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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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Walter AE, DeWerd LA. Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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Holm KM, Jäkel O, Krauss A. Water calorimetry-based kQfactors for Farmer-type ionization chambers in the SOBP of a carbon-ion beam. Phys Med Biol 2021; 66. [PMID: 34153952 DOI: 10.1088/1361-6560/ac0d0d] [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: 03/31/2021] [Accepted: 06/21/2021] [Indexed: 11/12/2022]
Abstract
The dosimetry of carbon-ion beams based on calibrated ionization chambers (ICs) still shows a significantly higher uncertainty compared to high-energy photon beams, a fact influenced mainly by the uncertainty of the correction factor for the beam qualitykQ. Due to a lack of experimental data,kQfactors in carbon-ion beams used today are based on theoretical calculations whose standard uncertainty is three times higher than that of photon beams. To reduce their uncertainty, in this work,kQfactors for two ICs were determined experimentally by means of water calorimetry for the spread-out Bragg peak of a carbon-ion beam, these factors are presented here for the first time. To this end, the absorbed dose to water in the12C-SOBP is measured using the water calorimeter developed at Physikalisch-Technische Bundesanstalt, allowing a direct calibration of the ICs used (PTW 30013 and IBA FC65G) and thereby an experimental determination of the chamber-specifickQfactors. Based on a detailed characterization of the irradiation field, correction factors for several effects that influence calorimetric and ionometric measurements were determined. Their contribution to an overall uncertainty budget of the finalkQfactors was determined, leading to a standard uncertainty forkQof 0.69%, which means a reduction by a factor of three compared to the theoretically calculated values. The experimentally determined values were expressed in accordance with TRS-398 and DIN 6801-1 and compared to the values given there. A maximum deviation of 2.3% was found between the experiment and the literature.
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Affiliation(s)
- Kim Marina Holm
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany.,Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.,Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.,Department of Physics and Astronomy, University of Heidelberg, Im Neuenheimer Feld 226, D-69120 Heidelberg, Germany
| | - Oliver Jäkel
- Department of Medical Physics in Radiation Oncology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany.,Heidelberg Institute for Radiation Oncology (HIRO), Heidelberg, Germany.,Heidelberg Ion Beam Therapy Center (HIT), University Hospital Heidelberg, Im Neuenheimer Feld 450, D-69120 Heidelberg, Germany
| | - Achim Krauss
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116 Braunschweig, Germany
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Pojtinger S, Nachbar M, Ghandour S, Pisaturo O, Pachoud M, Kapsch RP, Thorwarth D. Experimental determination of magnetic field correction factors for ionization chambers in parallel and perpendicular orientations. Phys Med Biol 2020; 65:245044. [PMID: 33181493 DOI: 10.1088/1361-6560/abca06] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Magnetic field correction factors are needed for absolute dosimetry in magnetic resonance (MR)-linacs. Currently experimental data for magnetic field correction factors, especially for small volume ionization chambers, are largely lacking. The purpose of this work is to establish, independent methods for the experimental determination of magnetic field correction factors [Formula: see text] in an orientation in which the ionization chamber is parallel to the magnetic field. The aim is to confirm previous experiments on the determination of Farmer type ionization chamber correction factors and to gather information about the usability of small-volume ionization chambers for absolute dosimetry in MR-linacs. The first approach to determine [Formula: see text] is based on a cross-calibration of measurements using a conventional linac with an electromagnet and an MR-linac. The absolute influence of the magnetic field in perpendicular orientation is quantified with the help of the conventional linac and the electromagnet. The correction factors for the parallel orientation are then derived by combining these measurements with relative measurements in the MR-linac. The second technique utilizes alanine electron paramagnetic resonance dosimetry. The alanine system as well as several ionization chambers were directly calibrated with the German primary standard for absorbed dose to water. Magnetic field correction factors for the ionization chambers were determined by a cross-calibration with the alanine in an MR-linac. Important quantities like [Formula: see text] for Farmer type ionization chambers in parallel orientation and the change of the dose to water due the magnetic field [Formula: see text] have been confirmed. In addition, magnetic field correction factors have been determined for small volume ionization chambers in parallel orientation. The electromagnet-based measurements of [Formula: see text] for [Formula: see text] MR-linacs and parallel ionization chamber orientations resulted in 0.9926(22), 0.9935(31) and 0.9841(27) for the PTW 30013, the PTW 31010 and the PTW 31021, respectively. The measurements based on the second technique resulted in values for [Formula: see text] of 0.9901(72), 0.9955(72), and 0.9885(71). Both methods show excellent accuracy and reproducibility and are therefore suitable for the determination of magnetic field correction factors. Small-volume ionization chambers showed a variation in the resulting values for [Formula: see text] and should be cross-calibrated instead of using tabulated values for correction factors.
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Affiliation(s)
- Stefan Pojtinger
- Physikalisch-Technische Bundesanstalt, Braunschweig, Germany. University Hospital Tübingen, Biomedical Physics, Tübingen, Germany
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Krauss A, Spindeldreier CK, Klüter S. Direct determination of [Formula: see text] for cylindrical ionization chambers in a 6 MV 0.35 T MR-linac. Phys Med Biol 2020; 65:235049. [PMID: 33300501 DOI: 10.1088/1361-6560/abab56] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
To ensure accurate reference dosimetry with ionization chambers in magnetic resonance linear accelerators (MR-linacs), the influence of the magnetic field on the response of the ionization chambers must be considered. The most direct method considering the influence of magnetic fields in dosimetry is to apply an appropriate absorbed-dose-to-water primary standard. At PTB, a new water calorimeter has been designed which is capable to determine Dw,Q in an MR-linac. The new device allows the direct calibration of ionization chambers in terms of absorbed dose to water for MR-linac irradiation conditions. Hence, the correction factors [Formula: see text] can be determined which replace the current radiation-quality dependent correction factors [Formula: see text] for dosimetry in the presence of magnetic fields. In cooperation with Heidelberg University Hospital,[Formula: see text] factors were measured at the 6 MV 0.35 T Viewray MR-linac for different cylindrical ionization chambers with sensitive volumes ranging from 0.015 cm3 to 0.65 cm3. The chambers were placed both perpendicular and parallel in respect to the magnetic field. Standard uncertainties of about 0.5% were achieved.
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Affiliation(s)
- A Krauss
- Department of Dosimetry for Radiation Therapy and Diagnostic Radiology, Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, D-38116, Braunschweig, Germany
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Holm KM, Weber U, Simeonov Y, Krauss A, Jäkel O, Greilich S. 2D range modulator for high-precision water calorimetry in scanned carbon-ion beams. ACTA ACUST UNITED AC 2020; 65:215003. [DOI: 10.1088/1361-6560/aba6d5] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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D'Souza M, Nusrat H, Renaud J, Peterson G, Sarfehnia A. First-stage validation of a portable imageable MR-compatible water calorimeter. Med Phys 2020; 47:5312-5323. [PMID: 32786081 DOI: 10.1002/mp.14448] [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: 02/04/2020] [Revised: 07/24/2020] [Accepted: 07/31/2020] [Indexed: 11/07/2022] Open
Abstract
PURPOSE The purpose of this study is to design a water calorimeter with three goals in mind: (a) To be fully magnetic resonance (MR)-compatible; (b) To be imaged using kV cone beam computed tomography (CBCT), MV portal imaging or MRI for accurate positioning; (c) To accommodate both vertical and horizontal beam incidence, as well as volumetric deliveries or Gamma Knife®. Following this, the calorimeter performance will be measured using an accelerator-based high-energy photon beam. METHODS A portable 4°C cooled stagnant water calorimeter was built using MR-compatible materials. The walls consist of layers of acrylic plastic, aerogel-based material acting as thermal insulation, as well as tubing for coolant to flow to keep the calorimeter temperature stable at 4°C. The lid contains additional pathways for coolant to flow through as well as two hydraulically driven stirrers. The water calorimeter was positioned in an Elekta Versa using kV CBCT imaging as well as orthogonal MV image pairs. Absolute absorbed dose to water was then determined under a 6 MV flattening filter-free (FFF) beam. This was compared against reference dosimetry results that were measured under identical conditions with an Exradin A1SL ionization chamber with a calibration coefficient directly traceable to the National Research Council Canada. RESULTS The dose to water determined with the calorimeter (n = 30) agreed with the A1SL ionization chamber reference dose measurements (n = 15) to within 0.25%. The uncertainty associated with the water calorimeter absorbed dose measurement was estimated to be 0.54% (k = 1). CONCLUSIONS An MR-compatible water calorimeter was successfully built and absolute absorbed dose to water under a conventional 6 MV FFF beam was determined successfully as a first-stage validation of the system.
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Affiliation(s)
- Mark D'Souza
- Department of Physics, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada
| | - Humza Nusrat
- Department of Radiation Oncology, University of Toronto, 2075 Bayview Ave., Toronto, ON, M4N 3M5, Canada.,Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada
| | - James Renaud
- Metrology Research Centre, National Research Council Canada, Montreal Rd., Ottawa, ON, K1A 0R6, Canada.,Medical Physics Unit, McGill University, 1001 Decarie Blvd., Montreal, QC, H4A 3J1, Canada
| | - Gerard Peterson
- Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada
| | - Arman Sarfehnia
- Department of Physics, Ryerson University, 350 Victoria St., Toronto, ON, M5B 2K3, Canada.,Department of Radiation Oncology, University of Toronto, 2075 Bayview Ave., Toronto, ON, M4N 3M5, Canada.,Department of Medical Physics, Sunnybrook Odette Cancer Centre, 2075 Bayview Ave, Toronto, ON, M4N 3M5, Canada.,Medical Physics Unit, McGill University, 1001 Decarie Blvd., Montreal, QC, H4A 3J1, Canada
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Renaud J, Palmans H, Sarfehnia A, Seuntjens J. Absorbed dose calorimetry. ACTA ACUST UNITED AC 2020; 65:05TR02. [DOI: 10.1088/1361-6560/ab4f29] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Krauss A, Kapsch RP. Direct determination ofkQfactors for cylindrical and plane-parallel ionization chambers in high-energy electron beams from 6 MeV to 20 MeV. ACTA ACUST UNITED AC 2018; 63:035041. [DOI: 10.1088/1361-6560/aaa71e] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Czarnecki D, Poppe B, Zink K. Monte Carlo-based investigations on the impact of removing the flattening filter on beam quality specifiers for photon beam dosimetry. Med Phys 2017; 44:2569-2580. [DOI: 10.1002/mp.12252] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 03/13/2017] [Accepted: 03/21/2017] [Indexed: 01/07/2023] Open
Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Wiesenstrasse 14 Giessen D-35390 Germany
- University Clinic for Medical Radiation Physics; Medical Campus Pius Hospital; Carl von Ossietzky University; Oldenburg Germany
| | - Björn Poppe
- University Clinic for Medical Radiation Physics; Medical Campus Pius Hospital; Carl von Ossietzky University; Oldenburg Germany
| | - Klemens Zink
- Institute of Medical Physics and Radiation Protection; University of Applied Sciences Giessen; Giessen D-35390 Germany
- Department of Radiotherapy and Radiation Oncology; University Medical Center Giessen and Marburg; Marburg D-35043 Germany
- Frankfurt Institute for Advanced Studies (FIAS); Ruth-Moufang-Straße 1; 60438 Frankfurt am Main Germany
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Osinga-Blättermann JM, Brons S, Greilich S, Jäkel O, Krauss A. Direct determination of k Q for Farmer-type ionization chambers in a clinical scanned carbon ion beam using water calorimetry. Phys Med Biol 2017; 62:2033-2054. [DOI: 10.1088/1361-6560/aa5bac] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Dufreneix S, Ostrowsky A, Le Roy M, Sommier L, Gouriou J, Delaunay F, Rapp B, Daures J, Bordy JM. Using a dose-area product for absolute measurements in small fields: a feasibility study. Phys Med Biol 2015; 61:650-62. [DOI: 10.1088/0031-9155/61/2/650] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Lárraga-Gutiérrez JM. Experimental determination of field factors ($\Omega _{{{Q}_{\text{clin}}},{{Q}_{\text{msr}}}}^{{{f}_{\text{clin}}},{{f}_{\text{msr}}}}$ ) for small radiotherapy beams using the daisy chain correction method. Phys Med Biol 2015; 60:5813-31. [DOI: 10.1088/0031-9155/60/15/5813] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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