SIMPLIFIED ORGAN RETENTION FUNCTIONS FOR PHYSIOLOGICALLY-BASED RECYCLING BIOKINETIC MODELS

Recent ICRP Publications on biokinetic models show a movement from sim ple schematic models to more complex, physiologically-based models. Su ch models require considerably greater computing resources to implemen t than their predecessors, effectively making them inaccessible to man y users. Fortunately, retention in most of tile compartments of these large recycling models can be adequately approximated by the sum of a few exponential functions compatible with the simple catenary models u sed almost exclusively in ICRP Publication 30. An eigenvalue method is used to solve the plutonium model of ICRP Publication 67 for intakes by inhalation, ingestion, and injection. The organ retention expressio ns so obtained are reduced by least squares minimization to functions consisting of the sum of a few exponential terms only. These simplifie d functions give committed doses accurate to within 5% and activities to within 10%. A similar treatment is used to obtain simplified expres sions for daily excretion rates of plutonium.