Background: Distinguishing benign complications after concurrent chemoradiotherapy (CCRT) from a local residual tumor in advanced head and neck squamous cell carcinoma (HNSCC) remains a clinical challenge. In this study, we propose criteria when considering physiological uptake patterns on F-18-fluorodeoxyglucose (FDG) PET/CT in patients with advanced HNSCC after CCRT.
Methods: We retrospectively reviewed FDG PET/CT images of 62 patients with advanced HNSCC, which were taken within 16 weeks following CCRT. Visual interpretation criteria were rated by three nuclear medicine physicians, independently, according to the uptake patterns of the primary site. The Cohen k coefficient was calculated to assess inter-reader agreement. The histology of the primary site within a 1 month of the PET/CT study was used as the gold standard for sensitivity, specificity, positive predictive value and negative predictive value.
Results: PET/CT was arranged at a median interval of 10.5 weeks (range 4-16 weeks) after CCRT, and the pathologic residual rate was 55.7% at the primary site. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of identifying residual disease were 91.1%, 50.0%, 68.9%, 82.3%, and 72.6%, respectively, by the previously established criteria, and 88.2%, 92.9%, 93.8%, 86.7%, and 90.3%, respectively, by our physiology-based criteria. Our visual rating criteria corrected 12 of 14 (84.6%) false-positive results from the established criteria, while two more false-negative cases identified with our criteria were proven to be small residual tumors.
Conclusions: By incorporating physiological changes following CCRT, our visual rating criteria improved the accuracy of the currently used FDG PET/CT visual rating system, especially the number of false-positive cases with advanced HNSCC after CCRT.