Document Type


Publication Date

Fall 8-12-1963


The investigation was designed to determine whether the rate at which a dose of ionizing radiation is delivered affects its ability to sterilize single cells grown in vitro. The cells were cultured using the techniques originally described by Puck and his co-workers, whereby mammalian cells may be treated as independent micro-organisms. This technique enables the description of a quantitative relationship between the dose delivered to a population of single cells and the fraction of the population “reproductively surviving," i.e. able to reproduce indefinitely. Doses of 100 to 1000 rads were delivered at dose—rates of 2.37, 16.9, and 44.9 rads per minute. At every dose level, 18 plates containing pre-irradiated feeder layers were inoculated with an equal number of S3 HeLa cells and divided into three sets of 6 plates. All three sets received the same total dose of cobalt 60 gamma radiation, but the first set received its dose at a rate of 2.37 rads per minute, the second, at 16.9 rads per minute, and the third at 44.9 rads per minute. These plates were then incubated for a period of about two weeks, after which they were fixed, stained and the number of colonies on each plate counted. In every case, it was found that the effectiveness of the radiation in sterilizing the cells was increased when the dose-rate was increased. The magnitude of the dose-rate effect at the cellular level was sufficient to account for published reports of variation in LD 50/30 for whole-body irradiated small mammals.