Variation of tumour radiosensitivity with time after anaesthetic

Transplanted C3H mouse mammary tumours were given single doses of X irradiation in air or oxygen at 1 atmosphere (atm) with or without anaesthesia of the recipient mice by ketamine and diazepam. The radiation response to single doses of 25 Gy was determined in terms of the time taken to reach 3.5 times the treatment volume. Under all conditions there was more growth delay in tumours irradiated in pure oxygen than in air. In both air and oxygen, the radiation response for anaesthetized animals tended to fall below the level for non-anaesthetized ones when only 10 min had elapsed after the administration of anaesthesia. After 25 min, the response in air was back to the level for the non-anaesthetized animals but the oxygen group now showed significant sensitization compared with the oxygen without anaesthetic group. After 40 min, the air group now showed slight sensitization and the oxygen group still showed significant sensitization by the anaesthetic. These results demonstrate the importance of the time interval between anaesthesia and irradiation of mouse tumours.