Objective        To compare the effect of ultra-microfractionated and conventional radiotherapy on glioma cells (GL261 cells).       Methods        GL261 cells underwent ultra-microfractionated radiotherapy at an interval of 3 min for each 0.2 Gy with a dose rate of 0.066  7 Gy/min and conventional radiotherapy at a dose rate of 4 to 6 Gy/min. Distribution of cell DNA damage

apoptosis and cell cycle was detected by comet assay and flow cytometry

respectively

on days 1

2 and 3 after treatment.       Results        Comet assay showed that ultra-microfractionated and conventional radiotherapy could cause similar DNA damages in GL261 cells. No significant difference was found in comet tail DNA %

tail length and tail moment at different time points between the two groups (P0.05). Flow cytometry showed that the cell survival rate was significantly lower at different time points after ultra-microfractionated radiotherapy than after conventional radiotherapy (P0.01). No significant difference was observed in distribution of cell cycle between the two groups (P0.05).        Conclusion        Ultra-microfractionated and conventional radiotherapy cause similar DNA damages in GL261 cells. However

the killing effect of ultra-microfractionated radiotherapy on GL261 cells is significantly stronger than that of conventional radiotherapy

which may be due to the difference in their DNA repairing mechanism.