A prospective clinical study of 18F-FAZA PET-CT hypoxia imaging in head and neck squamous cell carcinoma before and during radiation therapy

Hypoxia in head and neck squamous cell carcinoma (HNSCC) is associated with poor prognosis and outcome. 18F-Fluoroazomycin arabinoside (FAZA) is a positron emission tomography (PET) tracer developed to enable identification of hypoxic regions within tumor. The aim of this study was to evaluate the use of 18F-FAZA-PET for assessment of hypoxia before and during radiation therapy. Twelve patients with locally advanced HNSCC underwent 18F-FAZA-PET scans before and at fraction 7 and 17 of concomitant chemo-radiotherapy. A hypoxic voxel was defined as a voxel expressing a standardized uptake value (SUV) equal or above the SUVmean of the posterior contralateral neck muscles plus three standard deviations. The fractional hypoxic volume fraction (FHV) and the spatial move of hypoxic volumes during treatment were analyzed. A hypoxic volume could be identified in ten patients before treatment. FAZA-PET FHV varied from 0 to 54.3 % and from 0 to 41.4 % in the primary tumor and in the involved node, respectively. Six out of these ten patients completed all the FAZA-PET-computed tomography (CT) during the radiotherapy. In all patients, FHV and SUVmax values decreased. All patient presented a spatial move of hypoxic volume, but only three patients had newborn hypoxic voxels after 17 fractions. This study indicated that 18F-FAZA-PET could be used to identify and quantify tumor hypoxia before and during concomitant radio-chemotherapy in patients with locally advanced HNSCC. In addition to the information on prognostic value, the use of 18F-FAZA-PET allowed the delineation of hypoxic volumes for dose escalation protocols. However, due to fluctuation of hypoxia during treatment, repeated scan will have to be performed (i.e. adaptive radiotherapy). (orig.)