ENHANCEMENT OF RADIOSENSITIVITY OF RAT RHABDOMYOSARCOMA R1H WITH NORMOBARIC CARBOGEN AND HYPERBARIC-OXYGEN (HBO) USING CONVENTIONALLY FRACTIONATED-IRRADIATION

Hypoxic clonogenic cells are an important contributory factor in tumou r radioresistance. The objective of the present study was to evaluate whether hyperbaric oxygen enhances tumour radiosensitivity, using a co nventionally fractionated irradiation schedule, and whether the radios ensitizing potential id different from carbogen. Experiments were perf ormed using the rhabdomyosarcoma R1H model transplanted subcutaneously in the flank of WAG/Rij rats. A total of 30 X-ray fractions of 2 Gy w ere given either in air, normobaric carbogen or high pressure oxygen ( HPO) (240 kPa, 2.37 atm) without anaesthesia. The time taken to achiev e complete remission was 35.7 +/- 3.6 days, 36.7 +/- 2.7 days and 32.4 +/- 4.1 days for air, normobaric carbogen and HBO, respectively. The differences between air and HBO (p=0.002) and carbogen and HBO (p=0.01 5) were significant. Use of carbogen and HBO produced the same local c ontrol probability at 150 days and this was significantly higher than local control under ambient conditions (p<0.0001). It was concluded th at the time to achieve complete remission of the rat rhabdomyosarcoma R1H can be shortened by HBO. Furthermore, both HBO and carbogen give h igher local control probabilities than treatment under ambient conditi ons when used with a conventionally fractionated radiation schedule.