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 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 A new protective regimen against radiation damage to the thyroid gland during treatment with radiolabeled metaiodobenzylguanidine in children with neuroblastoma is introduced. This regimen uses combined thyroxine, methimazole, and potassium iodide.