Accurate proton stopping power images reconstructed using joint statistical dual energy CT: Experimental verification and impact of fan-beam CT scatter

Maria Medrano, Ruirui Liu, Tyler Webb, Tianyu Zhao, Jeffrey Williamson, Bruce Whiting, David G. Politte, Mariela Porras-Chaverri, Joseph A. O’Sullivan

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

2 Scopus citations


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.

Original languageEnglish
Title of host publicationMedical Imaging 2020
Subtitle of host publicationPhysics of Medical Imaging
EditorsGuang-Hong Chen, Hilde Bosmans
ISBN (Electronic)9781510633919
StatePublished - 2020
EventMedical Imaging 2020: Physics of Medical Imaging - Houston, United States
Duration: Feb 16 2020Feb 19 2020

Publication series

NameProgress in Biomedical Optics and Imaging - Proceedings of SPIE
ISSN (Print)1605-7422


ConferenceMedical Imaging 2020: Physics of Medical Imaging
Country/TerritoryUnited States


  • Alternating minimization
  • Collimation
  • Dual-energy computed tomography
  • Proton stopping power
  • Proton therapy
  • Scatter
  • Statistical image reconstruction


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