Comparison of efficacy of 2220 MBq versus 3700 MBq I-131 for ablation of thyroid remnant in patients with differentiated thyroid cancer.

AIM: We evaluated the efficacy of two doses of I-131 (2220 MBq versus 3700 MBq) after thyroid hormone withdrawal for thyroid remnant ablation postoperatively in patients with differentiated thyroid cancer (DTC). METHODS: A total of 133 patients with DTC were studied retrospectively. Group 1 (N.=48) included patients with a primary tumor less than 4 cm in mean diameter and confined to the thyroid gland that received an average ablation dose of 2220 MBq. Group 2 (N.=81) included patients with a primary tumor equal to or greater than 4 cm in mean diameter and/or with vascular invasion and/or intrathyroidal lymphovascular invasion and/or microscopic extrathyroidal extension that received an average ablation dose of 3700 MBq. There was no significant difference between the two groups in terms of demographic characteristics or the radioiodine uptake in the neck (2.86+2.31% versus 2.84+1.21%, P=0.97). The success of the remnant ablation was judged by the standard institutional protocol: I-123 whole body scan (WBS) and serum Thyroglobulin (Tg) level after thyroid hormone withdrawal or preparation with recombinant human TSH (rhTSH) 6-12 months after ablation. RESULTS: Overall, remnant ablation was successful in 121/133 (91%) patients. There was no statistically significant difference in the success of ablation between Group 1 and Group 2 (87.5% versus 93%, P=0.273). CONCLUSION: Therefore, for thyroid remnant ablation after thyroid hormone withdrawal, an administered I-131 dose of 2220 MBq is just as effective as 3700 MBq and has the potential for fewer longterm side effects.