Construction of two tomographic head models and comparison of dose distribution

This study describes the construction of two voxel head models by utilizing two different methods, the direct conversion from CT image data and the segmentation of tomographic color photographs into a set of homogeneous organs. For the latter method, each segmented organ has its own homogeneous density throughout the organ, whereas in the former method the density differs even in the same organ according to the CT gray numbers. Two kinds of head tomographic data were taken from the Visual Human Project of National Library of Medicine. The first model, CT_-HEAD was constructed by assigning the atomic composition and density to the CT data according to CT gray number versus density conversion table. The second model, PHOTO_-HEAD was segmented from tomographic photographs of the same person. The imaginary tumor volumes were defined at the center of brain in each model for dose comparison. The tumor and skull absorbed doses and flux distribution profiles on y=0 plane of the two models were calculated by MCNPX2.3 for 0.05-10 MeV photons and neutron beams designed for BNCT calculation incident upon the top of the head, and showed a good agreement within 10% in the result. The voxel model by the segmentation method used in health physics community to calculate the organ doses was verified to show similar dosimetric responses with the model by the CT number conversion method, where the original non-homogeneous densities are considered. (author)