| Qi Yaping,Wang Zhipeng,Yao Jintao,Liu Fubin,Jin Sunjun,Huang Ji,Yang Xiaoyuan,Zhang Jian,Wang Kun.Feasibility study of integrating medical Linac with electromagnet to measure magnetic factor of reference dosimetry for MRIgRT[J].Chinese Journal of Radiological Medicine and Protection,2023,43(4):291-296 |
| Feasibility study of integrating medical Linac with electromagnet to measure magnetic factor of reference dosimetry for MRIgRT |
| Received:December 06, 2022 |
| DOI：10.3760/cma.j.cn112271-20221206-00472 |
| KeyWords:MRIgRT Magnetic field Ionization chamber Magnetic factor |
| FundProject:国家重点研发计划资助(2021YFF0603600);基本科研业务经费(AKYCX2207) |
| Author Name | Affiliation | E-mail | | Qi Yaping | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Wang Zhipeng | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Yao Jintao | College of Mechanical Engineering, Anhui University of Science and Technology, Huainan 232001, China | | | Liu Fubin | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Jin Sunjun | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Huang Ji | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Yang Xiaoyuan | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Zhang Jian | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | | | Wang Kun | Division of Ionizing Radiation Metrology, National Institute of Metrology, Beijing 100029, China | wangkun@nim.ac.cn |
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| Abstract:: |
| Objective To study the influence of intensive magnet fields on radiation dose measurement, and to demonstrate the feasibility of measuring magnet field correction factor by a combination of medical linac with variable magnet fields in view of needing for accurate measurement of the doses from reference beam arising in MR image-guided radiotherapy.Methods A photon radiation field and a variable field with 6 MV nominal high voltage were produced by using conventional medical electron linear accelerator equipped with a pair of electromagnets with magnetic field strength up to 1.5 T. Both PTW30013 and PTW31010 ionization chambers were used to test the responses of ionization chambers under different magnetic field strengths at four orientations in which the angles between ionization chamber axis and magnetic field direction were 0°, 180°, 90° and 270°, respectively. The magnetic factors, kB,M was calculated and compared with the reported values in literature.Results The response of ionization chamber was proportional to the magnetic field strength before it reached to a peak around 1 T, and then fell down as the magnetic field continued to rise. When the magnetic field was 0.35 T, the magnetic factors of PTW31010 were 0.988 2±0.000 3 and 0.997 4±0.000 4 corresponding to 90° and 0° directions, the discrepancy between 0° scenario and literature was 0.05% ±0.04%. When the magnetic field reached 1.5 T, the magnetic factor of PTW30013 was 0.958 9±0.000 5 at the situation of 90°, which was 0.60% ±0.05% different from the literature value.Conclusions Conventional 6 MV medical accelerator equipped with electromagnet can be used to measure the magnetic field factor of reference dosimetry for MRIgRT. |
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