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

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Abstract
BACKGROUND During radiolabeled metaiodobenzylguanidine (MIBG) administration in children with neuroblastoma, the thyroid is protected from 123/131I 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. Cancer 2003;98:389–96. © 2003 American Cancer Society. DOI 10.1002/cncr.11523