Post-radiotherapy PET/CT for predicting treatment outcomes in head and neck cancer after postoperative radiotherapy

Purpose: The purpose of this study was to retrospectively review the role of post-treatment (post-tx) FDG-PET/CT scans in patients receiving postoperative intensity-modulated radiotherapy (IMRT) for head and neck squamous cell carcinomas (HNSCC). Materials and methods: Eighty-two patients with HNSCC treated with surgery and postoperative IMRT with or without chemotherapy from October 15, 2008 to December 31, 2014 that had post-tx PET/CT within 6 months of completing IMRT were included. PET/CT was considered positive based on multi-disciplinary review integrating clinical information. Survival analysis was performed using the Kaplan-Meier method. Categorical and continuous predictors of positive post-tx PET/CT were evaluated using Fisher’s exact test and logistic regression, respectively. Predictors for survival outcomes were evaluated with log-rank testing. A p ≤ 0.05 was considered statistically significant. Results: Median follow-up was 3.88 years. For all patients, 3-year overall survival (OS) and recurrence-free survival (RFS) were 71.8% and 61.3%, respectively. Patients with positive post-tx PET/CT had worse OS compared to those with negative post-tx PET/CT (log rank p < 0.001). For patients with positive post-tx PET/CT, 3-year OS was 11.2% compared to 89.9% for patients with negative post-tx PET/CT. The positive predictive value (PPV) of PET/CT was 100% for local recurrence (LR), regional recurrence (RR) and distant metastasis (DM). The negative predictive values (NPV) for LR, RR and DM were 89.0%, 89.2%, and 85.9%, respectively. Perineural invasion (p = 0.009), p16 status (p = 0.009), non-oropharyngeal primary site (p = 0.002), and the use of chemotherapy (p = 0.01) were independent predictors of positive PET/CT. Conclusions: Post-tx PET/CT after postoperative radiation is prognostic for survival outcomes. The PPV of post-tx PET for recurrence was excellent, allowing for early detection of recurrent disease. Post-tx PET/CT should be considered after postoperative radiation.