Can FDG PET predict radiation treatment outcome in head and neck cancer? Results of a prospective study

In head and neck cancer (HNC) various treatment strategies have been developed to improve outcome, but selecting patients for these intensified treatments remains difficult. Therefore, identification of novel pretreatment assays to predict outcome is of interest. In HNC there are indications that pretreatment tumour F-18-fluorodeoxyglucose (FDG) uptake may be an independent prognostic factor. The aim of this study was to assess the prognostic value of FDG uptake and CT-based and FDG PET-based primary tumour volume measurements in patients with HNC treated with (chemo)radiotherapy. A total of 77 patients with stage II-IV HNC who were eligible for definitive (chemo)radiotherapy underwent coregistered pretreatment CT and FDG PET. The gross tumour volume of the primary tumour was determined on the CT (GTV(CT)) and FDG PET scans. Five PET segmentation methods were applied: interpreting FDG PET visually (PETVIS), applying an isocontour at a standardized uptake value (SUV) of 2.5 (PET2.5), using fixed thresholds of 40% and 50% (PET40%, PET50%) of the maximum intratumoral FDG activity (SUVMAX) and applying an adaptive threshold based on the signal-to-background (PETSBR). Mean FDG uptake for each PET-based volume was recorded (SUVmean). Subsequently, to determine the metabolic volume, the integrated SUV was calculated as the product of PET-based volume and SUVmean. All these variables were analysed as potential predictors of local control (LC), regional recurrence-free survival (RRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS) and overall survival (OS). In oral cavity/oropharynx tumours PETVIS was the only volume-based method able to predict LC. Both PETVIS and GTV(CT) were able to predict DMFS, DFS and OS in these subsites. Integrated SUVs were associated with LC, DMFS, DFS and OS, while SUVmean and SUVMAX were not. In hypopharyngeal/laryngeal tumours none of the variables was associated with outcome. There is no role yet for pretreatment FDG PET as a predictor of (chemo)radiotherapy outcome in HNC in daily routine. However, this potential application needs further exploration, focusing both on FDG PET-based primary tumour volume, integrated SUV and SUVMAX of the primary tumour.