Early 18F-FDG-PET Response During Radiotherapy for HPV-Related Oropharyngeal Cancer May Predict Disease Recurrence

Abstract Purpose Early indication of treatment outcome may guide therapeutic de-escalation strategies in patients with human papillomavirus (HPV)-related oropharyngeal cancer (OPC). This study investigated the relationships between tumor volume and 18F-FDG-PET parameters before and during definitive radiotherapy with treatment outcomes. Methods and Materials Patients undergoing definitive (chemo)radiation for HPV-related/p16-positive OPC were prospectively enrolled on an IRB-approved study. 18F-FDG-PET/CT scans were performed at simulation and after 2 weeks at a dose of ∼20 Gy. Tumor volume and standardized uptake value (SUV) characteristics were measured. SUV was normalized to blood pool uptake. Tumor volume and PET parameters associated with recurrence were identified through recursive partitioning (RPART). Recurrence-free survival (RFS) and overall survival (OS) curves between RPART-identified cohorts were estimated using the Kaplan-Meier method and Cox models were used to estimate the hazard ratios (HR). Results From 2012 to 2016, 62 patients with HPV-related OPC were enrolled. Median follow-up was 4.4 years. RPART identified patients with intra-treatment SUVmax (normalized to blood pool SUVmean) > 6.7 with intra-treatment SUV40% > 2.75 as less likely to recur. For identified subgroups, results of Cox models showed unadjusted HR for RFS and OS (more likely to recur vs less likely) of 7.33 (90% CI 2.97 – 18.12) and 6.09 (90% CI 2.22 – 16.71), respectively and adjusted HR of 6.57 (90% CI 2.53 – 17.05) and 5.61 (90% CI 1.90 – 16.54) for RFS and OS, respectively. Conclusions PET parameters after 2 weeks of definitive radiotherapy for HPV-related OPC are associated with RFS and OS, thus potentially informing an adaptive treatment approach.