Long-Term Oncological Outcome Comparison between Intermediate- and High-Dose Radioactive Iodine Ablation in Patients with Differentiated Thyroid Carcinoma: A Propensity Score Matching Study

BACKGROUND: Radioactive iodine (RAI) ablation is recommended for most patients with differentiated thyroid carcinoma (DTC) after total thyroidectomy (TT). We aimed to compare long-term outcomes between intermediate-dose (100 mCi) and high-dose (150 mCi) RAI ablation therapy in patients with DTC using propensity score matching analysis. METHODS: This was a retrospective study of 1448 patients with DTC who underwent RAI ablation after TT. Propensity score matching was performed using the extent of operation, tumor size, extrathyroidal extension, multifocality, lymphatic invasion, vascular invasion, perineural invasion, number of positive lymph nodes (LNs), ATA risk stratification system, T stage, N stage, TNM stage, preoperative serum Tg and TgAb levels, and post-RAI serum Tg and TgAb levels. RESULTS: Recurrence rates in the intermediate- and high-dose groups were 3.1% and 5.6%, respectively. After propensity score matching, LN ratio >0.22 (HR, 2.915; 95% CI, 1.228–6.918; p=0.015) and serum Tg >10 ng/mL after RAI (HR, 3.976; 95% CI, 1.839–8.595; p < 0.001) were significant predictors of recurrence. Kaplan–Meier analysis showed no significant difference in DFS before or after propensity score matching (p=0.074 and p=0.378, respectively). CONCLUSIONS: Intermediate-dose RAI ablation for the adjuvant treatment of DTC is sufficient as compared to high-dose RAI ablation. Further prospective or multicenter studies should be conducted to clarify the prognosis of intermediate-dose RAI ablation.