Improved radiation protection of the thyroid gland with thyroxine, methimazole, and potassium iodide during diagnostic and therapeutic use of radiolabeled metaiodobenzylguanidine in children with neuroblastoma

BACKGROUND. During radiolabeled metaiodobenzylguanidine (MIBG) administration in children with neuroblastoma, the thyroid is protected from ^1231/311I uptake by potassium iodide. Despite this protection, up to 64% of patients develop thyroid dysfunction. The authors introduce a new method of radiation protection for the thyroid gland. METHODS. In a prospective cohort study, 34 children with neuroblastoma who received MIBG were given thyroxine, methimazole, and potassium iodide for protection of the thyroid gland. Protection started 1 day before the start of diagnostic ¹²³I-MIBG and was continued until 4 weeks after the last therapeutic ¹³¹I-MIBG dose. Follow-up measurements were performed every 3 months after the protection was stopped. Visualization of the thyroid on MIBG images was reviewed by three nuclear medicine physicians. Results were compared with a historic control group of children who had received potassium iodide for thyroid protection during MIBG administration. RESULTS. After a mean follow-up of 19 months, there were 23 evaluable patients. Thyroid function was normal in 86% of survivors compared with 44% of children in the historic control group (P = 0.011; Pearson chi-square test). Scintigraphic visualization of the thyroid diminished substantially after the new protection (21.5% vs. 5.3%, respectively; P = 0.000). CONCLUSIONS. The results of the current study indicate that compared with potassium iodide alone, combined thyroxine, methimazole, and potassium iodide protect the thyroid more effectively against radiation damage from ^123/131I during diagnostic and therapeutic MIBG administration in children with neuroblastoma.