High incidence of thyroid dysfunction despite prophylaxis with potassium iodide during 131I‐meta‐iodobenzylguanidine treatment in children with neuroblastoma

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Abstract
BACKGROUND Treatment modalities like targeted radiotherapy with 131I‐meta‐iodobenzylguanidine (131I‐MIBG) improve survival rates after neuroblastoma (NB). Radiation to the thyroid gland can lead to hypothyroidism and even malignancy. Because hypothyroidism after 131I‐MIBG treatment was reported, the current KI prophylaxis against thyroidal radiation damage was evaluated. METHODS The incidence, pathogenesis, and consequences of thyroid dysfunction among 42 NB patients treated with 131I‐MIBG were evaluated retrospectively. Efficacy of KI prophylaxis was established by measuring thyroidal radioiodide uptake. Thyroid damage was expressed as thyrotropin elevation (TE, plasma concentration of thyroid stimulating hormone ≥ 4.5 mU/L). RESULTS The mean followup was 2.3 years ( range, 0.1‐8.5). The mean number of treatments with 131I‐MIBG was 3.3. Of 428 scintigrams, uptake of 131I in the thyroid was visible in 92 (21.0%). Twenty two patients (52.4 %) presented TE after a mean period of 1.4 years (range, 0.1–5.8). Clinical signs of hypothyroidism were not observed. Eight patients received suppletion therapy with thyroxine. Thyrotropin elevation was transient in four patients. Of 25 survivors, with a mean followup of 3.5 years, 16 (64%) developed TE. No correlation was found between TE and thyroid visualization after 131I‐MIBG administration or the number of treatments. No abnormalities were seen by ultrasound imaging of the thyroid. CONCLUSIONS Occurrence of thyroid dysfunction after treatment with 131I‐MIBG for NB is high, in spite of KI prophylaxis. Close followup of thyroid function and structure is required in patients treated with 131I‐MIBG. New ways of protecting the thyroid during exposure to radioiodine should be developed. Cancer 2002;94:2081–9. © 2002 American Cancer Society. DOI 10.1002/cncr.10447