A comparative study of biological effects on tumor cells between low-dose-rate β-irradiation and high- dose-rate γ-irradiation

Objective: To elucidate the radiobiological mechanism underlying cancer treatment with low-dose-rate β-irradiation of 32P, by comparing the cell-killing pattern with high-dose-rate γ-irradiation of 60Co. Methods: HeLa cells were exposed to low-dose-rate β-irradiation of 32P or high-dose-rate γ-irradiation of 60Co. Comparisons were made between these two types of radiations, focusing on the cell-killing patterns evaluated by radiation-induced reproductive cell death( senescence) and necrotic cell death through X-gal senescence staining and tRypan blue exclusion method respectively. Results: The results showed that there were different cell-killing patterns in HeLa cells between 32P radiation at dose-rate of 0.375 cGy/min and that of 60Co at dose-rate of 206 cGy/min at 72 h post irradiation. In exposure to 32P, more HeLa cells were lost due to reproductive cell death than to 60Co. X-gal staining showed that senescent cell ratio in HeLa cells after exposure of 32P was higher than after that of 60Co which caused more necrotic cell death. Conclusions: More reproductive and less necrotic cell death contribute to total cell loss in HeLa cells by radiation of 32P than by 60Co. Understanding the underlying mechanism of radiobiology in different radiations is helpful in radiotherapy of malignant tumor by choosing a more reasonable and effective procedure of treatment. (author)