Experimental study of the magnetic field correction factor of ionization chambers in MR-Linac
10.3760/cma.j.cn113030-20240620-00242
- VernacularTitle:基于实验的磁共振加速器中电离室磁场修正因子研究
- Author:
Yaping QI
1
;
Jiahao LUO
;
Yuan TIAN
;
Zhipeng WANG
;
Sunjun JIN
;
Ji HUANG
;
Xiaoyuan YANG
;
Xin WANG
;
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:
Radiotherapy;
Magnetic resonance linac;
Magnetic field correction factor;
Magnetic field orientation
- From:
Chinese Journal of Radiation Oncology
2024;33(12):1119-1124
- CountryChina
- Language:Chinese
-
Abstract:
Objective:To measure the magnetic field correction factor of reference ionization chamber in a 1.5 T magnetic field and to explore the response of the ionization chamber among different angles between magnetic field and ionization chamber axis.Methods:A home-made magnetic compatible one-dimensional water tank was used to measure the response of PTW30013 and IBA FC65-G in 7 MV photon beam of Elekta Unity with and without magnetic field. The ionizing current was collected by PTW UNIDOS Tango electrometer. The effective measurement point of ionization chamber was positioned to the isocenter of MR-linac using electronic portal image device. The influence on water absorbed dose of reference point was obtained by Monte Carlo calculations.Results:The response of ionization chambers in strong magnetic field was related to the angle between chamber axis and magnetic field. The response of ionization chamber was significantly affected in perpendicular magnetic field with a deviation up to 4.54% compared to parallel magnetic field. The deviation between the magnetic field correction factors measured for parallel or reverse-parallel was 0.03%-0.24%. The magnetic field correction factors for PTW30013 and FC65-G measured in parallel magnetic field were 0.9934±0.0077 and 0.9990±0.0076, respectively.Conclusions:This study experimentally verifies that positioning the ionization chamber axis parallel to the magnetic field direction in MR-linac reference dosimetry can minimize the magnetic field impact. The determined magnetic field correction factor and uncertainty in 1.5 T magnetic field can provide necessary data for establishing an MR-linac reference dosimetry protocol.
