Fetal organ dosimetry for the Techa River and Ozyorsk Offspring Cohorts, part 2: radionuclide S values for fetal self-dose and maternal cross-dose.

One of the many objectives of the European Union's SOLO (Epidemiological Studies of Exposed Southern Urals Populations) project is to quantify the radiation dose-response following chronic in utero exposures to ionizing radiation. The project is presently conducting a pooled analysis of two cohorts of individuals born to exposed mothers-the Techa River Offspring Cohort (TROC) and the Ozyorsk Offspring Cohort (OOC). The TROC includes the offspring of mothers with external exposures to contaminated riverbanks and internal ingestions of (89)Sr, (90)Sr/(90)Y, and (137)Cs/(137m)Ba, while the OOC includes the offspring of mothers with external exposures seen within the Mayak plutonium production facilities and internal inhalation of (239)Pu and possibly (131)I. In the present study, a newly created Urals-based series of fetal and maternal models is employed to assess S values for all seven radionuclides. Among all fetal ages, S values ranged in magnitude from 10(-14) to 10(-10) Gy per Bq-s for fetal source organs and from 10(-18) to 10(-14) Gy per Bq-s from maternal source organs, depending upon particle type, particle energy, and fetal age. For a given radionuclide and fetal age, S values for fetal source organs were approximately two orders of magnitude higher than for maternal source organs. Little variation in S values was observed among fetal source organs, while variations of over 100 % with respect to the mean were observed for maternal source organs near the fetus. S value variations from maternal cross-fire were highly dependent on fetal position and separation distance from the maternal source organ. These radionuclide S values have been coupled with biokinetic models for use in cohort dose assessment within the SOLO project.

Fetal organ dosimetry for the Techa River and Ozyorsk offspring cohorts, part 1: a Urals-based series of fetal computational phantoms.

The European Union's SOLO (Epidemiological Studies of Exposed Southern Urals Populations) project aims to improve understanding of cancer risks associated with chronic in utero radiation exposure. A comprehensive series of hybrid computational fetal phantoms was previously developed at the University of Florida in order to provide the SOLO project with the capability of computationally simulating and quantifying radiation exposures to individual fetal bones and soft tissue organs. To improve harmonization between the SOLO fetal biokinetic models and the computational phantoms, a subset of those phantoms was systematically modified to create a novel series of phantoms matching anatomical data representing Russian fetal biometry in the Southern Urals. Using previously established modeling techniques, eight computational Urals-based phantoms aged 8, 12, 18, 22, 26, 30, 34, and 38 weeks post-conception were constructed to match appropriate age-dependent femur lengths, biparietal diameters, individual bone masses and whole-body masses. Bone and soft tissue organ mass differences between the common ages of the subset of UF phantom series and the Urals-based phantom series illustrated the need for improved understanding of fetal bone densities as a critical parameter of computational phantom development. In anticipation for SOLO radiation dosimetry studies involving the developing fetus and pregnant female, the completed phantom series was successfully converted to a cuboidal voxel format easily interpreted by radiation transport software.

Increase in accumulation of strontium-90 in the maternal skeleton during pregnancy and lactation: analysis of the Techa River data.

The unique contamination of the Techa River (Southern Urals, Russia) in the 1950s by long-lived (90)Sr allows investigation of the accumulation of bone-seeking elements in humans. This study is based on information compiled at the Urals Research Center for Radiation Medicine (Chelyabinsk, Russia) over a long period of time. It includes the results of in vivo measurements of (90)Sr-body burden with a whole body counter (WBC), data on personal medical examinations and residence and family histories. Data on 185 women from two Techa riverside villages Muslyumovo and Brodokalmak were selected. The settlements differ in terms of (90)Sr diet intake (higher in Muslyumovo than in Brodokalmak) and ethnicity (residents were mainly Slavs in Brodokalmak and Turkic in Muslyumovo). Results of a total of 555 WBC measurements performed in 1974-1997 were available for the women studied; maximum measured values reached 40 kBq/body. The women from each settlement were subdivided into three groups according to their childbearing history: pregnancy and lactation occurred (1) during the period of maximal (90)Sr intake (1950-1951); (2) after the period of maximal intake and (3) before this period or women who were childless. An increase was found in accumulation of (90)Sr in maternal skeleton during pregnancy and lactation (group 1) by a factor of 1.5-2 in comparison with non-pregnant, non-lactating women. This result was found in both Muslyumovo and Brodokalmak samples. An increase in accumulation of toxic elements in pregnant/lactating women is associated with increased radiation/toxic doses and risk for the women's health.

FISH analysis of translocations induced by chronic exposure to Sr radioisotopes: second set of analysis of the Techa River Cohort.

Fluorescent in situ hybridisation analysis of stable translocations was performed for 26 residents living along the Techa River (Russia), who were predominantly (95%) exposed to ingested strontium radioisotopes ((89)Sr and (90)Sr) resulting in exposure of their red bone marrow (RBM). Analysis was conducted at the Urals Research Center for Radiation Medicine, Public Health England and Leiden University Medical Center. Each laboratory scored 1000 cells per donor, which resulted in ∼1000 genome equivalents (GE) per donor. The age-dependent spontaneous level of translocations for each donor was evaluated on the basis of data published by Sigurdson et al. (International study of factors affecting human chromosome. Mutat. Res. 2008;652: :112-121). Reconstruction of doses was performed with the 'Techa River Dosimetry System' developed in 2009. In the studied donors, the range of individual cumulated RBM dose was from 0.3 to 3.7 Gy. Analysis of the yield of stable translocations dependent on the individual RBM dose from (89,90)Sr showed a linear dose-response relationship of 0.007 ± 0.002 translocation/GE cell/Gy (R = 0.61, p = 0.001). This set of results was in a good agreement with the previous data reported for 18 donors by Vozilova et al. (Preliminary FISH-based assessment of external dose for residents exposed on the Techa River.

Chronic low-dose exposure in the Techa River Cohort: risk of mortality from circulatory diseases.

The aim of the present study was to analyze the mortality from circulatory diseases for about 30,000 members of the Techa River cohort over the period 1950-2003, and to investigate how these rates depend on radiation doses. This population received both external and internal exposures from (90)Sr, (89)Sr, (137)Cs, and other uranium fission products as a result of waterborne releases from the Mayak nuclear facility in the Southern Urals region of the Russian Federation. The analysis included individualized estimates of the total (external plus internal) absorbed dose in muscle calculated based on the Techa River Dosimetry System 2009. The cohort-average dose to muscle tissue was 35 mGy, and the maximum dose was 510 mGy. Between 1950 and 2003, 7,595 deaths from circulatory diseases were registered among cohort members with 901,563 person years at risk. Mortality rates in the cohort were analyzed using a simple parametric excess relative risk (ERR) model. For all circulatory diseases, the estimated excess relative risk per 100 mGy with a 15-year lag period was 3.6 % with a 95 % confidence interval of 0.2-7.5 %, and for ischemic heart disease it was 5.6 % with a 95 % confidence interval of 0.1-11.9 %. A linear ERR model provided the best fit. Analyses with a lag period shorter than 15 years from the beginning of exposure did not reveal any significant risk of mortality from either all circulatory diseases or ischemic heart disease. There was no evidence of an increased mortality risk from cerebrovascular disease (p > 0.5). These results should be regarded as preliminary, since they will be updated after adjustment for smoking and alcohol consumption.

Does the cortical bone resorption rate change due to 90Sr-radiation exposure? Analysis of data from Techa Riverside residents.

The Mayak Production Association released large amounts of (90)Sr into the Techa River (Southern Urals, Russia) with peak amounts in 1950-1951. Techa Riverside residents ingested an average of about 3,000 kBq of (90)Sr. The (90)Sr-body burden of approximately 15,000 individuals has been measured in the Urals Research Center for Radiation Medicine in 1974-1997 with use of a special whole-body counter (WBC). Strontium-90 had mainly deposited in the cortical part of the skeleton by 25 years following intake, and (90)Sr elimination occurs as a result of cortical bone resorption. The effect of (90)Sr-radiation exposure on the rate of cortical bone resorption was studied. Data on 2,022 WBC measurements were selected for 207 adult persons, who were measured three or more times before they were 50-55 years old. The individual-resorption rates were calculated with the rate of strontium recirculation evaluated as 0.0018 year(-1). Individual absorbed doses in red bone marrow (RBM) and bone surface (BS) were also calculated. Statistically significant negative relationships of cortical bone resorption rate were discovered related to (90)Sr-body burden and dose absorbed in the RBM or the BS. The response appears to have a threshold of about 1.5-Gy RBM dose. The radiation-induced decrease in bone resorption rate may not be significant in terms of health. However, a decrease in bone remodeling rate can be among several causes of an increased level of degenerative dystrophic bone pathology in exposed persons.

Confirmation studies of Soviet research on immunological effects of microwaves: Russian immunology results.

This paper presents the results of a replication study performed to investigate earlier Soviet studies conducted between 1974 and 1991 that showed immunological and reproductive effects of long-term low-level exposure of rats to radiofrequency (RF) electromagnetic fields. The early studies were used, in part, for developing exposure standards for the USSR population and thus it was necessary to confirm the Russian findings. In the present study, the conditions of RF exposure were made as similar as possible to those in the earlier experiments: Wistar rats were exposed in the far field to 2450 MHz continuous wave RF fields with an incident power density in the cages of 5 W/m² for 7 h/day, 5 days/week for a total of 30 days, resulting in a whole-body SAR of 0.16 W/kg. Effects of the exposure on immunological parameters in the brain and liver of rats were evaluated using the complement fixation test (CFT), as in the original studies, and an additional test, the more modern ELISA test. Our results, using CFT and ELISA, partly confirmed the findings of the early studies and indicated possible effects from non-thermal RF exposure on autoimmune processes. The RF exposure resulted in minor increases in formation of antibodies in brain tissue extract and the exposure did not appear to be pathological. In addition, a study was conducted to replicate a previous Soviet study on effects from the injection of blood serum from RF-exposed rats on pregnancy and foetal and offspring development of rats, using a similar animal model and protocol. Our results showed the same general trends as the earlier study, suggesting possible adverse effects of the blood serum from exposed rats on pregnancy and foetal development of intact rats, however, application of these results in developing exposure standards is limited.

An image-based skeletal tissue model for the ICRP reference newborn.

Hybrid phantoms represent a third generation of computational models of human anatomy needed for dose assessment in both external and internal radiation exposures. Recently, we presented the first whole-body hybrid phantom of the ICRP reference newborn with a skeleton constructed from both non-uniform rational B-spline and polygon-mesh surfaces (Lee et al 2007 Phys. Med. Biol. 52 3309-33). The skeleton in that model included regions of cartilage and fibrous connective tissue, with the remainder given as a homogenous mixture of cortical and trabecular bone, active marrow and miscellaneous skeletal tissues. In the present study, we present a comprehensive skeletal tissue model of the ICRP reference newborn to permit a heterogeneous representation of the skeleton in that hybrid phantom set-both male and female-that explicitly includes a delineation of cortical bone so that marrow shielding effects are correctly modeled for low-energy photons incident upon the newborn skeleton. Data sources for the tissue model were threefold. First, skeletal site-dependent volumes of homogeneous bone were obtained from whole-cadaver CT image analyses. Second, selected newborn bone specimens were acquired at autopsy and subjected to micro-CT image analysis to derive model parameters of the marrow cavity and bone trabecular 3D microarchitecture. Third, data given in ICRP Publications 70 and 89 were selected to match reference values on total skeletal tissue mass. Active marrow distributions were found to be in reasonable agreement with those given previously by the ICRP. However, significant differences were seen in total skeletal and site-specific masses of trabecular and cortical bone between the current and ICRP newborn skeletal tissue models. The latter utilizes an age-independent ratio of 80%/20% cortical and trabecular bone for the reference newborn. In the current study, a ratio closer to 40%/60% is used based upon newborn CT and micro-CT skeletal image analyses. These changes in mineral bone composition may have significant dosimetric implications when considering localized marrow dosimetry for radionuclides that target mineral bone in the newborn child.

Reconstruction of (90)Sr intake for breast-fed infants in the Techa riverside settlements.

The Techa River (Southern Urals, Russia) was contaminated as a result of radioactive releases by the Mayak plutonium production facility during 1949-1956. The persons born after the onset of the contamination have been identified as the "Techa River Offspring Cohort" (TROC). The TROC has the potential to provide direct data on health effects in progeny that resulted from exposure of a general parent population to chronic radiation. The purpose of the present investigation is the estimation of (90)Sr intake from breast milk and river water in the period from birth to 6 months of life, necessary for an infant dose calculation. The investigation is based on all available data concerning radioactive contamination due to global fallouts and Mayak releases in the Southern Urals where extensive radiometric and radiochemical investigations of human tissues and environmental samples were conducted during the second half of the twentieth century. The strontium transfer factor from mother's daily diet to breast milk was estimated as 0.05 (0.01-0.13) d L(-1). Based on this transfer factor and data on (90)Sr water contamination, the average total (90)Sr intake for an infant born in the middle Techa River region was found to be equal to 60-80 kBq in 1950-1951. For the same period, calculations of (90)Sr intake using ICRP models gave values of 70-100 kBq. From 1952 onwards, the differences in intakes calculated using the two approaches increased, reaching a factor of 2-3 in 1953. The Techa River data provide the basis for improving and adapting the ICRP models for application to Techa River-specific population.