PET/CT in the management of differentiated thyroid cancer

tThe standard treatment of differentiated thyroid cancer (DTC) consists of surgery followed by iodine-131(131I) administration. Although the majority of DTC has a very good prognosis, more aggressive histo-logic subtypes convey a worse prognosis. Follow-up consists of periodically measurements of serumthyroglobulin, thyroglobulin antibodies and neck ultrasound and123I/131I whole-body scan. However,undifferentiated thyroid tumors have a lower avidity for radioiodine and the ability of DTC to concen-trate131I may be lost in metastatic disease. Positron emission tomography (PET)/computed tomography(CT) has been introduced in the evaluation of patients with thyroid tumors and the 2-[18F]-fluoro-2-deoxyd-glucose (18F-FDG) has been largely validated as marker of cell’s metabolism. According to the2015 American Thyroid Association guidelines,18F-FDG PET/CT is recommended in the follow-up ofhigh-risk patients with elevated serum thyroglobulin and negative131I imaging, in the assessment ofmetastatic patients, for lesion detection and risk stratification and in predicting the response to ther-apy. It should be considered that well-differentiated iodine avid lesions could not concentrate18F-FDG,and a reciprocal pattern of iodine and18F-FDG uptake has been observed. Beyond18F-FDG, other trac-ers are available for PET imaging of thyroid tumors, such as Iodine-124 (124I),18F-tetrafluoroborate andGallium-68 prostate-specific membrane antigen. Moreover, the recent introduction of PET/MRI, offersnow several opportunities in the field of patients with DTC. This review summarizes the evidences on therole of PET/CT in management of patients with DTC, focusing on potential applications and on elucidatingsome still debating points.