Uncertainty of stochastic parametric approach to bone marrow dosimetry of 89,90Sr.

The objective of this study is to evaluate the uncertainties of the dosimetric modeling of active marrow (AM) exposure from bone-seeking 89,90Sr. The stochastic parametric skeletal dosimetry (SPSD) model was specifically developed to study the long-term effects resulting from chronic 89,90Sr exposure in populations of the radioactively contaminated territories of the Southern Urals region of the Russian Federation. The method permits the evaluation of the dose factors (DF(AM ← TBV) and DF(AM ← CBV)), which convert the radionuclide activity concentration in trabecular (TBV) and cortical (CBV) bone volumes into dose rate in the AM, and their uncertainties. The sources of uncertainty can be subdivided into inherent uncertainties related to the individual variability of the simulated objects and introduced uncertainties related to model simplifications. Inherent uncertainty components are the individual variability of bone chemical composition, bone density, bone micro- and macro-architecture as well as AM distribution within the skeleton. The introduced uncertainties may result from the stylization of bone segment geometry, assumption of uniform cortical thickness, restriction of bone geometry and the selection of the applied voxel resolution. The inherent uncertainty depends on a number of factors of influence. Foremost, it is the result of variability of AM distribution within the skeleton. Another important factor is the variability of bone micro- and macro-architecture. The inherent uncertainty of skeletal-average dose factors was found to be about 40-50%. The introduced uncertainty associated with the SPSD model approach does not exceed 16% and mainly depends on the error of bone-shape stylization. The overall inherent and introduced uncertainties of DF(AM ← TBV) and DF(AM ← CBV) are below 55% and 63%, respectively. The results obtained will be incorporated into the stochastic version of the Techa River Dosimetry System (TRDS-2016MC) that provides multiple realizations of the annual doses for each cohort member to obtain both a central estimate of the individual dose and information on the dose uncertainty.

Dose estimates and their uncertainties for use in epidemiological studies of radiation-exposed populations in the Russian Southern Urals.

Many residents of the Russian Southern Urals were exposed to radioactive environmental pollution created by the operations of the Mayak Production Association in the mid- 20th century. There were two major releases: the discharge of about 1x1017 Bq of liquid waste into the Techa River between 1949 and 1959; and the atmospheric release of 7.4 * 1016 Bq as a result an explosion in the radioactive waste-storage facility in 1957. The releases into the Techa River resulted in the exposure of more than 30,000 people who lived in riverside villages between 1950 and 1961. The 1957 accident contaminated a larger area with the highest exposure levels in an area that is called the East Urals Radioactive Trace (EURT). Current epidemiologic studies of the exposed populations are based on dose estimates obtained using a Monte-Carlo dosimetry system (TRDS-2016MC) that provides multiple realizations of the annual doses for each cohort member. These dose realizations provide a central estimate of the individual dose and information on the uncertainty of these dose estimates. In addition, the correlation of individual annual doses over realizations provides important information on shared uncertainties that can be used to assess the impact of shared dose uncertainties on risk estimate uncertainty.This paper considers dose uncertainties in the TRDS-2016MC. Individual doses from external and internal radiation sources were reconstructed for 48,036 people based on environmental contamination patterns, residential histories, individual 90Sr body-burden measurements and dietary intakes. Dietary intake of 90Sr resulted in doses accumulated in active bone marrow (or simply, marrow) that were an order of magnitude greater than those in soft tissues. About 84% of the marrow dose and 50% of the stomach dose was associated with internal exposures. The lognormal distribution is well-fitted to the individual dose realizations, which, therefore, could be expressed and easily operated in terms of geometric mean (GM) and geometric standard deviation (GSD). Cohort average GM for marrow and stomach cumulative doses are 0.21 and 0.03 Gy, respectively. Cohort average dose uncertainties in terms of GSD are as follows: for marrow it is 2.93 (90%CI: 2.02-4.34); for stomach and the other non-calcified tissues it is 2.32 (90% CI: 1.78-2.9).

Bone marrow dosimetry for mice: exposure from bone-seeking 89,90Sr.

Studies of radiobiological effects in murine rodents exposed to internal radiation in the wild or in laboratory experiments require dosimetric support. The main problem of bone marrow (BM) dosimetry for bone-seeking ß-emitters is dosimetric modeling, because the bone is a heterogeneous structure with complex microarchitecture. To date, there are several approaches to calculating the absorbed dose in BM, which mostly use rough geometric approximations. Recently, in the framework of studies of people exposed to 90Sr in the Urals, a new approach (SPSD) has been developed. The aim of the current study was to test for the first time the possibility of extension of the SPSD approach elaborated for humans to mice. For this, computational phantoms of femur bones of laboratory animals (C57BL/6, C57BL/6 J, BALB/c, BALB/cJ) aged 5-8 weeks (growing) and > 8 weeks (adults) were created. The dose factors DFSr-90(BM ← TBV + CBV) to convert the Sr isotope activity concentration in a bone tissue into units of dose rate absorbed in the bone marrow were 1.75 ± 0.42 and 2.57 ± 0.93 µGy day-1 per Bq g-1 for growing and adult animals, respectively, while corresponding values for DFSr-89(BM ← TBV + CBV) were 1.08 ± 0.27 and 1.66 ± 0.67 µGy day-1 per Bq g-1, respectively. These results are about 2.5 times lower than skeleton-average DFs calculated assuming homogenous bone, where source and target coincide. The results of the present study demonstrate the possibility of application of the SPSD approach elaborated for humans to non-human mammals. It is concluded that the study demonstrates the feasibility and appropriateness of application of the SPSD approach elaborated for humans to non-human mammals. This approach opens up new prospects for studying the radiobiological consequences of red bone marrow exposure for both laboratory and wildlife mammals.

External dose reconstruction at the shore of the Metlinsky Pond in the former village of Metlino (Techa River, Russia) based on environmental surveys, luminescence measurements and radiation transport modelling.

The cohorts of people formerly living at the Techa River shoreline in the Southern Urals, Russia, are widely studied cohorts for the investigation of low-dose radiation effects to human health. The nuclear facilities of the Mayak Production Association (PA) discharged their radioactive effluents into the nearby Techa River, especially in the first years of operation. Health status of cohort member data is constantly being improved and updated. Consequently, there is a need to also improve and verify the underlying dosimetry, which gives information about the dose of cohort members. For the Techa River population, the dosimetry is handled in the Techa River Dosimetry System (TRDS). The present work shows results of a feasibility study to validate the TRDS at the location of the village of Metlino, a village just 7 km downstream from the Mayak PA. For this settlement there were two sources of external exposure, the contaminated banks of the Techa River and the contaminated shoreline of the nearby Metlinsky Pond. In the present study the north-western wall of a granary was used as a dose archive to validate dose estimates. Measurements of doses in brick accumulated over many decades and measurements of the current dose rate in bricks were combined with dose rate measurements in air above ground in front of the granary, historical contamination data and Monte-Carlo simulations. Air kerma estimates for 1949-1956 significantly different from zero could not be reconstructed for the Metlinsky Pond shoreline near the granary, but an upper dose limit could be estimated. Implications for TRDS-2016 are discussed.

Stochastic parametric skeletal dosimetry model for humans: General approach and application to active marrow exposure from bone-seeking beta-particle emitters.

The objective of this study is to develop a skeleton model for assessing active marrow dose from bone-seeking beta-emitting radionuclides. This article explains the modeling methodology which accounts for individual variability of the macro- and microstructure of bone tissue. Bone sites with active hematopoiesis are assessed by dividing them into small segments described by simple geometric shapes. Spongiosa, which fills the segments, is modeled as an isotropic three-dimensional grid (framework) of rod-like trabeculae that "run through" the bone marrow. Randomized multiple framework deformations are simulated by changing the positions of the grid nodes and the thickness of the rods. Model grid parameters are selected in accordance with the parameters of spongiosa microstructures taken from the published papers. Stochastic modeling of radiation transport in heterogeneous media simulating the distribution of bone tissue and marrow in each of the segments is performed by Monte Carlo methods. Model output for the human femur at different ages is provided as an example. The uncertainty of dosimetric characteristics associated with individual variability of bone structure was evaluated. An advantage of this methodology for the calculation of doses absorbed in the marrow from bone-seeking radionuclides is that it does not require additional studies of autopsy material. The biokinetic model results will be used in the future to calculate individual doses to members of a cohort exposed to 89,90Sr from liquid radioactive waste discharged to the Techa River by the Mayak Production Association in 1949-1956. Further study of these unique cohorts provides an opportunity to gain more in-depth knowledge about the effects of chronic radiation on the hematopoietic system. In addition, the proposed model can be used to assess the doses to active marrow under any other scenarios of 90Sr and 89Sr intake to humans.

Site-specific concentration of uranium in urine of workers of the hydrometallurgical plant of Stepnogorsk mining and chemical combine.

Radiation monitoring is an important radiation safety measure implemented at the hydrometallurgical plant of the Stepnogorsk mining and chemical combine (HMP SMCC, Republic of Kazakhstan). Follow-up of the workers and their regular medical examinations has laid the basis to create a cohort with the potential to be used in radiation epidemiology. The aim of current pilot study was to analyze the dose forming factors for workers of HMP SMCC. For this, bioassays samples collected from 54 workers employed at eight HMP workshops were measured using the "Agilent 7800 ICP-MS" mass spectrometer. Three years later, measurements were repeated for four workers with the highest concentrations of uranium in urine. The results of site-specific measurements of dose rates, long-lived alpha-particle activity concentrations and equivalent equilibrium volume activity of radon were derived from the archive of the HMP SMCC Service of Radiation and Toxic Safety and analyzed to fully evaluate the radiation situation at those workplaces. Maximum urine uranium concentrations were measured for workers at the extraction workshop and mechanical repair shop (up to 26.7 µg/L and 14.6 µg/L, respectively). Urinary uranium from workers employed at other sites was mainly (for about 72% of the samples) in the range of values that may occur in natural conditions (< 0.4 µg/L). A wide individual variability in uranium concentration in urine samples (from 60% to 200% of CV) was found. A linear dependence of cumulative effective dose on work experience was found with a slope of 7.5 mSv per year. This slope did not depend on working place. For the investigated workers, cumulative effective doses of workers were found in the range of low (< 100 mSv) and medium doses (100-500 mSv). It is concluded that the newly created cohort of HMP SMCC workers has the potential to improve the knowledge on health effects from low- and medium doses of ionizing radiation.

RADIATION SITUATION IN THE TERRITORIES AFFECTED BY MINING ACTIVITIES IN STEPNOGORSK AREAS, REPUBLIC OF KAZAKHSTAN: PILOT STUDY.

The Republic of Kazakhstan has a long history of mining activities, viz., gold and uranium. Mining activities represent sources of potential naturally occurring radionuclides contamination of the environment and human health of population. The aim of this study was to investigate the radiation situation of industrially modified environment in Stepnogorsk areas of Kazakhstan to understand the sources of contamination. Quite high values of ambient equivalent dose rates in air ~2.87 µSv h-1 were found in the Aqsu gold-mining site. The radon equivalent equilibrium volume activity (indoor) were in the range of 313-858 Bq m-3 in the study area buildings. The high values of activity concentration of natural radionuclides found in Aqsu soil samples were 226Ra-4060, 232Th-1170 and 40K-4080 Bq kg-1, respectively. However, our comprehensive surveys implied that the increased natural radiation background caused by the radionuclide transport from the tailing area did not have an impact, while evaluation of its potential radiation risks and remediation of the territories of the former gold mining should be needed.

Electron paramagnetic resonance and fluorescence in situ hybridization-based investigations of individual doses for persons living at Metlino in the upper reaches of the Techa River.

Waterborne releases to the Techa River from the Mayak Production Association in Russia during 1949-1956 resulted in significant doses to persons living downstream; the most contaminated village was Metlino, about 7 km from the site of release. Internal and external doses have been estimated for these residents using the Techa River Dosimetry System-2000 (TRDS-2000); the primary purpose is to support epidemiological studies of the members of the Extended Techa River Cohort. Efforts to validate the calculations of external and internal dose are considered essential. One validation study of the TRDS-2000 system has been performed by the comparison of calculated doses to quartz from bricks in old buildings at Metlino with those measured by luminescence dosimetry. Two additional methods of validation considered here are electron paramagnetic resonance (EPR) measurements of teeth and fluorescence in situ hybridization (FISH) measurements of chromosome translocations in circulating lymphocytes. For electron paramagnetic resonance, 36 measurements on 26 teeth from 16 donors from Metlino were made at the GSF-National Research Center for Environment and Health (16 measurements) and the Institute of Metal Physics (20 measurements); the correlation among measurements made at the two laboratories has been found to be 0.99. Background measurements were also made on 218 teeth (63 molars, 128 premolars, and 27 incisors). Fluorescence in situ hybridization measurements were made for 31 residents of Metlino. These measurements were handicapped by the analysis of a limited number of cells; for several individuals no stable translocations were observed. Fluorescence in situ hybridization measurements were also made for 39 individuals believed to be unexposed. The EPR- and FISH-based estimates agreed well for permanent residents of Metlino: 0.67 +/- 0.21 Gy and 0.48 +/- 0.18 Gy (mean +/- standard error of the mean), respectively. Results of the two experimental methods also agreed well with the estimates derived from the use of the TRDS-2000. For all persons investigated according to each technique, the EPR-measured dose to enamel was 0.55 +/- 0.17 Gy, and the TRDS-2000 prediction for the dose to enamel for these individuals is 0.55 +/- 0.07 Gy. The fluorescence in situ hybridization-based dose, 0.38 +/- 0.10 Gy, compared well to the TRDS-2000 prediction of external dose, 0.31 +/- 0.03 Gy, to red bone marrow for these persons. Validation of external doses at the remaining villages is an active area of investigation.

Age dependencies of 90Sr incorporation in dental tissues: comparative analysis and interpretation of different kinds of measurements obtained for residents on the Techa River.

Human teeth have been considered as dosimeters for decades. Methods include the in vivo measurement of 90Sr/90Y in teeth with a tooth-beta counter, the radiochemical determination of 90Sr in whole teeth, and the measurement of dose in teeth by use of electron paramagnetic resonance. Presented in this paper are results of 2,514 tooth-beta counter measurements, 334 radiochemical measurements, and 218 electron paramagnetic resonance measurements for residents living in settlements along the Techa River. All three kinds of measurements indicate a sharp peak that corresponds to the uptake of 90Sr by tooth tissue. The results can be interpreted in terms of an intake function for 90Sr only if the period of calcification of each individual tooth is considered--such detail on a tooth-by-tooth basis is presented in this paper. The conclusion is reached that the tooth-beta counter data are the most reliable in terms of reconstruction of 90Sr intake; this is due in part to the fact that the tooth-beta counter measures four teeth (all at position 1) with essentially the same time periods of mineralization and because there are a large number of tooth-beta counter measurements. The main utility of electron paramagnetic resonance measurements is considered to be the validation of estimates of external dose; but for this purpose teeth with 90Sr taken up into enamel must be avoided.