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In recent major international intercomparison exercises on intake and internal dose assessments from monitoring data, the results calculated by different participants varied significantly. Based on this experience the need for harmonisation of the procedures has been formulated within an EU 5th Framework Programme research project. The aim of the project, IDEAS, is to develop general guidelines for standardising assessments of intakes and internal doses. The IDEAS project started in October 2001 and ended in June 2005. The project is closely related to some goals of the work of Committee 2 of the ICRP and since 2003 there has been close cooperation between the two groups. To ensure that the guidelines are applicable to a wide range of practical situations, the first step was to compile a database of well-documented cases of internal contamination. In parallel, an improved version of an existing software package was developed and distributed to the partners for further use. A large number of cases from the database was evaluated independently by the partners and the results reviewed. Based on these evaluations, guidelines were drafted and discussed with dosimetry professionals from around the world by means of a virtual workshop on the Internet early in 2004. The guidelines have been revised and refined on the basis of the experiences and discussions in this virtual workshop. The general philosophy of the Guidelines is presented here, focusing on the principles of harmonisation, optimisation and proportionality. Finally, the proposed Levels of Task to structure the approach of internal dose evaluation are reported.

Publication No. 30 of the International Commission on Radiological Protection (ICRP) assigns the uranium oxides UO2 and U3O8 to transportability class Y, i.e. the half-life of these compounds in the lungs is about 500 days. This assignment seemed not to be in accordance with our experience resulting from incorporation surveillance during UO2 fuel element fabrication. Persons who worked in atmospheres containing UO2 aerosols with activity concentrations significantly above the derived air concentrations (DAC) for class Y U showed much lower activity in the lungs than would be expected according to the ICRP. To understand this discrepancy, aerosol concentrations and aerosol particle-size distributions at work places with the possibility of UO2 incorporation, the activity of urine and feces and the lung activity of persons working at these places were measured in an investigation program. The results are only consistent with the ICRP lung model if one uses a measured biological half-life in the lungs of 109 days and a measured AMAD of 8.2 micron instead of the ICRP standard assumptions of 500 days and 1.0 micron, respectively. ICRP Publication No. 30 recommends application of specific parameters for health physics instead of standard model values. For the special conditions in our UO2 fuel fabrication plant we therefore derive limits of air concentrations, lung activities and fecal and urinary activity concentrations by applying our measured particle-size and lung-retention parameters to the ICRP model. Our special derived limits in comparison to class Y limits for U after ICRP Publication No. 30 for a 1-micron AMAD and 500-day half-life (in brackets) are: (a) annual limit of intake: 6 X 10(4) Bq/y (1 X 10(3) Bq/y); (b) derived air concentration: 20 Bq/m3 (0.6 Bq/m3); (c) derived lung activity: 1.6 X 10(3) Bq; (d) derived fecal activity: 14 Bq/day; and (e) derived urine activity: 8.9 Bq/day. The committed dose equivalents calculated from our measured data and from our modified derived limits proved consistent for the different incorporation control methods (determination of air concentration, lung, fecal or urinary activity). The authors recommend that in accordance with ICRP Publication No. 30, the national rules and regulations on activity incorporation provide the possibility to derive special limits from specific work-place parameters such as particle-size distributions and biological half-lives, thus supplementing the ICRP standard assumptions of 1 micron AMAD and biological half-lives of 0.5 days for class D, 50 days for class W and 500 days for class Y compounds.

In the scope of the IDEAS project to develop General Guidelines for the Assessment of Internal Dose from Monitoring data, two databases were compiled. The IDEAS Bibliography database contains references dealing with problems related to cases of internal contamination. The IDEAS Internal Contamination Database now contains more than 200 cases of internal contamination. In the near future, the IDEAS Internal Contamination database will be made available to the internal dosimetry community. The database has several potential applications, including: training, testing biokinetic models, testing software for calculating intakes and doses from bioassay data, comparison of data from a new accidental intake with that from previous exposures to similar materials. The database is by no means complete, and this presentation is also an appeal for internal contamination cases to extend and update it.