Automatic application of ICRP biokinetic models in voxel phantoms for in vivo counting and internal dose assessment

As part of the improvement of calibration techniques of in vivo counting, the Laboratory of Internal Dose Assessment of the Institute of Radiological Protection and Nuclear Safety has developed a computer tool, 'OEDIPE', to model internal contamination, to simulate in vivo counting and to calculate internal dose. The first version of this software could model sources located in a single organ. As the distribution of the contamination evolves from the time of intake according to the biokinetics of the radionuclide, a new facility has been added to the software first to allow complex heterogeneous source modelling and then to automatically integrate the distribution of the contamination in the different tissues estimated by biokinetic calculation at any time since the intake. These new developments give the opportunity to study the influence of the biokinetics on the in vivo counting, leading to a better assessment of the calibration factors and the corresponding uncertainties.     

Practical application of the ICRP Human Respiratory Tract Model

The ICRP Publication 66 Human Respiratory Tract Model (HRTM) has been applied to calculate dose coefficients and bioassay functions using default values of parameters relating to the material and the subjects. The ICRP Task Group on Internal Dosimetry (INDOS) has developed a guidance document on application of the HRTM in situations where using specific information can improve dose assessments. INDOS is now revising the worker exposure documents (ICRP Publications 68 and 78). Application of the HRTM requires a review of the lung-to-blood absorption characteristics of inhaled radionuclides. Where appropriate, compound-specific absorption parameter values will be derived, and other compounds will be assigned to default Types using current information. Although no major changes to the HRTM are envisaged, this revision provides an opportunity for some refining and updating in the light of experience and new information.     

Italian intercomparison exercise on internal dose assessment

In 2001, the Radiation Protection Institute of ENEA promoted an Italian intercomparison exercise on internal dose assessment addressed to the qualified experts in radiation protection, following the coming into force in Italian law of the EURATOM 96/29 Directive. Five case studies of occupational exposure related to the Italian situation are used. The considered radioisotopes are: 60Co, 89Sr, 125I, 131I, and 222Rn + NORM (238U-235U-232Th). Data related to WBC, thyroid and urine excretion measurements, as well as radionuclide air concentration in the workplace, are provided to the participants. The results related to medical, industrial and Rn occupational exposure are well represented as means of log-normal distributions with values of the geometric standard deviation less than 2. A wider spread of results is present for the evaluation of occupational exposure to NORM.     

A computational study of the urinary excretion rates for 339Pu using new ICRP internal dosimetry models

A computational study of the urinary excretion rates for 239Pu has been carried out using a methodology which involved the solution of a complete compartmental model describing the biokinetic behaviour of inhaled plutonium aerosols in the human body. The methodology, after proper validation, was applied to investigate the dependence of urinary excretion rates for 239Pu on the transfer rates given in the complete compartmental model. For this purpose, the default values of the transfer/absorption rates were modified by factors of 2 and 4 and urinary excretion rates were computed on 1, 10, 100, 1000 and 10,000 d post-intake. The percentage variations in the urinary excretion rates as a result of the modified transfer rates were computed for exposures to Type M and S aerosols of 239Pu. These results facilitated the identification of parameters significantly affecting the short-term and long-term urinary excretion rates. In addition, time variations of the predicted ratios of 239Pu activity in daily urine to that in blood (excretion ratios) were studied for the three biokinetic models of plutonium: the ICRP 67 model, the modified ICRP 67 model with the compartment STI to urinary bladder removed and Luciani and Polig's model. All the computational results are presented and discussed in this paper.     

The ICRP protection quantities, equivalent and effective dose: their basis and application

Equivalent and effective dose are protection quantities defined by the The International Commission on Radiological Protection (ICRP). They are frequently referred to simply as dose and may be misused. They provide a method for the summation of doses received from external sources and from intakes of radionuclides for comparison with dose limits and constraints, set to limit the risk of cancer and hereditary effects. For the assessment of internal doses, ICRP provides dose coefficients (Sv Bq(-1)) for the ingestion or inhalation of radionuclides by workers and members of the public, including children. Dose coefficients have also been calculated for in utero exposures following maternal intakes and for the transfer of radionuclides in breast milk. In each case, values are given of committed equivalent doses to organs and tissues and committed effective dose. Their calculation involves the use of defined biokinetic and dosimetric models, including the use of reference phantoms representing the human body. Radiation weighting factors are used as a simple representation of the different effectiveness of different radiations in causing stochastic effects at low doses. A single set of tissue weighting factors is used to take account of the contribution of individual organs and tissues to overall detriment from cancer and hereditary effects, despite age- and gender-related differences in estimates of risk and contributions to risk. The results are quantities that are not individual specific but are reference values for protection purposes, relating to doses to phantoms. The ICRP protection quantities are not intended for detailed assessments of dose and risk to individuals. They should not be used in epidemiological analyses or the assessment of the possibility of occurrence and severity of tissue reactions (deterministic effects) at higher doses. Dose coefficients are published as reference values and as such have no associated uncertainty. Assessments of uncertainties may be appropriate in specific analyses of doses and risks and in epidemiological studies.     

ICRP recommendations on 'Managing patient dose in digital radiology'

The International Commission on Radiological Protection (ICRP) approved the publication of a document on 'Managing patient dose in digital radiology' in 2003. The paper describes the content of the report and some of its key points, together with the formal recommendations of the Commission on this topic. With digital techniques exists not only the potential to improve the practice of radiology but also the risk to overuse radiation. The main advantages of digital imaging: wide dynamic range, post-processing, multiple viewing options, electronic transfer and archiving possibilities are clear but overexposures can occur without an adverse impact on image quality. It is expected that the ICRP report helps to profit from the benefits of this important technological advance in medical imaging with the best management of radiation doses to the patients. It is also expected to promote training actions before the digital techniques are introduced in the radiology departments and to foster the industry to offer enough technical and dosimetric information to radiologists, radiographers and medical physicists to help in the optimisation of the imaging.     

IAEA/IDEAS intercomparison exercise on internal dose assessment

An Internet based intercomparison exercise on assessment of occupational exposure due to intakes of radionuclides has been performed to check the applicability of the 'General Guidelines for the Assessment of Internal Dose from Monitoring Data' developed by the IDEAS group. There were six intake cases presented on the Internet and 81 participants worldwide reported solutions to these cases. Results of the exercise indicate that the guidelines have a positive influence on the methodologies applied for dose assessments and, if correctly applied, improve the harmonisation of assessed doses.     

New method of voxel phantom creation: application for whole-body counting calibration and perspectives in individual internal dose assessment

The purpose of this work is to present an innovative approach for the creation and application of voxel phantoms associated with the Monte Carlo calculation (MCNP) for the calibration of whole-body counting systems dedicated to the measurement of fission and activation products. The new method is based on a graphical user interface called 'OEDIPE' that allows to simulate a whole measurement process using all measurement parameters, the final goal being to approach a numerical calibration of the facilities. The creation of voxel phantoms and validation of the method are presented in this paper using the IGOR phantom. Finally, the efficiency of the method is discussed, in particular, with the perspective of validating IGOR as a suitable human-equivalent phantom and for the assessment of uncertainties in dose estimation due to the inhomogeneous distribution of activity in the body, correlated to the bio-kinetic behaviour of the radionuclides.     

A structured approach for the assessment of internal dose: the IDEAS guidelines

The need for harmonisation of the procedures for internal dose assessment has been recognised within an EU research project under the 5th Framework Programme. The aim of the IDEAS project was to develop general guidelines for standardising assessments of intakes and internal doses. It started in October 2001 and ended in June 2005. The project is closely related to some goals of the work of Committee 2 of the International Commission on Radiological Protection and since 2003 there has been close co-operation between the two groups. The general philosophy of the guidelines is focusing on the principles of harmonisation, accuracy and proportionality. The proposed system of 'level of task' to structure the approach of internal dose evaluation is also reported. Some details of the internal structure of the guidelines for the different pathways of intake are provided.     

The work of committee 2 of ICRP on internal dosimetry

Following publication of new recommendations by ICRP, a series of publications on Occupational Intakes of Radionuclides (OIR) will give both dose coefficients for intakes of radionuclides and data for the interpretation of bioassay information. Account will be taken of revised tissue weighting factors given in the new recommendations and a number of additional developments. These include new human phantoms based upon medical imaging data for calculating doses to body tissues and the new Human Alimentary Tract Model. In addition, parameter values for the Human Respiratory Tract Model are being reviewed, radionuclide decay data are being updated and systemic models for a number of elements revised to take account of more recent data and to provide models that are appropriate for both dosimetry and for bioassay interpretation. The OIR series of publications will be accompanied by a supporting Guidance Document that will give advice on the interpretation of bioassay data.     

Voxel-based models representing the male and female ICRP reference adult--the skeleton

For the forthcoming update of organ dose conversion coefficients, the International Commission on Radiological Protection (ICRP) will use voxel-based computational phantoms due to their improved anatomical realism compared with the class of mathematical or stylized phantoms used previously. According to the ICRP philosophy, these phantoms should be representative of the male and female reference adults with respect to their external dimensions, their organ topology and their organ masses. To meet these requirements, reference models of an adult male and adult female have been constructed at the GSF, based on existing voxel models segmented from tomographic images of two individuals whose body height and weight closely resemble the ICRP Publication 89 reference values. The skeleton is a highly complex structure of the body, composed of cortical bone, trabecular bone, red and yellow bone marrow and endosteum ('bone surfaces' in their older terminology). The skeleton of the reference phantoms consists of 19 individually segmented bones and bone groups. Sub-division of these bones into the above-mentioned constituents would be necessary in order to allow a direct calculation of dose to red bone marrow and endosteum. However, the dimensions of the trabeculae, the cavities containing bone marrow and the endosteum layer lining these cavities are clearly smaller than the resolution of a normal CT scan and, thus, these volumes could not be segmented in the tomographic images. As an attempt to represent the gross spatial distribution of these regions as realistically as possible at the given voxel resolution, 48 individual organ identification numbers were assigned to various parts of the skeleton: every segmented bone was subdivided into an outer shell of cortical bone and a spongious core; in the shafts of the long bones, a medullary cavity was additionally segmented. Using the data from ICRP Publication 89 on elemental tissue composition, from ICRU Report 46 on material mass densities, and from ICRP Publication 70 on the distribution of the red bone marrow among and marrow cellularity in individual bones, individual elemental compositions for these segmented bone regions were derived. Thus, most of the relevant source and target regions of the skeleton were provided. Dose calculations using these regions will be based on fluence-to-dose response functions that are multiplied with the particle fluence inside specific bone regions to give the dose quantities of interest to the target tissues.     

Application of IDEAS guidelines: the IDEAS/IAEA intercomparison exercise on internal dose assessment

As part of the EU Fifth Framework Programme IDEAS project 'General Guidelines for the Evaluation of Incorporation Monitoring Data', and in collaboration with the International Atomic Energy Agency, a new intercomparison exercise for the assessment of doses from intakes of radionuclides was organised. Several cases were selected, to cover a wide range of practices in the nuclear fuel cycle and medical applications. The cases were: (1) acute intake of HTO, (2) acute inhalation of the fission products 137Cs and 90Sr, (3) acute inhalation of 60Co, (4) repeated intakes of 131I, (5) intake of enriched uranium and (6) single intake of Pu isotopes and 241Am. This intercomparison exercise especially focused on the effect of the Guidelines proposed by the IDEAS project for harmonisation of internal dosimetry.     

Worker inhalation dose coefficients for radionuclides not previously identified in ICRP publication 68

While inhalation dose coefficients are provided for about 800 radionuclides in International Commission on Radiological Protection (ICRP) Publication 68, many radionuclides of practical dosimetric interest for facilities such as high-energy proton accelerators are not specifically addressed, nor are organ-specific dose coefficients tabulated. The ICRP Publication 68 dosimetry concepts are used, along with updated radiological decay data and metabolic data, to calculate committed equivalent dose coefficients [h(T)(50)] and committed effective dose coefficients [e(50)] for radionuclides produced at the Oak Ridge National Laboratory's Spallation Neutron Source.     

General guidelines for the assessment of internal dose from monitoring data: progress of the IDEAS project

In recent major international intercomparison exercises on intake and internal dose assessments from monitoring data, the results calculated by different participants varied significantly. Based on this experience the need for harmonisation of the procedures has been formulated within an EU 5th Framework Programme research project. The aim of the project, IDEAS, is to develop general guidelines for standardising assessments of intakes and internal doses. The IDEAS project started in October 2001 and ended in June 2005. The project is closely related to some goals of the work of Committee 2 of the ICRP and since 2003 there has been close cooperation between the two groups. To ensure that the guidelines are applicable to a wide range of practical situations, the first step was to compile a database of well-documented cases of internal contamination. In parallel, an improved version of an existing software package was developed and distributed to the partners for further use. A large number of cases from the database was evaluated independently by the partners and the results reviewed. Based on these evaluations, guidelines were drafted and discussed with dosimetry professionals from around the world by means of a virtual workshop on the Internet early in 2004. The guidelines have been revised and refined on the basis of the experiences and discussions in this virtual workshop. The general philosophy of the Guidelines is presented here, focusing on the principles of harmonisation, optimisation and proportionality. Finally, the proposed Levels of Task to structure the approach of internal dose evaluation are reported.     

Technical basis for using nose swab bioassay data for early internal dose assessment

One of the challenges to the dose assessment team in response to an inhalation incident in the workplace is to provide the occupational physicians, operational radiation protection personnel and line managers with early estimates of radionuclide intakes so that appropriate consequence management and mitigation can be done. For radionuclides such as Pu, where in vivo counting is not adequately sensitive, other techniques such as the measurement of removable radionuclide from the nasal airway passages can be used. At Los Alamos National Laboratory (LANL), nose swabs of the ET1 region have been used routinely as a first response to airborne Pu releases in the workplace, as well as for other radionuclides. This paper presents the results of analysing over 15 years of nose swab data, comparing these with dose assessments performed using the Bayesian methods developed at LANL. The results provide empirical support for using nose swab data for early dose assessments. For Pu, a rule of thumb is a dose factor of 0.8 mSv Bq(-1), assuming a linear relationship between nasal swab activity and committed effective dose equivalent. However, this value is specific to the methods and models used at LANL, and should not be applied directly without considering possible differences in measurement and calculation methods.     

Evaluation of scattering factor values for internal dose assessment following the IDEAS guidelines: preliminary results

The IDEAS Guidelines for the assessment of internal doses from monitoring data suggest default measurement uncertainties (i.e. scattering factors, SFs) to be used for different types of monitoring data. However, these default values were mainly based upon expert judgement. In this paper, SF values have been calculated for different radionuclides and types of monitoring data using real data contained in the IDEAS Internal Contamination Database. Results are presented.     

Concepts of ISO for the monitoring of workers for internal exposure and the present approach for the dose assessment

Besides ongoing developments in the dosimetry of incorporated radionuclides, there are various efforts to improve the monitoring of workers for potential or real intakes of radionuclides. The disillusioning experience with numerous inter-comparison projects identified substantial differences between national regulations, concepts, applied programmes and methods and dose assessment procedures. Measured activities were not comparable because of severe differences between measuring frequencies and methods, but also results of case studies for dose assessments revealed differences of orders of magnitudes. Besides the general common interest in reliable monitoring results, at least the cross-border activities of workers (e.g. nuclear power plant services) require consistent approaches and comparable results. The International Standardisation Organisation (ISO) therefore initiated projects to standardise the monitoring of workers, the requirements for measuring laboratories and the processes for the quantitative evaluation of monitoring. This presentation is intended to give an introduction into some important aspects addressed in these standards: the need for a monitoring programme, the design of a monitoring programme: methods and intervals, reference levels and approaches for dose assessments.     

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.