Technological developments, as well as software upgrades to existing computerized tomography (CT) scanners, require a continuous review of the methods for estimating radiation risk from CT procedures. According to the International Commission on Radiological Protection (ICRP), such assessments should be based on absorbed doses in organs and tissues exposed to radiation. This work is devoted to the study of the influence of various characteristics of the CT (manufacturer, type of scanner, etc.) on the evaluation of radiation risks on the example of multiple exposures in standard CT procedures. As an example, the value of lifetime attribute risk (LAR) and lifetime attributable risk fraction (LARF) for 5 CT scans during the life of a woman aged 20, 25, 30, 45 and 50 years is estimated. The lifetime attributable risk of possible cancer induction was estimated according to the ICRP mathematical model (Publication 103) and using the medical and demographic characteristics of the Russian population, as well as scan protocol data for typical CT scanners of selected models. The results were obtained with the use of old and updated conversion factors for the DLP (Dose Length Product – a measure of the absorbed radiation dose for the whole CT examination) parameter to organ doses from a particular procedure. The lifetime attributable risk of possible cancer induction calculated using organ doses derived from old conversion factors was compared with the risk calculated with data for modern CT scanners with updated conversion factors. The LAR was evaluated over time for one CT examination, two, three, four and five different procedures during the patient's lifetime. It was found that to date such factor as software updates in the field of optimisation of scanning protocols or the CT scanner manufacturer still do not has a significant impact on the radiation risks associated with specific diagnostic procedures. The methods developed by the authors for calculating absorbed doses and radiation risks can be used in planning CT examinations and optimising patient dose loads on any modern CT scanners.

Computed tomography (CT) scan is a fairly accurate and reliable method for diagnosing various diseases, however, based on irradiation of the patient with ionizing radiation, it can lead to an excess risk of developing malignant neoplasms. According to the safety standards of the International Atomic Energy Agency, no patient can be exposed to medical radiation unless he or she has been informed of the risks associated with radiation exposure. This requirement is also contained in the Russian Radiation Safety Standards (NRB-99/2009). Radiation risk is estimated on the basis of calculated values of equivalent doses in the patient's organs and tissues using radiation risk models of the International Commission on Radiological Protection. This article is devoted to the improvement of the method for calculating equivalent doses in the organs and tissues of patients with computed tomography scan for further assessment of radiation risks. For 15 modern computed tomography scanners, with different geometry of patient scanning, the data necessary for calculating the equivalent doses in organs and tissues based on the parameters of the children's phantom were updated. The coefficients of conversion of the surrogate measure of the patient's radiation dose for the entire CT scan study, namely, the value of the "Dose Length Product" (DLP), into the values of equivalent doses in individual organs and tissues exposed to radiation were determined. The results of the calculation are given for five typical scan areas: chest, abdomen, pelvis, head and neck. In the course of simulation numerical modeling, organs and tissues with the highest equivalent doses were determined during CT scan examinations of children and adolescents. Unlike adult patients, for children and adolescents, the dose load on the surface of the bone is significantly lower and does not stand out in any of the considered types of CT scan examinations. It should be noted that with CT scan of the cervical spine, due to the specifics of the geometry of scanning new types of tomography scanners, the dose load on the thyroid gland of boys increased. The dose conversion factors obtained in this paper with estimates of standard deviations make it possible to assess the radiation risks of children and adolescents during examinations on modern CT scanners and optimize their dose loads.

The paper presents analysis of different factors affecting the uncertainty model for estimating ra-diation risk from computed tomography (CT). Uncertainties in radiation doses estimates caused by measurement (instrumental) errors or used dose estimation methods, the size of the scanned area and the type of CT scanner. The uncertainty of radiation dose due to measurement errors or dose estimation methods, the size of the scanned area and type of a CT scan may cause the uncertainties as well. Data used for calculating equivalent doses in individual organs and tissues and for calculating lifetime radiation risk of cancer development due to routine CT testing were updated. Conversion factors for DLP, a measure of radiation dose a patient received during CT exams of thoracic, abdomen and head organs, were determined and used for conversion of the CT doses to equivalent doses for individual organs and tissues exposed to radiation. Data for 15 state-of-the-art CT scanners with varying scanning geometry were updated. Uncertainties in life-time radiation risk were determined by estimating 95% confidence intervals for mean dose-proportionality ratios. Standard deviations related to specific dose distribution, scanning geometry and other factors that impact on uncertainty of radiation risk estimates were calculated. The standard deviations associated with the specifics of the dose distribution, scanning geometry and other factors affecting the uncertainties of radiation risk assessments were calculated. In the course of simulation modelling, organs and tissues were identified that are most exposed to radiation during CT of the chest, abdomen and head.

According to GLOBOCAN 2020 Statistics based on estimates for 36 cancers incidence and mortality in 185 countries produced by the International Agency for Research on Cancer (IARC) in 2020, the total number of cancer cases increased by 19.3 million new cases and the number of cancer deaths increased by 10 million new cancer deaths. According to statistics, 1 of 5 people develops cancer during their life, and one of 8 men and one of 11 women die from the disease. The cancer burden to 2040 is expected to increase by 28.4 million cases. The dynamics of incidence and mortality from malignant neoplasms in the Russia is registered by the P. Hertsen Moscow Oncology Research Institute (MORI), branch of the National Medical Research Radiolog-ical Centre of the Ministry of Health of the Russian Federation. The data received in 2019 and 2010 were compared. The increase in cancer incidence over 10 years was 24%. However, thyroid cancer incidence surpasses other cancers incidence by 58%. The following main risk factors for potential regional induction of thyroid cancer are: the environmental situation in regions of Russia, the effects of the Chernobyl accident, and health effects of population exposed to radiation, approved with modern medical equipment. Based on epidemiological studies, it has been numerically proven that the above listed main risk factors are responsible for the significant increase in thyroid cancer incidence in Russia.

The current recommendations of the International Commission on Radiological Protection (ICRP) are based on the classification of exposure situations as: planned, emergency and existing exposure situations. In planned situations, annual risk limits are set to limit human exposure. However, in emergency exposure situations or in existing exposure situations, permanent (annual) source control is not always possible, so the radiation protection strategy by monitoring the individual annual risk limit cannot always be practically implemented either. The purpose of this work is to assess the radiation safety of the population currently residing (at the beginning of 2022) in six districts of the Bryansk region: contaminated with radionuclides as a result of the Chernobyl accident: in Gordeevsky, Zlynkovsky, Klimovsky, Klintsovsky, Krasnogorsky and Novozybkovsky districts. Assessment of the current state of radiation safety of the population is based on calculations of the radiation detriment from chronic exposure due to living in contaminated areas, considering uncertainties of the reconstructed exposure doses and the parameters of mathematical risk models for the population. Radiation damage is calculated according to the modern ICRP methodology. Based on the general principle of conservative assessment of safety, the calculated upper 95% confidence limits (95% CL) of radiation detriment are compared with the corresponding lifetime radiation detriment limit, 3.510-3, determined by the Russian radiation safety standards (NRB-99/2009) under normal exposure conditions for the nominal period 70 years of life for the public. The radiation safety of the population of the Klimovsky district corresponds to the normal conditions of exposure from technogenic sources of ionizing radiation. Among the population of the remaining five contaminated districts of the Bryansk region, critical groups have been identified, the radiation detriment for which exceeds the limit 3.510-3 for normal conditions of public exposure in planned situations. The results of this work can be used in the preparation of recommendations for health authorities to improve medical monitoring of exposed citizens living in territories contaminated with radionuclides, as well as in the development of regulatory documents for the provision of targeted medical care to people from high radiation risk groups with the use of personalized medicine methods.

Purpose: Investigation of the influence of the possible uncertainty of exposure doses of Russian participants in the liquidation of the consequences of the Chernobyl accident on the assessment of radiation risks of the incidence of solid cancer in this cohort. Material and methods: Epidemiological and dosimetric data on a cohort of Russian participants in the liquidation of the consequences of the accident at the Chernobyl NPP, registered in the National Radiation and Epidemiological Register (NRER), are used as initial data for assessing radiation risks. The assessment of radiation risks is carried out by the statistical method of maximum likelihood in the framework of a linear non-threshold model of excess relative risk. Uncertainties in the liquidator’s exposure dose in the adopted risk assessment method are considered in the form of two error models. Dose estimates based on data from individual dosimeters are characterized by a classical model of measurement errors. In the case of estimates of unknown individual doses from group dosimetry data or group route doses, the Berkson assignment error model is used. Results: A method for assessing radiation risks has been developed, accounting for the uncertainty in dose estimates, based on the observed likelihood function. When taking into account the uncertainty of estimates of individual doses in the cohort of Russian liquidators, the estimate of the coefficient of the excess relative rate per dose unit (ERR/Gy) for the incidence of solid malignancies decreases by 7%, compared with the estimate obtained directly from the doses registered in the NRER database. The ERR/Gy estimate derived from the doses recorded in the NRER database was 0.69 with a 95% confidence interval (CI) of 0.37–1.04. The estimate of ERR/Gy, obtained accounting for the uncertainty in estimates of individual doses of liquidators, was 0.64 at 95% CI (0.33–0.98). This estimate bias is not significant, since it is within 95% CI for both ERR/Gy estimates, the statistical range of which is of the order of magnitude of the estimates themselves. Conclusions: Considering the uncertainty of individual dose estimates in the cohort of Russian liquidators, the estimate of the excess relative rate per dose unit (ERR/Gy) for the incidence of solid cancer does not statistically significantly differ from the estimate obtained directly from the doses registered in the NRER database. The bias in the estimate of the radiation risk coefficient observed, due to the dose uncertainty introduced into the calculation, is due to the statistical properties of the traditional radiation risk models used for radiation epidemiology. The results obtained confirm the high stability and validity of the radiation risk assessments obtained earlier from the doses registered in the NRER for the Russian cohort of Chernobyl liquidators. Further research will allow generalization of the developed method for assessing radiation risks, accounting for the uncertainty of dose estimates, based on the observed likelihood function, to other types of radiation epidemiological risk studies, including case-control and case-cohort studies.

Currently, the system of standards and rules of radiation protection considers the need to con-straint the absorbed radiation doses in order to prevent the development of deterministic effects of ionizing radiation on humans. Deterministic effects in terms of mortality include bone marrow syndrome with a dose threshold of 1 Gy, gastrointestinal syndrome and pneumonitis with dose thresholds of 6 Gy. For inclusion in international radiation safety standards, a threshold of 0.5 Gy for cardiovascular and cerebrovascular diseases is being discussed. The wide experience of ra-diation-epidemiological studies shows that the deterministic effects of mortality are not limited to those effects that are currently considered in the system of standards and rules of radiation pro-tection. This paper presents estimates of radiation risks of mortality from diseases of the circula-tory system (CSD) and the digestive system, as well as dose thresholds corresponding to these effects, in the Russian cohort of liquidators of the Chernobyl accident registered in the National Radiation and Epidemiological Register (NRER), who have registered doses from external whole-body exposure to gamma radiation within 1 Gy. The risks were estimated over the follow-up peri-od 1986-2020. The stability of estimated radiation risks of mortality from CSD and from the di-gestive system diseases in relation to the uncertainty of personal doses received by liquidators has been studied. The absorbed doses received by 11% of the liquidators were estimated from the data of personal dosimeters, the maximum error was about 50%. For the remaining 89% of liquidators, group and route doses were registered, and the maximum uncertainty of individual doses was about 500%. For CSD mortality, the excess relative rates per 1 Gy (ERR/Gy) were 0.361 and 0.349, excluding and considering dose uncertainties, respectively. For mortality from diseases of the digestive system, ERR/Gy=0,791 excluding dose uncertainty and ERR/Gy=0,726 with considering dose uncertainty. Uncertainties in individual dose estimates result in 5% and 8% reductions in ERR/Gy estimates (for CSD mortality and digestive disease, respectively). This re-duction in risk estimates is not related to a bias in the dose estimates. It is caused by the statistical properties of radiation risk models in conventional radiation epidemiology. If the excessive mor-tality from the studied causes is attributed to deterministic effects, then the estimates of the corre-sponding dose thresholds, considering the uncertainty of individual doses, also increase quite slightly: for CSD – from 0,028 Gy to 0,029 Gy, and for diseases of the digestive system – from 0,013 Gy to 0,014 Gy. The obtained results confirm the high stability and validity of radiation risk assessments of non-oncological diseases obtained earlier from the doses of Russian partici-pants in the liquidation of the consequences of the Chernobyl accident registered in the unified federal database of the NRER.

This work is devoted to a comparative analysis of the assessment of radiation risks of medical diagnostic exposure of patients using a method based on the recommendations of the International Commission on Radiological Protection (ICRP) and the method presented in the methodological recommendations of Rospotrebnadzor (MR 2.6.1.0215-20). In the course of the study, the authors analyzed the results of calculations of the lifetime attributable risk of oncological mortality calculated by these methods. As an example, the procedure of a single passage of computed tomography of the chest organs without contrast was considered. In the first case, the risk value was calculated using the methodology of ICRP Publication 103 based on organ doses for the following ages of men and women: examination at 22, 27, 32, 37, 42, 47, 52, 57, 62, 67, 72, 77, 82 and at 87 years old. In the second case, the data given in the tables presented in the methodological recommendations were considered, but without considering hereditary effects. The analysis was carried out for two cases: when the difference between effective doses between computed tomography procedures did not exceed 30%, and when the difference was more than 30%. The authors of the work found that the difference in the risk assessment between the two methods exceeds 1.5 times for the age groups of 65 years and older, for men and women, if the effective doses are close. If the difference in dose between the two procedures was more than 30%, then a 1.5-fold difference in risks was observed in age groups 60 years and older. Risk assessment was performed with account of age and gender characteristics, as well as with the use of medical and demographic data of the Russian population.

One of the main tasks of the National Radiation Epidemiological Registry (NRER) is monitoring the health status of people exposed to radiation as a result of the Chernobyl accident, and provid-ing them with targeted medical care. To optimize the use of resources dedicated to mitigating health effects of the accident, it is reasonable to identify the people at the higher radiation risk, needing the priority medical care. Radiation risk is directly proportional to radiation dose the indi-viduals received, and also depends on the age, sex of the exposed persons and their baseline (in the absence of radiation) risk rates. Among all the people been registered in the NRER the Cher-nobyl cleanup workers (liquidators) received the highest radiation doses. To determine the group of higher radiation risk of solid cancer among liquidators, an estimate of the attributable radiation fraction, ARF, was used. Among the all liquidators observed in the NRER in 2020, 709 persons, 1.45%, were at the higher risk group of solid cancer, with ARF values exceeding the critical value of 15%. If the critical value of ARF drops to 10%, the group at the higher risk increases to 28% of the total number of the cohort members. The size of the group at the higher risk can be increased or reduced with the use of critical ARF values, depending on the current social and economic sit-uations. However, according to the international experience and assessment results presented in the paper, the critical ARF value may be selected within the range between 10 and 20%.

Currently the application of diagnostic imaging procedures is extended. After the COVID-19 out-break the number of radiological examinations have increased significantly. The number of re-peated radiological examinations increased as well. Although the risk of cancer from single radi-ological scanning is small, risk from multiple imaging has not been estimated yet. The develop-ment of methodology for assessment of cancer risks from multiple radiological examinations is needed. This paper presents the procedure for assessment of radiation risks from multiple radio-logical examinations of any type. The validity of the developed approach was tested on the ex-ample of assessment of lifetime attributable risk (LAR) of cancer incidence from multiple com-puted tomography (CT) examinations, the results are discussed in the paper. The authors devel-oped the method for estimating radiation detriment from multiple radiological CT scans for re-maining life years. The method is based on equivalent radiation doses to organs and tissues of a patient’s body. Tables of LARs values per dose unit for males and females within the age range 0-95 years and a step of 5 years were designed. The tables were computed for the following cancer sites: bladder, breast, colon, bone marrow, liver, lungs, esophagus, ovary, stomach, thy-roid and other solid. The authors estimated cancer risks for a female, she was exposed to radia-tion from CT scanning. The female’s risks assessed with the developed methodology were com-pared with radiation risks estimated with mathematical model ICRP (Publication 103). The com-parison showed that the difference between risks estimated with the developed method and the risks estimated with the ICRP model did not exceed 12%. In models sex and age were account-ed, medical and demographic data applicable to the Russian population were taken into account as well.

As stated in the Basic sanitary rules of radiation safety, radiation risk is one of the main character-istics of radiation safety. Before the work persons involved in cleanup operations after radiation accidents should be informed about subsequent risks to their health. However, mathematical models for radiation risk prediction and methods for its calculation are currently at the stage of scientific research and have not yet been standardized for solving practical problems of risk pre-diction. At the international level, UNSCEAR, ICRP and WHO developed radiation risk models on the basis of radiation-epidemiological data on survivors of Hiroshima and Nagasaki atomic bombings in August 1945. In recent decades, data on radiation-epidemiological follow-up of co-horts contained people exposed to radiation after the Chernobyl accident in 1986, in particular NRER data, have been used to identify and assess radiation risks. The radiation risk models iden-tified from the Chernobyl cohorts of exposed individuals differ from the models identified from the Japanese cohort, which leads, respectively, to different projections of lifetime radiation risk. The purpose of this work is to compare quantitatively the possible lifetime radiation risks of can-cer for a cohort of Russian liquidators of the Chernobyl accident, evaluated with radiation risk models developed by UNSCEAR, WHO and NRER. It is shown that after 2020, 1297 cases of cancer are expected in the cohort of Russian liquidators, this figure is 2.4 times higher than esti-mates obtained with the international models. The radiation risk model of leukemia, built on the basis of NRER follow-up data, predicts 145 cases of leukemia in the observed cohort of liquida-tors, which is 8 times higher than the values estimated with the use of international models. Since the liquidators of the considered cohort are generally over 50 years old, the results obtained may indicate the need to adjust the dose limits established by the current radiation safety standards based on ICRP risk models for people over 50 years old.

The paper considers radiation risks of solid cancer incidence and mortality, as well as risk of leu-kemia incidence (other than chronic lymphocytic leukemia) among Russian Chernobyl cleanup workers (liquidators). The study of the cohort of liquidators carried out at the National Radiation Epidemiological Registry (NRER) was based on the follow-up data collected from 1992 over 2019. The size of the Chernobyl cleanup workers cohort exceeded 65 thousand people, their av-erage age at the time of entering the exclusion zone was 34 years, the average external gamma radiation dose received by liquidators during their cleanup work was about 0.133 Gy. Radiation-induced risks of solid cancer incidence and mortality in the study cohort were statistically signifi-cant, the risk magnitude rose with increasing the follow-up length. For the maximum follow-up period, from 1992 over 2019, the excess relative risk coefficient for solid cancer incidence was ERR/Gy=0.62, 95% CI (0.29; 0.98), and excess relative risk coefficient for solid cancer mortality was ERR/Gy=0.74, 95% CI (0.32; 1.22), the estimated coefficients were in good agreement with similar coefficients calcu-lated for the Russian liquidators with the use of ICRP radiation risk models. Non-parametric esti-mates of relative radiation risk within the same dose intervals for solid cancers and for leukemias in the cohort of liquidators were statistically significant for radiation doses above 0.150 Gy. For radiation doses below 0,150 Гр the linear non-threshold model is conservative, i.e. there was ev-idence for statistically significant radiation risk of leukemia incidence among liquidators during the first 11 years after the accident, from 1986 over 1997, ERR/Gy=4.41, 95% CI (0.24; 14.23). In later years, until 2018 there was no evidence of radiation-related risk of leukemia incidence. Out-comes of future studies will impact on optimization of radiological protection, development of reference levels for Russian general public exposure and improvement of the system for delivery of targeted medical care to people exposed to radiation.

Some areas of the Russian Federation were contaminated with radionuclides released as a re-sult of the Chernobyl accident. The current paper clarifies some items of the previously published study based on NRER (National Radiation-Epidemiological Registry, the Registry) data. The pre-vious issue presented estimates of radiation risks of cancer incidence among the population of four the most contaminated regions of the Russian Federation: Bryansk, Kaluga, Oryol and Tula oblasts. Risks of thyroid cancer are estimated with account of screening effect. The cohort con-sisted of more than 327 thousand people resided in the contaminated areas. The average dose to the thyroid of children and adolescents was 0.174 Gy, the average dose to the thyroid of adults was 0.035 Gy. Thyroid cancer was diagnosed in 1549 members of the cohort during the follow-up period from 1991 over 2019, among them 423 cases were children and adolescents at the accident and 1126 cases were adults. Significant increase in thyroid cancer incidence was ob-served in adults exposed internally through the intake of iodine-131 at a young age. The statisti-cally significant radiation risk of thyroid cancer persists over 30 years after exposure. The risk de-creases with increasing the attained age. In people exposed to radiation before the age of 1 year and reaching the age of 20 years, the coefficient of excess relative risk of thyroid cancer (ERR/Gy) was 4.61. Radiation associated thyroid cancer is attributed to 20.6% of the cohort mem-bers exposed internally through the intake of radioiodine isotopes in their childhood and adoles-cence, and thyroid cancer from intake of radioiodine is attributed to 58% of cases exposed to ra-diation under 4 years of age. Marked screening effect (ES) was found during the disease diag-nosing, screening coefficient was 5.6 for children and 2.1 for adults. There were not attributed to radiation statistically significant risks of solid cancers, including radiation induced breast cancer in females, in the cohort of people resided in the areas contaminated with radionuclides. Radia-tion risk of leukemia was also not identified, although the average value of excess relative risk in men exceeded zero. Further observations of the cohort of persons resided in areas contaminated with radionuclides will increase the statistical power of radiation-epidemiological studies and clarify the assessment of radiation risks of human for chronic exposure at low doses.

In the absence of man-made sources of ionizing radiation health risks are related primarily to non-malignant diseases, particularly circulation diseases. However, risks of radiation-induced non-cancer diseases can make a notable contribution to the overall radiation-associated detri-mental effects to the human health. The impacts of harm caused by radiation induced non-cancer and cancer diseases are comparable. That is why the study of risks of non-cancer diseas-es for health of the Chernobyl cleanup workers is actual scientific problem, it is also essential for radiation protection. The aim of the study is to estimate radiation risks of incidence and mortality from non-cancer diseases identified in the Russian cohort of the Chernobyl liquidators during the follow-up period. All considered non-communicable diseases have proven diagnoses identified according to ICD-10 chapters and code sets. The data for the study are available in the system of the National Radiation Epidemiological Registry (NRER). For estimating risks of low radiation doses the linear non-threshold (LNT) model was used. For 9 of 19 disease diagnosis codes in-vestigated for statistical significance of associations between excess incidence of a disease and radiation dose received by liquidators can be considered as significant code sets. These are the following diseases: 1) Diseases of the blood and blood-forming organs and certain disorders in-volving the immune mechanism (D50-D89); 2) Diseases of the endocrine system, nutritional dis-orders and disorders of metabolism (E00-E90); 3) Mental and behavioural disorders (F00-F99); 4) Diseases of the nervous system (G00-G99); 5) Diseases of the circulatory system (I00-I99); 6) Diseases of the respiratory system (J00-J99); 7) Diseases of the digestive system (K00-K93); 8) Diseases of the musculoskeletal system and connective tissue (M00-M99); 9) Diseases of the genitourinary system (N00-N99). Diseases of the blood and blood-forming organs and certain disorders involving the immune mechanism (D50-D89); diseases of the circulatory system (I00-I99); blood diseases (D50-D89) are characterized by the highest radiation risk coefficients (ERR/Gy). The estimates are ERR/Gy=0.55 and ERR/Gy=0.57, respectively. To date, epidemiolog-ical studies provide sufficient evidence for the existence of statistically significant radiation risks of the circulatory system diseases (I00-I99). For estimating contribution of non-cancer diseases to the overall radiation detriment further research is required.

Purpose: In an article prepared on the basis of the conclusion of the Russian Scientific Commission on Radiological Protection (RSCRP) at the Department of Medical Sciences of the Russian Academy of Sciences "Assessment of the radiological consequences of the Chernobyl accident after 35 years according to the National Radiation and Epidemiological Register" (NRER), the main conclusions of the large-scale radiation-epidemiological studies carried out. Material and methods: The work uses information NRER – liquidators of the consequences of the Chernobyl accident and the Branch Register of FMBA of Russia – liquidators. When assessing the excess relative risk of malignant neoplasms, the EPICURE. Results: The current status of the National Radiation and Epidemiological Register, which is currently functioning within the framework of the Law of the Russian Federation of 30.12.2012 No. 329-FZ “On Amendments to Certain Legislative Acts of the Russian Federation in terms of ensuring that changes in the health status of certain categories of citizens are taken into account exposed to radiation". For the first time in an integral form, the article presents the medical radiological consequences of the accident at the Chernobyl nuclear power plant for the population of Russia. It was found that an increase in the incidence of thyroid cancer due to incorporated exposure to 131I was found in a cohort of children and adolescents (28 856 people) who received radiation doses of more than 200 mGy in 1986. There was no increase in the incidence of thyroid cancer among the adult population. Analysis of the incidence of solid cancers in the territories of the Bryansk, Kaluga, Tula and Oryol regions contaminated with radionuclides did not reveal an increase in the frequency of this pathology for children and adults. It is shown that in the cohort of liquidators of the Chernobyl accident, who received radiation doses of more than 150 mGy (35 303 people), an increase in the incidence of leukemia during the first 11 years after the accident at the Chernobyl nuclear power plant and solid cancers was revealed in comparison with the spontaneous level. Conclusions: The article points out serious limitations associated with a high degree of uncertainty in the received personal dosimetric data on liquidators in 1986–1987. and the need to use the total dose from all types of radiation (professional, emergency, medical, natural) to calculate the radiation risk. RSCRP emphasizes the high urgency of continuing work on reducing the uncertainty of dosimetry data and assessing the radiological consequences of the Chernobyl accident based on a comprehensive analysis of the NRER data.

Purpose: Calculations of radiation detriment to the population currently living (in 2020) in the territories of Russia contaminated with 137Cs after the Chernobyl accident in 1986. Material and methods: Radiation detriment was calculated in two ways: according to the original ICRP method, and approximate calculation as the product of the nominal risk factor of RSS-99/2009 by the effective dose (nominal radiation detriment). For ICRP calculations, equivalent doses were estimated using the dose coefficients of the US Environmental Protection Agency (EPA). The number of the studied population at the beginning of 2020 was 142676 people, 65205 men and 77471 women. This is mainly the population of the Bryansk region and Tula region, 85.5 % and 10 % of the total population, respectively. The average accumulated effective dose of the population was 30.6 mSv, and the maximum individual accumulated dose was 707 mSv. Results: In 2020, for men at the age of 44 and for women at the age of 55, the nominal radiation detriment is approximately equal to the value of radiation detriment calculated using the ICRP method. At the same time, the nominal detriment is significantly (up to 2.3 times) underestimated for younger and overestimated for older ages. In 2020, the critical population groups with the highest accumulated doses and maximum radiation detriment are men aged 34 and women aged 35. For these population groups, the average accumulated effective doses were 35.3 mSv and 39.2 mSv, and the average radiation detriment was 2.6×10–3 and 4.2×10–3, for men and women, respectively. For 11.8 % of the population (8.3 % of men and 14.8 % of women), the individual radiation detriment calculated using the ICRP method exceeds the value of 3.5×10–3, which corresponds to the maximum increase in individual risk for the population over 70 years of exposure, established by RSS-99/2009 for normal exposure conditions. The maximum radiation detriment of 3.9×10–2 was found for a woman of the Krasnogorsky district of the Bryansk region at the age of 37 years, with an accumulated effective dose of 392 mSv. Conclusion: The results of this work can be used in preparing recommendations to health authorities on improving medical supervision of exposured citizens living in areas contaminated with radionuclides, as well as in developing regulatory documents for the provision of targeted medical care to people from high radiation risk groups using personalized medicine methods.