Background: Tumour hypoxia and a high tumour metabolism increase radioresistance in patients with head and neck squamous cell carcinoma (HNSCC). The aim of this study was to evaluate the correlation between hypoxia ([(18)F]HX4 PET) and glucose metabolism ([(18)F]FDG PET) molecular imaging.
Material and methods: [(18)F]HX4 and [(18)F]FDG PET/CT images of 20 HNSCC patients were acquired prior to (chemo)radiotherapy, in an immobilisation mask, with a median time interval of seven days (NCT01347281). Gross tumour volumes of the primary lesions (GTVprim) and pathological lymph nodes (GTVln) were included in the analysis. [(18)F]FDG PET/CT images were rigidly registered to the [(18)F]HX4 PET/CT images. The maximum and mean standardised uptake values (SUVmax, SUVmean) within both GTVs were determined. In addition, the overlap was compared between the [(18)F]HX4 high volume ([(18)F]HX4 HV) with a tumour-to-muscle ratio > 1.4 and the [(18)F]FDG high volume ([(18)F]FDG HV) with an SUV > 50% of the SUVmax. We report the mean ± standard deviation.
Results: PET/CT scans including 20 GTVprim and 12 GTVln were analysed. There was a significant correlation between several [(18)F]FDG and [(18)F]HX4 parameters, the most pronounced being the correlation between [(18)F]FDG HV and [(18)F]HX4 HV (R = 0.93, p < 0.001). The fraction of the GTVprim with a high HX4 uptake (9 ± 10%) was on average smaller than the FDG high fraction (51 ± 26%; p < 0.001). In 65% (13/20) of the patients, the GTVprim was hypoxic. In four of these patients the [(18)F]HX4 HV was located within the [(18)F]FDG HV, whereas for the remaining nine GTVprim a partial mismatch was observed. In these nine tumours 25 ± 21% (range 5-64%) of the HX4 HV was located outside the FDG HV.
Conclusions: There is a correlation between [(18)F]HX4 and [(18)F]FDG uptake parameters on a global tumour level. In the majority of lesions a partial mismatch between the [(18)F]HX4 and [(18)F]FDG high uptake volumes was observed, therefore [(18)F]FDG PET imaging cannot be used as a surrogate for hypoxia. [(18)F]HX4 PET provides complementary information to [(18)F]FDG PET imaging.