Localization of medullary thyroid carcinoma after surgery using 11C-methionine pet/ct: Comparison with 18F-FDG PET/CT

Abstract

Tumor localization is difficult in patients with medullary thyroid carcinoma (MTC) that have persistent hyper-calcitoninemia after thyroidectomy. In this study, the 11C-methionine positron emission tomography/computed tomography (PET/CT) was compared with the 18F-FDG PET/CT for diagnostic sensitivity in detecting residual or metastatic disease. 11C-methionine PET/CT and 18F-FDG PET/CT were performed on 16 consecutive patients with MTC that had persistent hypercalcitoninemia after surgery in this prospective, single-center study. Patient- and lesion-based analyses were performed using a composite reference standard which was the sum of the lesions confrmed by all combined modalities, including neck ultrasonography (US) with or without fne needle aspiration cytology, CT, bone scan, magnetic resonance imaging (MRI), and surgery. By patient-based analysis, the sensitivities of 11C-methionine PET/CT and 18F-FDG PET/CT were both 63%. By lesion-based analysis, the sensitivity of 11C-methionine PET/CT was similar to 18F-FDG PET/CT (73% vs. 80%). Excluding hepatic lesions, which could not be detected because of physiological uptake of me-thionine by the liver, the sensitivity of 11C-methionine PET/CT was better than 18F-FDG PET/CT especially for detecting cervical lymph node lesions; however, it was not superior to US. All patients with serum calcitonin levels ≥ 370 pg/mL showed uptake by 11C-methionine PET/CT and 18F-FDG PET/CT. This preliminary data showed that despite its similar sensitivity to 18F-FDG PET/CT for detecting residual or metastatic MTC, 11C-methionine PET/CT provided minimal additional information compared to combined 18F-FDG PET/CT and neck US. © The Japan Endocrine Society.