A SOURCE MODEL FOR EFFICIENT BRACHYTHERAPY COMPUTATIONS WITH MONTE-CARLO

Monte Carlo techniques have the potential for producing accurate brach ytherapy dose distributions in heterogeneous finite geometries. Howeve r, for routine clinical use, computational speed must be adequate. fas t, all-particle, CT-based Monte Carlo code called PEREGRINE is being d eveloped at Lawrence Livermore National Laboratory for radiation treat ment planning. As one feature, the code will produce accurate dose dis tributions 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 spectru m and (perhaps anisotropic) angular distribution. In particular, for a nisotropic emission the polar angle is determined by a random-number d riven empirical function constructed from a source's measured or preco mputed fluence emission pattern. Source model parameters are presented for iodine and iridium sources. While designed for the PEREGRINE prog ram, this source model can be used in any Monte Carlo code. (C) 1996 A merican Association of Physicists in Medicine.