A source model for efficient brachytherapy computations with Monte Carlo

Monte Carlo techniques have the potential for producing accurate brachytherapy dose distributions in heterogeneous finite geometries. However, for routine clinical use, computational speed must be adequate. A fast, all-particle, CT-based Monte Carlo code called PEREGRINE is being developed at Lawrence Livermore National Laboratory for radiation treatment planning. As one feature, the code will produce accurate dose distributions from brachytherapy sources in heterogeneous geometries. For efficiency, brachytherapy sources in this model are treated as points or line segments. Radiation is emitted with the proper energy spectrum and (perhaps anisotropic) angular distribution. In particular, for anisotropic emission the polar angle is determined by a random-number driven empirical function constructed from a source's measured or precomputed fluence emission pattern. Source model parameters are presented for iodine and iridium sources. While designed for the PEREGRINE program, this source model can be used in any Monte Carlo code.