The European intercomparison of in-vivo monitoring laboratories: the EIVIC-2020 project.

The EIVIC project was launched in 2020, and the main goal was the organisation of a European intercomparison of in-vivo monitoring laboratories dealing with direct measurements of gamma-emitting radionuclides incorporated into the body of exposed workers. This project was organised jointly by members of EURADOS Working Group 7 on internal dosimetry (WG7), the Federal Office for Radiation Protection (BfS, Germany) and the Radioprotection and Nuclear Safety Institute (IRSN, France). The objective was to assess the implementation of individual-monitoring requirements in EU Member States on the basis of in-vivo measurements and to gain insight into the performance of in-vivo measurements using whole-body counters. In this context, a total of 41 in-vivo monitoring laboratories from 21 countries, together with JRC (EC) and IAEA participated. The results were submitted in terms of activity (Bq) of the radionuclides identified inside phantoms that were circulated to all participants. The measured data were compared with reference activity values to evaluate the corresponding bias according to the standards ISO 28218 and ISO 13528. In general, the results of the different exercises are good, and most facilities are in conformity with the criteria for the bias and z-scores in the ISO standards. Furthermore, information about technical and organisational characteristics of the participating laboratories was collected to test if they had a significant influence on the reported results.

EURADOS education and training activities.

This paper provides a summary of the Education and Training (E&T) activities that have been developed and organised by the European Radiation Dosimetry Group (EURADOS) in recent years and in the case of Training Courses over the last decade. These E&T actions include short duration Training Courses on well-established topics organised within the activity of EURADOS Working Groups (WGs), or one-day events integrated in the EURADOS Annual Meeting (workshops, winter schools, the intercomparison participants' sessions and the learning network, among others). Moreover, EURADOS has recently established a Young Scientist Grant and a Young Scientist Award. The Grant supports young scientists by encouraging them to perform research projects at other laboratories of the EURADOS network. The Award is given in recognition of excellent work developed within the WGs' work programme. Additionally, EURADOS supports the dissemination of knowledge in radiation dosimetry by promoting and endorsing conferences such as the individual monitoring (IM) series, the neutron and ion dosimetry symposia (NEUDOS) and contributions to E&T sessions at specific events.

EURADOS STRATEGIC RESEARCH AGENDA 2020: VISION FOR THE DOSIMETRY OF IONISING RADIATION.

Since 2012, the European Radiation Dosimetry Group (EURADOS) has developed its Strategic Research Agenda (SRA), which contributes to the identification of future research needs in radiation dosimetry in Europe. Continued scientific developments in this field necessitate regular updates and, consequently, this paper summarises the latest revision of the SRA, with input regarding the state of the art and vision for the future contributed by EURADOS Working Groups and through a stakeholder workshop. Five visions define key issues in dosimetry research that are considered important over at least the next decade. They include scientific objectives and developments in (i) updated fundamental dose concepts and quantities, (ii) improved radiation risk estimates deduced from epidemiological cohorts, (iii) efficient dose assessment for radiological emergencies, (iv) integrated personalised dosimetry in medical applications and (v) improved radiation protection of workers and the public. This SRA will be used as a guideline for future activities of EURADOS Working Groups but can also be used as guidance for research in radiation dosimetry by the wider community. It will also be used as input for a general European research roadmap for radiation protection, following similar previous contributions to the European Joint Programme for the Integration of Radiation Protection Research, under the Horizon 2020 programme (CONCERT). The full version of the SRA is available as a EURADOS report (www.eurados.org).

Validation of a Monte Carlo efficiency calibration procedure for a partial body counter system with a voxel model of the LLNL torso phantom.

Virtual models of real phantoms used with Monte Carlo methods facilitate the calibration and other studies associated with whole-body and partial-body counting systems. In this investigation, a voxel model of an LLNL torso phantom, available physically in the in vivo laboratory at KIT, was created from computed tomography scans. Series of measurements with a high-purity germanium detector and the real torso phantom, loaded with different radioactive organs, have been carried out. Computer simulations of these measurement setups were performed with the aid of MCNPX, using a coarsened voxel phantom and a validated model of the germanium detector. The results of simulations were compared with data from the measurements and an agreement within the uncertainties was found. The voxel model could therefore be validated. The results of the simulations were then used to quantify the activity of (241)Am impurities detected in the liver loaded with (239)Pu.

Development, implementation and quality assurance of biokinetic models within CONRAD.

The work of the Task Group 5.2 'Research Studies on Biokinetic Models' of the CONRAD project is presented. New biokinetic models have been implemented by several European institutions. Quality assurance procedures included intercomparison of the results as well as quality assurance of model formulation. Additionally, the use of the models was examined leading to proposals of tuning parameters. Stable isotope studies were evaluated with respect to their implications to the new models, and new biokinetic models were proposed on the basis of their results. Furthermore, the development of a biokinetic model describing the effects of decorporation of actinides by diethylenetriaminepentaacetic acid treatment was initiated.

Internal dosimetry: towards harmonisation and coordination of research.

The CONRAD Project is a Coordinated Network for Radiation Dosimetry funded by the European Commission 6th Framework Programme. The activities developed within CONRAD Work Package 5 ('Coordination of Research on Internal Dosimetry') have contributed to improve the harmonisation and reliability in the assessment of internal doses. The tasks carried out included a study of uncertainties and the refinement of the IDEAS Guidelines associated with the evaluation of doses after intakes of radionuclides. The implementation and quality assurance of new biokinetic models for dose assessment and the first attempt to develop a generic dosimetric model for DTPA therapy are important WP5 achievements. Applications of voxel phantoms and Monte Carlo simulations for the assessment of intakes from in vivo measurements were also considered. A Nuclear Emergency Monitoring Network (EUREMON) has been established for the interpretation of monitoring data after accidental or deliberate releases of radionuclides. Finally, WP5 group has worked on the update of the existing IDEAS bibliographic, internal contamination and case evaluation databases. A summary of CONRAD WP5 objectives and results is presented here.

EURADOS work on internal dosimetry.

European Radiation Dosimetry Group (EURADOS) Working Group 7 is a network on internal dosimetry that brings together researchers from more than 60 institutions in 21 countries. The work of the group is organised into task groups that focus on different aspects, such as development and implementation of biokinetic models (e.g. for diethylenetriamine penta-acetic acid decorporation therapy), individual monitoring and the dose assessment process, Monte Carlo simulations for internal dosimetry, uncertainties in internal dosimetry, and internal microdosimetry. Several intercomparison exercises and training courses have been organised. The IDEAS guidelines, which describe - based on the International Commission on Radiological Protection's (ICRP) biokinetic models and dose coefficients - a structured approach to the assessment of internal doses from monitoring data, are maintained and updated by the group. In addition, Technical Recommendations for Monitoring Individuals for Occupational Intakes of Radionuclides have been elaborated on behalf of the European Commission, DG-ENER (TECHREC Project, 2014-2016, coordinated by EURADOS). Quality assurance of the ICRP biokinetic models by calculation of retention and excretion functions for different scenarios has been performed and feedback was provided to ICRP. An uncertainty study of the recent caesium biokinetic model quantified the overall uncertainties, and identified the sensitive parameters of the model. A report with guidance on the application of ICRP biokinetic models and dose coefficients is being drafted at present. These and other examples of the group's activities, which complement the work of ICRP, are presented.

PERSONALISED BODY COUNTER CALIBRATION USING ANTHROPOMETRIC PARAMETERS.

Current calibration methods for body counting offer personalisation for lung counting predominantly with respect to ratios of body mass and height. Chest wall thickness is used as an intermediate parameter. This work revises and extends these methods using a series of computational phantoms derived from medical imaging data in combination with radiation transport simulation and statistical analysis. As an example, the method is applied to the calibration of the In Vivo Measurement Laboratory (IVM) at Karlsruhe Institute of Technology (KIT) comprising four high-purity germanium detectors in two partial body measurement set-ups. The Monte Carlo N-Particle (MCNP) transport code and the Extended Cardiac-Torso (XCAT) phantom series have been used. Analysis of the computed sample data consisting of 18 anthropometric parameters and calibration factors generated from 26 photon sources for each of the 30 phantoms reveals the significance of those parameters required for producing an accurate estimate of the calibration function. Body circumferences related to the source location perform best in the example, while parameters related to body mass show comparable but lower performances, and those related to body height and other lengths exhibit low performances. In conclusion, it is possible to give more accurate estimates of calibration factors using this proposed approach including estimates of uncertainties related to interindividual anatomical variation of the target population.

TECHNICAL RECOMMENDATIONS FOR MONITORING INDIVIDUALS FOR OCCUPATIONAL INTAKES OF RADIONUCLIDES.

The TECHREC project, funded by the European Commission, will provide Technical Recommendations for Monitoring Individuals for Occupational Intakes of Radionuclides It is expected that the document will be published by the European Commission as a report in its Radiation Protection Series during 2016. The project is coordinated by the European Radiation Dosimetry Group (EURADOS) and is being carried out by members of EURADOS Working Group 7 (Internal Dosimetry). This paper describes the aims and purpose of the Technical Recommendations, and explains how the project is organised.

THE EURADOS-KIT TRAINING COURSE ON MONTE CARLO METHODS FOR THE CALIBRATION OF BODY COUNTERS.

Monte Carlo (MC) methods are numerical simulation techniques that can be used to extend the scope of calibrations performed in in vivo monitoring laboratories. These methods allow calibrations to be carried out for a much wider range of body shapes and sizes than would be feasible using physical phantoms. Unfortunately, nowadays, this powerful technique is still used mainly in research institutions only. In 2013, EURADOS and the in vivo monitoring laboratory of Karlsruhe Institute of Technology (KIT) organized a 3-d training course to disseminate knowledge on the application of MC methods for in vivo monitoring. It was intended as a hands-on course centered around an exercise which guided the participants step by step through the calibration process using a simplified version of KIT's equipment. Only introductory lectures on in vivo monitoring and voxel models were given. The course was based on MC codes of the MCNP family, widespread in the community. The strong involvement of the participants and the working atmosphere in the classroom as well as the formal evaluation of the course showed that the approach chosen was appropriate. Participants liked the hands-on approach and the extensive course materials on the exercise.

LESSONS LEARNED FROM THE EURADOS SURVEY ON INDIVIDUAL MONITORING DATA AND INTERNAL DOSE ASSESSMENTS OF FOREIGNERS EXPOSED IN JAPAN FOLLOWING THE FUKUSHIMA DAIICHI NPP ACCIDENT.

European Radiation Dosimetry Group e.V. (EURADOS) survey on individual monitoring data and dose assessment has been carried out for 550 foreigners returning home after being exposed in Japan to intakes of radionuclides (mainly (131)I, (132)I, (132)Te, (134)Cs and (137)Cs) as a consequence of the Fukushima Daiichi NPP accident. In vivo and in vitro measurements were performed in their respective countries at an early stage after that accident. Intakes of radionuclides were detected in 208 persons from Europe and Canada, but the committed effective dose E(50) was below the annual dose limit for the public (<1 mSv) in all the cases. Lessons learned from this EURADOS survey are presented here regarding not only internal dosimetry issues, but also the management of the emergency situation, the perception of the risk of health effects due to radiation and the communication with exposed persons who showed anxiety and lack of trust in monitoring data and dose assessments.

Parameter uncertainty analysis of a biokinetic model of caesium.

Parameter uncertainties for the biokinetic model of caesium (Cs) developed by Leggett et al. were inventoried and evaluated. The methods of parameter uncertainty analysis were used to assess the uncertainties of model predictions with the assumptions of model parameter uncertainties and distributions. Furthermore, the importance of individual model parameters was assessed by means of sensitivity analysis. The calculated uncertainties of model predictions were compared with human data of Cs measured in blood and in the whole body. It was found that propagating the derived uncertainties in model parameter values reproduced the range of bioassay data observed in human subjects at different times after intake. The maximum ranges, expressed as uncertainty factors (UFs) (defined as a square root of ratio between 97.5th and 2.5th percentiles) of blood clearance, whole-body retention and urinary excretion of Cs predicted at earlier time after intake were, respectively: 1.5, 1.0 and 2.5 at the first day; 1.8, 1.1 and 2.4 at Day 10 and 1.8, 2.0 and 1.8 at Day 100; for the late times (1000 d) after intake, the UFs were increased to 43, 24 and 31, respectively. The model parameters of transfer rates between kidneys and blood, muscle and blood and the rate of transfer from kidneys to urinary bladder content are most influential to the blood clearance and to the whole-body retention of Cs. For the urinary excretion, the parameters of transfer rates from urinary bladder content to urine and from kidneys to urinary bladder content impact mostly. The implication and effect on the estimated equivalent and effective doses of the larger uncertainty of 43 in whole-body retention in the later time, say, after Day 500 will be explored in a successive work in the framework of EURADOS.

Analysis of the effects of inter-individual variation in the distribution of plutonium in skeleton and liver.

One important parameter for biokinetic plutonium modelling is the ratio between the contents of plutonium in liver and skeleton. Autopsy data show a vast inter-individual variation in the partitioning between these organs. The capacity of recent biokinetic models for plutonium to reproduce these variations was studied. Autopsy data for plutonium amounts in liver and skeleton for both (238)Pu and (239)Pu isotopes can be merged into a single data set following several statistical tests. Simulations with different parameter values generate a mapping between the autopsy values and the model parameters. The observed partitioning distribution can be transformed into a distribution of transfer rates, which would result in the observed data. Besides, the variation in the partitioning between liver and skeleton leads via biliary pathway to a variation in the excretion ratio. This can be used to estimate an individual partitioning factor, which can be used in individual case assessments.

Dead layer thickness characterization of an HPGe detector by measurements and Monte Carlo simulations.

To fully characterize the front dead layer (DL) of an HPGe detector at low photon energy range, its intrinsic efficiency curve was measured using a (241)Am radioactive source in 10-60 keV energy range. A comparison between experimental efficiency and MCNPX results showed that the DL value of 0.4 µm initially quoted by the manufacturer has to be changed to 7.5 µm to reproduce measurements.

Simulation of phoswich detectors using MCNPX and EGSNRC.

The in vivo monitoring Lab at KIT uses two phoswich detectors for routine lung counting. A simplified model of one of them has been implemented in the two Monte Carlo codes EGSnrc and MCNPX. The active part of the detector consists of a crystal of NaI(Tl) and one of CsI(Tl): the energy deposited in both the crystals have been studied to consider the effect of the anticoincidence logic, present in the read-out electronics of the detectors and not yet studied with Monte Carlo simulations. Only the NaI(Tl) crystal has then been used to study the escape peaks at several energies, which are more prominent at low energies. The results from the two codes have been compared. The comparison of the codes predictions for the escape peaks has been then extended using the model of a germanium detector.

Quality management system and accreditation of the in vivo monitoring laboratory at Karslruhe Institute of Technology.

The in vivo monitoring laboratory (IVM) at Karlsruhe Institute of Technology (KIT), with one whole body counter and three partial-body counters, is an approved lab for individual monitoring according to German regulation. These approved labs are required to prove their competencies by accreditation to ISO/IEC 17025:2005. In 2007 a quality management system (QMS), which was successfully audited and granted accreditation, was set up at the IVM. The system is based on the ISO 9001 certified QMS of the central safety department of the Research Centre Karlsruhe the IVM belonged to at that time. The system itself was set up to be flexible and could be adapted to the recent organisational changes (e.g. founding of KIT and an institute for radiation research) with only minor effort.

Comparison of stretched and sitting configurations for partial-body measurements.

The partial-body counter currently installed at KIT is under redesign to add whole-body counting capabilities and replace the current phoswich detectors with HPGe ones, capable of detecting low energy photons ((210)Pb, (241)Am). Different configurations for the positioning of the subject have been tested with the aid of Monte Carlo simulations and the performances attainable with a sitting and a lying configuration were compared. The optimal placement of the detectors was also defined. The simulations were used to estimate the counting efficiencies and also to estimate the Compton scattering produced by (40)K, in turn used to calculate the minimum detectable activities.

Theoretical assessment of whole body counting performances using numerical phantoms of different gender and sizes.

A goal of whole body counting (WBC) is the estimation of the total body burden of radionuclides disregarding the actual position within the body. To achieve the goal, the detectors need to be placed in regions where the photon flux is as independent as possible from the distribution of the source. At the same time, the detectors need high photon fluxes in order to achieve better efficiency and lower minimum detectable activities. This work presents a method able to define the layout of new WBC systems and to study the behaviour of existing ones using both detection efficiency and its dependence on the position of the source within the body of computational phantoms.

New developments in internal dosimetry models.

This paper describes new biokinetic and dosimetric models, especially those being developed by ICRP which will be used in the forthcoming documents on Occupational Intakes of Radionuclides. It also presents the results of a working group within the European project CONRAD which is being continued within EURADOS. This group is implementing the new models, performing quality assurance of the model implementation (including their description) and giving guidance to the scientific community on the application of the models for individual dose assessment.

EURADOS coordinated action on research, quality assurance and training of internal dose assessments.

EURADOS working group on 'Internal Dosimetry (WG7)' represents a frame to develop activities in the field of internal exposures as coordinated actions on quality assurance (QA), research and training. The main tasks to carry out are the update of the IDEAS Guidelines as a reference document for the internal dosimetry community, the implementation and QA of new ICRP biokinetic models, the assessment of uncertainties related to internal dosimetry models and their application, the development of physiology-based models for biokinetics of radionuclides, stable isotope studies, biokinetic modelling of diethylene triamine pentaacetic acid decorporation therapy and Monte-Carlo applications to in vivo assessment of intakes. The working group is entirely supported by EURADOS; links are established with institutions such as IAEA, US Transuranium and Uranium Registries (USA) and CEA (France) for joint collaboration actions.