Modelling of the relationship between cell dimensions and mean electron dose delivered to the cell nucleus: application to five radionuclides used in nuclear medicine

The mean dose delivered to the cell nucleus by electron emissions of 99Tcm, 123I, 111In, 67Ga and 201Tl was evaluated at the subcellular level. Models were applied assuming uniform distributions of radioactivity throughout the nucleus, the cytoplasm or the cell membrane, allowing computation of the total absorbed fraction φ and S-values to the cell nucleus as a function of cell dimensions. The graphs of φ plotted according to cell dimensions show that the dose to the cell nucleus strongly depends on the subcellular distribution of radioactivity, the nucleus radius Rnucl and the cytoplasmic thickness e. To ease future calculations, third-degree polynomials have been separately fitted to the relationship between the mean absorbed dose to the nucleus for activity accumulated in the nucleus, cytoplasm or surface of the cell membrane. We found a good agreement between our computations and the values obtained by the polynomials. The relative difference between the two methods is always less than 0.7%, 2.8% and 4.5% respectively for nuclear, cell membrane and cytoplasmic distributions. (author)