Feasibility study of integrating medical Linac with electromagnet to measure magnetic factor of reference dosimetry for MRIgRT
10.3760/cma.j.cn112271-20221206-00472
- VernacularTitle:光子辐射场配置电磁场研究磁共振引导放疗(MRIgRT)参考剂量磁场因子的可行性
- Author:
Yaping QI
1
;
Zhipeng WANG
;
Jintao YAO
;
Fubin LIU
;
Sunjun JIN
;
Ji HUANG
;
Xiaoyuan YANG
;
Jian ZHANG
;
Kun WANG
Author Information
1. 中国计量科学研究院电离辐射计量科学研究所，北京 100029
- Keywords:
MRIgRT;
Magnetic field;
Ionization chamber;
Magnetic factor
- From:
Chinese Journal of Radiological Medicine and Protection
2023;43(4):291-296
- CountryChina
- Language:Chinese
-
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.
