International Commission On Radiological Protection Models Research Articles

Forty-eight-year follow-up of a female worker exposed to highly enriched uranium via chronic and acute inhalation.

The United States Transuranium and Uranium Registries (USTUR) is a unique resource of data and materials for studying biokinetics of uranium in the human body. In this study, bioassay data and post-mortem organ activities from a female whole-body USTUR donor who was exposed to highly enriched uranium were analyzed using the IMBA Professional Plus® software to derive the best estimate of the total intake. The resulting radiation doses delivered to this individual's whole body and major target organs were calculated from estimated intake based on case-specific dose coefficients derived using the AIDE® software. Both intake and dose calculations were carried out using the biokinetic and dosimetric models recommended by the International Commission on Radiological Protection (ICRP) in its Occupational Intakes of Radionuclides publication series. Different exposure scenarios including chronic and acute inhalation intakes were tested. A combination of a chronic inhalation intake and two acute inhalation intakes appears to best describe the bioassay data. To fit this female individual's autopsy data, the transfer rate from the liver to the blood was increased by a factor of 8 and the transfer rate from the kidneys to the blood was decreased by a factor of 2.2. This resulted in the best fit to all data (p=0.519). The total intake was estimated to be 44.1kBq, and the committed effective dose was 211mSv with 96.8% contributed by 234U. 96.6% of the committed effective dose was contributed by the lungs. The remaining 3.4% of the committed effective dose was contributed by all systemic tissues and organs with the highest contribution (0.40%) from the red bone marrow. It is concluded that the current ICRP models, with the adjustment for smoking status, adequately describe uranium biokinetics for this individual except retention in the liver and kidneys. However, this study was based on a single case and may not be sufficient to identify any apparent sex-specific differences in uranium biokinetics.

Incidence risk assessment of secondary cancer due to radiotherapy of women with rectal cancer using BEIR VII, EPA, and ICRP models.

Radiotherapy has a significant side effect known as radiation-induced secondary cancer. This study aims to evaluate the dose and secondary cancer risk for women with rectal cancer treated with three-dimensional conformal radiation therapy (3D-CRT) to the organs at risk (OARs) and some sensitive organs using different types of radiation-induced cancer risk prediction models, including Biological Effects of Ionizing Radiation (BEIRVII), Environmental Protection Agency (EPA) and International Commission on Radiological Protection (ICRP), and compare the results of the different models for same organs. Thirty female patients with rectal cancer were considered and dose calculations were based on the PCRT-3D treatment planning system, while the radiotherapy of the patients had been performed using Shinva linear accelerator with a total dose of 45 Gy at 25 fractions. Planning target volume (PTV), OARs, and some sensitive organs were contoured, three models were used to evaluate secondary cancer risk (SCR) using the excess relative risk (ERR) and excess absolute risk (EAR). The bladder presents the highest risk, in terms of ERR, and the femur head and uterus in terms of EAR from the three models (BEIR VII, EPA, and ICRP). Based on the obtained results, radiotherapy of rectal cancer is relatively higher for the bladder and femur head, compared to the risk for other organs, the kidney risk is significantly lower. It was observed that the SCR from the ICRP model was higher compared to BEIR VII and EPA models.

Development of alimentary tract organs for ICRP pediatric mesh-type reference computational phantoms

In line with the activities of Task Group 103 under the International Commission on Radiological Protection (ICRP), the present study was conducted to develop a new set of alimentary tract organs consisting of the oral cavity, oesophagus, stomach, small intestine, and colon for the newborn, 1 year-old, 5 year-old, 10 year-old, and 15 year-old males and females for use in the pediatric mesh-type reference computational phantoms (MRCPs). The developed alimentary tract organs of the pediatric MRCPs, while nearly preserving the original topology and shape of those of the pediatric voxel-type reference computational phantoms (VRCPs) of ICRP Publication 143, present considerable anatomical improvement and include all micrometre-scale target and source regions as prescribed in ICRP Publication 100. To investigate the dosimetric impact of the developed alimentary tract organs, organ doses and specific absorbed fractions were computed for certain external exposures to photons and electrons and internal exposures to electrons, respectively, which were then compared with the values computed using the current ICRP models (i.e. pediatric VRCPs and ICRP-100 stylised models). The results showed that for external exposures to penetrating radiations (i.e. photons >0.04 MeV), there was generally good agreement between the compared values, within a 10% difference, except for the oral mucosa. For external exposures to weakly penetrating radiations (i.e. low-energy photons and electrons), there were significant differences, up to a factor of ∼8300, owing to the geometric difference caused by the anatomical enhancement in the MRCPs. For internal exposures of electrons, there were significant differences, the maximum of which reached a factor of ∼73 000. This was attributed not only to the geometric difference but also to the target mass difference caused by the different luminal content mass and organ shape.

Assessment and interpretation of internal doses: uncertainty and variability

Internal doses are calculated on the basis of knowledge of intakes and/or measurements of activity in bioassay samples, typically using reference biokinetic and dosimetric models recommended by the International Commission on Radiological Protection (ICRP). These models describe the behaviour of the radionuclides after ingestion, inhalation, and absorption to the blood, and the absorption of the energy resulting from their nuclear transformations. They are intended to be used mainly for the purpose of radiological protection: that is, optimisation and demonstration of compliance with dose limits. These models and parameter values are fixed by convention and are not subject to uncertainty. Over the past few years, ICRP has devoted a considerable amount of effort to the revision and improvement of models to make them more physiologically realistic. ICRP models are now sufficiently sophisticated for calculating organ and tissue absorbed doses for scientific purposes, and in many other areas, including toxicology, pharmacology and medicine. In these specific cases, uncertainties in parameters and variability between individuals need to be taken into account.

Biokinetic models for radiocaesium and its progeny

The International Commission on Radiological Protection (ICRP) is preparing a series of reports that will provide updated biokinetic and dosimetric models and dose coefficients for occupational intake of radionuclides. The biokinetic modelling scheme continues a trend in ICRP reports towards physiologically realistic descriptions of the time-dependent behaviour of absorbed radionuclides and their radioactive progeny. This paper proposes systemic biokinetic models for caesium isotopes and their ingrowing chain members and examines the dosimetric implications of the proposed models. Comparisons of D68 = tissue dose per unit input to blood based on current ICRP models for workers (ICRP Publication 68, 1994) with DP = corresponding values based on the proposed biokinetic models (but using the dosimetry models of Publication 68) yields the following ranges of the ratios DP:D68 for the tissues addressed in Publication 68: 0.5–25 for 130Cs (T1/2 = 29.2 min), 0.6–9.5 for 134mCs (2.9 h), 0.7–1.7 for 131Cs (9.69 d), 0.7–1.1 for 134Cs (2.06 y), 0.5–1.9 for 137Cs (30.2 y) and 0.2–3.7 for 135Cs (2.3 × 106 y). The large differences in the derived dose coefficients for some tissues and caesium isotopes, particularly short-lived isotopes, result mainly from differences in predictions of the time-dependent distributions of caesium in the body. For example, the proposed model and the current ICRP model for occupational intake of caesium predict peak kidney contents of ∼22% and ∼0.4%, respectively, following intravenous injection of stable caesium. Based on the proposed models for caesium and its progeny, the only dosimetrically significant chain members of caesium isotopes with half-life ≥10 min are 137mBa, which represents 32–85% of the estimated tissue doses from injected 137Cs, and 134Cs, which represents 4–53% of the estimated tissue doses from injected 134mCs.

RELIABILITY OF A NEW BIOKINETIC MODEL OF ZIRCONIUM IN INTERNAL DOSIMETRY: PART I, PARAMETER UNCERTAINTY ANALYSIS

The reliability of biokinetic models is essential in internal dose assessments and radiation risk analysis for the public, occupational workers, and patients exposed to radionuclides. In this paper, a method for assessing the reliability of biokinetic models by means of uncertainty and sensitivity analysis was developed. The paper is divided into two parts. In the first part of the study published here, the uncertainty sources of the model parameters for zirconium (Zr), developed by the International Commission on Radiological Protection (ICRP), were identified and analyzed. Furthermore, the uncertainty of the biokinetic experimental measurement performed at the Helmholtz Zentrum München-German Research Center for Environmental Health (HMGU) for developing a new biokinetic model of Zr was analyzed according to the Guide to the Expression of Uncertainty in Measurement, published by the International Organization for Standardization. The confidence interval and distribution of model parameters of the ICRP and HMGU Zr biokinetic models were evaluated. As a result of computer biokinetic modelings, the mean, standard uncertainty, and confidence interval of model prediction calculated based on the model parameter uncertainty were presented and compared to the plasma clearance and urinary excretion measured after intravenous administration. It was shown that for the most important compartment, the plasma, the uncertainty evaluated for the HMGU model was much smaller than that for the ICRP model; that phenomenon was observed for other organs and tissues as well. The uncertainty of the integral of the radioactivity of Zr up to 50 y calculated by the HMGU model after ingestion by adult members of the public was shown to be smaller by a factor of two than that of the ICRP model. It was also shown that the distribution type of the model parameter strongly influences the model prediction, and the correlation of the model input parameters affects the model prediction to a certain extent depending on the strength of the correlation. In the case of model prediction, the qualitative comparison of the model predictions with the measured plasma and urinary data showed the HMGU model to be more reliable than the ICRP model; quantitatively, the uncertainty model prediction by the HMGU systemic biokinetic model is smaller than that of the ICRP model. The uncertainty information on the model parameters analyzed in this study was used in the second part of the paper regarding a sensitivity analysis of the Zr biokinetic models.

UNCERTAINTIES ANALYSIS FOR THE PLUTONIUM DOSIMETRY MODEL, DOSES-2005, USING MAYAK BIOASSAY DATA

The Doses-2005 model is a combination of the International Commission on Radiological Protection (ICRP) models modified using data from the Mayak Production Association cohort. Surrogate doses from inhaled plutonium can be assigned to approximately 29% of the Mayak workers using their urine bioassay measurements and other history records. The purpose of this study was to quantify and qualify the uncertainties in the estimates for radiation doses calculated with the Doses-2005 model by using Monte Carlo methods and perturbation theory. The average uncertainty in the yearly dose estimates for most organs was approximately 100% regardless of the transportability classification. The relative source of the uncertainties comes from three main sources: 45% from the urine bioassay measurements, 29% from the Doses-2005 model parameters, and 26% from the reference masses for the organs. The most significant reduction in the overall dose uncertainties would result from improved methods in bioassay measurement with additional improvements generated through further model refinement. Additional uncertainties were determined for dose estimates resulting from changes in the transportability classification and the smoking toggle. A comparison was performed to determine the effect of using the model with data from either urine bioassay or autopsy data; no direct correlation could be established. Analysis of the model using autopsy data and incorporation of results from other research efforts that have utilized plutonium ICRP models could improve the Doses-2005 model and reduce the overall uncertainty in the dose estimates.

CONTENTS OF CESIUM, IODINE, STRONTIUM, THORIUM, AND URANIUM IN SELECTED HUMAN ORGANS OF ADULT ASIAN POPULATION

Contents of cesium, iodine, strontium, thorium, and uranium in some selected human organs were estimated for adult Asian population using data obtained in four Asian countries: China, India, Philippines, and Republic of Korea, as part of a Coordinated Research Program of the International Atomic Energy Agency on "Ingestion and Organ contents of elements of importance in radiation protection." These countries together represent more than 40% of the world population. Highly sensitive analytical techniques were employed to measure cesium in skeletal muscle, iodine in thyroid, strontium in skeleton, thorium and uranium in skeleton, liver, kidneys, and lungs where, in comparison to other organs, these elements are present in higher concentrations. The organ contents for adult Asian population, when compared with the corresponding data proposed for Reference Man by International Commission on Radiological Protection (ICRP), showed about 40 times lower kidneys content and about 10 times lower skeleton content of uranium. The content of thorium in skeleton for Asian population was also half of the ICRP Reference Man value. Interestingly, organ contents for the other elements such as iodine in thyroid, cesium in skeletal muscle, and strontium in skeleton were comparable for Asian and the Caucasian population (represented by ICRP Reference Man). Organ contents for these elements were also calculated by applying the new ICRP models of these elements to their daily intakes. The comparison of the calculated and measured organ contents showed that despite uncertainties in the organ content values arising due to the inter-country variations in daily dietary intakes, the contents were within a factor of two to three. This observation is significant since human data both on organ contents and ingestion were obtained at environmental level of intakes. The study suggests that currently available ICRP models for these elements are quite realistic.

Effect of uncertainty in transfer rates for the ICPR publication 67 biokinetic model on dose estimation for 239Pu from results of individual monitoring. International Commission on Radiological Protection.

The radiation dose due to internal exposures from 239Pu is mainly estimated by measuring actual urinary or faecal excretion of activity and comparing those values with the standard excretion rates calculated from the models of the International Commission on Radiological Protection (ICRP). Recently, on the other hand, uncertainties in the ICRP's models and parameters are under consideration because of the paucity of human data. In addition, there is a possibility of variation between individuals. A code has been developed to reproduce the ICRP's dose coefficients and excretion rates for 239Pu, which is one of the most important elements for occupational exposure. By using this code, the respective transfer rates for the ICRP Publication 67 biokinetic model were modified, and the effect owing to these changes on present hazard assessment was investigated. As a result, it was shown that dose estimates for workers exposed to 239Pu were not very sensitive to changes in these transfer rates.

Influence of gender differences in the carbon pool on dose factors for intakes of tritium and 14C-labeled compounds.

The ICRP's biokinetic models for five tritium-labeled and five 14C-labeled compounds (not including radiopharmaceutical compounds and excepting carbon monoxide) incorporate a compartment representing the body carbon pool. Using the ICRP models, as coded into the Genmod-PC internal dosimetry code, higher dose coefficients are calculated for females than for ICRP's Reference Man. The ICRP's committed effective dose coefficients for the ingestion of tritiated water and organically bound tritium by the adult male are 1.8 x 10(-11) and 4.2 x 10(-11) Sv Bq(-1), respectively. Using the Genmod-PC code, the corresponding dose coefficients for the adult female are 2.2 x 10(-11) and 6.2 x 10(-11) Sv Bq(-1), which are 25% and 46% greater than the adult male's. Similarly, the ICRP's dose coefficient is 5.8 x 10(-10) Sv Bq(-11) for an intake of organically bound 14C by the adult male, and the estimated dose coefficient using Genmod is 54% greater for the adult female. The carbon retention half-time for an average adult female is calculated as 51 d and that for an average adult male, 38 d; the latter is similar to the carbon half-time of 40 d recommended by International Commission on Radiological Protection (ICRP). The longer turnover time of whole body carbon in females is one factor that causes the dose coefficients for females to be higher than those of males; a second factor is the smaller whole body mass of ICRP's Reference Woman compared to Reference Man.

Biokinetics of a Uranium Octoxide-Bearing Aerosol Formed in a New Laser Enrichment Process: Implications for Human Exposure

This study forms part of a programme of work to investigate the biokinetics of uranium in aerosols formed during laser isotopic separation at a new uranium enrichment processing facility (Ansoborlo et al., 1994). These aerosols can consist of UO2, Umetal and U3O8 in different proportions and contain an ultrafine component. A previous study (Henge-Napoli et al., 1994) identified an aerosol consisting of 85% UO2/Umetal and 15% U3O8 with up to 20% of the activity associated with an ultrafine component. The ultrafine fraction was shown to consist of small clusters of 0.1 um particles. This material had similar absorption characteristics to the default values recommended in the International Commission on Radiological Protection (ICRP) Publication 66 (ICRP, 1994) for compounds with moderate absorption rates (Type M). Workers can be exposed to two different types of uranium aerosols which in normal conditions are a mixture of UO2+Umetal. However, due to the high pyrophoricity of uranium metal, a fire could ignite which would alter the initial composition. Although considerable information exists on the biokinetics of U3O8 (Stradling et al., 1989) there is a paucity of data available on aerosols formed during uranium fires. The aim of this study was to use material-specific physiochemical data and biokinetic data, obtained from animal experiments, to provide a basis for deriving dose limits and assessing monitoring procedures. The study employed the most recent recommendations, models and methodologies of the ICRP ICRP Publications 60 (ICRP, 1991), 66 (ICRP, 1994), 68 (ICRP, 1994) and 69 (ICRP, 1995). All computer codes used were developed specifically to implement the latest ICRP models.

Interpretation of Whole-Body Monitoring and Bioassay Data

The intake of radioactivity into the body presents many challenges for the dosimetrist who seeks to determine the intake and hence the dose received by the person. Investigation and other levels can be set by using the human biokinetic models proposed by the International Commission on Radiological Protection (ICRP). Measurement of radioactivity in air can be related to uptake and dose based upon these models but with large uncertainties due to the wide spatial variations in activity in the workplace. The use of in vivo monitoring, including body monitoring and bioassay measurements, is necessary if a significant intake is anticipated or occurs. The measurement of particle size, chemical form and radioactivity has to be interpreted using the ICRP models initially. However, individuals vary anatomically and in other ways which affect the metabolism of radionuclides and it is important to obtain the best estimate of intake which is consistent with all the measurements made, taking into account any uncertainties. The assessment of intakes for a wide variety of radionuclides, including tritium, fission products, uranium, thorium, plutonium and higher actinides, will be examined against a changing background of biokinetic models produced by ICRP. Comparisons between techniques used in different European laboratories will be considered as the basis for a unified approach to internal dose assessment.

Interpretation of Whole-Body Monitoring and Bioassay Data

The intake of radioactivity into the body presents many challenges for the dosimetrist who seeks to determine the intake and hence the dose received by the person. Investigation and other levels can be set by using the human biokinetic models proposed by the International Commission on Radiological Protection (ICRP). Measurement of radioactivity in air can be related to uptake and dose based upon these models but with large uncertainties due to the wide spatial variations in activity in the workplace. The use of in vivo monitoring, including body monitoring and bioassay measurements, is necessary if a significant intake is anticipated or occurs. The measurement of particle size, chemical form and radioactivity has to be interpreted using the ICRP models initially