Endocrine Abstracts

Purpose: This retrospective study is evaluated the efficacy of three doses of I-131 (1110 MBq vs 3700 MBq vs 5550 MBq) in differentiated thyroid carcinoma patients with cut-off serum thyroglobulin (TG) level after two weeks of thyroid hormone withdrawal for postoperative thyroid remnant ablation.

Methods: A total of 97 patients with differentiated thyroid cancer treated with total thyroidectomy and radioactive iodine (RAI) therapy were enrolled. Doses of 1110 MBq, 3700 MBq, and 5550 MBq were determined based on the surgical records and pathologic results of each patient. Serum TG test was performed one week before radioiodine treatment and two weeks after the thyroid hormone stoppage(preTG; ng/dl) and cut-off preTG level was below 5 ng/dl. After six months of RAI treatment, complete ablation,which defined as showing no uptake in diagnostic I-131 scan, stimulated TG of less than 1.0 ng/dl, and TG antibody of less than 100 ng/dl was investigated, and statistically analyzed.

Results: After initial therapy, 76 patients (78.4%) were in complete ablation, with 77.8% (7/9) in 1110 MBq group, 80.0% (60/75) in 3700 MBq group, and 69.2% (9/13) in 5500 MBq group. There was no statistically significant difference in complete ablation between different radiation dose groups (P = 0.681). Serum preTG level did not show a statistically significant difference between the three groups (P = 0.091). The serum preTG level (adjusted odds ratio (OR) = 1.70, 95% confidence intervals (CI) 1.07–2.69, P = 0.024) and stimulated TG level at the time of RAI (adjusted OR = 1.4, 95% CI 1.14–1.68, P < 0.001) were significantly independent predictors of complete ablation.

Conclusion: RAI therapy with 1110 MBq seems to besufficient for ablation if thepreTG level was below 5 ng/dl in patients with differentiated thyroid cancer.