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Lessons learned from interlaboratory comparisons of bioassay data interpretation


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Workshop on Internal Dosimetry of Radionuclides - Occupational, Public and Medical Exposure - 9-12 September 2002 - New College, Oxford, United Kingdom H. Doerfel1, A. Andrasi2, M. Bailey3, V. Berkovski4, C.-M. Castellani5, C. Hurtgen6, J.-R. Jourdain7, B. LeGuen8 1 Forschungszentrum Karlsruhe GmbH, Karlsruhe 2 KFKI Atomic Energy Research Institute, Budapest 3 National Radiological Protection Board, Chilton, Didcot 4 Radiation Protection Institute, Kiev 5 ENEA Institute for Radiation Protection, Bologna 6 Belgian Nuclear Research Centre, Mol 7 IRSN (Institut de Radioprotection et de Sûreté Nucléaire), Fontenay-aux-Roses 8 Electricité de France, Saint-Denis

Résumé

When a set of bioassay data is given to two different dosimetrists, it is likely that these data will be interpreted differently, that different methods and dosimetric models will be applied, and therefore different numerical solutions will be obtained. Thus, it is important for laboratories dealing with internal dosimetry to undergo performance testing procedures to demonstrate the correctness of methods applied and also the consistency of the results with those obtained by other laboratories. In this context the interlaboratory comparisons of bioassay data interpretation are of major importance. Several intercomparison exercises have already been organised at national and international levels. The largest one by now was the "3rd European Intercomparison Exercise on Internal Dose Assessment", which has been organised in the framework of the EULEP/EURADOS Action Group „Derivation of Parameter Values for Application to the New Model of the Human Respiratory Tract for Occupational Exposure“. This intercomparison took into account some aspects which have not been considered in previous intercomparison exercises, such as air monitoring, natural radionuclides, exposure of the public and artificially created cases. Seven case scenarios, dealing with H-3, Sr-90, I-25, Cs-137, Po-210, U-238 and Pu-239, have been analysed by 50 participants, 43 representing 18 European countries and 7 from five countries outside Europe. On average there were 35 responses per case with a total of about 240 answers, this giving a quite good overview on the state of the art of internal dosimetry. The results in terms of intake and committed effective dose were log-normally distributed with the geometric standard deviation ranging from 1.15 for the cases dealing with H-3 and Cs-137, respectively, up to 2.4 for the cases dealing with Pu-239. The ratio between the minimum and the maximum of the reported results ranges from one order of magnitude for the H-3 and Cs-137 cases up to five orders of magnitude for the Pu-239 cases. In general it was found that the spread of the results increases with the radiotoxicity of the involved radionuclides. 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 pattern of intake, and the choice of model. The most important lesson learned from the intercomparison exercise was the need to develop agreed guidelines for internal dose evaluation procedures to promote harmonisation of assessments between organisations and countries. For this reason, recently a project entitled "General guidelines for the estimation of committed effective dose from incorporation monitoring data" (Project Acronym IDEAS) has been initiated in the 5th EU Framework Programme. Specific objectives of the project are to (i) enable dosimetry services across Europe to assess the same radiation dose from any given set of monitoring data, (ii) reduce uncertainties and thus (iii) improve confidence in internal dose assessment.