Endocrine Abstracts

Introduction: Complete ablation of residual thyroid tissue in patients with papillary thyroid cancer decreases locoregional recurrence, distant metastases and cancer death. No single group achieved 100% complete ablation post first ablation dose with variable successful complete ablation rate. In patients who failed to achieve complete ablation a reablation dose is recommended to have complete ablation outcome. Post second ablation dose some patients still have small residual thyroid tissue in the neck, that warrants small third ablation dose of ¹³¹I to achieve complete ablation.

Aim: The aim of the current study is to compare ablation outcome post 30 mCi ablation dose of ¹³¹I used as a second and as a third ablation dose.

Patients and methods: Retrospective analysis of data of 372 patients with papillary thyroid cancer confined to the thyroid gland referred post total thyroidectomy for ¹³¹I ablation was performed. All received first ablation dose of 100 mCi of ¹³¹I. Presence of residual thyroid tissue in follow-up ¹³¹I whole body scan (WBS) with elevated unsuppressed serum thryoglobulin (Tg) level indicate incomplete ablation outcome. Those patients received 30 mCi of ¹³¹I reablation on outpatient basis. Patients post second ablation dose with small residual thyroid tissue in the neck seen in follow-up ¹³¹I WBS 6–9 months post second ablation dose with elevated serum Tg level received a third ablation dose of 30 mCi. Follow-up WBS and Tg level were performed 6–9 months post third dose to assess ablation outcome.

Results: Complete ablation rate post first dose was reported in 249 patients (66.9%). Out of the remaining 123 patients complete ablation was achieved post 30 mCi second ablation dose in 89 patients (72.4%) with an overall complete ablation post two doses achieved in 338 patients (90.9%). A third ablation dose of 30 mCi was given to the remaining 34 patients. Complete ablation was reported in 26 patients (76.5%), with statistically insignificant difference (P>0.05) between complete ablation outcome using 30 mCi as a second or as a third ablation dose. Successful complete ablation post three doses of ¹³¹I (total dose of 160 mCi) was achieved in 364 patients (97.8%).

Conclusion: Complete ablation outcome rate between second and third ablation doses of 30 mCi of ¹³¹I are comparable with no statistically significant difference.