The requirements and limitations of computer simulations applied to proton computed tomography

We report on recent research with computer simulations on the concept and design of a proton computed tomography (pCT) instrument for proton treatment planning based on the measurement and analysis of individual protons. The requirements for a realistic simulation of such a device is discussed. Two types of simulation programs are presented: the first based on a simple, two-dimensional parameterized Monte Carlo, the second implemented using the Geant4 toolkit. The utility of these programs is evaluated.