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1.5T 磁共振加速器X线束剂量学特性测试
李明辉, 田源, 张可, 门阔, 戴建荣
国家癌症中心/国家肿瘤临床医学研究中心/中国医学科学院北京协和医学院肿瘤医院放疗科 100021
Dosimetric characteristics test of 1.5T magnetic resonance accelerator
Li Minghui, Tian Yuan, Zhang Ke, Men Kuo, Dai Jianrong
Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/ Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100021, China
Abstract：Objective The Lorentz force produced by magnetic field deflects the paths of secondary electrons. The X-ray beam dosimetry characteristics of the magnetic resonance accelerator (MR-Linac) are different from conventional accelerators. The purpose of this study was to measure and analyze the X-ray beam dosimetry characteristics of 1.5T MR-Linac. Methods In May 2019, our hospital installed a Unity 1.5T MR-Linac and measured it with magnetic field compatible tools. The measurement indexes include:surface dose, maximum dose point depth, beam quality, off-axis dose profile center, beam symmetry, penumbra width, output changes of different gantry angles. Results The average surface dose was 40.48%, and the average maximum dose depth was 1.25cm. The center of the 10cm×10cm beam field was offset by 1.47mm to the x2 side and 0.3mm to the y2 side. The x-axis symmetry was 101.33%, and the penumbra width on both sides was 6.86mm and 7.14mm, respectively. The y-axis symmetry was 100.85%, and the penumbra width on both sides was 5.92mm and 5.95mm, respectively. The maximum deviation of output dose with different gantry angles reached 1.50%. Conclusions The surface dose of MR-Linac tend to be consistent, and the depth of the maximum dose point became shallower. The off-axis in the x-axis direction was shifted to the x2 side, which resulting in worse symmetry and penumbra asymmetry. The output dose at different angles has obvious variation and needs correction.
Li Minghui,Tian Yuan,Zhang Ke et al. Dosimetric characteristics test of 1.5T magnetic resonance accelerator[J]. Chinese Journal of Radiation Oncology, 2020, 29(11): 963-967.
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2020, Vol. 29 
