The Role of (18)F-FDOPA PET/CT in Recurrent Medullary Thyroid Cancer Patients with Elevated Serum Calcitonin Levels

OBJECTIVES: To evaluate the diagnostic performance of (18)F-dihydroxyphenylalanine (FDOPA) positron emission tomography/computed tomography (PET/CT) in the detection of medullary thyroid carcinoma (MTC) recurrence in patients with elevated calcitonin levels. METHODS: The patients who had undergone (18)F-FDOPA PET/CT imaging for elevated calcitonin levels after primary surgery of MTC were included in the study. addition, if available (18)F-fluorodeoxyglucose (FDG) PET/CT and Gallium-68 ((68)Ga)- DOTATATE PET/CT images of the patients were evaluated retrospectively. The sensitivity and diagnostic performance of (18)F-DOPA PET/CT were investigated. RESULTS: A total of 14 patients (9 F and 5 M; median age: 45) were included in the analysis. Three patients had MEN IIA syndrome and 1 patient had MEN IIB syndrome, 10 patients had a diagnosis of sporadic MTC. Median calcitonin levels of the patients were calculated as 757.5 (min-max: 28.5-7911) pg/mL. Nine patients and 5 patients had undergone ultrasound and contrast-enhanced computed tomography (ceCT) of the neck, respectively, before (18)F-FDOPA PET/CT imaging. (18)F-FDOPA PET/CT revealed pathological uptake in the thyroid bed, lymph nodes, and distant organs in three, five and two patients, respectively. Median maximum standardized uptake value for the recurrent or metastatic lesions were calculated as 6.4 (min-max: 1.9-18.4). The sensitivity of (18)F-FDOPA PET/CT in the detection of recurrent disease was calculated as 64%. Eight patients had (68)Ga-DOTATATE PET/CT and 7 of them had (18)F-FDG PET/CT within 3 months period before (18)F-FDOPA PET/CT. (18)F-FDOPA PET/CT revealed recurrent disease in 4 of 5 and 2 of the 5 patients who had negative (18)F-FDG PET/CT and negative (68)Ga- DOTATATE PET/CT, respectively. CONCLUSION: (18)F-FDOPA PET/CT can detect recurrence in about two- thirds of patients with elevated calcitonin levels after primary surgery for MTC. Due to variable differentiation degree, different receptor status, and clinical behavior of MTC, all three radiopharmaceuticals can be beneficial and are complementary to each other in patient management.