RADIATION-INDUCED CHROMOSOME DAMAGE IN HUMAN PFRIPHERAL BLOOD LYMPHOCYTES IN VITRO .I. RBE AND DOSE-RATE STUDIES WITH FAST NEUTRONS

Human peripheral blood lymphocytes were irradiated in vitro, before or after stimulation with phytohemagglutinin, with neutrons from uranium fission, at different doses and dose rates, or with acute X-rays (250 kV). Cells were examined at their first mitotic division in culture for chromosome aberrations. An almost 1000-fold difference in neutron dose rate (0.057-50 rad/min, doses up to 150 rad) did not change the frequency of aberrations in cells irradiated after stimulation. A small dose-rate effect was observed for cells irradiated in the non-stimulated condition but this was thought to be due to a differential stimulation of less heavily radiation-damaged cells. The data for the induction of dicentric aberrations by X-rays were in agreement with Evans' earlier findings of an almost linear dose-response curve. Since the dose-response relationship after neutrons was linear, a mean relative biological effectiveness value of approx. 3.5, which did not vary much over the wide range of doses used, was obtained for the induction of dicentrics by fast neutrons (mean energy approx. 0.7 MeV) relative to X-rays. © 1969.