Clinical role of 18F-FDG PET/CT for detection of radioactive iodine refractory differentiated thyroid cancer.

In clinical settings, an estimated 10% differentiated thyroid cancer (DTC) cases become radioactive iodide refractory (RAIR), which lack a molecular marker and have fewer treatment selections. A higher uptake of 18F-fluorodeoxyglucose (18F-FDG) might indicate poor prognosis for DTC. This study aimed to evaluate the clinical value of 18F-FDG psitron emission tomography/computed tomography (PET/CT) for the early diagnosis of RAIR-DTC and high-risk DTC. A total of 68 DTC patients were enrolled and underwent 18F-FDG PET/CT for the detection of recurrence and/or metastasis. 18F-FDG uptake was evaluated in patients with different postoperative recurrence risks or TNM stages and compared between RAIR and non-RAIR-DTC based on its maximum standardized uptake value and tumor/liver (T/L) ratio. The final diagnosis was judged by histopathology and follow-up data. Of 68 DTC cases, 42 were RAIR and 24 non-RAIR, with 2 not determined. A total of 263 of 293 lesions detected on 18F-FDG PET/CT were confirmed to be locoregional or metastatic after follow-up. The T/L ratio was significantly higher for RAIR than for non-RAIR (median 5.18 vs 1.44; P < .01) and also significantly higher in postoperative patients at high-risk of recurrence than at low to medium risk (median 4.90 vs 2.16; P < .01). 18F-FDG PET/CT exhibited a sensitivity of 83.3% and specificity of 87.5% for identifying RAIR, with a cutoff T/L value of 2.98. 18F-FDG PET/CT has the potential to diagnose RAIR-DTC early and identify the high-risk DTC. The T/L ratio is a useful parameter for the detection of RAIR-DTC patients.