CYTOGENETIC SIGNATURE FOR IONIZING-RADIATION

A stable, easily measurable biological 'signature' for past exposure t o densely ionizing radiation would be of significant value to estimate environmental radiation risk. Defined here, the S-ratio is the ratio of complete to incomplete chromosome translocations. It constitutes a clastogenic signature that appears to be stable over time, independent of dose, and varies inversely with the relative biological effectiven ess (RBE) of the radiation. In vitro measurements resulted in a ratio of similar to 2 for densely ionizing radiation (Fe-56 and C-12 ions) i n contrast to a Value of similar to 10 for sparsely ionizing radiation (X-and gamma-rays). The measured ratio was similar to 2 for bleomycin and benzene. Such a distinctive clastogenic signature should facilita te better estimates of neutron dose for A-bomb survivors, as well as a causal connection between early exposure to densely ionizing radiatio n and late development of cancer.