BACKGROUND

During the last few years the ICRP has developed a new generation of more realistic internal dosimetry models, including the Human Respiratory Tract Model (ICRP Publication 66 [ICRP 1994]) and recycling systemic models for actinides (ICRP Publications 67 and 69 [ICRP 1993, ICRP 1995])). The 3^rd European Intercomparison Exercise on Internal Dose Assessment gave special consideration to the effects of the new models and the choice of input parameters on the assessment of internal doses from monitoring results [Doerfel et al. 2000]). It also took into account some aspects which have not been considered in previous exercises, such as air monitoring, natural radionuclides, exposure of the public, artificially created cases and artificially reduced information. Seven case scenarios were distributed, dealing with H-3, Sr-90, I-125, Cs-137, Po-210, U-238 and Pu-239, and covering different intake scenarios and all monitoring techniques. Results were received from 50 participants, 43 representing 18 European countries and 7 from five countries outside Europe. So it was by far the largest exercise of this type carried out to date. Most participants attempted more than half of the cases. Thus on average there were 35 responses per case with a total of about 240 answers, giving a good overview of the state of the art of internal dosimetry. The results in terms of intake and committed effective dose appeared to be log-normally distributed with the geometric standard deviation ranging from 1.15 for the cases dealing with H-3 and Cs-137, up to 2.4 for the cases dealing with Pu-239.  These figures reflect the large differences in the individual results which varied in the worst case over a range of five orders of magnitude. A key feature of the exercise was a Workshop, involving most of the participants, at which each case and the various approaches taken to assessing it were discussed.  Several reasons for the differences in the results were identified, including different assumptions about the pattern of intake, and the choice of model. 

The most important conclusion of the exercise was the need to develop agreed guidelines for internal dose evaluation procedures in order to promote harmonisation of assessments between organisations and countries, which has special importance in the European Union (EU) because of the mobility of workers between member states. This was the reason to launch the IDEAS project in the 5^th EU Framework Programme (EU Contract No. FIKR-CT2001-00160).