A computer simulation study of optimal thyroid radiation protection during investigations involving the administration of radioiodine-labelled Pharmaceuticals

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Abstract
The administration of I for thyroid blocking carried risks, at least in certain categories of patients. A theoretical study by computer simulation of the efficacy of various thyroid blocking regimes, was carried out. In the case of injected 125I- or 131I-iodide, substantial thyroid protection may theoretically be achieved by a single oral dose of inorganic I, e.g., a 90% reduction in radiation dose is produced by only 20 mg I. Repeating the initial blocking dose is of little value. A single blocking dose affords poor protection against radioiodine released from labeled plasma proteins. Both for short-lived proteins such as fibrinogen, and for the longer-lived proteins such as albumin, the optimum dosage schedule appears to be stable I given daily for 2-3 wk, e.g., 10 mg daily for a fortnight will reduce thyroid irradiation by a factor of 10 following injection of 125I-fibrinogen.