Thyroid hormone replacement one day before 131I therapy in patients with well-differentiated thyroid cancer

Objective: The current study aimed to determine the efficacy of radioiodine-131 (131I) ablation therapy with thyroid hormone replacement one day before 131I administration in patients with well-differentiated thyroid cancer (DTC). Methods: This retrospective study included 29 patients who underwent 131I therapies twice for DTC during 6-12 months.  Since all the patients obviously had residual lesions by their serum thymoglobulin levels or their scintigrams at the first therapies, they underwent the second 131I therapies without diagnostic scintigraphy after the first therapies. After confirming the sufficient elevation of TSH concentration, thyroid hormone replacement was resumed one day before 131I administration　(3.7-7.4GBq).  The ablation rate of thyroid remnant at the first 131I therapy was evaluated by comparing 131I post-therapeutic images of the two treatments. Results: Three patients were administrated thyroid hormone after 131I therapy because of insufficient TSH concentration under thyroid hormone withdrawal. In the remaining 26 patients, 41 thyroid remnant accumulations were detected in all 26 patients at the first 131I therapy. Based on the second 131I post-therapeutic images, successful ablation was confirmed in 24 of 26 patients (92.3%) and 38 of 41 sites (92.7%), which was comparable with historically reported ablation rates. Conclusion: Thyroid hormone replacement one day before 131I therapy could provide a sufficiently high ablation rate in patients with DTC.