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MR‐guided proton therapy: Impact of magnetic fields on the detector response
Author(s) -
Fuchs Hermann,
PadillaCabal Fatima,
Zimmermann Lukas,
Palmans Hugo,
Georg Dietmar
Publication year - 2021
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.14660
Subject(s) - magnetic field , proton , detector , physics , ionization chamber , beam (structure) , lorentz force , proton therapy , atomic physics , dipole , ionization , nuclear magnetic resonance , optics , nuclear physics , ion , quantum mechanics
Purpose To investigate the response of detectors for proton dosimetry in the presence of magnetic fields. Material and Methods Four ionization chambers (ICs), two thimble‐type and two plane‐parallel‐type, and a diamond detector were investigated. All detectors were irradiated with homogeneous single‐energy‐layer fields, using 252.7 MeV proton beams. A Farmer IC was additionally irradiated in the same geometrical configuration, but with a lower nominal energy of 97.4 MeV. The beams were subjected to magnetic field strengths of 0, 0.25, 0.5, 0.75, and 1 T produced by a research dipole magnet placed at the room’s isocenter. Detectors were positioned at 2 cm water equivalent depth, with their stem perpendicular to both the magnetic field lines and the proton beam’s central axis, in the direction of the Lorentz force. Normality and two sample statistical Student’s t tests were performed to assess the influence of the magnetic field on the detectors’ responses. Results For all detectors, a small but significant magnetic field‐dependent change of their response was found. Observed differences compared to the no magnetic field case ranged from +0.5% to −0.7%. The magnetic field dependence was found to be nonlinear and highest between 0.25 and 0.5 T for 252.7 MeV proton beams. A different variation of the Farmer chamber response with magnetic field strength was observed for irradiations using lower energy (97.4 MeV) protons. The largest magnetic field effects were observed for plane‐parallel ionization chambers. Conclusion Small magnetic field‐dependent changes in the detector response were identified, which should be corrected for dosimetric applications.