Monte Carlo Simulations of Photon Absorbed Fractions in a Frog Voxel Phantom

For radiation protection of the environment, a voxel-based frog phantom was developed using cryosection data, which have been available on a Web site of the Lawrence Berkeley National Laboratory. The voxel-based frog phantom includes 16 segmented organs/tissues: brain, blood vessel, duodenum, eye, heart, ileum, kidneys, intestine, liver, lung, nerve, skeleton, soft tissue, spleen, stomach, and stomach contents. The voxel-based frog phantom has a mass of ${\hbox{3.37 }}\times {\hbox{ 10}}^{-2}\ {\hbox{kg}}$. The dimensions are $7.1\ (\hbox{length})\ \times \hbox{3.3}\ (\hbox{width}) \times \hbox{2.4}\ (\hbox{height})\ \hbox{cm}^{3}$. The voxel size is $ \hbox{0.0175}\ \times \hbox{0.0175} \times \hbox{0.0175}\ \hbox{cm}^{3}$. In this paper, the voxel-based frog phantom is applied to evaluating photon absorbed fractions (AFs) in the segmented organs/tissues. The sources were assumed to be monoenergetic in the photon energy range from 10 keV to 4 MeV. The radiation transport was simulated using the Monte Carlo method. Consequently, it was confirmed that the photon AFs for organ self-absorption are dependent on the masses of the source/target organs. It would appear that the photon AFs for organ self-absorption are expressed by a continuous function of photon energy emitted by the source. The photon AFs for organ crossfire might be subject to the geometry effect, such as size and shape of source/target and distance between the source and target.