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Updated: Jan 26, 2026
Dosimetry for Cell Irradiation using Orthovoltage 40-300 kV X-Ray Facilities
Published on: February 20, 2021
Effect of low magnetic field on single-diode dosimetry for clinical use
Chang Heon Choi1, Jong Min Park2, Hyun Joon An1
1Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea; Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Republic of Korea; Biomedical Research Institute, Seoul National University Hospital, Seoul, Republic of Korea.
Purpose:
To evaluate the effect of a low magnetic field (B-field, 0.35 T) on QED™ for clinical use.
Methods:
Black and Blue QED were irradiated using tri-Co-60 magnetic resonance image-guided radiation therapy systems with and without the B-field. For both detectors, angular dependence of the beam orientation was evaluated by rotating the gantry and detector in parallel and perpendicular directions to the B-field. Angular dependence betweenthe directions of both QED and B-field was also measured. Response on the depth and output factor of both detectors was investigated for parallel and perpendicular setups, respectively.
Results:
When Black QED was placed on a surface, detector response decreased by 1.8% and 4.5% for parallel and perpendicular setups, respectively, owing to the B-field. The angular dependence of the beam orientation was not affected by B-field for both detectors. There was a significant angular dependence between Black QED and B-field direction and for the Black QED when the gantry was rotated. Owing to the B-field, the detector response at 90° decreased by 2.4%, response of Black QED on the depth was changed only on the surface, and output factor of Black QED was changed only on the surface. The response of Blue QED was not affected by the B-field for all examined situations.
Conclusions:
Using Black QED on a surface in the same position as that in the calibration requires some correction to the B-field. Blue QED does not require correction as it is not affected by the B-field.
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