Monitoring persistent and recurrent differentiated thyroid carcinoma: Diagnostic performance of 18F-FDG PET/CT

Abstract Background A significant sub-group of patients with differentiated thyroid carcinoma of follicular origin (DTC) shows recurrence and disease progression after radioactive iodine treatment (RAI), hence precise identification of the tumor localisation is essential. The aim was to evaluate the performance of Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography coupled with computed tomography ( 18 F-FDG PET/CT) in the follow-up of DTC and to assess the therapeutic impact of this examination. Methods This is a cross-sectional, monocentric study conducted at the nuclear medicine department between November 2019 and November 2023. This study included 30 patients monitored for DTC and explored by 18 F-FDG PET/CT in the setting of persistent residual disease or recurrence. Results During follow-up, refractory DTC was diagnosed in 23 patients (77%) with an incomplete structural response and thyroglobulin (Tg) level exceeded 100 ng/ml in 50% of cases. For the seven remaining patients classified as having an incomplete biochemical response, 18 F-FDG PET scans identified cervical lymph node metastases in two patients. Overall PET performances were 89.3%, 94%, 85.7%, 96% and 93% for sensitivity, specificity, positive predictive value, negative predictive value, and accuracy respectively. The results of 18 F-FDG PET/CT led to a change in treatment plan in 30% of cases. Conclusions 18 F-FDG PET/CT has demonstrated its usefulness in detecting refractory lesions after RAI with a significant impact on therapeutic management. It would be interesting to increase the follow-up time and the sample size in order to better study its prognostic value.