Study subjects
RECURRENCE
All patients included in this study were diagnosed with NPC and underwent FDG PET/CT scans before and after definitive radiotherapy (with or without chemotherapy), between 2008 and 2019. The study population also met the following criteria: (1) subjects were more than 20 years of age; (2) the interval between definitive radiotherapy and follow-up FDG PET/CT was less than 6 months; and (3) the PET images were acquired with the same spatial resolution within the study population. We excluded patients who were treated for recurrence before the follow-up FDG PET/CT. Patients with the PET/CT image data loss were also excluded. Consequently, 145 patients were included in this study. Figure Flow chart of study subjects and FDG PET processing.This study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Samsung Medical Center (protocol code 2020-06-127; date of approval: 15 July 2020). The requirement of written informed consent from enrolled subjects was waived by the Institutional Review Board of Samsung Medical Center due to the retrospective study design.