Endocrine Abstracts

Purpose: This retrospective study is intended to determine the dose of radioactive iodine using thyroglobulin levels measured after two weeks of thyroid hormone withdrawal in patients with differentiated thyroid cancer.

Methods : Patients who were diagnosed as differentiated thyroid cancer and treated with radioiodine after total thyroidectomy were enrolled. Serum thyroglobulin test (preTG; ng/dl) was performed 1 week before radioiodine treatment and 2 weeks after thyroid hormone stoppage. They received 30 mCi, 100 mCi, and 150 mCi of radioactive iodine in consideration of preTG, post-operative pathologic stage, surgeon’s recommendation, and patient selection. After 6 months of radioiodine treatment, complete ablation was investigated. Complete ablation was defined as showing no uptake in diagnostic I-131 scan, stimulated thyroglobulin of less than 1.0 ng/dl and thyroglobulin antibody of less than 100 ng/dl. Patients with preTG less than 3.09 were divided into 30 mCi, 100 mCi, and 150 mCi groups, and the complete ablation of each group was investigated and statistically analyzed.

Results : Seventy patients (female=55, mean age=48 yrs; 21–78 yrs) with a preTG level of 3.09 or less were investigated. Patients were divided into 30 mCi (n=7, mean preTG=1.11; 0.04–3.09), 100 mCi (n=51, mean preTG=0.80; 0.04–3.09), 150 mCi (n=12, preTG=1.23; 0.1–2.8) groups. Complete ablation rates were 71.4% (5/7), 86.3% (44/51) and 75.0% (9/12), respectively. When each group was compared through the Kruskal-Wallis test, there was no statistically significant difference in complete ablation between treatment groups (P=0.458). There was no statistically significant difference between the two groups in the Mann-Whitney test (30 mCi vs 100 mCi, P=0.313; 30 mCi vs 150 mCi, P=0.868; 100 mCi vs 150 mCi, P=0.340).

Conclusion : 30 mCi is recommended if thyroglobulin levels measured after two weeks of thyroid hormone withdrawal in patients with differentiated thyroid cancer is 3.09 or less than.