Changes in Oxygen Tension During Radiotherapy of Head and Neck Tumours

Abstract

Increased knowledge about changes that occur in tumour oxygenation during radiotherapy and the biological factors causing these changes can be useful in the development of optimal radiation treatments. The aims of this study were a) to study changes in the oxygen tension (pO₂) of human head and neck tumours during radiotherapy in relationship to changes in cell density and vascular density, and b) to investigate whether the pO₂, measured before or during therapy, can be used to predict the therapeutic outcome. Preliminary data from the first 11 patients included in the study are reported. The pO₂ was measured before treatment (11 patients) and once a week during therapy (8 patients), using polarographic needle electrodes. Cell density and vascular density were determined from biopsies taken after each pO₂ measurement in 5 patients. Significant fluctuations in pO₂ occurred during therapy. Changes in hypoxic fraction; i.e., fraction of pO₂ readings below 2.5 mmHg, 5 mmHg or 10 mmHg, coincided with changes in cell density, but not with changes in vascular density, which suggests that the changes in hypoxic fraction were caused by changes in oxygen consumption rather than supply. Response evaluation after a median follow-up time of 19 months showed that progressive disease occurred among the patients with highly hypoxic tumour, regardless of whether hypoxic fraction before treatment or after two weeks of radiotherapy was considered.