Very little is known about the correlation between the radiobiological hypoxic fraction (rHF) and other measures of tumour oxygenation during fractionated irradiation. In the present study the rHF is determined in untreated human FaDu and GL squamous cell carcinoma in nude mice and in tumours irradiated with 10 fractions in 2 weeks and 20 fractions in 4 weeks, using tumour control as the experimental endpoint. The results were compared with measurements of the pO2, the interstitial fluid pressure (IFP) and the relative viable tumour area. In FaDu tumours the radiobiological hypoxic fractions (rHFs) before and during irradiation were not statistically different from 100%. Depending on the assumptions made for D0, the rHFs of GL tumours were between 0.2 and 4% or 30 and 53%. The median pO2 values were 2.8 mmHg for untreated FaDu tumours and 0.2 mmHg for GL tumours (p < 0.001). The median IFP values were 2.6 mmHg in FaDu and 5.3 mmHg in GL tumours (p = 0.01). No important changes in the pO2 and IFP values were observed during fractionated irradiation. The relative viable tumour area during irradiation decreased by 83% in FaDu tumours (p = 0.002) and by 54% in GL tumours (p = 0.003). It is concluded that differences in rHF exist between FaDu and GL tumours before and during fractionated irradiation and that these differences are not reflected by pO2 and IFP values and the relative viable tumour area.
