A Comparison of 1850 (50 mCi) and 3700 MBq (100 mCi) 131-Iodine Administered Doses for Recombinant Thyrotropin-Stimulated Postoperative Thyroid Remnant Ablation in Differentiated Thyroid Cancer

Objective: Recently, a multicenter study in differentiated thyroid cancer (DTC) patients showed that 3700 MBq 131-iodine (131I) after recombinant human TSH (rhTSH) had a successful thyroid ablation rate similar to that obtained after thyroid hormone withdrawal. We investigated whether 1850 MBq 131I had a similar successful rate to 3700 MBq in patients prepared with rhTSH. Design: A total of 72 patients with DTC were randomly assigned to receive 1850 (group A, n = 36) or 3700 MBq (group B, n = 36) 131I after rhTSH. One injection of 0.9 mg rhTSH was administered for 2 consecutive days; 131I therapy was delivered 24 h after the last injection, followed by a posttherapy whole-body scan. Successful ablation was assessed 6–8 months later. Results: Successful ablation (no visible uptake in the diagnostic whole-body scan after rhTSH stimulation) was achieved in 88.9% of group A and B patients. Basal and rhTSH-stimulated serum thyroglobulin was undetectable (<1 ng/ml) in 78.9% of group A and 66.6% of group B patients (P = 0.46). Similar rates of ablation were obtained in both groups also in patients with node metastases. Conclusion: Therapeutic 131I activities of 1850 MBq are equally effective as 3700 MBq for thyroid ablation in DTC patients prepared with rhTSH, even in the presence of node metastases.