抄録
The effects of cell concentration on the surviving fractions were studied using in vitro cultured L5 and HeLa cells in the logarithmic growth phase. Following various X-ray doses under well-oxygenated conditions, the surviving fraction was determined using the colony forming ability as an end point. With increasing the numbers of cells plated, the survivals of L5 cells decreased for each X-ray dose, while the survivals of HeLa cells remained constant. For L5 cells this effect of cell concentration on the surviving fraction was also observed when irradiated with X-rays under hypoxic conditions, when exposed to neutrons under well-oxygenated conditions, when growth medium was replaced seven days post irradiation and when incubated in enriched growth medium. No significant difference was observed between the dose response curves for L5 cells and those for HeLa cells when relatively small number of cells was inoculated. However, when the number of cells plated was relatively high, the survival of L5 for a given dose was lower than that of HeLa. These results suggest that the in vitro cell system in which diluted cell suspensions are used for experiments on radiosensitivity is not always good model for the in situ cell system.
