Background

The determination of internal doses is an essential component of individual monitoring programmes for workers.  It may also be needed for members of the public, who may have intakes of radionuclides in nuclear medicine and also in normal life following accidental releases of radionuclides into the environment.

Assessment of internal doses requires the interpretation of the monitoring data in terms of intake and/or internal dose taking into account many influencing factors and assumptions, such as the physical and chemical characteristics of the radioactive substances, the mode of intake, the biokinetic and energy absorption processes, the individual parameters, etc. 

Because of the large number of influencing factors and assumptions it may happen that two experts come to different results in terms of intake and committed dose for the same set of monitoring data. This was demonstrated in various intercomparison exercises such as the 3rd European Intercomparison Exercise on Internal Dose Assessment which was carried out from 1997 to 1999 within the framework of a joint EULEP-EURADOS Action Group. This intercomparison exercise gave special consideration to the effects of the new models at that time and the choice of input parameters on the assessment of internal doses from monitoring results. 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.

This intercomparison can be considered to represent the state of the art of internal dosimetry in the participating countries at the end of the last century. The results of each case in terms of intake and committed effective dose were found to be 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.

There was a close cooperation between IDEAS and the INDOS group of the ICRP. The INDOS group recognized the need for harmonization of internal dosimetry as well. Thus, a special guidance document for the application of the ICRP recommendations was developed by the INDOS group based in the IDEAS Guidelines. After completion of the guidance document, however, some members of the ICRP claimed the guidance document to be too prescriptive. Thus, in 2007 the guidance document was withdrawn and some members of the INDOS group left the ICRP.