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Evaluating the Reliability of Biokinetic and Dosimetric Models and Parameters Used to Assess Individual Doses for Risk Assessment Purposes

How well does Reference Man represent a real person when calculating radiation dose? This publication addresses this question by looking in some detail at the sources of uncertainty in the different models which make up Reference Man. A chapter is devoted to each of the models, which are: gastrointestinal tract, respiratory tract, uptake through wounds and absorption through skin, biokinetic and dosimetric. External exposure from a radioactive cloud or ground deposition is also covered. The development of models from their relatively simple ICRP30 versions to the current complex versions as typified by the ICRP60 respiratory tract model is described with helpful anatomical diagrams. Various models are compared and it seems that no factor which might affect model parameters is overlooked, e.g. the liquid gastric emptying varies according to gender, age and time of day. This is a very rigorous description, but the question the reader finds himself wanting to ask is, `Can you put a figure on the reliability of the dose estimation?' This question is dealt with in the final chapters and sadly the answer is that the more quantitative assessment methods cannot be used because generally there just is not enough data and the problem is to complex. Iodine-131 ingestion is a rare exception. The only usable method is a subjective assessment of uncertainty by experts. As an example, it is applied to a list of radionuclides commonly encountered in environmental releases from nuclear facilities. This comes as rather an anticlimax but the stated intention is not to provide comprehensive uncertainty figures but to present the strengths and weaknesses of the current models and hopefully to stimulate the necessary research. Nuclear medicine physicists should note that this commentary is primarily about environmental exposures to radioactive elements and not medical exposure to radiopharmaceuticals. In conclusion, if you enjoyed reading ICRP23 you will enjoy this publication.