Biological indicators of radiation exposure. Experimental study of radiation-induced changes of thymidine level in human serum

The study summarizes the results of the search for a reliable quantitative biochemical indicator system for ionizing radiation in man. Thymidine seems to be a promising indicator in the serum. The analysis of thymidine is based on the inhibited incorporation of 125I-UdR into DNA of fibroblast cells in the presence of serum of the irradiated mice. Maximal inhibition of the I-UdR-incorporation occurs 4 hours after irradiation. The data from animal experiments show in the dose range between 0.005 and 1 Gy a dose effect relationship which was multiply reproduced. The main objective of the experiments is to test the transferability of results from mouse to man. What little is known on these effects in humans was learned from investigations in radiotherapy patients. Up to now, 22 radiotherapy patients have been examined and in no case dose dependency for the increase of thymidine concentration in human serum as a function of radiation dose has been observed. Among the tumour patients investigated, three groups were found to be of special interest: one group with a low initial thymidine concentration increasing after irradiation, a second group of patients with a high initial thymidine concentration decreasing after irradiation and a third group with a middle initial thymidine concentration not changing after irradiation. A dependency of the effect from time, as it occurs in the mouse, has not been observed in man until now. Thus the applicability of this biochemical indicator system as evidence of a radiation exposure in man has not been proven. (orig./MG)