[The bio-effects of high single-dose radiation on xenografts of Lewis lung carcinoma].

Objective To investigate the bio-effects of high single-dose radiation on xenografts of Lewis lung carcinoma.Methods Female 8-week-old C57mice bearing 4-6mm diameter Lewis lung carcinoma tumors in the hind legs were divided into 3groups,control group(0Gy),high single-dose group(12Gy/one fraction/day)and routine radiation group(22 Gy/11fraction/15d).The mean biological effective dose(BED)of both radiation groups was 26.4Gy.Changes in hypoxia,DNA damage and cell cycle of the tumor cells at 1,3,8,15and 21d after first irradiation was assessed by immunofluorescence and flow-cytometry and the tumor growth curve was also made.Results Compared to the fractionated treatment,the tumor growth was delayed after single dose irradiation. The percent of hypoxic cells after single dose radiation was lower than fractioned irradiation at 3,8,15dafter first radiation.The foci ofγ-H2AX showed that the single dose caused heavier DNA damages than fractioned irradiation at 1,3dafter first radiation.The decline of G0 /G1 percentage and increase of G2 /M percentage of cells was found in both radiation schedules,but the G2 /M percentage after single dose radiation was higher.Conclusion In the C57 mice bearing Lewis lung carcinoma,the high single-dose regimen inhibits the tumor growth more than fractioned irradiation.We hypothesized that conversion of high single-dose to BED using the LQ formalism under estimated the in vivo effect of hypofractionated radiation.