field and these recommendations should be used together with a review of current literature.
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Affiliation(s)
- Jarrad Begg
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia.
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia.
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia.
| | - Urszula Jelen
- St Vincents Clinic, GenesisCare, Darlinghurst, NSW, 2010, Australia
| | - Zoe Moutrie
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
| | - Chris Oliver
- Primary Standards Dosimetry Laboratory, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
| | - Lois Holloway
- Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Liverpool, NSW, 2170, Australia
- Ingham Institute for Applied Medical Research, Liverpool, NSW, 2170, Australia
- South Western Sydney Clinical School, University of New South Wales, Liverpool, NSW, 2170, Australia
- Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia
- Institute of Medical Physics, University of Sydney, Camperdown, NSW, 2505, Australia
| | - Rhonda Brown
- Australian Clinical Dosimetry Service, Australian Radiation Protection and Nuclear Safety Agency, Yallambie, VIC, 3085, Australia
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Tanadini-Lang S, Budgell G, Bohoudi O, Corradini S, Cusumano D, Güngör G, Kerkmeijer LGW, Mahmood F, Nill S, Palacios MA, Reiner M, Thorwarth D, Wilke L, Wolthaus J. An ESTRO-ACROP guideline on quality assurance and medical physics commissioning of online MRI guided radiotherapy systems based on a consensus expert opinion. Radiother Oncol 2023; 181:109504. [PMID: 36736592 DOI: 10.1016/j.radonc.2023.109504] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 01/25/2023] [Indexed: 02/05/2023]
Abstract
OBJECTIVE The goal of this consensus expert opinion was to define quality assurance (QA) tests for online magnetic resonance image (MRI) guided radiotherapy (oMRgRT) systems and to define the important medical physics aspects for installation and commissioning of an oMRgRT system. MATERIALS AND METHODS Ten medical physicists and two radiation oncologists experienced in oMRgRT participated in the survey. In the first round of the consensus expert opinion, ideas on QA and commissioning were collected. Only tests and aspects different from commissioning of a CT guided radiotherapy (RT) system were considered. In the following two rounds all twelve participants voted on the importance of the QA tests, their recommended frequency and their suitability for the two oMRgRT systems approved for clinical use as well as on the importance of the aspects to consider during medical physics commissioning. RESULTS Twenty-four QA tests were identified which are potentially important during commissioning and routine QA on oMRgRT systems compared to online CT guided RT systems. An additional eleven tasks and aspects related to construction, workflow development and training were collected. Consensus was found for most tests on their importance, their recommended frequency and their suitability for the two approved systems. In addition, eight aspects mostly related to the definition of workflows were also found to be important during commissioning. CONCLUSIONS A program for QA and commissioning of oMRgRT systems was developed to support medical physicists to prepare for safe handling of such systems.
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Affiliation(s)
- Stephanie Tanadini-Lang
- Department of Radiation Oncology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland.
| | - Geoff Budgell
- Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Wilmslow Road, Manchester iM20 4BX, UK
| | - Omar Bohoudi
- Amsterdam UMC, Vrije Universiteit Medical Centre, Dept. of Radiation Oncology, de Boelelaan 1117, 1081 HV Amsterdam, the Netherlands
| | - Stefanie Corradini
- Department of Radiation Oncology, University Hospital, LMU Munich, 81377 Munich, Germany
| | - Davide Cusumano
- Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy; Mater Olbia Hospital, Olbia, SS, Italy
| | - Görkem Güngör
- Department of Medical Physics, Graduade School of Health Sciences, Istanbul Medipol University, Istanbul, Turkey
| | - Linda G W Kerkmeijer
- Department of Radiation Oncology, Radboud University Medical Center Nijmegen, the Netherlands
| | - Faisal Mahmood
- Laboratory of Radiation Physics, Department of Oncology, Odense University Hospital, Odense, Denmark; Department of Clinical Research, University of Southern Denmark, Odense, Denmark
| | - Simeon Nill
- The Joint Department of Physics, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, UK
| | - Miguel A Palacios
- Amsterdam UMC, Vrije Universiteit Medical Centre, Dept. of Radiation Oncology, de Boelelaan 1117, 1081 HV Amsterdam, the Netherlands
| | - Michael Reiner
- Department of Radiation Oncology, University Hospital, LMU Munich, 81377 Munich, Germany
| | - Daniela Thorwarth
- Section for Biomedical Physics, Department of Radiation Oncology, University of Tübingen, Tübingen, Germany
| | - Lotte Wilke
- Department of Radiation Oncology, University Hospital Zurich, University of Zurich, 8091 Zurich, Switzerland
| | - Jochem Wolthaus
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
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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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D'Souza M, Nusrat H, Iakovenko V, Keller B, Sahgal A, Renaud J, Sarfehnia A. Water calorimetry in MR‐linac: Direct measurement of absorbed dose and determination of chamber. Med Phys 2020; 47:6458-6469. [DOI: 10.1002/mp.14468] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2019] [Revised: 07/22/2020] [Accepted: 08/11/2020] [Indexed: 11/10/2022] Open
Affiliation(s)
- Mark D'Souza
- Department of Physics Ryerson University 350 Victoria St. Toronto ONM5B 2K3Canada
| | - Humza Nusrat
- Department of Radiation Oncology University of Toronto 2075 Bayview Ave. Toronto ONM4N 3M5Canada
| | - Viktor Iakovenko
- Department of Radiation Oncology University of Toronto 2075 Bayview Ave. Toronto ONM4N 3M5Canada
| | - Brian Keller
- Department of Radiation Oncology University of Toronto 2075 Bayview Ave. Toronto ONM4N 3M5Canada
| | - Arjun Sahgal
- Department of Radiation Oncology University of Toronto 2075 Bayview Ave. Toronto ONM4N 3M5Canada
| | - James Renaud
- Meterology Research Centre National Research Council Canada Montreal Rd. Ottawa ONK1A OR6Canada
- Medical Physics Unit McGill University 1001 Decarie Blvd. Montreal QCH4A 3J1Canada
| | - Arman Sarfehnia
- Department of Physics Ryerson University 350 Victoria St. Toronto ONM5B 2K3Canada
- Department of Radiation Oncology University of Toronto 2075 Bayview Ave. Toronto ONM4N 3M5Canada
- Department of Radiation Oncology McGill University 1001 Decarie Blvd. Montreal QCH4A 3J1Canada
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