Overlap of highly FDG-avid and FMISO hypoxic tumor subvolumes in patients with head and neck cancer

Abstract

Background: PET imaging may be used to personalize radiotherapy (RT) by identifying radioresistant tumor subvolumes for RT dose escalation. Using the tracers [18F]-fluorodeoxyglucose (FDG) and [18F]-fluoromisonidazole (FMISO), different aspects of tumor biology can be visualized. FDG depicts various biological aspects, e.g., proliferation, glycolysis and hypoxia, while FMISO is more hypoxia specific. In this study, we analyzed size and overlap of volumes based on the two markers for head-and-neck cancer patients (HNSCC). Material and methods: Twenty five HNSCC patients underwent a CT scan, as well as FDG and dynamic FMISO PET/CT prior to definitive radio-chemotherapy in a prospective FMISO dose escalation study. Three PET-based subvolumes of the primary tumor (GTVprim) were segmented: a highly FDG-avid volume VFDG, a hypoxic volume on the static FMISO image acquired four hours post tracer injection (VH) and a retention/perfusion volume (VM) using pharmacokinetic modeling of dynamic FMISO data. Absolute volumes, overlaps and distances to agreement (DTA) were evaluated. Results: Sizes of PET-based volumes and the GTVprim are significantly different (GTVprim>VFDG>VH >VM; p