Multimodal imaging with 18F-FDG-PET/CT and 111In-Octreotide SPECT in patients with metastatic medullary thyroid carcinoma

OBJECTIVE: The aim of our study was to determine the role of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) and indium-111 Octreotide single photon emission tomography (111In-Octreotide SPECT) in the evaluation of metastatic medullary thyroid carcinoma (MMTC). METHODS: Twenty-five MMTC patients were retrospectively evaluated. All patients had undergone whole-body 18F-FDG-PET/CT including 20 who had also undergone 111In-Octreotide SPECT within a maximum interval of 6 weeks. Diagnostic contrast-enhanced computed tomography (CT) alone or as part of 18F-FDG-PET/CT examination was performed in all patients. RESULTS: Contrast-enhanced CT detected a total of 131 lesions including 79 enlarged lymph nodes and 14 bone lesions. 18F-FDG-PET/CT visualized a total of 92 true positive lesions (SUVmax range 1.1-10.0, mean 4.0 ± 1.7) including 66 lymph nodes, 7 of which were not enlarged on CT, and 8 bone metastases. In the 20 patients studied with both techniques, a total of 64 and 46 true positive lesions were detected by 18F-FDG-PET/CT and 111In-Octreotide SPECT, respectively. In particular, 18F-FDG uptake was found in 43 lymph nodes and in 7 bone metastases whereas 111In-Octreotide uptake was detected in 27 lymph nodes and in 10 bone metastases. CONCLUSIONS: In MMTC patients, 18F-FDG-PET/CT provides a useful contribution mainly in evaluating lymph node involvement whereas 111In-Octreotide SPECT can contribute to the detection and somatostatin receptor characterization especially of bone lesions.