An EGS4 user code with voxel geometry and a voxel phantom generation system

An EGS4 (Electron Gamma Shower Version 4) user code with voxel geometry (the UCPIXEL code) has been developed in order to make accurate dose evaluation by using human voxel phantoms. The voxel data have a format devised by GSF. This format can compress so large amount of high-resolution voxel data that required memory for computation is greatly reduced. UCPIXEL can treat 8 basic irradiation geometries (AP, PA, RLAT, LLAT, ROT, ISO, AB, BA) and cylindrical pseudo-environmental radiation source with arbitrary size, energy and directional distribution. In addition, UCPIXEL can model contaminated soil with arbitrary area and depth under a phantom and radiation from the soil. By using a post-processor, effective dose equivalent, effective dose and organ doses can be evaluated from the output of UCPIXEL. Preliminary results of effective dose calculated by using UCPIXEL for a Japanese voxel phantom are demonstrated and compared with the previous results for MIRD-type phantoms. We have also developed an intelligent system which automatically constructs a voxel phantom from CT data. We introduce this system and preliminary results are shown. (author)