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

Background and purpose: 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. Materials and methods: 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. Results: 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. Conclusion: In patients with persistent hypoxia after 2 weeks of treatment, the hypoxic subvolumes showed mostly a geographically relatively stable conformation