Radiosensitivity of atomic bomb survivors as determined with a micronucleus assay.

If A-bomb survivors include a disproportionately large number of either radioresistant or radiosensitive persons, the surviving population would provide a biased estimate of the true risk of radiogenic cancer. To test this hypothesis, the in vitro X-ray sensitivities of peripheral blood lymphocytes obtained from 937 A-bomb survivors were measured with a cytokinesis-blocking micronucleus assay. Background frequencies (no irradiation in vitro) of micronuclei show a wide distribution. Frequencies in both males and females tend to increase with increasing donor age. Frequencies in females are significantly higher than those in males. Donor age decreases the sensitivity of lymphocytes to in vitro X-ray exposure at a rate of about 0.001 micronuclei per cell per year per gray. There is no effect of donors' sex on in vitro radiation sensitivity. Atomic bomb radiation and cigarette smoking had no significant effect on background and X-ray-induced micronuclei frequencies. Thus there is no difference in radiosensitivity of peripheral blood lymphocytes between proximally and distally exposed survivors.