I. Radiobiological Considerations

Abstract

At this Congress two years ago, Dr. Scott, Dr. Thomlinson and I spoke about oxygen as a factor effecting radiosensitivity. We gave reasons for believing that the administration of oxygen to patients just prior to and during each X-ray treatment might increase the chance of the successful eradication of the tumour. Our inference was based on the one hand on the knowledge of the way in which the sensitivity of cells changes with the oxygen tension in their immediate environment, and on the other, on the belief that some tumours contain anoxic foci of greater or lesser extent. This belief, which has been commonly held by pathologists, was supported by a consideration of the histological structure of some human tumours examined by Thomlinson (Thomlinson and Gray, 1955). Finally, laboratory experiments were described in which these ideas were put to the test (Gray, Conger, Ebert, Hornsey and Scott, 1953). As you will recall, Scott found that administration of oxygen, even at 1 atmosphere pressure, could greatly increase the effectiveness of X radiation in bringing about the regression of a tumour. The regression produced by 1000 r given while the animal was breathing oxygen approximately matched that due to a dose of between 1500 and 2000 r given while the animal was breathing air. These results have since been quantitatively confirmed by Scott, who has found that under the same conditions, damage to skin is only increased by about 20 per cent by oxygen administration.