Effects of different doses of radioactive iodine for remnant ablation on successful ablation and on long-term recurrences in patients with differentiated thyroid carcinoma.

OBJECTIVES: The aim of this study was to compare ablation success and disease-free survival (DFS) on the basis of different ablation doses.
METHODS: This retrospective study enrolled differentiated thyroid carcinoma patients who underwent total thyroidectomy and radioactive remnant ablation at the Asan Medical Center between January 2000 and December 2004. Radioactive iodine doses of 30 mCi (group A), 80 mCi (group B), and 150 mCi (group C) were administered according to the patients' risk of recurrences based on the clinicopathologic parameters at the time of surgery. Ablation success was defined as absence of abnormal uptake on diagnostic whole-body scan.
RESULTS: Among 1024 patients, successful ablation was achieved in 81.7% in group A, in 89.5% in group B, and in 94.8% in group C (P<0.001). A total of 100 patients (9.8%) had clinical recurrences during 6.6 years of median follow-up. DFS was evaluated according to ablation success in each dose group. There were no significant differences in DFS. Side effects of radioactive iodine were negligible with dose up to 80 mCi; however, 2% of patients developed permanent salivary dysfunction in group C.
CONCLUSION: In cases of different ablation doses administered according to patients' risk of recurrences, we found that a higher dose of radioiodine was associated with a higher rate of ablation success compared with lower doses. However, successful ablation was not associated with a reduction in clinical recurrences. The optimal dose for ablation must be adjusted according to the risk group of individual patients to avoid unnecessary radiation and maximize therapeutic efficacy.