Reliability of post-chemoradiotherapy F-18-FDG PET/CT for prediction of locoregional failure in human papillomavirus-associated oropharyngeal cancer.

OBJECTIVES: Although widely adopted, the accuracy of post-chemoradiotherapy (CRT) 18F-fluorodeoxygluocose positron emission tomography/computed tomography (PET/CT) for predicting locoregional failure (LRF) in human papillomavirus-related (HPV+) oropharyngeal cancer (OPC) remains poorly characterized. We assessed the predictive value of 3-month PET/CT response for LRF in this population. MATERIALS AND METHODS: 101 consecutive patients with stage III-IV HPV+ OPC who underwent definitive CRT with pre-treatment and 3-month post-CRT PET/CT at our institution from 3/2005-3/2011 were included. 3-month PET/CT response was re-classified as complete-response (CR), near-CR, or incomplete-response (<CR) for each the primary site and neck. Accuracy of 3-month PET/CT for predicting local failure (LF) and regional failure (RF) was analyzed. RESULTS: Among 98 patients with an evaluable primary tumor, LF occurred in 2/67 patients with CR, 0/20 with near-CR, and 1/11 with <CR on 3-month PET/CT. Of 98 node-positive patients, RF occurred in 6/80 with CR, 2/9 with near-CR, and 0/7 with <CR in the neck at 3 months. Sensitivity and positive predictive value (PPV) of 3-month PET/CT response for LF and RF were low (0-33%), despite a high negative predictive value (NPV) (91-98%). SUVmax thresholds or % change did not improve the accuracy of 3-month PET/CT. Use of additional PET/CT surveillance after 3 months in 67 patients accurately detected both LF (96%) and RF (97%). CONCLUSIONS: In the largest study to-date of PET/CT response assessment in HPV+ OPC, 3-month PET/CT response demonstrated high NPV for LRF, though with disappointing sensitivity and PPV. Subsequent PET/CT surveillance showed potential utility for early detection of LRFs.