Radiochemical purity of iodine-131 labelled metaiodobenzylguanidine infusion fluids: a report from clinical practice.

Iodine-131 labelled metaiodobenzylguanidine ([131I]MIBG) has a diagnostic and therapeutic role in the management of neural crest tumours, particularly neuroblastoma, malignant phaeochromocytoma and paraganglioma. With therapeutic amounts of [131I]MIBG it is essential that the amount of free [131I]iodide, the most important impurity, is known. In clinical practice the percentage of free [131I]iodide seen in a [131I]MIBG infusion concentrate increased from 2.2% +/- 0.67% to 3.6% +/- 0.39% (mean +/- SD; n = 23) 1 day after production. At the time of use the percentage of free [131I]iodide was always below our upper limit of acceptance of 5%. Since 5% of free [131I]iodide is within practical reach in our environment, a higher percentage at the time of preadministration quality control is not accepted in the Netherlands Cancer Institute.