Dose-rate effects in mammalian cells: V. dose fractionation effects in noncycling c3h [formula omitted] cells

Abstract

Multiple gamma ray dose fractionation effects were studied using contact-inhibited C3H 10T 1 2 murine fibroblast cultures in an attempt to simulate conditions in tissues with low rates of cell turnover. Multifraction survival curves were determined for different doses per fraction using 12 hour interfraction intervals 7 days per week. Isoeffect curves were generated from the multifraction survival curves. For doses per fraction greater than approximately 1.0 Gy, these isoeffect curves were similar to those derived from tissue reactions in humans and experimental animals published previously. For doses per fraction below 1.0 Gy, the isoeffect curves became essentially flat, thus deviating appreciably from the total dose which would be predicted by extrapolating the NSD equation to achieve an isoeffect. The existence of a non-repairable component of gamma ray damage can be inferred from this finding, which has implications both for basic radiobiology, and radiotherapy.