Practical experience of the application of ICRP models in internal dose assessment

The introduction of the Ionising Radiations Regulations 1999 in the UK, which came into force on 1 January 2000, led to significant changes in internal dose assessment. Before this date, assessments were based on the methodology from ICRP Publication 26 and, in general, made use of simple models such as those detailed in ICRP Publication 30. However, the introduction of the new Regulations required the use of ICRP Publication 60 methodology, and, at the same time, the latest ICRP biokinetic models were introduced. Many of these newer models were considerably more complex than the ones they replaced. In particular, the use of 'recycling', where activity is constantly recirculated between different organs, meant that the models could not simply be implemented by use of the Skrable formula, as detailed in ICRP Publication 30. This paper outlines two aspects of the application of these latest ICRP models. First, the problems encountered during implementation of these models are detailed, and secondly, it covers the practical experience of using the resulting computer programs for internal dose assessment.