Sensitization of mouse tumours using fractionated X-irradiation.

The response of 3 different tumours to single doses and fractionated irradiation with and without misonidazole was compared. The osteosarcoma BS2 showed no significant drop in sensitization for 2 fractions compared with a single dose. The rapidly shrinking carcinoma NT and the non-shrinking fibrosarcoma showed a significant drop in the SER as the radiation dose was fractionated. This is consistent with effective reoxygenation occurring in both tumours. No sensitizing effect was observed in the fibrosarcoma for 5 fractions each given with metronidazole. When only 2 out of 5 fractions were given with the drug misonidazole, they were slightly more effective with the first 2 than with the last 2 fractions.