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Permanent link (DOI): https://doi.org/10.7939/R38P5VM8D

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Dose Response of Selected Radiation Detectors in a Magnetic Field Open Access

Descriptions

Other title
Subject/Keyword
Ion Chamber
Solid State Detector
Linac-MR
Dosimetry
Dose Response
Magnetic Field
Radiation Detection
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Reynolds, Michael W
Supervisor and department
Rathee, Satyapal (Medical Physics)
Fallone, B. Gino (Medical Physics)
Examining committee member and department
Thomson, Rowan (Physics)
Robinson, Don (Medical Physics)
Fallone, B. Gino (Medical Physics)
Rathee, Satyapal (Medical Physics)
Mackenzie, Marc (Medical Physics)
Department
Department of Oncology
Specialization
Medical Physics
Date accepted
2015-05-12T09:42:23Z
Graduation date
2015-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
With the advent and development of hybrid Linac-MR technology, we will be able to track and treat lesions in real time. This will permit the narrowing of radiotherapy margins and escalation of dose, augmenting the therapeutic outcome of radiotherapy. The addition of a magnetic field to the treatment volume introduces difficulties in the measurement of the output radiation of the accelerator. This work investigates the dose response of various ionisation chambers and solid state detectors within a magnetic field in various relative orientations of photon beam, magnetic field, and detector axis. The orientations of interest can be divided as per the directions of the magnetic field and detector axis, with the radiation direction static; the magnetic field direction is set either transverse or longitudinal to the incident radiation, and the detector axis can independently be parallel or perpendicular to the incident radiation. The well benchmarked Monte Carlo code PENELOPE is used to model the dose deposition in the active volumes of the various detectors in air and in a water tank as a function of magnetic field strength in the orientations of interest. When physically possible, the dose response of the detectors in the relevant orientations is measured experimentally with the aid of small transverse and longitudinal electromagnets. The dose response of the detectors is defined as the ratio of dose deposited with magnetic field, to that without magnetic field. Dose response of all detectors as a function of magnetic field strength was found to have a strong dependence on the relative orientations of incident 6 MV radiation, magnetic field, and detector axis. Specifically, a chamber specific correction factor is required when detectors are used within a transverse magnetic field; this correction factor will also be orientation specific. Longitudinal field orientations, in contrast, seem to require no correction up to near 1.0T, thereafter a small orientation independent correction is needed. Water tank simulations show that radiation penumbras cannot in general be measured accurately in transverse fields; however, longitudinal magnetic fields do not cause issues in penumbra measurement. For the purposes of dose determination, longitudinal magnetic fields are preferred.
Language
English
DOI
doi:10.7939/R38P5VM8D
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
M. Reynolds, B. Fallone, and S. Rathee, “Dose response of selected ion chambers in applied homogeneous transverse and longitudinal magnetic fields,” Med. Phys. 40(4), 042102 (2013)M. Reynolds, B.G. Fallone, and S. Rathee, “Dose response of selected solid state detectors in applied homogeneous transverse and longitudinal magnetic fields,” Med. Phys. 41(9), 092103 (2014)

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