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IDEAS Report Summary

Project ID: FIKR-CT-2001-00160
Funded under: FP5-EAECTP C
Country: Italy

General guideline

The consortium collated and analysed experience on the assessment of internal dose from incorporation monitoring data. A wide range of radionuclides was covered, with emphasis on the actinides (e.g. uranium, plutonium), fission products (e.g. caesium, strontium) and activation products (e.g. cobalt). From this experience a general philosophy for the evaluation of incorporation monitoring data has been derived based on the following principles: (i) Harmonisation: A well-defined procedure is needed and for this reason the process is defined here primarily by means of a series of flow-charts. For routine monitoring situations, where typically there is only one measurement relating to each intake, it is reasonably straightforward to define a procedure.

However, in special monitoring situations, where typically there is more than one measurement and quite possibly more than one type of measurement different options for data handling can easily lead to different evaluated doses, even when the same model, parameter values and software are used. Proposals are made here for a systematic approach to dose assessment in all these situations. (ii) Accuracy: It is recognised that the uncertainties associated with assessed internal dose can be considerable, especially for the actinides, which are difficult to detect in the body and have relatively high dose coefficients. If the initial estimate of dose exceeds 1mSv, it could well be that the possibility of a substantially higher dose (e.g. 6mSv) cannot easily be excluded. It is then important to make best use of the available information. (iii) Proportionality: The effort applied to the evaluation of incorporation monitoring data should broadly correspond to the expected level of exposure, and the complexity of the case.

On the one hand, if the exposure is likely to be very low with respect to the dose limits, simple evaluation procedures with a relatively high uncertainty may be applied. On the other hand, if the monitoring values indicate the exposure to be close to or even above the dose limits, more sophisticated evaluation procedures will need to be applied. Based on this general philosophy the following "Levels of task" has been defined: Level 0: Annual dose <0.1mSv. No evaluation of dose needed. Level 1: Simple, "reference" evaluation, with ICRP defaults used for all parameter values, except where there is better a priori information available (annual dose typically 0.1 - 1mSv). Level 2: Sophisticated evaluation using additional information to give more realistic assessment of dose; comparisons are made of the model predictions with the data, to choose between alternative parameter values, or to find optimum parameter values (dose from the intake typically 1 - 6mSv). Level 3: More sophisticated evaluation, which applies to cases where there are comprehensive data available, as would be the situation after an accident. The evaluation is an extension of Level 2, typically to parameters relating to the subject. The fundamental approach at this Level is to adjust the model parameter values systematically, until the goodness of fit is acceptable (dose from the intake typically > 6mSv). Based on the "Level-of-task-structure" the General Guidelines have been defined. These guidelines provide: (i) background information about the biokinetic models and the corresponding bioassay functions which should be used for the interpretation of incorporation monitoring data, (ii) detailed information about the handling of the monitoring data, including general aspects considering the handling of single data and multiple data sets, the handling of extended exposures and the number and type of data required for the dose assessment and special aspects considering the processing of data before use, the assessment of the uncertainty on data, the handling of data below the limits of detection, the handling of data influenced by chelation therapy and the identification of rogue data. The general guidelines are illustrated by well-defined flowcharts, giving detailed guidance to the assessors on how to evaluate the incorporation monitoring data in any situation. Potential end-users and applications.

It is considered that there are three groups of potential users of the guidelines: (1) Health physicists who perform routine and special incorporation monitoring in order to assess the internal dose due to the occupational handling of radioactive materials or due to incidental or accidental intakes. (2) Groups of experts involved in developing guidance or standards relating to exposure to radioactive materials, in particular members of the ICRP Task Group on Internal Dosimetry, who are developing revisions of ICRP Publications 30/68 and 54/78. (3) National and international authorities who define and control radiation protection standards and procedures.

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