Evaluation of Radiation Dose Resulting from the Ingestion of [3H]- and [14C]thymidine in the Rat

Summary

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 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, 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.