Верификация радиоэкологической модели на инструментальных данных удельной активности 131I в траве в Мазовии и Богемии после аварии на ЧАЭС (по материалам «Пражского» и «Варшавского» сценариев проекта МАГАТЭ EMRAS)

The analysis of instrumental data of “Prague” and “Warsaw” scenarios on the dynamics of 131I specific activities in the grass is carried out. Reconstruction of the 131I the specific activities dynamics in the grass in the Mazovia and Bohemia localities is performed in three models: direct calculation the input data of the “Prague” and “Warsaw” scenarios, homogeneous cloud, heterogeneous rain and heterogeneous cloudhomogeneousrain. The actual 137Cs fallout densities in the grass sampling sites in average more than 2.9 times for Prague and 2 times for Warsaw. Effective rain during the main fallout at the grass sampling sites, reconstructed on the model of a homogeneous cloud is 3–4 times more than at the nearest weather stations during this time. A realistic scenario of the input data leading to the optimal agreement of the calculated and instrumental data is revealed. It is shown that direct calculations and the homogeneous cloud model give almost identical results and lead to a significantly better agreement with the instrumental data than the an inhomogeneous cloud model. The calculated and instrumental data show a significant decrease in the 131I specific activity in the grass after the end of the main fallout due to its flushing from the grass surface by strong prolonged rain 13 and 19 days after the accident in Mazovia and 30 and 35 days in Bohemia. Uncertainties in the results of reconstruction of the dynamics of 131I and 137Cs activities in vegetation are estimated. The meangeometric values and standard mean-geometric deviations of the calculation/ 8instrumental data ratios are: 0.8–1.1 and 1.8–1.9 for grass.Выполнен анализ инструментальных данных «Пражского» и «Варшавского» сценариев о динамике удельных активностей 131I в траве. Проведена реконструкция динамики удельных активностей 131I в траве в населенных пунктах с ее измерениями. Реконструкция выполнена по трем моделям: прямого расчета по входным данным сценариев, однородного и неоднородного радиоактивного облака. Фактические плотности выпадений 137Cs в местах отбора травы в среднем больше плотностей выпадения, реконструированных по модели прямого расчета, в 2,9 раза для Праги и в 2 раза для Варшавы. Эффективные осадки за время основных выпадений в местах отбора проб травы, реконструированные по модели однородного облака, в 3–4 раза больше, чем на ближайших к ним метеостанциях. Выявлен реалистический сценарий входных данных, приводящий к оптимальному согласию расчетных и инструментальных данных. Модели прямого расчета и однородного облака дают практически совпадающие между собой результаты и приводят к лучшему согласию с инструментальными данными, чем модель неоднородного облака; расчетные и инструментальные данные показывают значимое уменьшение удельной активности 131I в траве после окончания основных выпадений за счет ее смыва с поверхности травы сильными продолжительными осадками через 13 и 19 суток после аварии в Мазовии и через 30 и 35 суток в Богемии. Размахи среднегеометрических значений и стандартных среднегеометрических отклонений отношений расчет/инструментальные данные составляют 0,8–1,1 в Мазовии и 1,8–1,9 в Богемии. Регрессионные зависимости диаграмм рассеивания расчетные/инструментальные данные практически параллельны диагонали с угловым коэффициентом, равным 0,94 для однолетней и 0,86 для многолетней травы

Assesment of patient doses and possible approaches for implementation of optimization procedures in PET/CT examinations in the Russian Federation

A dose survey of positron emission tomography (PET) examinations was performed in 12 regions of the Russian Federation, where the effective dose values were assessed for the various types of PET examinations. The comparison to similar published data show that the patient doses in Russia are higher than in other countries. Low-dose CT protocols and justification of multiphase CT protocols should be considered for future optimization and radiation protection of patients

Measurements of long-term external and internal radiation exposure of inhabitants of some villages of the Bryansk region of Russia after the Chernobyl accident

A Nordic-Soviet programme was initiated in 1990 to evaluate the external and internal radiation exposure of the inhabitants of several villages in the Bryansk region of Russia. This area was one of the number of areas particularly affected by the nuclear accident at the Chernobyl Nuclear Power Plant in 1986. Measurements were carried out yearly until 1998 and after that more irregularly; in 2000, 2006 and 2008 respectively. The effective dose estimates were based on individual thermoluminescent dosemeters and on in vivo measurements of the whole body content of (137)Cs (and (134)Cs during the first years of the programme). The decrease in total effective dose during the almost 2 decade follow-up was due to a continuous decrease in the dominating external exposure and a less decreasing but highly variable exposure from internal irradiation. In 2008, the observed average effective dose (i.e. the sum of external and internal exposure) from Chernobyl (137)Cs to the residents was estimated to be 0.3mSvy(-1). This corresponds to 8% of the estimated annual dose in 1990 and to 1% of the estimated annual dose in 1986. As a mean for the population group and for the period of the present study (2006-2008), the average yearly effective dose from Chernobyl cesium was comparable to the absorbed dose obtained annually from external exposure to cosmic radiation plus internal exposure to naturally occurring radionuclides in the human body. Our data indicate that the effective dose from internal exposure is becoming increasingly important as the body burdens of Chernobyl (137)Cs are decreasing more slowly than the external exposure. However, over the years there have been large individual variations in both the external and internal effective doses, as well as differences between the villages investigated. These variations and differences are presented and discussed in this paper

Radioecological modeling of the 131I activity dynamics in the pasture vegetation of Mazovia in the year of the Chernobyl accident: Reconstruction, verification, reliability assessments

A radioecological model, which is a system of linear differential equations describing the dynamics of the transport of 137Cs and 131I radionuclides along the food chain after their release into the atmosphere after the Chernobyl accident, was used to reconstruct “instrumental” data of the 131I activities in the grass pastures in the central part of Mazovia. Four atmospheric models were used for the reconstruction: direct calculation, homogeneous cloud – inhomogeneous rainfall, inhomogeneous cloud – homogeneous rainfall, and a model with recalculation of the 137Cs and 131I activities in the atmosphere. The “instrumental” data were reconstructed based on data from direct measurements of the 131I activity in lawn grass. It has been shown that the direct calculation and homogeneous cloud models lead to a better agreement of the calculated and reconstructed “instrumental” data than the inhomogeneous cloud model. The arithmetic mean ratio of the calculated and reconstructed “instrumental” data lie in a range of 0.84 to 0.95 for the direct calculation and homogeneous cloud models, and in a range of 1.7 to 3.0 for the inhomogeneous cloud model. The mean geometric deviation for all models is constant and equal to 1.7. Instrumental and reconstructed “instrumental” data show a significant decrease in the specific activity of 131I in grass due to its wash-off by continuous rainfall, both during rainfall and after most of the deposition takes place. Due to this effect, the coefficient of the 131I retention on grass in the form of the maximum activity ratio to the 137Cs deposition density decreases from 34 to 1.4 m2/kg while it increases from 1 to 29 kBq/m2 as the result of the rainfall growth from 0 to 40 mm

Assessment of patient doses and corresponding radiation risks from PET/CT examinations in the Russian Federation

In the current study we evaluated the structure of positron emission tomography combined with computed tomography (PET/CT) diagnostics in the Russian Federation. Patient effective doses, organ doses and corresponding radiation risks for the most common PET/CT examinations were evaluated. Data was collected in 12 regions of the Russian Federation in the period 2012-2017 in 19 facilities (26 PET/CT scanners, corresponding to more than 60 % of the scanners in the country). Typical administered activities and DLP values for the CT protocols were estimated with the subsequent calculation of typical organ and effective doses from external and internal exposure. Lifetime radiation detriment-adjusted risks were calculated based on both the effective dose and organ absorbed doses considering the gender of the patient. The results of the dose survey indicate that the most common PET/CT examinations are whole body and brain examinations with 18F-FDG (performed in 26 and 8 surveyed departments respectively). Other PET/CT examinations are significantly less common. The highest patient doses were calculated for whole body PET/CT examinations - about 20 mSv. The doses increase up to 35-40 mSv if multiphase CT scan was performed, the CT scan composed up to 70-90 % of the total effective dose. Lifetime detriment-adjusted risk was estimated for PET/CT examinations of the brain as 2·10 -4 ; for pelvic as 5·10 -4 , and may reach up to 10 -3 for whole body PET/CT examinations. Comparison of risks assessed by two approaches indicated that the simplified risk assessment based on effective dose overestimated the risk for PET/CT examinations of the brain (both genders) and for whole body and pelvic examinations (males only). Overall, differences in male and female patients can reach up to the 30 %

Potential for the establishment of national CT diagnostic reference levels in the Russian Federation

Computed tomography (CT) is a widespread diagnostic modality that is commonly associated with relatively high patient doses. Hence, optimization of radiation protection of the patients from CT examinations is extremely important. An integrant part of radiation protection in medicine is a system of diagnostic reference levels (DRLs). The aim of the study was to evaluate the possibility of establishing DRLs for typical CT examinations on national level in the Russian Federation. The study is based on the dose surveys performed in different regions of Russia in 2009-2017. Data was collected on the mostcommon native and multiphase CT examinations as well as whole body CT as a part of positron emission tomography combined with computed tomography (PET/CT) examinations. Establishment of DRLs on the region level in Russia iscomplicated due to the high number of regions and limited availability of dose data. Comparison between typical dose distributions indicated no significant regional differences, hence allowing establishing DRLs on the national level. The 75% percentiles of both DLP and effective dose distributions were proposed as the preliminary values of national DRLs. It was proposed to establish DRLs for whole native CT examinations or for one phase of multiphase CT examination

Radioecological modeling of the 131I activity dynamics in different types of grass vegetation in the Chernobyl accident year

The dynamics of 137Cs and 131I radioactivity in the crude biomass of the grass fodder and food vegetation in Mazovia, Poland, in 1986, the year of the Chernobyl accident, has been estimated. Density of 137Cs and 131I in the soil and vegetation have been measured as a function of rainfall and biomass density as of the time most of the fallout took place. A method is described to convert the instrumental data for the radionuclide activity dynamics in vegetation of one type to vegetation of other types. The results of such data conversion from lawn grass to other types of food and fodder grass vegetation are presented. A method is described for adjusting the dynamics of the radionuclide transport through the food chain components (pasture grass, green meat – milk – human body) by normalizing successively the estimated data in each next component for the average value of the instrumental data ratio to the estimated data in the preceding component. The proposed methods are intended to generate a mutually consistent base of estimated and reconstructed instrumental data: 137Cs and 131I activity in the atmosphere – rainfall – 137Cs fallout density on terrain – specific activity of 131I in vegetation. Such radioecological database will provide for a longer reliability of the estimated 131I specific activity dynamics in milk and in human body and, in the long run, when estimating the thyroid internal exposure doses

Verification of radioecological models to the instrumental data of the specific activity ¹³¹I in a grass in Mazovia and Bohemia after the Chernobyl accident (from “Prague” and “Warsaw” scenarios of the IAEA project EMRAS

The analysis of instrumental data of “Prague” and “Warsaw” scenarios on the dynamics of 131I specific activities in the grass is carried out. Reconstruction of the 131I the specific activities dynamics in the grass in the Mazovia and Bohemia localities is performed in three models: direct calculation the input data of the “Prague” and “Warsaw” scenarios, homogeneous cloud, heterogeneous rain and heterogeneous cloudhomogeneousrain. The actual 137Cs fallout densities in the grass sampling sites in average more than 2.9 times for Prague and 2 times for Warsaw. Effective rain during the main fallout at the grass sampling sites, reconstructed on the model of a homogeneous cloud is 3–4 times more than at the nearest weather stations during this time. A realistic scenario of the input data leading to the optimal agreement of the calculated and instrumental data is revealed. It is shown that direct calculations and the homogeneous cloud model give almost identical results and lead to a significantly better agreement with the instrumental data than the an inhomogeneous cloud model. The calculated and instrumental data show a significant decrease in the 131I specific activity in the grass after the end of the main fallout due to its flushing from the grass surface by strong prolonged rain 13 and 19 days after the accident in Mazovia and 30 and 35 days in Bohemia. Uncertainties in the results of reconstruction of the dynamics of 131I and 137Cs activities in vegetation are estimated. The meangeometric values and standard mean-geometric deviations of the calculation/ 8instrumental data ratios are: 0.8–1.1 and 1.8–1.9 for grass