The comparative survival of clonogenic cells of a murine epithelioma after irradiation in mice breathing air, oxygen and carbon dioxide, or hyperbaric oxygen

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Abstract
Transplantation assays were used to determine the fraction of clonogenic cells surviving in isologous transplanted squamous carcinomas after irradiation in vivo in mice breathing air, 5 per cent CO2 in O2, or O2 at three atmospheres absolute (OHP). The results of single-dose irradiation indicated that the percentages of cells which were severely hypoxic under the three conditions were, respectively: 13, 6·8 and 4·3. A series of experiments in which a first exposure of 1,000 R was given in air and a second exposure of 1,000 R, after 36 hours, in air or OHP failed to provide evidence either that hypoxic cells surviving the first dose of irradiation became “reoxygenated” during the 36 hour interval, or that the second dose in OHP was more effective than that in air. The findings are discussed in relation to other recently published data from experiments in which different tumours and techniques were used to seek evidence of “reoxygenation” or to study the influence on tumour response of the gas breathed during irradiation.