Value of Dedicated Head and Neck F-FDG PET/CT Protocol in Detecting Recurrent and Metastatic Lesions in Post-surgical Differentiated Thyroid Carcinoma Patients with High Serum Thyroglobulin Level and Negative I 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 I 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 F-FDG PET/CT scan in DTC patients with high serum Tg level and negative I WBS.

Methods: 69 post-surgical DTC patients with high serum Tg level and negative post ablation I WBS were enrolled in this study. All DTC patients underwent head and neck ultrasound, CT scan and whole-body F-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 F-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 F-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 F-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 (SUV) threshold was 4.5 with a good diagnostic value (sensitivity of 92.3% and specificity of 100%). The dedicated head and neck F-FDG PET/CT protocol altered the treatment plan in 33 (47.8%) out of 69 DTC patients with high serum Tg level and negative I WBS.

Conclusion: Dedicated head and neck F-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 I WBS.