Dose Rate: Its Effect on the Survival of HeLa Cells Irradiated with Gamma Rays

Abstract

Ionizing radiations produce their effect on living material owing to the processes of ionization and excitation which follow the absorption of radiant energy. For a given type of radiation, the energy absorbed per gram (that is, the dose in rads) is the most important single factor affecting the biological response. In the case of relatively sparsely ionizing radiation, however, such as Xand y-rays, the rate of energy absorption (the dose rate) is also of fundamental importance. Since about 1920 there have been reports in the literature that dose rate modifies such radiation effects as division delays in chick tissue cultures (1), chromosome aberrations in Tradescantia (2), cleavage delay in Arbacia eggs (3) and growth inhibition of roots of Vicia faba (4). During the past decade, many extensive investigations have been reported concerning the influence of dose rate on the LD50(30o) for small mammals exposed to whole-body irradiation (5-12). The present communication describes a series of experiments in which HeLa cells, cultured in vitro, were irradiated with cobalt-60 7-rays at three different dose rates. The aim of the investigation was to determine whether the dose-rate effect commonly observed with small mammals could be fully accounted for at the cellular level, or whether a systemic effect on the whole animal was involved.