The Use of 18F-FDG PET/CT in Patients with Recurrent Differentiated Thyroid Cancer

Objectives: 18 Fluorine-fluorodeoxyglucose ( 18 F-FDG) positron emission tomography/computed tomography (PET/CT) is used to monitor the recurrence in thyroid cancer patients when there is suspicion of metastases.De-differentiated lesions become 18 F-FDG avid with a more aggressive clinical course.The aim of this study was to investigate the use of 18 F-FDG PET/CT in differentiated thyroid cancer.Methods: Forty-six patients, either with a negative radioiodine scan or clinical progression and suspicions for metastases with differentiated thyroid cancer that were referred to our department for 18 F-FDG PET/CT scan and evaluated retrospectively.PET/CT findings were correlated with clinical and histopathological findings, serum thyroglobulin (Tg), and anti-Tg levels.Results: Twenty-six patients (56.2%) were positive for recurrence in 18 F-FDG PET/CT images.Positive 18 F-FDG PET/CT findings were significantly correlated with the disease stage and Tg levels.Maximum standardized uptake value did not correlate with other findings or patients' profiles.The cut-off value for Tg was at 52.5 ng/mL having 73.08% sensitivity, 75% specificity, 79.17% positive predictive value, and 68.18% negative predictive value for 18 F-FDG PET/CT imaging.Conclusion: 18 F-FDG PET/CT is useful for detecting recurrence in differentiated thyroid cancer.Increased Tg levels and stage of the disease were significantly correlated with 18 F-FDG positivity.18 F-FDG positivity may also provide information about the de-differentiation process that may support the treatment plan.Keywords: Thyroid cancer, 18 F-FDG PET/