The separate contributions of all source regions to organ doses from 131I and 123I administered to the bodywere calculated using voxelized reference phantoms. The photon and electron components oforgan doses were also evaluated for each source region. The MCNPX Monte Carlo particletransport code was utilized for dose calculations. All organs and tissues of male andfemale phantoms were taken into account as source regions with their correspondingcumulated activities. The results showed that cumulated activities assigned to sourceregions and inter-organ distances were two factors that strongly affected the contributionof each source to the organ dose. The major contribution of the dose to the main sourceregions arose from self-irradiation of electrons, while for nearby organs it was due tophotons emitted by the main source organs. In addition, self-irradiation plays animportant role in the dose delivered to most target organs for lower thyroid uptakes.
