Development and verification of THORplan--a BNCT treatment planning system for THOR.

THORplan is a treatment planning system under continuous development and refinement at Tsing Hua University, Taiwan, for BNCT purpose. New features developed for homogeneous model calculation include material grouping model, and voxel data reconstruction model. Material grouping model is a two-step grouping method, tissue-volume-percent grouping method followed by atom-gram-density grouping method. The root mean square difference of neutron flux due to material grouping is <0.8%. In the voxel data reconstruction model, voxel neutron dose is calculated based on the material composition and dose of individual atom of each voxel, which is calculated by linear interpolation from the dose of individual atom of neighboring cells tallied in MCNP calculation. The detailed voxel model is used to benchmark the accuracy of the new features developed for the homogeneous model calculation. The maximum error of the neutron flux and dose of voxels using the homogeneous cell model is 5% and 7%, respectively. Big improvement of accuracy of voxel dose over the original dose calculation model based on F6 tally is observed at locations containing very heterogeneous compositions.