Evaluation of radiation dose resulting from the ingestion of [3H]-and [14C]thymidine in the rat

Average doses to rat tissues from the ingestion of 2-[14C]thymidine were compared with those from methyl-[3H]thymidine or 6-[3H]thymidine. [14C]thymidine gave the highest dose to spleen and small intestine. Doses to other tissues from [14]thymidine were almost the same or lower compared with those from [3H]thymidine, irrespective of the 9 times higher β-ray energy of 14C than that of 3H. In the case of [14C]thymidine, most of the dose was given by radioactivity incorporated into the organic tissue constituents (non-volatile radioactivity). In the case of [3H]thymidine, the dose contributions by non-volatile radioactivity were very small and major contributions were rather from volatile radioactivity (3HHO), formed by degradation of [3H]thymidine. No significant difference in their total doses was found between the two [3H]precursors, but the dose from non-volatile radioactivity alone was 2-3 times higher with methyl-[3H]thymidine than with 6-[3H]thymidine. Estimates of dose to cell nuclei in various tissues after ingestion of [3H]thymidine were also made in order to predict more precisely possible radiation hazards. (author)