Tissue and subcellular distribution of bismuth radiotracer in the rat: considerations of cytotoxicity and microdosimetry for bismuth radiopharmaceuticals

The whole-body clearance, organ distribution, and subcellular distribution of no-carrier-added and carried-added intraperitoneally administered bismuth radiotracers (205Bi-206Bi) has been determined in Sprague-Dawley rats. Differences in clearance rate kinetics were observed for this study with the administration of neutral solutions of tracers in a carbonate buffer compared to other studies with other chemical forms. The final organ distribution was not strongly dependent on administered chemical form. We provide definitive evidence that bismuth does indeed enter subcellular organelles such as the nucleus and the mitochondria, which had 30-50% and 10-25%, respectively, of activity in kidney tissue. The kidneys were the main sink for radiotracer with uptake ranging from 20 to 50% of total body activity. The calculated energy deposition by recoil nuclei after alpha emission of potentially therapeutically useful 212Bi was found to equal or exceed the alpha energy deposition per organelle if the source is inside the cell nucleus or mitochondria