EFFECTS OF FRACTIONATION AND DOSE-RATE IN PDR-BRACHYTHERAPY OF B14-FIBROBLASTS

Purpose: Present radiobiological studies for different cell lines in v itro demonstrate the equivalence and efficacy of continuous low-dose-r ate brachytherapy (LDR-BT) and pulsed dose rate brachytherapy (PDR-BT) when using small and frequent dose pulses. The aim of this study was to examine monolayer fibroblast cultures in vitro to examine the biolo gical effects of different pulse doses and dose rates under clinically conditiones. Material and Methods: B14 cells, Hy B14 FAF 28, peritone al fibroblasts, were cultured in multi-well plates and exposed to a PD R radiation source at a distance of 9 mm. The following PDR-schemes we re compared: dose per pulse: 1 Gy, 2.5 Gy and 5 Gy to a total dose of 5 Gy/5 h (overall time), 10 Gy/10 h, 20 Gy/20 h and 30 Gy/30 h. The pu lse duration for the examination of dose rate effects was 20 min, 30 m in or 52 min corresponding to a pulse dose rate of 300 cGy/h, 200 cGy/ h or 115 cGy/h. Treatment endpoints were cell survival measured by dye exclusion test and clonogenic cell survival. Results: Cell survival d ecreased for pulse doses of 5 Gy compared to 2.5 Gy or 1 Gy per pulse (mean dose rate 200 to 300 cGy/h). No differences were observed with d ose rates during irradiation of 300 cGy/h, 200 cGy/h or 115 cGy/h (20 Gy/1 Gy). Conclusion: Radiobiological effects of PDR-BT are dependent on the dose per pulse, with differences in biological effects only wit h a dose per pulse of more than 2.5 Gy, considering the described in-v itro conditiones. More examinations with a more pronounced difference in dose rate will be continued for evaluation of dose rate effects.