Reduction in Proliferative Life Span of Human Diploid Cells after Exposure to a Reactor Radiation Beam

Cultured human diploid fibroblasts were exposed to various doses of thermal neutrons delivered from a 5-MW KUR reactor. Irradiated cultures showed an apparent shortening of the life span, the magnitude of which was dependent on dose. The dose vs life-span response curve did not have an initial shoulder. The D0 of the exponential slope was 260 rad. Furthermore, the dose-survival response curve for colony formation had no shoulder, and its D0 was 55 rad. The relative biological effectiveness (RBE) of the high-LET particles to X rays for late effects was estimated at 3.0, though the RBE values for acute effects were dose dependent.