Detection of recurrence adjacent to surgical clips using FDG-PET/CT and contrast enhanced CT (CECT) in squamous cell carcinoma of the head and neck (HNSCC)

1520 Objectives: Our aim was to determine the diagnostic accuracy of FDG-PET/CT using various reading scales and use CECT as an adjunct to better define post-surgical anatomy in the identification of recurrence adjacent to surgical clips (SC). Methods: A total of 97 foci with increased FDG uptake located next to SCs were assessed using PET/CT and CECT in 40 HNSCC pts. Diagnostic validation was done by biopsy or follow-up (median 12 mo). SUV lean body mass (SUVlbm), tm-to-liver (T/L), tm-to-mediastinal blood pool (T/MBP), tm-to-submandibular gland (T/SMG), tm-to-contralateral (T/CL) ratios were calculated. ROC analyses were performed. CECT findings were evaluated for the presence of soft tissue abnormalities. Results: Both T/L and T/MBP ratios yielded more favorable results compared to other ratios. SUVlbm of 3.3 yielded the best cut-off for identification of malignancy adjacent to SCs. CECT had an inferior sensitivity but comparable specificity and increased reading confidence of PET/CT by providing exquisite morphologic information. Conclusions: In the identification of recurrece adjacent to SCs, 1. FDG PET/CT had a superior accuracy to CECT, but CECT increases interpretation confidence 2. Both T/L and T/MBP ratios yielded higher PPV, specificity and accuracy than T/CL and T/SMG ratios.