Dual PET/CT with 18F-DOPA and 18F-FDG in metastatic medullary thyroid carcinoma and rapidly increasing calcitonin levels: Comparison with conventional imaging

BackgroundTo evaluate the role of a multi-imaging PET with 18F-DOPA and 18F-FDG in comparison with conventional imaging (CI) in recurrent medullary thyroid carcinoma (MTC).Methods18 MTC patients who had thyroidectomy were included; they presented with elevated and rapidly increasing calcitonin levels during follow up. CI had revealed metastatic deposits in 9 patients. Patients were referred to us for a PET/CT with 18F-DOPA and 18F-FDG. Histologic/cytologic confirmation of recurrent MTC was obtained in at least one PET-positive lesion in all patients.ResultsFoci of abnormal uptake were observed in 15 patients at 18F-DOPA and in 11 at 18F-FDG; 8 patients showed the same number of positive lesions with both tracers, 2 showed more lesions on 18F-FDG, 1 was positive at 18F-FDG alone and 5 at 18F-DOPA alone. In 3 patients with a DOPA-positive loco-regional relapse a re-operation with curative intent was offered. SUVmax values were higher for 18F-FDG compared to 18F-DOPA (mean 12.7 ± 4.1 vs. 5.5 ± 2.1, p < 0.05). Calcitonin was higher in PET-positive patients compared to PET negative ones, while no significant differences were observed between 18F-DOPA and 18F-FDG positive patients.ConclusionsIn MTC patients with rapidly increasing calcitonin levels during follow up, 18F-DOPA has a good sensitivity and a complementary role with 18F-FDG PET/CT in detecting metastatic deposits. In our experience, the sensitivity of a multi-imaging 18F-DOPA & 18F-FDG PET/CT approach is greater than that obtained with CI. The higher SUVmax values found with 18F-FDG in some patients may reflect more aggressive tumors.