Effects of continuous low dose-rate irradiation: computer simulations.

The effects of continuous low dose-rate irradiation are studied with a computer model that incorporates cell kinetics and the accumulation and repair of radiation damage. This theoretical approach independently explores the effects on survival curves of a phase block, inherited damage and proliferation by dying cells. The computer model is a Monte Carlo simulation which follows the evolution in time of the family trees of a growing cell population under continuous irradiation. The model uses as input the measured phase-specific survival curves for acute exposures and the cell kinetic parameters to generate survival curves for continuous low dose-rate irradiations. Cell survival curves for Chinese hamster lung cells (V79) for dose rates ranging from 15 to 500 cGy/h have been generated using various model assumptions. The model shows that for these cells a G2 block will maximize cell killing for an optimum dose rate near 75 cGy/h. The effect on survival curves of inherited damage, as well as that of the proliferation by dying cells, is shown to increase monotonically with decreasing dose rates, and to be quite large at low dose rates.