DETERMINATION OF THE RADIATION-DOSE FROM ADMINISTERED APOLIPOPROTEIN TRACERS IN HUMANS

Radioactive tracers are routinely used in investigation of the metabol ism of apolipoprotein kinetics. Here, metabolic studies of apolipoprot ein tracers labelled with radioiodine were analysed to determine the a bsorbed radiation dose received by the subject. This analysis used com partmental modelling techniques to evaluate the radiation dose to vari ous organs and the total body resulting from radioiodinated tracer inj ection. In this approach, we combined the published kinetic models of iodine and those of specific apolipoproteins. From the solution of the integrated compartmental models, residence times of the radiation in various source organs, in particular the thyroid, whole body, bladder, and red bone marrow, have been determined for the apolipoproteins apo A-I, apoA-II, very-low-density lipoprotein (VLDL)-apoB, and low-densit y lipoprotein (LDL)-apoB, each labelled with iodine 123, 133, 124, 131 , 126, and 125. These tabulated values were used to calculate radiatio n doses to the different target organs. The thyroid is the organ that receives the largest dose of delivered radiation, and the importance o f the duration of administration of iodine salts in blocking radiation to the thyroid is demonstrated. Optimal block times of 28 days for I- 131 and 42 days for I-125-labeled apolipoprotein tracers are proposed. When such a protocol is followed, the radiation dose to the thyroid a nd other organs is small by comparison to radiation doses allowed for workers whose occupation exposes them to radiation. The importance of frequent voiding to reduce the radiation dose to the bladder has also been demonstrated. Copyright (C) 1997 by W.B. Saunders Company.