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Technical Note: Ion chamber angular dependence in a magnetic field
Author(s) -
Reynolds Michael,
Rathee Satyapal,
Fallone B. Gino
Publication year - 2017
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.12405
Subject(s) - ionization chamber , monte carlo method , magnetic field , physics , detector , computational physics , beam (structure) , ionization , orientation (vector space) , optics , photon , atomic physics , ion , geometry , statistics , mathematics , quantum mechanics
Purpose There have been several studies investigating dose deposition effects within radiation detectors in the presence of a magnetic field. However, to date there has only been a passing investigation which explicitly investigates detector dose–response as a function of detector orientation. Herein we will investigate the dose–response as a function angular orientation of a PR 06C ionization chamber. We will also benchmark the Monte Carlo code PENELOPE with the newly developed magnetic field Fano test. Methods The PENELOPE Monte Carlo package was used to simulate a PR 06C ionization chamber in 0.35 T through 1.5 T magnetic fields oriented either parallel or orthogonal to an incident 6 MV radiation beam. The ionization chamber was rotated through a number of polar and azimuthal angles. The dose deposited within the chamber at each angular position and magnetic field strength was scored then normalized to that deposited in the same orientation with no magnetic field. The simulation was also benchmarked via a Fano test in magnetic field. Results The Fano test yielded a 0.4% difference between simulation and expected result, which is similar to previous findings and sufficient for the purposes of this study. The angular dose–response map in all cases where the magnetic field is oriented orthogonal to the radiation beam is quite varied and can range from 0.89 to 1.08. Angular deviations as small as 3° can lead to dose–response changes in excess of 1%. When the magnetic field is parallel to the photon beam, the angular dose–response map is homogeneous and less than 1% below 1.0 T. Conclusions Within a magnetic field‐oriented orthogonal to the radiation beam, the ionization chamber dose–response fluctuates greatly as a function of polar and azimuthal angle, where a parallel field yields a more homogeneous dose–response.