Possible explanation of radioresistance of glioblastoma in situ

The response of human glioblastoma to radiation was studied in the logarithmic phase and in the plateau phase of growth, and was compared with those of HeLa S3 irradiated under identical conditions. There was no major difference in the in vitro survival curve parameters between glioblastoma and HeLa in the logarithmic growth phase. However, the surviving fractions for glioblastoma with radiation doses in the range used clinically were higher not only when irradiated in the logarithmic growth phase, but also when subcultured 6 hours after irradiation in the plateau phase, than those for HeLa treated under identical conditions. This suggests that the relatively low cure rate of glioblastoma can be partially explained by the intrinsic radiosensitivity in the logarithmic growth phase and by a high survivng fraction for cells irradiated in the plateau phase