Anaesthesia and efficacy of hyperbaric oxygen in radiation therapy

Respiration of pure oxygen at 200 kPa (two atmospheres) has been shown to be effective in achieving significant reductions in the TCD50 for fractionated radiation therapy of a number of experimental tumours (Suit and Maeda, 1967; Suite and Suchato, 1967, Suit et al., 1977). This improvement in results was of large magnitude and was observed with all fractionation schedules where two or more fractions were employed. The ratio of TCD50 air/TCD50 O2 at 200 kPa was in the range of 1.60–1.87 (Suit et al., 1977). The effectiveness of hyperbaric oxygen with a single dose of radiation was much less impressive, viz. a ratio of 1.12 (Suit and Maeda, 1967). In all of these experiments the mice were anaesthetized with sodium pentobarbital (0.05 mg/g body weight). In the study discussed in this letter this ratio was much smaller in non-anaesthetized than in anaesthetized mice, viz. 1.23 v. 2.0.