Development of the Efficient Modeling Method with Complicated Human Geometry for Monte-Carlo Treatment Planning System

A new multi-modal Monte-Carlo treatment planning system (developing code: JCDS-FX) is being developed to implement accurate treatment planning for boron neutron capture therapy. JCDS-FX employs multi-purpose Monte-Carlo code: PHITS as dose calculation engine. For calculation of dose distribution for a human body, JCDS-FX can make a precise voxel model consisting of pixel based voxel cells like 0.4×0.4×2.0 mm voxel in order to perform high-accuracy dose estimation. However, the miniaturization of the voxel size causes calculation time to increase. The aim of this study is to investigate sophisticated modeling method which can perform Monte-Carlo calculation for human geometry efficiently. Thus, we devised a new voxel modeling method “Multistep lattice-voxel method” which can configure an efficient voxel model that combines different voxel sizes by utilizing the lattice function over and over. To verify the performance of the calculation with the modeling method, several calculations for human geometry were carried out. The verification results proved that the method enabled to reduce calculation time substantially while keeping the high-accuracy dose estimation. Several verifications with complicated human geometry are being performed at present. And we are still carrying out sophistication of the modeling method to work toward practical use of the new treatment planning system with more precise computational dosimetry.