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. Among the three precursors, 14C]thymidine gave the highest dose to spleen and small intestine. The doses to other tissues from 14C]thymidine were almost the same or lower as compared with those from 3H]thymidine, irrespective of the 9 times higher beta-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, however, the dose contributions by non-volatile radioactivity were very small and the 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 the dose to cell nuclei in various tissues after the ingestion of 3H]thymidine were also made in order to predict more precisely possible radiation hazards.