Exploratory geographical analysis of hypoxic subvolumes using 18F-MISO-PET imaging in patients with head and neck cancer in the course of primary chemoradiotherapy

Hypoxia in head and neck tumours is associated with poor prognosis and outcome, and can be visualized using 18F-MISO-PET imaging; however, it is not clear whether the size and location of hypoxic subvolumes remain stable during therapy. In a pilot project, we conducted an exploratory analysis of persistent tumour hypoxia during treatment. Sixteen patients with locally advanced head and neck tumours underwent consecutive 18F-MISO-PET scans before and during primary chemoradiotherapy. The size, location and overlap of the hypoxic subvolumes were analysed using a semi-automatic algorithm based on a tumour to normal tissue ratio of 1.5. Quantitative evaluation showed tumour hypoxia in week 0 in 16 out of 16 and in week 2 in 5 out of 14 patients. For the five patients with persistent hypoxia, both increased and decreased hypoxic subvolumes could be observed. Mean hypoxic subvolume overlap was 55% of the hypoxic volume of the first scan and 72% of the hypoxic volume of the second scan. A stationary (in four out of five patients) and dynamic component (in three out of five patients) could be differentiated. In patients with persistent hypoxia after 2weeks of treatment, the hypoxic subvolumes showed mostly a geographically relatively stable conformation.