METHODOLOGY OF RECONSTRUCTION OF INDIVIDUALIZED EXPOSURE DOSES FOR PERSONS RESIDING AT RADIOACTIVELY CONTAMINATED TERRITORIES OF UKRAINE. / METODYKA REKONSTRUKTsIÏ INDYVIDUALIZOVANYKh DOZ OPROMINENNIa OSIB, ShchO MEShKAIuT' NA RADIOAKTYVNO ZABRUDNENYKh TERYTORIIaKh UKRAÏNY.

OBJECTIVE: Development of methodology for reconstruction of individualized exposure doses for persons residing atradioactively contaminated after Chornobyl accident territories.Materials and methods of research. The methodology is based on the data of radio-ecological (ground, meal) anddosimetric (WBC measurements) monitoring held in Ukraine in 1986-2013, the results of which are saved in databases of Central Ecological and Dosimetric Register of Radiation Protection Laboratory of NRCRM. It is presentedfour levels of individualization of exposure doses. Each subsequent level of the model is based on the previous oneand takes into account additional parameters, and as a result a model of the next level comprises more number ofexposure situations and provides more accurate estimates. Using the methodology it is necessary to select a modelof such level that enables to solve in the best way the assignments posed before a researcher. For the population ofradioactively contaminated territories, two main ways of exposure are considered: (a) external gamma-exposurefrom radionuclides in the ground, and (b) internal exposure from consumption of radioactively contaminated meal.The dose is evaluated from all the main radionuclides of radioactive accident deposition, and in case of internalexposure after 1986 - only from radio-isotopes of cesium (134Cs and 137Cs). RESULTS: Individualized doses are evaluated for different age groups of population residing in 10 raions of the mostcontaminated after Chornobyl accident Oblasts of Ukraine: Zhytomyr, Kyiv, Rivne and Chernihiv Oblasts. Dose esti-mates are presented weighted by the number of residents in settlements of specific raions. Among them are: thedose for 1986, doses accumulated during the first 15 years after the accident (1986-2000), and during the periodof 32 years after the accident (1986-2017). CONCLUSIONS: Average raion dose reconstructed for adult residents of the most radioactively contaminatedNarodychy Raion of Zhytomyr Oblast in 1986 was 18 mSv, and accumulated during the whole period after the acci-dent was 51 mSv. The lowest doses among abovementioned 10 raions were obtained by persons residing at the ter-ritory of Kozelets and Ripky Raions of Chernihiv Oblast. Average dose for them in 1986 constituted 1.3 and 1.7 mSv,and the one accumulated during 32 years was 6.1 and 6.2, respectively.

Reconstruction of individualized doses of subjects from the Ukrainian State Register - of Persons that Affected due to Chornobyl accident and reside in Korosten raion of Zhytomyr oblast. / REKONSTRUKTsIIa INDYVIDUALIZOVANYKh DOZ SUB'IeKTIV DERZhAVNOGO REIeSTRU UKRAÏNY OSIB, IaKI POSTRAZhDALY VNASLIDOK ChORNOBYL'S'KOÏ KATASTROFY, ShchO PROZhYVAIuT' V KOROSTENS'KOMU RAY̆ONI ZhYTOMYRS'KOÏ OBLASTI.

STUDY OBJECTIVE: To elaborate an ecological dosimetric model of reconstruction individualized exposure doses of subjects from the State Register of Ukraine (SRU) - of persons, affected due to Chornobyl accident and reside at the radioactive contaminated territory of Korosten raion of Zhytomyr Oblast, and to calculate exposure doses for those persons. MATERIALS AND METHODS: In the paper, an ecological dosimetric model is presented which is elaborated in order to individualize exposure doses of people who reside in Korosten raion of Zhytomyr Oblast and are registered in SRU. The model is based on the results of radio ecological and dosimetric monitoring held in the period of 1986-2013 at the territory of northern oblasts of Ukraine. Annual dose over each post accidental year consists of the two compo nents: (a) annual effective dose of external gamma exposure (due to radioactive fallout on the ground), and (b) internal exposure of the whole body (due to consumption of meal contaminated by radioactive isotopes). For 1986, the dose of internal exposure is evaluated out of all main radionuclides of radioactive accidental fallout, and after 1987 only for radioisotopes of caesium (134Cs and 137Cs). The parameterization of the model is based on the pre vious experience in working out a complex of ecological dosimetric models for estimation of referent exposure doses of Ukrainian population. RESULTS AND CONCLUSIONS: Individualized doses of external and internal exposure (annual and accumulated) are estimated for the population of various age groups that resides in the settlements of Korosten raion (totally about 100 settlements). Separately the doses are presented for rural settlements of the raion and for the city of Korosten for each year of the post accidental period of 1986-2016. Estimates of doses are given that were accumulated: (a) during 15 years just after the accident, (b) for the period of 2000-2016, and (c) for 30 year period after the acci dent. Mean dose accumulated for 30 years after the Chornobyl accident by residents of rural settlements of Korosten raion is estimated as 19.8 mSv, and for inhabitants of the Korosten city as 20.9 mSv. On condition of permanent res idence in the raion, residents of about 66 % settlements of Korosten raion accumulated the doses in the interval 5 20 mSv during 30 years after the accident. For the residents of about 25 % settlements the accumulated dose is in the interval 20-50 mSv, and for 7 % of settlements it exceeds 50 mSv.

Estimation of radiation risk in presence of classical additive and Berkson multiplicative errors in exposure doses.

In this paper, the influence of measurement errors in exposure doses in a regression model with binary response is studied. Recently, it has been recognized that uncertainty in exposure dose is characterized by errors of two types: classical additive errors and Berkson multiplicative errors. The combination of classical additive and Berkson multiplicative errors has not been considered in the literature previously. In a simulation study based on data from radio-epidemiological research of thyroid cancer in Ukraine caused by the Chornobyl accident, it is shown that ignoring measurement errors in doses leads to overestimation of background prevalence and underestimation of excess relative risk. In the work, several methods to reduce these biases are proposed. They are new regression calibration, an additive version of efficient SIMEX, and novel corrected score methods.

Generalized results of individualized exposure doses reconstruction for the subjects of Ukrainian State Register of persons, affected due to Chernobyl accident. / UZAGAL'NENI REZUL'TATY REKONSTRUKTsIi INDYVIDUALIZOVANYKh DOZ SUB'IeKTIV DERZhAVNOGO REIeSTRU UKRAiNY OSIB, IaKI POSTRAZhDALY VNASLIDOK ChORNOBYL'S'KOi KATASTROFY.

Since 2007, the department of dosimetry of NRCRM has been working for to supply the Ukrainian State Register (SRU) of persons affected due to Chernobyl accident by exposure doses estimations. As of now, the individualization of doses has been performed for nine raions located in Kyiv, Zhytomyr, Rivne and Chernihiv oblasts. The structure of raion-specific models used for the reconstruction of individualized doses was described in detail in the previous 19-th issue of this journal (2014). The choice conditions for persons from the SRU using which for each raion there was formed a contingent of persons for whom the dose could be reconstructed. During the period of 2007-2015, the individualized dose was reconstructed for 244226 persons in 9 raions, representing ~ 58% of all registered in the SRU inhabitants of the raions. The calculation results were transferred to the SRU in formats adapted to the common database structure of the SRU. For each person who satisfied the conditions of selection there were estimated: (1) possible absorbed internal exposure dose of the thyroid by radioiodine in 1986 (assuming that the person in 1986 lived in the same village and was enlisted in the SRU); (2) annual doses of external, internal and total exposure of the whole body for a period of observation in the SRU; (3) total exposure dose of whole body accumulated during the period of observation in the SRU; (4) the total cumulative dose of feasible exposure during the period since 1986 till the decision to be registered in the SRU. There are presented the generalized results of the SRU subjects distribution for different raions in dependence on intervals of doses accumulated at different periods after the accident. The raion matrix tables show the dynamics of accumulation of doses by the SRU subjects both for their stay on the account and for the period of their possible residence registration in the settlement since 1986. The directions for further research to be implemented for increasing the number of persons for whom it is possible to calculate individualized dose have been formulated.

Basic Principles and Practices of Integrated Dosimetric Passportization of the Settlements in Ukraine. / OSNOVNI PRYNTsYPY TA DOSVID PROVEDENNIa KOMPLEKSNOi DOZYMETRYChNOi PASPORTYZATsIi NASELENYKh PUNKTIV UKRAiNY.

OBJECTIVE: The purpose of the review is to demonstrate the results of dosimetric passportization (performed in 1991-2014) for the settlements of Ukraine which suffered from radioactive contamination caused by the Chornobyl accident. The dosimetric passportization played a key role in the National program on the liquidation of aftermath of the Chornobyl accident directed on recovery through all stages of the current radiation situation control and decision support touching upon various types of interventions and social benefits to the population of radioactively contaminated areas. The works being performed under dosimetric passportization did not have analogues among the researches which took place after other large-scale industrial and municipal accidents as well their scales as the duration of both radio-ecological and dosimetric monitoring.The new methodological approaches to the assessment of so-called passport doses of a settlement as well as to the definition of the concept of annual dose being the dose used to make decisions for providing both direct and indirect emergency countermeasures for the settlements of Ukraine became pioneering ones. During all the post-accident period there were issued sixteen collections of general dosimetric passportization data which accumulate the results of hundreds of thousands spectrometric, radiochemical and radiation levels measurements and WBC measurements carried out in 1991-2014.The annual passport doses calculated on the basis of these measurements (including their components) are unique information that quantifies the level and time dynamics of the radiation situation for each of the 2161 settlements of 74 raions in 12 oblasts during all the post-accident period. Thanks to the works of dosimetric passportization of the settlements of Ukraine there were created databases to be unique in their structure and content with quantitative characteristics of the territorial and temporal distribution, the dynamics of changes of a number of important radiological parameters, namely over 500 thousands of measurements of concentration of 137Cs and 90Sr in the local foodstuff (milk and potatoes); there are more than 1.3 million of measurements of the cesium content in the body of residents of the settlements of Ukraine; there are 100 thousands of dose estimates (both internal and external ones were measured separately) of inhabitants living on the radioactively contaminated areas. The results of the dosimetric passportization served as one of the main exposure criteria for generalized aftermath of the Chornobyl accident represented in the National reports for the first 15, 20 and 25 years after the accident.

Interpretation of results of radioiodine measurements in thyroid for residents of Ukraine (1986). / INTERPRETATsIIa REZUL'TATIV VYMIRIuVAN' VMISTU RADIOiODU U ShchYTOPODIBNIi ZALOZI MEShKANTsIV UKRAiNY (1986 RIK).

OBJECTIVE: The purpose of this research is to make analysis, revision and estimation both reliability and accuracy of all measurements of radioiodine in the thyroid for residents of Ukraine, which were performed in 1986, and to justify the calibration factors to be applied for interpretation of measurements performed by non-calibrated devices. MATERIALS AND METHODS: The radioiodine activity in the thyroid for residents of the most contaminated oblasts of Ukraine has been calculated on the base of 150 thousands direct measurements of the content of 131I in thyroid obtained in the frames of the thyroid monitoring in 1986. A method for the calculation of measurement errors has been developed and the accuracy of the errors has been determined assuming that the density of errors' distribution for main parameters of the measurements is close to Gaussian. Using the results of laboratory measurements, the calibration factors have been determined for integrated radiometers SRP-68-01 - devices which were often used to perform the thyroid dosimetric monitoring. RESULTS: The distribution of estimates on the content of radioiodine in thyroid is close to the lognormal one with geometric mean being equal to 4.8 kBq and geometric standard deviation being equal to 3.8. Most of these estimates (90 %) are in the range of 0.58-47 kBq, and the main set of their relative errors (90 %) are between 0.1 and 0.6. Thus, the model of thyroid activity observation with classical additive error has been obtained.

Individualized internal exposure doses reconstruction for the persons of Ukraine State Register: Report 2. Locally-specific models and doses of persons living in Kozelets and Ripky raions of Chernihiv oblast. / Rekonstrukciya individualizirovannyx doz vnutrennego oblucheniya sub""ektov Gosudarstvennogo Registra Ukrainy: Soobshhenie 2. Lokal''no-specificheskie modeli i dozy oblucheniya zhitelej Kozeleckogo i Repkinskogo rajonov Chernigovskoj oblasti.

Study objective. Development a system of models and procedures for the individualized internal exposure doses reconstruction for the subjects of Ukrainian State Register of persons, affected due to the Chornobyl accident (SRU) and residing in radioactive contaminated territories of Kozelets and Ripky raions of Chernihiv oblast. Materials and methods. A description the schematic diagram and mathematical equations of ecological-dosimetric models are given that allow to reconstruct the individualized exposure doses from consumption of food contaminated with radiocesium of Chornobyl origin for inhabitants of two raions of Chernihiv oblast. Parameterization of the reconstruction models is based on the mathematical analysis of results for radioecological (radiocesium milk contamination) and dosimetric (radiocesium human body burden) monitorings, that were calculated in the period of 1986-2012 in the settlements of raions under consideration. Due to quite low level of radioactive cesium depositions on the ground in 1986, the territory of these raions was divided into two "territorial zones": TZ-1, an area where the 137Cs ground depositions density in 1986 exceeds 37 kBq/m2, and TZ-2, an area where this rate does not exceeds 37 kBq/m2. For each territorial zone in each raion, the initial time moment (year) was introduced in the reconstruction model. Since this year the concept of the so-called "reference dose" has been using. Its value was assigned to all persons, regardless of the results and availability of monitoring. The results of radioecological and dosimetric monitorings were used for setting in raion specific functions: the annual average concentration of 137Cs in milk per unit of 137Cs ground depositions for Kozelets raion, function of the temporary dynamic of 137Cs concentration in milk for Ripky raion, absolute raion milk equivalent of the diet (ARMEr), and relative age dependent intake of radiocesium with the diet. Results and conclusions. Models for individualized internal exposure doses reconstruction were applied to 27811 SRU subjects from Kozelets raion and 14553 SRU subjects from Ripky raion. Results of doses individualization are given as annual average values of internal and summarized (internal and external) exposure doses for the period of 1987-2012, as well as the distribution of SRU subjects of different raions according to the intervals of accumulat-ed doses over the entire period of observation.

Individualized internal exposure doses reconstruction for the persons of Ukraine State Register: Report 1. Locally-specific models and doses of persons living in Rokytne raion of Rivne oblast, Ovruch raion of Zhytomyr oblast and Ivankiv raion of Kyiv oblast. / Rekonstrukcija individualizirovannyh doz vnutrennego obluchenija subektov Gosudarstvennogo Registra Ukrainy: Soobshhenie 1. Lokal''no-specificheskie modeli i dozy obluchenija zhitelej Rokitnovskogo rajona Rovenskoj oblasti, Ovruchskogo rajona Zhitomirskoj oblasti i Ivankovskogo rajona Kievskoj oblasti.

Study objective. Dosimetric support of the Ukrainian State Register of persons, affected due to the Chornobyl accident (SRU). Development the system of models and procedures for the individualized internal doses reconstruction for the subjects of SRU residing in radioactive contaminated territories of Rokytne raion of Rivne oblast, Ovruch raion of Zhytomyr oblast and Ivankiv raion of Kyiv oblast. Materials and methods. A detailed description for the schematic diagram of the methodology and mathematical relations of ecological-dosimetric models are given. It allows to reconstruct the individualized doses from the ingestion of food contaminated by radiocesium after the Chornobyl accident for the subjects of SRU from three raions of Rivne, Zhytomyr and Kyiv oblasts. Phenomenologically, the developed models are close to the previously developed complex of ecological and dosimetric models intended to estimate the reference doses for the entire population of Ukraine. Calibration of model parameters is based on mathematical treatment for results of extensive radioecological (radiocesium milk contamination) and dosimetric (radiocesium burden in human body) monitorings, that were provided in the period of 1986-2012 in the settlements of raions under consideration. Completeness and periodicity of radioecological and dosimetric monitorings allowed to realize the settlement-specific approach for dose reconstruction, wherein for each settlement either the function of radiocesium intake with diet or the function of time-variation of radiocesium concentration in the local cow's milk were established. Absolute raion milk equivalent of the diet (ARMEr) and relative age dependent intake of radiocesium with diet are specified as a raion-specific functions for each raion. ARMEr is used to calculate the doses of adults in the settlement for which the function was specified. RRI is used to calculate the doses for the subjects of four children age groups (< 2 years old, 3-7 years old, 8-12 years old, 13-17 years old). Results and conclusions. Models for individualized internal exposure doses reconstruction of SRU subjects are developed. The individualized doses are estimated for 28711 SRU subjects from Rokytne raion, 18790 SRU subjects from Ivankiv raion and 41585 SRU subjects from Ovruch raion. Results of doses individualization are given as annual average doses for the period of 1987-2012. The distribution of SRU subjects of different raions over the intervals of doses accumulated over the entire observation period is also given. Values of total (from internal and external exposure) doses for SRU subjects of the raions under consideration are given, as well.

Reconstruction of individual thyroid doses to the Ukrainian subjects enrolled in the Chernobyl Tissue Bank.

The Chernobyl Tissue Bank (CTB) is an organisation that collects and stores samples of tumoral thyroid tissue obtained from Ukrainian and Russian subjects who were treated surgically for a thyroid cancer and had been exposed to (131)I from the Chernobyl accident. By 2012, the CTB had collected specimens of thyroid tissue from 2267 residents of Ukraine for the purpose of radiation research. Arithmetic mean thyroid doses and uncertainties have been estimated for all but 24 subjects for whom residence at the time of exposure was not found. The subjects have been classified into six groups or sub-groups according to the type of dosimetry-related information that is available for each of them. Excluding the 325 subjects with negligible radiation exposure, the arithmetic mean of the thyroid dose over all subjects is estimated as 0.4 Gy, with individual values ranging from <1 mGy to 13 Gy. The uncertainties in the individual thyroid dose estimates, characterised by the geometric standard deviations of their probability distributions, range from 1.3 to 8.7, with an arithmetic mean of 3.2.

Estimating thyroid masses for children, infants, and fetuses in Ukraine exposed to (131)I from the Chernobyl accident.

For the purpose of improving retrospective internal thyroid dose estimations for children and adolescents following the Chernobyl accident, age- and gender-dependent thyroid masses have been estimated for the children of Kiev and Zhytomyr oblasts, which are two of the most contaminated regions of Northern Ukraine. For children ages 6-16 y, the thyroid masses were based on the measurements by ultrasound of the thyroid volumes of about 60,000 children performed by the Sasakawa Memorial Health Foundation in the 1990s. For children aged 0 to 36 mo, because thyroid mass values for Ukrainian children were not found in the literature, autopsies were performed for the specific purpose of this paper. Thyroid mass values for children aged 3-5 and 17-18 y were either interpolated or extrapolated from the measured data sets. The results for children aged 6-16 y indicate that the thyroid masses of rural children are, on average, slightly higher (by about 8%) than the thyroid masses of urban children. The geometric means of the thyroid masses were estimated as 5.2 g, 9.0 g, and 15.8 g for boys and 5.2 g, 9.4 g, and 16.0 g for girls aged 5, 10, and 15 y, respectively. Those values are greater than the reference values that ICRP recommends for iodine-sufficient populations, thus reflecting the fact that the northern part of Ukraine is iodine-deficient.

Estimation of the thyroid doses for ukrainian children exposed in utero after the chernobyl accident.

This paper describes methods for estimating thyroid doses to Ukrainian children who were subjects of an epidemiological study of prenatal exposure and presents the calculated doses. Participants were 2,582 mother-child pairs in which the mother had been pregnant at the time of the Chernobyl accident on 26 April 1986 or in the 2-3 mo following when (131)I in fallout was still present. Among these, 1,494 were categorized as "exposed;" a comparison group of 1,088 was considered "relatively unexposed." Individual in utero thyroid dose estimates were found to range from less than 1 mGy to 3,200 mGy, with an arithmetic mean of 72 mGy. Thyroid doses varied primarily according to stage of pregnancy at the time of exposure and level of radioactive contamination at the location of residence. There was a marked difference between the dose distributions of the exposed and comparison groups, although nine children in the latter group had calculated doses in the range 100-200 mGy. For those children who were born after the accident and prior to the end of June 1986, postnatal thyroid doses were also estimated. About 7.7% (200) of the subjects received thyroid doses after birth that were at least 10% of their cumulative doses.

A screening study of thyroid cancer and other thyroid diseases among individuals exposed in utero to iodine-131 from Chernobyl fallout.

BACKGROUND: Like stable iodine, radioiodines concentrate in the thyroid gland, increasing thyroid cancer risk in exposed children. Data on exposure to the embryonic/fetal thyroid are rare, raising questions about use of iodine 131 (I-131) in pregnant women. We present here estimated risks of thyroid disease from exposure in utero to I-131 fallout from the Chernobyl nuclear accident. METHODS: We conducted a cross-sectional thyroid screening study (palpation, ultrasound, thyroid hormones, and, if indicated, fine needle aspiration) from 2003 to 2006. Participants were 2582 mother-child pairs from Ukraine in which the mother had been pregnant at the time of the accident on April 26, 1986, or 2 months after the time during which I-131 fallout was still present (1494 from contaminated areas, 1088 in the comparison group). Individual cumulative in utero thyroid dose estimates were derived from estimated I-131 activity in the mother's thyroid (mean 72 mGy; range 0-3230 mGy). RESULTS: There were seven cases of thyroid carcinoma and one case of Hurthle cell neoplasm identified as a result of the screening. Whereas the estimated excess odds ratio per gray for thyroid carcinoma was elevated (excess odds ratio per gray 11.66), it was not statistically significant (P = 0.12). No radiation risks were identified for other thyroid diseases. CONCLUSION: Our results suggest that in utero exposure to radioiodines may have increased the risk of thyroid carcinoma approximately 20 yr after the Chernobyl accident, supporting a conservative approach to medical uses of I-131 during pregnancy.

Design and operation of the internal dosimetry program for the Chornobyl 'shelter implementation plan'.

The paper discusses the system of individual monitoring for internal exposure, deployed by the Ukrainian Radiation Protection Institute as an integral component of the Shelter Implementation Plan (SIP) at the Chornobyl industrial site. SIP anticipates involving of up to 10,00 workers of numerous SIP contractors. A typical daily shift comprises several hundred workers. Most of them have a direct contact with the irradiated nuclear fuel, fuel-contained aerosols and other contaminated materials on the industrial site. The hierarchical SIP individual monitoring program has been designed with consideration of peculiarities of SIP exposure conditions and aims at the timely and reliable identification of intakes, assessment of doses and initiation of measures for prevention of further intakes.

Post-Chernobyl thyroid cancers in Ukraine. Report 2: risk analysis.

On April 26, 1986, the worst nuclear reactor accident to date occurred at the Chornobyl (Chernobyl) power plant in Ukraine. Millions of people in Ukraine, Belarus and Russia were exposed to radioactive nuclides, especially (131)I. Since then, research has been conducted on various subgroups of the exposed population, and it has been demonstrated that the large increase in thyroid cancer is related to the (131)I exposure. However, because of study limitations, quantified risk estimates are limited, and there remains a need for additional information. We conducted an ecological study to investigate the relationship between (131)I thyroid dose and the diagnosis of thyroid cancer in three highly contaminated oblasts in Northern Ukraine. The study population is comprised of 301,907 persons who were between the ages of 1 and 18 at the time of the Chornobyl accident and were living in 1,293 rural settlements in the three study oblasts. Twenty-four percent of the study population had individual thyroid dose estimates and the other 76% had "individualized" estimates of thyroid dose based on direct thyroid measurements taken from a person of the same age and gender living in the same or nearby settlement. Cases include 232 thyroid cancers diagnosed from January 1990 through December 2001, and all were confirmed histologically. Dose-response analyses took into account differences in the rate of ultrasound examinations conducted in the three study oblasts. The estimated excess relative risk per gray was 8.0 (95% CI = 4.6-15) and the excess absolute risk per 10,000 person-year gray was estimated to be 1.5 (95% CI = 1.2-1.9). In broad terms, these estimates are compatible with results of other studies from the contaminated areas, as well as studies of external radiation exposure.

Questionnaire- and measurement-based individual thyroid doses in Ukraine resulting from the Chornobyl nuclear reactor accident.

The U.S. National Cancer Institute (NCI), in cooperation with the Ministries of Health of Belarus and of Ukraine, is involved in epidemiological studies of thyroid diseases presumably related to the Chornobyl accident, which occurred in Ukraine on 26 April 1986. Within the framework of these studies, individual thyroid absorbed doses, as well as uncertainties, have been estimated for all members of the cohorts (13,215 Ukrainians and 11,918 Belarusians), who were selected from the large group of children aged 0 to 18 whose thyroids were monitored for gamma radiation within a few weeks after the accident. Information on the residence history and dietary habits of each cohort member was obtained during personal interviews. The methodology used to estimate the thyroid absorbed doses resulting from intakes of (131)I by the Ukrainian cohort subjects is described. The model of thyroid dose estimation is run in two modes: deterministic and stochastic. In the stochastic mode, the model is run 1,000 times for each subject using a Monte Carlo procedure. The geometric means of the individual thyroid absorbed doses obtained in the stochastic mode range from 0.0006 to 42 Gy. The arithmetic and geometric means of these individual thyroid absorbed doses over the entire cohort are 0.68 and 0.23 Gy, respectively. On average, the individual thyroid dose estimates obtained in the deterministic mode are about the same as the geometric mean doses obtained in the stochastic mode, while the arithmetic mean thyroid absorbed doses obtained in the stochastic mode are about 20% higher than those obtained in the deterministic mode. The distributions of the 1000 values of the individual thyroid absorbed dose estimates are found to be approximately lognormal, with geometric standard deviations ranging from 1.6 to 5.0 for most cohort subjects. For the time being, only the thyroid doses resulting from intakes of (131)I have been estimated for all subjects. Future work will include the estimation of the contributions to the thyroid doses resulting from external irradiation and from intakes of short-lived ((133)I and (132)Te) and long-lived ((134)Cs and (137)Cs) radionuclides, as well as efforts to reduce the uncertainties.

Post-Chornobyl thyroid cancers in Ukraine. Report 1: estimation of thyroid doses.

About 1.8 EBq of 131I was released into the atmosphere during the Chornobyl accident that occurred in Ukraine on April 26, 1986. More than 10% of this activity was deposited on the territory of Ukraine. Beginning 4-5 years after the accident, an increase in the incidence of thyroid cancer among children, believed to be caused in part by exposure to 131I, has been observed in different regions of Ukraine. A three-level system of thyroid dose estimation was developed for the reconstruction of thyroid doses from 131I for the entire population of Ukrainian children aged 1 to 18 at the time of accident: (1) At the first level, individual doses were estimated for the approximately 99,000 children and adolescents with direct measurements of radioactivity in the thyroid (so-called direct thyroid measurements) performed in May-June of 1986; (2) at the second level, group doses by year of age and by gender were estimated for the population of 748 localities (with 208,400 children aged 1-18 in 1986) where direct thyroid measurements of good quality were performed on some of the residents; and (3) at the third level, group doses by age and by gender were estimated for the population of the localities where no thyroid measurements were made in 1986. The third-level doses were then aggregated over the population of each oblast. Data, models and procedures required for each level of thyroid dose estimation are described in the paper. At the first level, individual doses were found to range up to 27,000 mGy, with geometric and arithmetic means of 100 and 300 mGy, respectively. At the second level, group doses were found to be highest for the younger children (aged 1 to 4 years); doses for the older children (aged 16 to 18 years) were 3.5 times smaller. At the third level, average population-weighted doses were found to exceed 35 mGy in the five northern oblasts closer to the Chornobyl reactor site; to be in the 14- to 34-mGy range in seven other oblasts, Kyiv city and Crimea; and to be less than 13 mGy in all other oblasts.

Remediation strategies for rural territories contaminated by the Chernobyl accident.

The objective of the present paper is to derive remediation strategies for rural settlements contaminated by the Chernobyl accident in which annual doses to a critical group still exceed 1 mSv. Extensive radioecological data have been collected for 70 contaminated settlements. A dose model based on these data resulted in estimates that are on average close to and a bit less than the official dose estimates ('catalogue doses') published by the responsible Ministries of Belarus, Russia and Ukraine. For eight remedial actions that can be applied on a large scale, effectiveness and costs have been assessed in light of their dependence on soil type, contamination level and on the degree of previous application of remedial actions. Remediation strategies were derived for each of the 70 settlements by choosing remedial actions with lowest costs per averted dose and with highest degree of acceptability among the farmers and local authorities until annual doses are assessed to fall below 1 mSv. The results were generalised to 11 contamination/internal-dose categories. The total numbers of rural inhabitants and privately owned cows in the three countries distributed over the categories were determined and predicted until the year 2015. Based on these data, costs and averted doses were derived for the whole affected population. The main results are (i) about 2000 Sv can be averted at relatively low costs, (ii) the emphasis on reducing external exposures should be increased, (iii) radical improvement of hay-land and meadows and application of Prussian blue to cows should be performed on a large scale if annual doses of 1 mSv are an aim to be achieved, (iv) additional remedial actions of importance are fertilising of potato fields, distribution of food monitors and restriction of mushroom consumption, and (v) for inhabitants of some settlements (in total about 8600) annual doses cannot be reduced below 1 mSv by the remedial actions considered.

Internal exposure from the ingestion of foods contaminated by 137Cs after the Chernobyl accident--report 2. Ingestion doses of the rural population of Ukraine up to 12 y after the accident (1986-1997).

Doses from the ingestion of 134Cs and 137Cs during 12 y following the Chernobyl accident have been estimated for approximately 3 million persons living in rural areas of the Zhitomir, Rivne, and Kyiv Oblasts of northern Ukraine. This assessment is based upon an extensive monitoring campaign that provided measurements of 137Cs in more than 120,000 samples of milk and in more than 100,000 persons; such measurements were made in approximately 4,500 locations. Two approaches were used for the dose assessment. In the first approach a so-called reference dose is estimated for each settlement on the basis of measured 137Cs concentration in milk, determination of the milk equivalent of diet, and consumption rates; a further assumption is that a high fraction of the food consumed is produced locally. The reference dose is used as the official dose estimate, which is the basis for any decision on possible financial compensation and economic privileges. In a second step, the so-called real age-dependent dose is estimated from the results of whole body counter measurements and the kinetics of radiocesium in the human body. Real doses above 0.5, 5, and 50 mSv were received by about 40%, 10%, and 0.2%, respectively, of the considered population. With the exception of 1986, for which the monitoring results were limited, the real individual doses derived from whole-body counting are consistently lower than the reference doses. However, this difference declined from a factor of 3-4 in 1987-1989 to a factor of approximately 1.5 in the mid 1990's. The difference between reference and real doses is attributed to the effectiveness of countermeasures implemented after the accident. The effectiveness of these countermeasures decreased with time due to increasing economic problems in Ukraine. The collective reference and real doses of the rural population due to the intake of 134Cs and 137Cs are estimated to be 13,300 and 5,300 person-Sv, respectively. Thus, about 8,000 person-Sv is estimated to have been averted by countermeasures.

Internal exposure from the ingestion of foods contaminated by 137Cs after the Chernobyl accident. Report 1. General model: ingestion doses and countermeasure effectiveness for the adults of Rovno Oblast of Ukraine.

The Chernobyl accident, which occurred in April 1986, resulted in the atmospheric release of about 70--100 PBq of 137Cs. This paper examines the doses to the adult population of the northern part of Rovno Oblast, Ukraine, from ingestion of 137Cs. Fallout of 137Cs in these regions was lower than in other regions of Ukraine. However, the transfer of 137Cs from soil to milk in the region considered is high (up to 20 Bq L-1 per kBq m-2) and results in the predominance of internal doses compared to those from external exposure. Numerous measurements of 137Cs soil deposition, 137Cs milk contamination, and 137Cs body burden have been made in the area and form the basis of a general model of internal exposure from the ingestion of foods contaminated by 137Cs. This paper has two main purposes. The first is to develop the general phenomenological description of the process leading to internal exposure from the ingestion of 137Cs contaminated foods in the situation where different countermeasures are realized. The second is to apply the model for the adult population of the northern part of the Rovno Oblast (first report) for the limited time period of up to six years after the accident. The doses actually received by the adults are estimated to be four to eight times smaller than the doses calculated for the situation without countermeasures.

Effective doses due to external irradiation from the Chernobyl accident for different population groups of Ukraine.

A model for the external exposure of the Ukrainian population after the Chernobyl accident was developed. It is based on extensive measurements of external gamma-exposure rates (EGER) in air and of external effective doses of members of five population groups. Questionnaires were used to determine the occupancy times of members of the population groups at three types of locations; inside houses, outdoors, and outside of the home settlement. Behavior factors are defined as the ratio of individual external doses to a reference dose for a phantom standing permanently over an open field with the same average 137Cs activity per unit area as in the settlement. The behavior factors were derived for five population groups (children younger than seven years, the age group from eight to seventeen years, employees, agricultural workers, and pensioners) by two methods: first from direct measurements of individual doses by thermoluminescent dosimetry and an experimental determination of the average 137Cs activity per unit area in the settlement of interest; and second from external gamma-exposure rates in air at various types of locations and from the questionnaire data. The methods were found to be consistent and the results were used to calculate external exposures of the five population groups in the years 1987 through 1991.