The effect of chronic reductions in the arterial partial pressure of oxygen on the radiation response of an experimental tumour

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Abstract
Tumor response to radiation in animals in which the PaO2 [arterial partial O2 pressure] is chronically reduced was studied. The purpose was to simulate the condition of cancer patients undergoing radiotherapy in the presence of chronically low PaO2 values as might be expected in patients with chronic respiratory disease. Mice bearing transplantable KHT sarcomas were kept in a 12% O2 environment prior to (10-16 days), during and following the radiation treatment of their tumors. During the period of low PaO2 (about 50 mm Hg) exposure, Hb levels in the mice increased by approximately 50%. Because of this increase, the response, determined using a growth delay assay of the tumors irradiated at reduced PaO2 was the same as that observed for tumors in mice breathing air throughout the experiment. In mice with reduced PaO2 levels maintained at normal Hb concentration by periodic bleeding, tumor response was similar to that of mice with acute PaO2 reductions. Chronic PaO2 reductions in the absence of Hb compensation may have a detrimental effect on the success of radiation treatment.