DOSIMETRY OF INTRAVENOUSLY ADMINISTERED O-15 LABELED WATER IN MAN - AMODEL-BASED ON EXPERIMENTAL HUMAN DATA FROM 21 SUBJECTS

Models based on uniform distribution of tracer in total body water und erestimate the absorbed dose from (H2O)-O-15 because of the short half -life (2.04 min) of O-15, which leads to non-uniform distribution of a bsorbed dose and also complicates the direct measurement of organ rete ntion curves. However, organ absorbed doses can be predicted by the pr esent kinetic model based on the convolution technique. The measured t ime course of arterial (H2O)-O-15 concentration following intravenous administration represents the input function to organs. The impulse re sponse of a given organ is its transit time function determined by blo od flow and the partition of water between tissue and blood. Values of these two parameters were taken from the literature. Integrals of the arterial input function and organ transit time functions were used to derive integrals of organ retention functions (organ residence times) . The latter were used with absorbed dose calculation. software (MIRDO SE-2) to obtain estimates for 24 organs. From the mean values of organ absorbed doses, the effective dose equivalent (EDE) and effective dos e (ED) were calculated From measurements on 21 subjects. the average v alue for both EDE and ED was calculated to be 1.2 mu Sv . MBq(-1) comp ared with a value of about 0.5 mu Sv . MBq(-1) predicted by uniform wa ter distribution models. Based on the human data, a method of approxim ating (H2O)-O-15 absorbed dose values from body surface area is descri bed.