18 F-FDG PET/CT Combined with Serum Tg and BRAF V600E Mutation for Evaluating Recurrence/Metastasis in RAIR-DTC: Subgroup Analysis and Clinical Decision-Making Value

Abstract

Objective:

This study evaluated the clinical diagnostic efficacy of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) for recurrence and/or metastasis in patients with radioactive iodine-refractory differentiated thyroid cancer (RAIR-DTC) and analyzed its correlation with serum thyroglobulin (Tg), BRAF^V600E mutation status, and postoperative clinical risk stratification.

Method:

A retrospective analysis was conducted on the ¹⁸F-FDG PET/CT images and clinical data of 47 patients with RAIR-DTC. The diagnostic sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated, and the receiver operating characteristic curve was used to determine the optimal cutoff value of Tg. The correlation between maximum standardized uptake value (SUV_max) and clinical pathological characteristics was analyzed.

Results:

For ¹⁸F-FDG PET/CT in detecting RAIR-DTC recurrence/metastasis, the diagnostic sensitivity was 94.87%, specificity 64.71%, PPV 92.50%, and NPV 73.33%. Regarding Tg, the optimal cutoff value for predicting RAIR-DTC recurrence/metastasis was 29.6 ng/mL, with an area under the curve of 0.7677. Further subgroup analysis showed that the serum Tg level in the PET/CT-positive group (212.56 ± 102.90 ng/mL) was significantly higher than that in the PET/CT-negative group (86.53 ± 69.67 ng/mL; t = 2.119, p = 0.039). In terms of clinical stage, the PET/CT positivity rate was significantly higher in patients with advanced RAIR-DTC (clinical stage III/IV) than in those with early-stage disease (81.82% versus 57.14%; p = 0.033). Correlation analysis revealed a positive correlation between ¹⁸F-FDG PET/CT- derived SUV_max and clinical stage (Pearson correlation coefficient, r = 0.361, p = 0.042). Furthermore, the SUV_max in the BRAF^V600E-mutant group was significantly higher than that in the BRAF^V600E wild-type group (7.84 ± 3.50 versus 3.85 ± 1.26; t = −4.219, p = 0.039). In addition, the detection rate of ¹⁸F-FDG PET/CT for RAIR-DTC recurrence/metastasis was significantly superior to that of Iodine-131 (¹³¹I) single-photon emission computed tomography/computed tomography (SPECT/CT) (88.89% versus 52.78%; Z = 2.652, p = 0.041).

Conclusions:

¹⁸F-FDG PET/CT exhibits high diagnostic efficacy for RAIR-DTC recurrence/metastasis, with its positivity and SUV_max significantly correlated with serum Tg, clinical stage, and BRAF^V600E mutation. Clinically, this supports three key strategies: (1) Prioritize ¹⁸F-FDG PET/CT follow-up for patients with Tg > 29.6 ng/mL, BRAF^V600E positivity or postoperative high risk; (2) consider treatment escalation for PET/CT-positive patients with SUV_max > 7.0; and (3) combine ¹⁸F-FDG PET/CT with ¹³¹I SPECT/CT to guide personalized management of RAIR-DTC.