Post-operative PET/CT improves the detection of early recurrence of squamous cell carcinomas of the oral cavity

•Use of PET/CT for post-operative radiation planning is associated with increased detection of early recurrence.•Patients with intermediate risk clinicopathologic risk factors disproportionately benefit from post-operative PET/CT due to a higher likelihood of major treatment intensification.•Use of post-operative PET/CT is associated improved disease-free survival among patients with intermediate risk clinicopathologic risk factors. We evaluate the impact of post-operative 18-fluorodeoxyglucose positron emission tomography with computed tomography (PET/CT) for radiation planning on the detection of early recurrence (ER) and treatment outcomes in oral squamous cell carcinoma (OSCC). We retrospectively reviewed the records of patients treated with post-operative radiation between 2005 and 2019 for OSCC at our institution. Extracapsular extension and positive surgical margins were classified as high risk features; pT3-4, node positivity, lymphovascular invasion, perineural invasion, tumor thickness >5 mm, and close surgical margins were considered intermediate risk features. Patients with ER were identified. Inverse probability of treatment weighting (IPTW) was used to adjust for imbalances between baseline characteristics. 391 patients with OSCC were treated with post-operative radiation. 237 (60.6%) patients underwent post-operative PET/CT planning vs. 154 (39.4%) who were planned with CT only. Patients screened with post-operative PET/CT were more likely to be diagnosed with ER than those planned with CT only (16.5 vs. 3.3%, p