Tumour oxygenation during fractionated radiotherapy - Comparison with size-matched controls

The effect of fractionated irradiation on the oxygenation status of experim ental tumours was investigated using polarographic assessment of the pO(2) distribution. Since an improvement in tumour oxygenation could simply be th e result of tumour shrinkage, a comparison of pO(2) readings of untreated s ize-matched control tumours was performed. Irradiation was carried out usin g 6 fractions of 6 Gy applied within 11 days. A comparison of polarographic pO(2) data with size-matched untreated tumours revealed a significant impr ovement in oxygenation after the irradiation. The median pO(2) was 0.9 +/- 0.1 mmHg for unirradiated tumours at a volume of 180 mm(3), while the corre sponding data for irradiated tumours of comparable size were 2.3 +/- 0.5 mm Hg on day 21 and 4.8 +/- 0.9 mmHg on day 28 after start of irradiation. Fro m these results it can be concluded that the improvement of oxygenation aft er fractionated irradiation is not solely the result of a reduced tumour vo lume.