General guidelines for the estimation of committed effective dose from incorporation monitoring data : (Project IDEAS - EU contract no. FIKR-CT2001-00160)

Doses from intakes of radionuclides cannot be measured but must be assessed from monitoring, such as whole body counting or urinary excretion measurements. Such assessments require application of a biokinetic model and estimation of the exposure time, material properties, etc. Because of the variety of parameters involved, the results of such assessments may vary over a wide range, according to the skill and the experience of the assessor. The need for harmonisation of assessment procedures has been recognised in a research project carried out under the EU 5 th Framework Programme. The aim of the project IDEAS (partly funded by the European Commission under contract No. FIKR-CT2001-00160) was to develop general guidelines for assessments of intakes and internal doses from individual monitoring data. The IDEAS project started in October 2001 and ended in June 2005. To ensure that the guidelines are applicable to a wide range of practical situations, a database was compiled of cases of internal contamination that include monitoring data suitable for assessment. About 50 cases from the database were analized by different assessors, the results were collated, and differences in assumptions identified, with their effects on the assessed doses. From the results, and other investigations, draft guidelines were prepared, to provide a systematic procedure for estimating the required parameter values that are not part of the measurement data. A virtual workshop was held on the Internet, open to internal dosimetry professionals, to discuss the draft guidelines, which were revised accordingly. In collaboration with the IAEA, an intercomparison exercise on internal dose assessment was then conducted, which was also open to all involved in internal dosimetry. Six cases were developed and circulated with a copy of the revised guidelines, which participants were encouraged to follow, to test their applicability and effectiveness. The results were collated and a Workshop held to discuss the results with the participants. The guidelines were refined on the basis of the experience and discussion. The guidelines are based on a general philosophy of: • Harmonisation: by following the Guidelines any two assessors should obtain the same estimate of dose from a given data set. • Accuracy: the "best" estimate of dose should be obtained from the available data. • Proportionality: the effort applied to the evaluation should be proportionate to the dose - the lower the dose, the simpler the process should be. Following these principles, the Guidelines use the following "Levels of task" to structure the approach to an evaluation: Level 0: Annual dose 6 mSv). The guidelines provide: • Background information about the biokinetic models and the corresponding bioassay functions for the interpretation of monitoring data. • Detailed information about the handling and evaluation of monitoring data. • A structured approach to dose assessment consisting of a step-by-step procedure described in well-defined flowcharts with accompanying explanatory text.