Comparison of efficacy of 2 220 MBq versus 3 700 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 (2 220 MBq versus 3 700 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 2 220 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 3 700 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 2 220 MBq is just as effective as 3 700 MBq and has the potential for fewer longterm side effects.