RISK ASSESSMENT OF THE NUCLEAR-MEDICINE PATIENT

Two types of risk are identified following the administration of a rad iopharmaceutical to a patient: the risk to the patient, and the risk t o critical groups exposed to the patient. The method for quantifying t he risk to the patient is described in terms of estimating the effecti ve dose. The main limitations in these estimates for adult and paediat ric patients are uncertainties in the biokinetic data, and the assumpt ion of a uniform distribution of activity in each organ. Effective dos es from most nuclear medicine procedures will not exceed twice the ann ual dose from natural background radiation in the UK. Lack of human pl acental transfer data is now the main limitation to estimating fetal d oses. The characteristics of two methods which can be used to derive t he dose to critical groups exposed to nuclear medicine patients are re viewed. It is shown that studies using either method have indicated th at the current recommendations in the UK for restricting the exposure of these groups and the recommendation recently proposed for restricti ng the exposure of pregnant members of staff are not appropriate. Revi sed recommendations for restricting the behaviour of patients administ ered iodine-131 should await the results of a current multicentre tria l. The method to estimate the dose to a breast-fed infant from a mothe r administered a radiopharmaceutical is outlined, and the recently rev ised guidance for interrupting breast feeding is summarised. When a re commendation for controlling risk is to be derived from dosimetry data obtained from a number of individuals, an outstanding issue to be res olved is the value (e.g. 95% upper confidence limit) on which it shoul d be based.