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Magnetic resonance imaging based radiotherapy treatment planning: problems, solutions, and applications Open Access


Other title
magnetic resonance imaging
treatment planning
Type of item
Degree grantor
University of Alberta
Author or creator
Baldwin, Lesley
Supervisor and department
Fallone, Gino (Oncology)
Examining committee member and department
Ten Haken, Randall (Radiation Oncology, University of Michigan)
Wilman, Alan (Biomedical Engineering)
Sloboda, Ron (Oncology)
Rathee, Satyapal (Oncology)
Robinson, Don (Oncology)
Department of Physics

Date accepted
Graduation date
Doctor of Philosophy
Degree level
Despite their unmatched soft-tissue contrast, Magnetic Resonance (MR) images suffer from wide-ranging image distortions; this has raised questions about their suitability as an imaging modality upon which to base conformal radiation therapy treatment plans. This thesis addresses image distortion as it relates to the implementation of MR-based radiation therapy treatment planning (MR-RTP). A grid phantom was imaged at 3T to determine the 3D distortion field using in-house software. Using multiple images, both machine- and object-related sources of distortion were separated such that individual evaluation of distortion sources is possible. Over the imaging volume, nonlinearities in the gradients led to peak-to-peak image distortions of up to 11 mm. For in-vivo distortion quantification, the method was augmented with a modified gradient echo sequence which measures the phase evolution due to underlying field inhomogeneities. The amount of distortion measured using this technique is dependent upon both patient anatomy and sequence parameters, but was found to contribute 5.7 mm at maximum. The methods presented can be combined to provide comprehensive distortion rectification such that mean residual image distortion is reduced to well below the pixel resolution. Finally, distortion quantification and correction methods were applied to a clinical MR-RTP study of prostate patients. The dosimetric consequences of distortion correction were investigated by comparing 3D conformal and intensity modulated radiation therapy plans developed based on both uncorrected and corrected MRI data sets. Total image distortions and those directly affecting the prostate and organs at risk (OARs) were assessed and target doses, OAR doses, and dose volume histograms were compared. Maximum distortion (from all sources) was 7.8 mm. With the exception of two patients, changes in plan dosimetry were insignificant (<2% / <1Gy). Two patients who were poorly position suffered larger distortions in the target region which led to dosimetric differences of up to 4.2%.
License granted by Lesley Baldwin ( on 2010-08-20T20:41:51Z (GMT): 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. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of the above terms. The author reserves all other publication and other rights in association with the copyright in the thesis, and except as herein 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.
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