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Proceedings Paper

Accurate proton stopping power images reconstructed using joint statistical dual energy CT: experimental verification and impact of fan-beam CT scatter
Author(s): Maria Medrano; Ruirui Liu; Tyler Webb; Tianyu Zhao; Jeffrey Williamson; Bruce Whiting; David G. Politte; Mariela Porras-Chaverri; Joseph A. O'Sullivan
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Paper Abstract

Proton radiotherapy has the potential to provide clinically effective treatment and highly conformal dose delivery when the rapid dose falloff at the end of its proton-beam range is correctly aligned to the distal margin of the clinical target volume. However, in current clinical practice an additional 2-3.5% safety margin must be added to the proton range to account for uncertainties in the estimation of proton-beam range when using stopping-power ratios (SPRs) derived from single-energy CT scans. Several approaches have been proposed to estimate stopping power by using dual-energy CT (DECT) and have been shown through theoretical analysis to outperform single-energy CT (SECT) under the presence of tissue composition and density variations. Our lab previously proposed a joint statistical image reconstruction (JSIR) method built on a basis-vector model (BVM) tissue parameterization for SPR estimation, which was shown to perform comparatively better than other DECT image- and sinogram-domain decomposition approaches on simulated as well as experimental data. This comparison, however, assumed theoretical SPR values calculated from the samples’ known compositions and densities as ground truth and used the mean excitation energy and effective electron density from ICRU reports along with a simplified version of the Bethe-Bloch equation to determine SPR reference values. Furthermore, CT scans were acquired with an assumed ideal point source at a narrow beam collimation; thus, the signal formation assumed by our JSIR process neglected scatter and off-focal radiation. In this paper, we verify the accuracy of our method by comparing the SPR values derived from JSIR-BVM to direct measurements of relative SPR, as well as present a preliminary study on the impact of fan-beam scatter radiation on JSIR-BVM SPR prediction accuracy.

Paper Details

Date Published: 16 March 2020
PDF: 9 pages
Proc. SPIE 11312, Medical Imaging 2020: Physics of Medical Imaging, 113121S (16 March 2020); doi: 10.1117/12.2549788
Show Author Affiliations
Maria Medrano, Washington Univ. in St. Louis (United States)
Ruirui Liu, Washington Univ. in St. Louis (United States)
Tyler Webb, Washington Univ. in St. Louis (United States)
Tianyu Zhao, Washington Univ. in St. Louis (United States)
Jeffrey Williamson, Washington Univ. in St. Louis (United States)
Bruce Whiting, Univ. of Pittsburgh (United States)
David G. Politte, Mallinckrodt Institute of Radiology (United States)
Mariela Porras-Chaverri, Univ. of Costa Rica (Costa Rica)
Joseph A. O'Sullivan, Washington Univ. in St. Louis (United States)

Published in SPIE Proceedings Vol. 11312:
Medical Imaging 2020: Physics of Medical Imaging
Guang-Hong Chen; Hilde Bosmans, Editor(s)

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