  Proton computed tomography (pCT) is an image modality that will improve
treatment planning for patients receiving proton radiation therapy compared
with the current treatment techniques, which are based on X-ray CT.
Reconstruction of a pCT image requires solving a large and sparse system of
linear equations, which should be accomplished within a few minutes in order to
be clinically practical. Analyzing the efficiency of potentially clinical
reconstruction implementations requires multiple quality pCT data sets. The
purpose of this paper is to describe the simulator that was developed to
generate realistic pCT data sets to be used in testing the efficiency of
reconstruction algorithms, in particular string-averaging and block-iterative
projection algorithms using sparse matrix formats on General Purpose Graphics
Processing Units (GPGPU)s.
