Monte Carlo simulation of X-ray and gamma-ray photon transport on a graphics-processing unit

Graphics-processing units (GPUs) suitable for general-purpose numerical computation are now available with performances in excess of 1 Teraflops, faster by one to two orders of magnitude than conventional desktop CPUs. Monte Carlo particle transport algorithms are ideally suited to parallel processing architectures and so are good candidates for acceleration using a GPU. We have developed a general-purpose code that computes the transport of high energy (>1 keV) photons through arbitrary 3-dimensional geometry models, simulates their physical interactions and performs tallying and variance reduction. We describe a new algorithm, the particle-per-block technique, that provides a good match with the underlying GPU multiprocessor hardware design. Benchmarking against an existing CPU-based simulation running on a single-core of a commodity desktop CPU demonstrates that our code can accurately model X-ray transport, with an approximately 35-fold speed-up factor.