[18F] Fluorodeoxyglucose positron emission tomography/computed tomography scan and liquid biopsy at 12 weeks posttreatment for surveillance of locoregionally advanced nasopharyngeal carcinoma.

PURPOSE In nasopharyngeal carcinoma (NPC), the 12-week period following radiotherapy (RT) represents a critical surveillance window for detecting residual disease and distant metastasis. We aim to assess the role of PET/CT And cfEBV DNA levels at 12 weeks post-RT in the surveillance of locoregionally advanced nasopharyngeal carcinoma (LA-NPC). METHODS Patients with stage III-IVa LA-NPC were included. PET/CT scans were conducted both pre-treatment And at 12 weeks post-RT. cfEBV DNA was assessed pre-treatment, at 4, 12, And 24 weeks post-RT, And subsequently at 3- to 6-month intervals. The primary endpoint was the negative predictive value (NPV) of 12-week PET/CT for identifying locoregional residual disease (RD) and/or distant metastasis (DM). RESULTS Between 2018 And 2021, 506 eligible patients were prospectively enrolled (median follow-up: 45.2 months). At 12 weeks post-RT, RD was identified in 22 patients (4.3%), DM in 30 patients (5.9%), And both RD And DM in 6 patients (1.2%). For overall RD and/or DM, 12-week PET/CT demonstrated An NPV of 96.3%, sensitivity of 72.4%, specificity of 93.3%, positive predictive value (PPV) of 58.3%, And accuracy of 90.9%. The corresponding values for 12-week cfEBV DNA were An NPV of 91.7%, sensitivity of 41.7%, specificity of 34.5%, PPV of 93.8%, And accuracy of 87.0%. Among subgroups defined by 12-week cfEBV DNA levels, patients with undetectable cfEBV DNA showed a 96.8% NPV for PET/CT, whereas those with detectable cfEBV DNA demonstrated an 85.0% sensitivity for PET/CT. CONCLUSION PET/CT performed at 12 weeks post-RT is a reliable tool for surveillance in LA-NPC, facilitating the optimization of follow-up strategies and enabling timely therapeutic interventions. The combined use of PET/CT and cfEBV DNA provides valuable risk-stratified insights for managing patients effectively.