RESUMO
PURPOSE: This study sought to evaluate and compare the utility of 18-F-fluorodihydroxyphenylalanine (18F-DOPA) and 18-F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) for identification of lesions in patients with recurrent medullary thyroid carcinoma (MTC). In addition, we analyzed the correlation between the calcitonin (Ct), carcinoembryonic antigen (CEA) levels, each doubling time (DT), and PET positivity. We evaluated the reliability of the 150 pg/mL Ct cutoff set by the American Thyroid Association guidelines for further imaging (including 18F-DOPA PET/CT). METHODS: We prospectively recruited 18 patients with recurrent MTC, identified by elevation of Ct or CEA. Each patient underwent a 18F-FDG PET/CT and a 18F-DOPA PET/CT. RESULTS: Abnormal uptakes were detected with 18F-DOPA (n=12) and 18F-FDG (n=9), (sensitivity of 66.7% vs. 50%; p<0.01). Twenty-eight lesions were detected with 18F-DOPA vs. 16 lesions with 18F-FDG (1.56±1.5 vs. 0.89±1.18 lesions per patient; p=0.01). None of our patients showed additional lesions with 18F-FDG in comparison to 18F-DOPA. Patient-based detection rate increased significantly with Ct levels ≥150 pg/mL vs. Ct<150 pg/mL for both 18F-DOPA (sensitivity 90.9% vs. 28.6%; p=0.013) and 18F-FDG PET/CT (sensitivity 72.7% vs. 14.3%; p=0.025). Using a CEA cutoff of ≥5 ng/mL, detection rates of 18F-DOPA and 18F-FDG PET/CT were 81.1% and 72.7%, respectively. No correlation between Ct-DT or CEA-DT and PET positivity was found. Histological confirmation was obtained in eight patients. CONCLUSIONS: 18F-DOPA PET/CT appears to be superior to 18F-FDG PET/CT in detecting and locating lesions in patients with recurrent MTC. This technique tends to be especially useful in patients with negative results in other imaging modalities and Ct≥150 pg/mL or CEA≥5 ng/mL.
