THE INFLUENCE OF TRACER LOCALIZATION ON THE ELECTRON DOSE-RATE DELIVERED TO THE CELL-NUCLEUS

The radiation dose rate delivered by electron emissions of (TC)-T-99m, I-123, In-111, Ga-67 and Tl-201 was evaluated at the subcellular leve l. Methods: Spherical models of sources were used to simulate various cellular localizations of radionuclides. These models were applied to large lymphocytes, assuming uniform distributions of radioactivity thr oughout the nucleus, the cytoplasm or the cell membrane surface. Resul ts: The graphs of the absorbed dose rate plotted according to the dist ance from the center of the cell show that the dose rate strongly depe nds on the subcellular distribution of the radioisotope. The absorbed dose rate D(0) at the center of the cell delivered by a constant cellu lar radioactivity of Tc-99m,I-123, In-111, Ga-67 and Tl-201 is respect ively 94, 21, 18, 74 and 76 times higher if the radioactivity is local ized within the cell nucleus than if it is situated only on the cell m embrane. D(0) for subcellular localizations was compared to D(0) obtai ned by assuming uniform distribution of radioactivity throughout the c ell. This latter assumption may underestimate the dose rate from 2.8- to 3.2-fold if the tracer is exclusively localized within the nucleus or overestimate from 4.3- to 30-fold if the tracer is localized within the cytoplasm or on the cell membrane, depending on the radionuclide. Conclusion: Such findings show that the localization of radiopharmace uticals at the subcellular level plays a crucial role in determining t he actual dose delivered to the cell nucleus in diagnostic nuclear med icine procedures.