Efficiency of modulated and dose rate altered flattening filter free beams in high dose per fractionradiotherapy applications on the survival of prostate cancer cell lines

Background: the radiobiological effect of high dose rate fff beams on the du-145 cells was investigated with sbrt plans which have >10 gy. methods and materials: to compare the radiobiological effect on du-145 cell line four experiments designed: (1) the constant dose rate of 6 mv and 6 mv fff with increased dose per pulse (2) the effect of dose per pulse while increasing instantaneous dose rate for 6 mv and 6 mv fff, (3) the effect of increased average dose rate for 6 mv fff and (4) the effect of protracted treatment time and modulation of 6 mv fff beams. the survival fraction was counted with wst. results: ff and fff for 6 mv with same dose rate and treatment time has no effect on cell survival. significant differences was observed on survival which were irradiated with 6 mv 600 mu/min and 6 mv fff 1400 mu/min (p=0.024). there was no difference between 6 mv fff 600 mu/min and 6 mv fff 1400 mu/min for 10 gy. the significant survival difference obtained for 20 gy. the survival percentages for both 10 gy and 20 gy with cyberknife were obtained higher than fff. conclusion: our in-vitro study presented here show that higher dose rate and reduced treatment time might become a crucial factor for sbrt especially which has >10 gy fraction dose.