STRUCTURE OF THE PROJECT
Work Package 1 entitled Collection of incorporation cases was devoted to the collection of data by means of bibliographic research (survey of the open literature), contacting and collecting data from specific organisations and using information from existing databases on incorporation cases. Two databases were prepared and some reference cases for the performance of WP 3 selected.
The first database is the so-called IDEAS Bibliography Database, which collects information present in the open literature or in other reports dealing with internal contamination cases. The structure of the database permits the user to view the database, search it and input new data. More than 500 references have been collected. From these, references were selected that contained descriptions of cases suitable for internal dose assessment (well documented cases).
The second database, the IDEAS Internal Contamination Database, was set up to collate, in a given format, the descriptions of the selected well documented cases (contamination scenarios and follow up measurements). Its structure permits the collection of all the information needed for internal dose assessment i.e. the description of the working area and characteristics of the work, date and modalities of the initiating event, actions taken, physical and chemical characteristics of the contaminant, etc. For each contamination case, the participating partners entered the available information and monitoring data into a structured spreadsheet file for transfer into the database. Currently this database contains more than 200 cases.
Besides the use of the databases for the purpose of the IDEAS project, they also provide useful tools for the scientific community interested in internal dosimetry for studying internal contamination cases. They have been put in a restricted web page presently available to the IDEAS partners only, but will be made accessible to everybody in the near future.
In Work Package 2 (Preparation of evaluation software) an existing computer code IMIE [Berkovski 2002] was to be used as a platform for testing existing methods and approaches for bioassay data interpretation and methods developed in the project.
The IMIE (Individual Monitoring of the Internal Exposure) computer code was chosen for evaluation of the selected reference case studies. IMIE was developed for the purposes of retrospective dosimetry. It gives to the assessor a powerful and flexible tool for the analysis and interpretation of multiple bioassay measurements. IMIE helps the assessor to make judgements about the history of intakes and corresponding doses on the basis of individual monitoring data. In particular it permits the user to review and compare simultaneously different possible exposure condition combinations and to select the degree of automation from fully automated to completely manual. Within WP2 the IMIE code was improved and fitted to the special requirements of the IDEAS project. For example, a new optimisation algorithm of numerical deconvolution of monitoring data was developed and a new probabilistic algorithm based on statistical methods was introduced. WP2 thus provided the participants with a useful and flexible tool for the dose evaluation process of WP3.
In Work Package 3, Evaluation of incorporation cases, selected reference cases from WP1 were evaluated using the IMIE software provided by WP2. The current version of another computer code, IMBA Expert™ [Birchall et al, 2003; Strom 2002], was also made available to the participants to support the evaluation procedures.
The choice of cases to be evaluated was made on the basis of the characteristics of the radioisotope or mixture present in the case scenario, the complexity present in the monitoring data set (e.g. multiple types of monitoring data) and special issues to be considered in the guidelines. The evaluation and analysis of selected cases was carried out in accordance with the scheduled work program of WP3. For this purpose 68 cases covering different circumstances and 17 radionuclides were selected from the IDEAS Internal Contamination Database and distributed among the partners for detailed evaluation. Fifty-two of the 68 selected cases have been evaluated, 29 of them by two or more assessors. For some cases the same assessor provided additional evaluations related to different radioisotopes.
The selected cases were evaluated using the IMIE and IMBA Expert™ codes using different assumptions and making relevant comments. The best estimates of the calculated intake and committed effective dose were given for each case, together with notes on important issues related to the guidelines. The results were presented in detail as Microsoft® Word documents and summarised in Microsoft® Excel files in a fixed format. They were collected in the IDEAS Evaluation of Cases Database established for this purpose. Ninety-five independent evaluations on 52 cases have been collected in the database. The IDEAS Evaluation of Cases Database provides possibilities, among others, to view the results of evaluations, to search within the database according to different aspects, to compare different evaluations on the same case and has links to the IDEAS Internal Contamination Database.
From the evaluations various items were identified where guidance is needed. One important set refer to the handling of the monitoring data (i.e. assessment of uncertainty on data, handling of data below the lower limit of detection, identification of rogue data etc.). another set refers to the definition of parameter values for the evaluation of the monitoring data (i.e. definition of the time pattern of intake, identification of the pathway of intake, selection of absorption type, AMAD value, f1 values and GI tract transit times etc.). Other items include special aspects of data handling, such as the handling of early data, data affected by DTPA therapy, and 241Am ingrowth in vivo due to 241Pu decay.
The task of WP 3 was completed by defining the general features of the evaluation of monitoring data, thus providing a basis for the general guidelines. Nevertheless the IDEAS Evaluation of Cases Database will be open for further entries after completion of the project. Thus the IDEAS Evaluation of Cases Database of WP 3 would be together with the IDEAS Bibliography Database and the IDEAS Internal Contamination Database of Work Package 1 a powerful tool not only for the project itself but also for education and training of internal dose assessors worldwide.
In Work Package 4, Development of the general guidelines, the partners derived a common strategy for the evaluation of monitoring data, drafted the general guidelines and discussed it with internal dosimetry experts by means of a “virtual” workshop based on the internet (www.ideas-workshop.de). The discussion was used to improve the common strategy and the general guidelines.
Some of the IDEAS contractors were members of the ICRP Working Party on Bioassay Interpretation, which was involved in the development of an ICRP Supporting Guidance Document on The Interpretation of Bioassay Data. The aim is for this to complement the planned Occupational Intakes of Radionuclides (OIR) document that will replace ICRP Publications 30, 54, 68 and 78. Work on the ICRP Guidance Document is now carried out within the ICRP Committee 2 Task Group on Internal Dosimetry (INDOS), of which several members of the IDEAS consortium are also members. The aims of this Guidance Document are similar to those of the IDEAS project. Thus the development of both documents has been done in close cooperation to ensure that the IDEAS guidelines and the ICRP Guidance Document are consistent with each other. There are, however some difference in scope. In particular, the ICRP Guidance Document will relate to the forthcoming ICRP Recommendations and the revised biokinetic and dosimetric models being applied in the OIR document (such as the Human Alimentary Tract Model, HATM), whereas the IDEAS Guidelines relate to the current models. However, the draft ICRP Guidance Document is following similar principles and a structured approach to assessments, based on the IDEAS Guidelines.
In Work Package 5 (Practical testing of general guidelines) the validity of the draft guidelines was tested by means of a dose assessment intercomparison exercise open to participants from all over the world (4th European Intercomparison Exercise on Internal Dose Assessment).
In parallel, the IAEA had planned to organise a new intercomparison exercise on internal dose assessment among the member states of the Agency. In view of the common goals many advantages were identified in organising a joint IDEAS/IAEA exercise. This would save effort and costs for both the IDEAS project and the IAEA and it would probably result in the largest intercomparison exercise ever, providing much more information about the state of the art of internal dosimetry than an exercise on a European scale could do. The joint IDEAS/IAEA intercomparison exercise was organised in a similar way to the IDEAS Virtual Workshop on the internet (www.ideas-workshop.de).
The results of the joint IDEAS/IAEA intercomparison exercise were discussed with the participants in a workshop organised by the IAEA in Vienna. Based on these discussions the IDEAS general guidelines were finalised.
The last step of WP5 was the publication of the final version of the IDEAS general guidelines and their submission to national and international bodies for approval.