Post-Treatment FDG-PET/CT Hopkins Criteria Predict Locoregional Recurrence After Definitive Radiotherapy for Oropharyngeal Squamous Cell Carcinoma

Purpose/Objective(s) Surveillance after definitive radiotherapy for oropharyngeal squamous cell carcinoma (OPSCC) is critical to confirm clinical complete response, as a subset of patients develop locoregional recurrences (LRR). The Hopkins Criteria are a standardized qualitative system for assessing response using post-treatment PET/CT and are validated for overall (OS) and progression-free survival (PFS). We hypothesized that the Hopkins Criteria score is independently prognostic for LRR. Materials/Methods We conducted an institutional retrospective study of adult patients with newly-diagnosed node-positive non-metastatic OPSCC treated with definitive (chemo)radiotherapy. Patients were eligible if they completed a pre- and post-radiotherapy PET/CT within 24 weeks after treatment. The primary outcome was the cumulative incidence of locoregional recurrence/persistence. A single board-certified nuclear medicine physician assigned Hopkins scores, which were considered either positive (scores 4-5) or negative (scores 1-3). Results Between 2004-2018, 259 patients were included in this analysis, while an additional 221 were excluded, most commonly due to lack of post-treatment PET/CT [37%] or N0 disease [22%]. Most patients were men (90%), 47% had never smoked, 86% had p16+/HPV+ tumors, and 39% had T3-4 tumors. Nearly all (98%) received concurrent chemotherapy, while 11% received induction chemotherapy. Median clinical follow-up was 40 months. Following radiotherapy, the first post-treatment PET/CT was positive (score 4-5) at the primary site in 32 patients (12%), cervical lymph nodes in 26 patients (10%), and either the primary site or neck in 50 patients (19%). This PET/CT was performed at a median of 3.3 months [range, 1.6-6.0] after radiotherapy. Thirty-four (13%) LRRs were observed. The sensitivity, specificity, negative predictive value, and overall accuracy of the Hopkins score for LRR were 68%, 88%, 95%, and 85%. The 36-month cumulative incidence of LRR was greater among patients with Hopkins scores 4-5 (45% vs. 5%, multivariable-adjusted HR 14.16, P Conclusion There is a lack of consensus reporting standards for response assessment after definitive radiotherapy for OPSCC. The Hopkins Criteria are an easily-implemented standard that appear to offer high accuracy for recurrence and death. These data support an initial PET/CT at least three months after radiotherapy to limit unnecessary diagnostic procedures.