Experimental evaluation of the impact of low tesla transverse magnetic field on dose distribution in presence of tissue interfaces |
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| Affiliation: | 1. U.O.C. Fisica Sanitaria, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario “A. Gemelli” IRCCS, Roma, Italy;2. Istituto di Radiologia, Università Cattolica del Sacro Cuore, Roma, Italy;3. Istituto di Fisica, Università Cattolica del Sacro Cuore, Roma, Italy;4. U.O.C. Radioterapia Oncologica, Dipartimento di Diagnostica per immagini, Radioterapia Oncologica ed Ematologia, Fondazione Policlinico Universitario “A. Gemelli” IRCCS, Roma, Italy;1. Department of Radiation Oncology, Saitama Medical University International Medical Center, 1397-1 Yamane, Hidaka, Saitama 350-1298, Japan;2. Department of Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan;3. Division of Medical Physics, Department of Information Technology and Medical Engineering, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan;4. Radiation Physics Section, Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-Ku, Tokyo 113-8677, Japan;5. Center for Cancer Control and Information Services, National Cancer Center, 5-1-1 Tsukiji, Chuo-Ku, Tokyo 104-0045, Japan;6. Particle Therapy Division, Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, 6-5-1 Kashiwanoha, Kashiwa City, Chiba 277-8577, Japan;7. Department of Medical Physics, Tokyo Women’s Medical University, 8-1 Kawatamachi, Shinjuku, Tokyo 162-8666, Japan;8. Department of Radiology, Graduate School of Medical Sciences, Nagoya City University, 1 Kawasumi, Mizuho-cho, Mizuho-ku, Nagoya, Aichi 467-8601, Japan;9. Department of Radiation Oncology, Kindai University Faculty of Medicine, 377-2 Ohno-Higashi, Osaka-Sayama, Osaka 589-8511, Japan;2. ViewRay Incorporated, Oakwood Village, OH;1. Graduate School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan;2. Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan;1. Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan;2. Graduate School of Health Sciences, Kumamoto University, 4-24-1 Kuhonji, Kumamoto, Japan;3. Kokura Memorial Hospital, 3-2-1 Asano, Kokura, Fukuoka, Japan;4. Saga Heavy Ion Medical Accelerator in Tosu, 3049 Koga-machi, Tosu, Saga, Japan;5. National Hospital Organization Kyushu Medical Center, 1-8-1 Jigyouhama, Fukuoka, Japan |
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| Abstract: | PurposeAim of this study is to experimental evaluate the impact of a 0.35 T transverse magnetic field on dose distribution in presence of tissue-air and tissue-lung interfaces.MethodsThe investigation was carried out using MRIdian (ViewRay, Cleveland, Ohio) and it consisted of comparing experimental measurements performed by Gafchromic EBT3 film dosimetry, to Montecarlo simulations, carried out in the presence and, as well as, the absence of the magnetic field.A preliminary dose calibration was planned on MRIdian, arranging 3 × 3 cm2 film pieces in a water slab phantom and exposing them at different beam-on times, in a dose range equal to 0.1–12.1 Gy.All experimental measurements were then carried out using the calibrated films and delivering one single beam orthogonally to three different phantoms: without inhomogeneity, with an air gap and with a lung inhomogeneity.The dose distributions measured by EBT3 films in presence of magnetic field were compared to those calculated in the presence and, as well as, the absence of the magnetic field, in terms of gamma analysis. A quantification of electron return effect (ERE) was also performed.ResultsAll the tested plans considering the magnetic field show a gamma-passing rate higher than 98% for 3%/3 mm gamma analysis.In presence of tissue-air interface, the electron return effect causes an over-dosage of +31.9% at the first interface and an under-dosage of −33% at the second interface. The dosimetric variations in presence of tissue-lung interface results to be smaller (+0.8% first interface, −1.3% second interface).ConclusionThe impact of 0.35 T magnetic field is not negligible and it can be effectively modelled by the Montecarlo dose calculation platform available in the MRIdian TPS. |
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| Keywords: | Dosimetric verification MR guided radiotherapy Gafchromic EBT3 |
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