18F-FET PET/CT in Advanced Head and Neck Squamous Cell Carcinoma: an Intra-individual Comparison with 18F-FDG PET/CT

Purpose To assess the diagnostic value of O -2-fluoro-18(F)-ethyl- l -tyrosine ( 18 F-FET) positron emission tomography/computed tomography (PET/CT) for patients with advanced head and neck squamous cell carcinoma compared with 18F-fluoro-2-deoxy- d -glucose ( 18 F-FDG) PET/CT at initial staging and following radiochemotherapy. Procedures Thirteen patients were prospectively enrolled; each of them underwent an 18 F-FDG PET/CT and 18 F-FET PET/CT before treatment. Ten of those were scanned 10 weeks after treatment. Results Sensitivity, specificity, and accuracy for 18 F-FDG PET/CT (primary and lymph node metastases) at initial staging were 89%, 50%, and 81%. For 18 F-FET PET/CT the numbers were 70%, 90%, and 74%. Sensitivity, specificity, and accuracy for 18 F-FDG PET/CT at follow-up were 71%, 65%, and 67%. For 18 F-FET PET/CT the numbers were 29%, 100%, and 83%. Additionally, 18 F-FDG PET/CT detected a higher number of second malignancies or distant metastases. Conclusions 18 F-FET is no substitute for 18 F-FDG. Although it is more specific, too many malignant lesions are missed due to its lower sensitivity.