Computational aspects of treatment planning for neutron capture therapy

[摘要] (cont.) This study compares two methods of neutron beam source definition commonly used in BNCT treatment planning calculations, the phase space file (MCNP surface source file) and source variable probability distributions (MCNP SDef). To facilitate the comparison, a novel software tool was developed to analyze MCNP surface source files and construct MCNP SDef representations. This tool was applied to the MIT FCB, which has a well-validated Monte Carlo model. Each source type (surface source file and SDef) was used to simulate transport of the beam through voxel models of the modified Snyder head phantom, where doses were calculated. Compared to the surface source file, the initial dose calculations with the SDef produced significant errors of ~15%. Using a patched version of MCNP that allowed the observed radial dependence of the relative azimuthal angle to be modeled in the SDef, errors in all dose components in the head phantom at Dmax were reduced to acceptably small levels with none being statistically significant except for the induced photon error of 0.5%. Errors in the calculated doses introduced by sampling the azimuthal component of particle direction uniformly in the SDef vary spatially, are phantom-dependent, and thus cannot be accurately corrected by a simple scaling of doses.

[发布机构] Massachusetts Institute of Technology