Ion chamber magnetic field correction factors measured via microDiamond cross-calibration from a conventional linac to MRI-linac
Publication Name
Frontiers in Physics
Abstract
Magnetic field correction factors are required for performing reference dosimetry on Magnetic Resonance Imaging Linear accelerators (MRI-linacs). Methods for measuring magnetic field correction factors usually require specialized equipment and expertise. Our work investigated the use of a microDiamond detector to cross-calibrate an ion chamber between a conventional linac and MRI-linac as a method to measure ion chamber magnetic field correction factors for the MRI-linac. Ratios of the microDiamond and ion chamber were measured on a conventional linac, parallel MRI-linac at 0 T, parallel MRI-linac at 1 T and perpendicular MRI-linac at 1.5 T. The beam quality dependence of the microDiamond was investigated by comparing the measurements on the conventional linac and parallel MRI-linac at 0 T. The magnetic field dependence of the microDiamond was investigated comparing the measurements on a parallel MRI-linac at 0 and 1 T. The ion chamber magnetic field correction factors were calculated by comparing the conventional linac and parallel MRI-linac at 1 T and the conventional linac and perpendicular MRI-linac at 1.5 T for the parallel and perpendicular factors respectively. The FC65-G and PTW30013 ion chambers were investigated. For a parallel MRI-linac, with a beam quality of (Formula presented.) = 0.632, we measured magnetic field correction factors of 0.988 ± 0.016 (k = 2) and 0.987 ± 0.016 (k = 2) for a FC65-G and PTW30013 respectively, where k is the coverage factor. For a perpendicular MRI-linac, with a beam quality of (Formula presented.) = 0.701, we measured magnetic field correction factors of 0.995 ± 0.020 (k = 2) and 0.983 ± 0.020 (k = 2) for a FC65-G and PTW30013 respectively. The results showed agreement with previously published work which used different approaches. Our work demonstrates the use of a microDiamond to calculate the ion chamber magnetic field correction factor using measurements on a conventional linac and MRI-linac. The high level of uncertainty in our results means the method at present can only be used for validation of magnetic field correction factors.
Open Access Status
This publication may be available as open access
Volume
10
Article Number
925890
Funding Number
1036078
Funding Sponsor
National Health and Medical Research Council