Value of Dedicated Head and Neck 18F-FDG PET/CT Protocol in Detecting Recurrent and Metastatic Lesions in Post-surgical Differentiated Thyroid Carcinoma Patients with High Serum Thyroglobulin Level and Negative 131I Whole-body Scan

OBJECTIVES In clinical practice, approximately 10-25% of post-surgical differentiated thyroid carcinoma (DTC) patients with high serum thyroglobulin (Tg) and negative 131I whole-body scan (WBS) have poor prognosis due to recurrent or metastatic lesions after radioactive iodine treatment. The purpose of this study was to evaluate the value of 18F-FDG PET/CT scan in DTC patients with high serum Tg level and negative 131I WBS. METHODS 69 post-surgical DTC patients with high serum Tg level and negative post ablation 131I WBS were enrolled in this study. All DTC patients underwent head and neck ultrasound, CT scan and whole-body 18F-FDG PET/CT, based on the dedicated head and neck protocol. RESULTS Overall, 92 lesions were detected in 43 (62.3%) out of 69 patients with positive 18F-FDG PET/CT scan, compared to only 39 lesions detected on CT scan in 26 (37.7%) out of 69 patients. The sensitivity, accuracy and negative predictive value of 18F-FDG PET/CT were 88%, 87% % and 76%, respectively, which were significantly higher than those of CT scan (67.2%, 54.3% and 48.8%, respectively) (P<0.01). Specificity and positive predictive value of 18F-FDG PET/CT (90.5% and 95.2%, respectively) were similar to those of CT scan (95.2% and 96.2%, respectively) (P>0.05). The maximum standardized uptake value (SUVmax) threshold was 4.5 with a good diagnostic value (sensitivity of 92.3% and specificity of 100%). The dedicated head and neck 18F-FDG PET/CT protocol altered the treatment plan in 33 (47.8%) out of 69 DTC patients with high serum Tg level and negative 131I WBS. CONCLUSION Dedicated head and neck 18F-FDG PET/CT protocol showed a higher diagnostic value, compared to CT scan and played an important role in detecting recurrent or metastatic lesions in post-surgical DTC patients with high serum Tg level and negative 131I WBS.