Influence of nonuniform activity distribution on cellular dosimetry

Dosimetry of nonuniformly distributed 210Po,67Cu, and 123I was evaluated for a single cell, modeled as a homogeneous unity-density sphere with a radius of 7.7 mum, which is typical of a B-cell lymphoma cell. A Visual Basic program was used to calculate S factors and radial absorbed dose-rate profiles for these radionuclides, taking into account their individual radiation energy spectra. The resulting absorbed doses were compared with those for uniform activity distributions of the respective radionuclides. It was shown that detailed radiation energy spectra are required for accurate cell-level dosimetry, especially for Auger-electron emitters. Nonuniform intracellular activity distributions do not affect the cell-to-cell S factor (i.e., S(C <-- C)) dramatically but greatly influence the cell-to-nucleus S factor (i.e., S(C <-- N)).