Abstract
Introduction: This study aims to determine the role of the FDG-PET in the staging of patients with Differentiated Thyroid Cancer (DTC) who have high Tg levels after thyroidectomy.
Material and methods: Thirty-three DTC patients who performed FDG-PET scans after thyroidectomy were selected for this retrospective study. All patients had Tg levels over 10 ng/ml. FDG-PET was performed on patients six weeks after surgery. 2 weeks later FDG-PET imaging, patients received 131-I radioiodine treatment (RIT) except those with lymph node involvement. After RIT, post-ablation therapy whole body scan (TWBS) was performed on the patients.
Results: Twelve patients (36.4%) without involvement outside the thyroid bed, both on the FDG-PET and TWBS, were remissed completely. In 21 patients (63.4%), there was involvement outside the thyroid bed on the FDG-PET and/or TWBS. Eleven patients (33.3%) had distant organ involvement in the FDG-PET and/or TWBS. Patients with involvement outside the thyroid bed had higher Tg levels than others. The disease was completely or partially regressed in the patients with distant organ involvement who had negative FDG-PET scans and positive TWBS results. The disease tended to progress in patients with distant organ involvement who had higher SUVmax levels on FDG-PET.
Conclusion: Our data suggest that the FDG-PET scan, performed on the DTC patients with high Tg levels at the time of staging, would be the right approach. This approach will be useful, especially in demonstrating lymph node involvement and predicting prognosis. The results of FDG-PET may also change the treatment management.

Key words: FDG-PET, DTC, Thyroglobulin, Thyroidectomy