Tehran University of Medical Sciences
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Davood Beiki

Low versus high radioiodine dose in postoperative ablation of residual thyroid tissue in patients with differentiated thyroid carcinoma: a large randomized clinical trial


Authors: Fallahi B, Beiki D, Takavar A, Fard-Esfahani A, Ansari Gilani K, Saghari M, Eftekhari M,
Keywords: ablation therapy, differentiated thyroid carcinoma, radioiodine
Nucl Med Commun , Vol.33, No.3, 2012,Page:,Number of Page:275-282

Objectives: Radioiodine ablation of thyroid tissue remains the cornerstone of treatment for patients with differentiated thyroid carcinoma after thyroidectomy. Selecting an optimal dose of radioiodine for successful ablation is a continuous challenge in these patients.
Methods: We compared the treatment response of 341 patients with thyroidectomy randomly allocated to the high-dose group, 3700MBq (170 patients), versus the low-dose group, 1110MBq (171 patients), for radioiodine ablation therapy in a double-blind randomized clinical trial. The response to treatment was defined as successful or unsuccessful according to post-therapy ultrasonography of the neck, serum thyroglobulin (Tg), anti-Tg, and functioning residual tissue after 6-month and 12-month intervals. The major criteria of successful ablation were Tg <2 ng/ml, anti-Tg < 100 IU/ml, and absent remnant in the offlevothyroxine state. Additional radioiodine doses were administered in cases showing no significant response to the first therapy. Finally, the initial outcome, the total hospitalization time, and the cumulative I-131 doses during the 12-month course of the study were compared between the subgroups.
Results: The rate of initial successful ablation was 51.6% in all patients, 39.2% in the low-dose group, and 64.1% in the high-dose group. The corresponding success rates at the end of the 12-month follow-up without additional treatment were 55.1, 41.5, and 68.8%, respectively. The relative risk (RR) of unsuccessful ablation for the low-dose versus the high-dose group was 1.695 [95% confidence interval (CI), 1.34–2.14]. In the low-dose group, more patients needed a second dose of I-131, resulting in a higher cumulative activity (median, 4810 vs. 3700MBq, P < 0.0001) and more inpatient time (median 4 vs. 3 days) in comparison with the high-dose group. The covariate factors predicting the treatment response, in order of significance, were&