Discrepancies in Dose Calibrator Assays for Various Forms of Therapeutic Iodine-131

Abstract

Differences in product packaging have the potential to yield differences in assays for the same quantity of radioactivity. We report on the assay variance between packaging of sodium iodide I-131 in capsules and in solutions. We have observed differences of sufficient magnitude that, under certain circumstances, could result in reports of misadministrations to the Nuclear Regulatory Commission when in fact, none has occurred. Establishment of appropriate calibration factors and development of separate dose calibrator potentiometer settings for liquid and capsule dosage forms can minimize the problem.