Prognostic Significance of FDG-PET Metabolic Tumor Parameters for Patients Treated by Re-Irradiation for Local-Regionally Recurrent Head and Neck Cancer

Abstract

To evaluate the prognostic value of metabolic tumor parameters measured on 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging in patients treated by primary re-irradiation for local-regionally recurrent head and neck cancer. The medical records of 80 consecutive patients who underwent re-irradiation to a median dose of 60 Gy for biopsy-proven local-regionally recurrent or second primary head and neck cancer between November 1998 and December 2015 were analyzed. Re-irradiation was defined as any overlap between the initial and re-irradiation dose distributions. Potential correlations of FDG-PET maximum standardized uptake value (SUV) and total metabolic tumor volume (MTV) with the clinical endpoints of overall survival, progression-free survival, local-regional control, and distant control were explored using the Kaplan-Meier method. Multivariate analysis was performed using Cox proportional hazard and logistic regression to determine predictors of outcomes. Twenty-nine of the 80 patients were re-irradiated for grossly measurable disease and had evaluable FDG-PET metrics. The median age was 68 years (range 26 to 85 years). Twenty-patients (70%) received concurrent systemic therapy.The median MTV was 364.2 cc (range, 0 to 3546 cc). The 2-year estimates of overall survival, progression-free survival, local-regional control, and distant control were 25%, 25%, 24%, and 79%, respectively. Both MTV as a continuous variable and using the median value as cut-off were predictive of decreased survival (p<0.05, for both). A trend towards decreased progression-free survival (p=0.05) and local-regional control (p=0.07) was also observed with increasing MTV. There were no associations between maximum SUV and any of the clinical endpoints. On multivariate analysis considering time interval between radiation courses, p16 status, and number of foci treated, MTV was the only variable associated with increased mortality (p=0.007, HR = 4.79; 95% CI: 1.75, 13.16). The PET-derived parameter MTV was demonstrated to be of adverse prognostic significance for patients treated by re-irradiation for local-regionally recurrent head and neck cancer. MTV may serve as a potentially valuable factor for risk stratification and for guiding treatment in future re-irradiation trials.