Voxel anthropomorphic models as a tool for internal dosimetry

Specific Absorbed Fractions (SAF), which specify the fraction of the energy emitted by radioactivity in a given organ which is absorbed in the source organ itself and in other organs, are a prerequisite for the calculation of dose from internally deposited radioactive emitters. Extensive calculations of SAFs for monoenergetic photon sources were performed using Monte Carlo photon transport codes together with voxel anthropomorphic models based on computed tomographic data of real persons of various ages. These models offer greater realism with respect to organ topology than the mathematical phantoms commonly used up to now. Selected results are compared with those from the literature derived using the Oak Ridge mathematical phantoms. Some general results of other authors were confirmed by the present results, whereas for some source-target organ combinations discrepancies of up to one or two orders of magnitude were found, depending on photon energy and the location and masses of the organs involved. Agreement for the different model types of the organ absorbed doses per administered activity for radionuclides was Found to be much better than that of the SAF values.