Quality assurance for the use of computational methods in dosimetry: activities of EURADOS Working Group 6 'Computational Dosimetry'.

Working Group (WG) 6 'Computational Dosimetry' of the European Radiation Dosimetry Group promotes good practice in the application of computational methods for radiation dosimetry in radiation protection and the medical use of ionising radiation. Its cross-sectional activities within the association cover a large range of current topics in radiation dosimetry, including more fundamental studies of radiation effects in complex systems. In addition, WG 6 also performs scientific research and development as well as knowledge transfer activities, such as training courses. Monte Carlo techniques, including the use of anthropomorphic and other numerical phantoms based on voxelised geometrical models, play a strong part in the activities pursued in WG 6. However, other aspects and techniques, such as neutron spectra unfolding, have an important role as well. A number of intercomparison exercises have been carried out in the past to provide information on the accuracy with which computational methods are applied and whether best practice is being followed. Within the exercises that are still ongoing, the focus has changed towards assessing the uncertainty that can be achieved with these computational methods. Furthermore, the future strategy of WG 6 also includes an extension of the scope toward experimental benchmark activities and evaluation of cross-sections and algorithms, with the vision of establishing a gold standard for Monte Carlo methods used in medical and radiobiological applications.

Internal dose assessments: uncertainty studies and update of ideas guidelines and databases within CONRAD project.

The work of Task Group 5.1 (uncertainty studies and revision of IDEAS guidelines) and Task Group 5.5 (update of IDEAS databases) of the CONRAD project is described. Scattering factor (SF) values (i.e. measurement uncertainties) have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Based upon this work and other published values, default SF values are suggested. Uncertainty studies have been carried out using both a Bayesian approach as well as a frequentist (classical) approach. The IDEAS guidelines have been revised in areas relating to the evaluation of an effective AMAD, guidance is given on evaluating wound cases with the NCRP wound model and suggestions made on the number and type of measurements required for dose assessment.

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.

Development and application of anthropomorphic voxel phantom of the head for in vivo measurement.

The in vivo measurement of the activity deposited in the skeleton is a very useful source of information on human internal contaminations with transuranic elements, e.g. americium 241, especially for long time periods after intake. Measurements are performed on the skull or the larger joints such as the knee or elbow. The paper deals with the construction of an anthropomorphic numerical phantom based on CT scans, its potential for calibration and the estimation of the uncertainties of the detection system. The density of bones, activity distribution and position of the detectors were changed in individual simulations in order to estimate their effects on the result of the measurement. The results from simulations with the numerical phantom were compared with the results of physical phantoms.

Evaluation of committed effective doses from internal contamination of 241Am using experimentally determined parameters of the contaminant.

Internal contamination of workers with 241Am has occurred a few times since the beginning of the 1970s, mainly in the workplace where radionuclide sources were produced, and later on, also during liquidation of radioactive waste. Contamination in workers was measured in vivo and bioassay was performed. Solubility of aerosol in lungs was studied by in vitro dissolution test with a simulant solution of the extracellular airway lining fluids. Model calculation for the estimation of intakes was done with the experimentally obtained parameters of aerosol, with modified times of intake, with scattering factors, including Types A and B errors, and with corrections on skull size for in vivo measurements. For most cases, an acceptable fit to the experimental data was obtained; for two cases with intakes taking place long time ago ( approximately 30 y), some changes in the model are necessary.

Analysis of a case of internal contamination with cobalt radioisotopes.

Internal contamination by compounds of cobalt radioisotopes occurs time to time at nuclear power plants. Intakes and committed effective doses are estimated by biokinetic models described in ICRP publications. The paper deals with a case of internal contamination of a worker engaged in a maintenance task at NPP Dukovany. In this case significant discrepancy was observed between intakes based on various datasets (whole body counting, analysis of urine and faeces) when default model setting was used. The reason of this phenomenon was searched for. Three different least square methods of fits were used to find out possible effect of a fitting method. The measured data were fitted by set of biokinetic functions, which covered all intake ways (ingestion and inhalation) and types (M, S, different AMADs and different f1) of the contaminant. The biokinetic model of cobalt needs further improvements as to find better agreement between data fit from direct measurements and bioassay.

CRUCIAL PARAMETERS FOR PROPER SIMULATION OF THE DETECTOR USED IN IN VIVO MEASUREMENTS.

Mathematical calibration is an increasingly popular technique among laboratories with a whole- or partial-body counters. A mathematical calibration employing a voxel phantom and Monte Carlo radiation transport code simulations has many benefits and can overcome many limitations of detector efficiency calibration using physical anthropomorphic phantoms. This publication tries to identify key factors for detector modelling. The influence of such parameters depends on energy and thus is studied in the gamma energy range of detectable radionuclides, i.e. from 15 keV to 1.5 MeV.

A simple physical phantom for an intercomparison exercise on 241Am activity determination in the skull.

A simple hemispherical phantom has been designed and prepared for the EURADOS intercomparison exercise on (241)Am activity determination in the skull (2011-13). The phantom consists of three parts that substitute bone and soft tissues. (241)Am is deposited on the surfaces of the bone-substituting part. The design and assumed composition of phantom parts are discussed. A preparation of the voxel representation of the phantom is described. The spectrum of a real measurement of the physical phantom agrees well with the simulation. The physical phantom, and its voxel representation, is provided to the participants of the intercomparison exercise.

Head calibration phantoms for actinides: measurements and simulations.

The paper deals with the physical skull phantoms Bundesinstitut fuer Strahlenschutz and BPAM-001, which are used in order to calibrate in vivo detection systems for estimation of (241)Am activity in the skeleton. Their voxel models were made and used in the Monte Carlo simulations. The results of the simulation were compared with measurements and reasonable agreement was observed. Several aspects such as materials and source distributions used in the models were discussed.

Results of an internal dose assessment intercomparison exercise after a EURADOS/IAEA training course.

A training course named 'European Radiation Dosimetry Group/International Atomic Energy Agency Advanced Training Course on Internal Dose Assessment' was held in Czech Technical University in Prague from 2 to 6 February 2009. The course, jointly organised by the two organisations, had the aim of providing guidance on the application of IDEAS guidelines and of disseminating the results of EC CONRAD Project in relation to internal dosimetry (Work Package 5). At the end of the course a dose assessment exercise was proposed to participants. Four artificial cases, named exercises left to participants, were used to check the capabilities of application of the IDEAS guidelines, gained by participants during the event. The participants had to use both hand calculations and dedicated software, in limited time (7 h). Forty per cent of participants had solved all four cases in the allotted time. The results of the dose assessment were analysed to gain experience in types of errors assessors may make during the evaluations. The result of this intercomparison exercise was promising: half of the results in each case were equal to the 'reference evaluation estimate', which was obtained by applying the guidelines correctly.

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.

Comparison of geometries for in vivo measurements of actinides in the skull.

In vivo measurement of actinide activity in the skeleton is a valuable source of information on human internal contamination. Estimates of skeleton activity are based on measurements of the knee, elbow or skull. Different laboratories use different measurement geometries. Different calibration phantoms and detectors are used, making a comparison of detection efficiencies rather difficult. This paper compares various head measurement geometries when using MC simulations with a voxel head phantom.

Microwave applicators for thermotherapy of benign prostatic hyperplasia: a primer.

Microwave thermotherapy for treatment of benign prostatic hyperplasia (BPH) is becoming increasingly more common. This article provides an introduction to the functional principles of microwave antennas for delivery of energy to the prostatic gland. Different antenna designs (monopole, dipole, and helical coil types) and impedance matching are discussed.

Pharmacokinetic profile of the immunomodulating compound adamantylamide dipeptide (AdDP), a muramyl dipeptide derivative in mice.

A pharmacokinetic profile of 14C-AdDP with uniformly labelled alanine was investigated. It was shown that the distribution phase after an i.v. administration is very short with a half-life of 2.1 min. The half-life of elimination phase after the i.v. administration is about 2.85 hours, that is longer than those of MDP and its derivatives. The total body clearance (30 ml/min/kg) is caused predominantly by metabolism of the compound. All the radioactivity found in urine in a 48 hours interval after a s.c. administration represents only 3.1% of the administered dose. Only a smaller part of the excreted radioactivity is formed by unmetabolised AdDP. The concentration curve after a s.c. administration is characterized by a very fast absorption with a half-life shorter than 1 minute. The distribution and elimination phases are prolonged (20 min, 11 hours respectively) in comparison with an i.v. injection. The decreased absolute bioavailability after a s.c. administration (65%) is probably not biologically significant because of a slower release of the compound from the site of the s.c. administration. A relatively very high radioactivity was found in liver, kidney, thymus, spleen and brain very soon which suggest a very good penetration into tissues. It is an agreement with the high apparent distribution volume of peripheral compartment and higher lipophilicity of AdDP as compared to MDP.