Biodistribution and Dosimetry of Free 211At, 125I- and 131I- in Rats

I-131 is widely used for therapy in the clinic and I-125 and I-131, and increasingly At-211, are often used in experimental studies. It is important to know the biodistribution and dosimetry for these radionuclides to determine potential risk organs when using radiopharmaceuticals containing these radionuclides. The purpose of this study was to investigate the biodistribution of I-125(-), I-131(-), and free At-211 in rats and to determine absorbed doses to various organs and tissues. Male Sprague Dawley rats were injected simultaneously with 0.1-0.3MBq I-125(-) and 0.1-0.3MBq I-131(-), or 0.05-0.2MBq At-211 and sacrificed 1 hour to 7 days after injection. The activities and activity concentrations in organs and tissues were determined and mean absorbed doses were calculated. The biodistribution of I-125(-) was similar to that of I-131(-) but the biodistribution of free At-211 was different compared to I-125(-) and I-131(-). The activity concentration of radioiodine was higher compared with At-211 in the thyroid and lower in all extrathyroidal tissues. The mean absorbed dose per unit injected activity was highest to the thyroid. I-131 gave the highest absorbed dose to the thyroid, and At-211 gave the highest absorbed dose to all other tissues studied.