Radiation protection and health of personnel of contracting enterprises participating in works for transformation of the object "shelter" of SSE Chornobyl NPP into an ecologically safe system.

UNLABELLED: Transformation of the object "Shelter" (OS) of SSE Chornobyl NPP into an ecologically safe system is one of the most important state programs in Ukraine. Both medical and dosimetric measures on healthcare of personnel participating in these works ranks the main place among most actual problems of contemporary clinical radiobiology, radiation hygiene, and radiation protection. The study objective was to work out and implement the medical and biophysical checking of the health status and workability both with radiation protection of personnel executing works on transformation of OS into an ecologically safe system. MATERIALS AND METHODS. The interdependent complex program of medical and biophysical (for internal and external irradiation) control of personnel executing the production tasks under conditions of ionizing radiation impact and open sources of ionizing radiation. Realization of medical examination envisages the estimation of the status of haemopoietic, immune, endocrine, respiratory systems, organ of vision, nervous system, psychics status and psychophysiological adaptation, ear, both with circulatory, digestive, urogenital, and bone-muscular system. There were 19434 cases of medical control of personnel in total. RESULTS: Results of the input medical control testify to the following: 4698 (48.90%) were admitted to work, 4909 (51.10%) were rejected. Individual annual effective doses of irradiation in the major part of cases did not exceed 12 mSv. There were 1845 cases of 239+240Pu content in excrements exceeding the level of 1.5 mBq/sample at a current biophysical control. Individual doses of internal irradiation at that did not exceed 1 mSv. CONCLUSIONS: The program of medical and biophysical service for reconstruction works on the OS proved its necessity and efficiency as its results showed that under the unique radiation-hygienical conditions not engineering challenges and technical problems but issues of how to save the health and workability of people and prevent the overdose of personnel including due to an internal irradiation are most critical.

Contribution of internal exposures to the radiological consequences of the Chernobyl accident.

The main pathways leading to exposure of members of the general public due to the Chernobyl accident were external exposure from radionuclides deposited on the ground and ingestion of contaminated terrestrial food products. The collective dose to the thyroid was nearly 1.5 million man Gy in Belarus, Russia and Ukraine with nearly half received by children and adolescents. The collective effective dose received in 1986-2005 by approximately five million residents living in the affected areas of the three countries was approximately 50,000 man Sv with approximately 40% from ingestion. That contribution might have been larger if countermeasures had not been applied. The main radionuclide contributing to both external and internal effective dose is 137Cs with smaller contributions of 134Cs and 90Sr and negligible contribution of transuranic elements. The major demonstrated radiation-caused health effect of the Chernobyl accident has been an elevated incidence of thyroid cancer in children.

Autoimmune thyroiditis and exposure to iodine 131 in the Ukrainian cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: results from the first screening cycle (1998-2000).

CONTEXT: Due to the Chornobyl accident, millions were exposed to radioactive isotopes of iodine and some received appreciable iodine 131 (131I) doses. A subsequent increase in thyroid cancer has been largely attributed to this exposure, but evidence concerning autoimmune thyroiditis (AIT) remains inconclusive. OBJECTIVE: The objective of the study was to quantify risk of AIT after 131I exposure. DESIGN/SETTING/PARTICIPANTS: Baseline data were collected from the first screening cycle (1998-2000) of a large cohort of radiation-exposed individuals (n = 12,240), residents of contaminated, iodine-deficient territories of Ukraine. Study individuals were under the age of 18 yr on April 26, 1986, and had thyroid radioactivity measurements made shortly after the accident. OUTCOMES: AIT was defined a priori based on various combinations of elevated antibodies to thyroid peroxidase (ATPO), TSH, and clinical findings; elevated ATPO were considered to be an indicator of thyroid autoimmunity. RESULTS: No significant association was found between 131I thyroid dose estimates and AIT, but prevalence of elevated ATPO demonstrated a modest, significant association with 131I that was well described by several concave models. This relationship was apparent in individuals with moderately elevated ATPO and euthyroid, thyroid disease-free individuals. CONCLUSIONS: Twelve to 14 yr after the Chornobyl accident, no radiation-related increase in prevalence of AIT was found in a large cohort study, the first in which 131I thyroid doses were estimated using individual radioactivity measurements. However, a dose-response relationship with ATPO prevalence raises the possibility that clinically important changes may occur over time. Thus, further follow-up and analysis of prospective data in this cohort are necessary.

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.

Thyroid carcinoma in children and adolescents in Ukraine after the Chernobyl nuclear accident: statistical data and clinicomorphologic characteristics.

BACKGROUND: The increase in the number of childhood thyroid carcinoma cases in Ukraine after the Chernobyl nuclear accident in 1986 prompted the development of a registry of thyroid carcinoma cases at the Institute of Endocrinology and Metabolism in Kiev. In the current study, the authors report the statistical data and clinicomorphologic features of the cases included in this registry. METHODS: To study the incidence, and age and gender distribution of thyroid carcinoma in Ukraine, the authors compiled complete clinical information from cases diagnosed and treated at the Institute of Endocrinology and Metabolism and statistical reports submitted to the registry from 27 regions of Ukraine. Morphologic features of the resected tumors were examined and were included in the database. RESULTS: During the 5 years preceding the Chernobyl nuclear accident, a total of 59 cases of thyroid carcinoma were identified in the birth to 18 years age group (25 in children age < or = 14 years and 34 in adolescents ages 15-18 years). Between 1986 and 1997, the total number of thyroid carcinomas in Ukrainian children and adolescents was 577 (358 children and 219 adolescents). Morphologically, the thyroid tumors overwhelmingly were papillary carcinomas, and the majority of these also showed a follicular and/or solid growth pattern. Lymph node metastases and other extrathyroidal spread were common, thus necessitating total thyroidectomy and lymph node dissections in many patients. CONCLUSIONS: Between 1990 and 1997, a significant increase in the incidence of thyroid carcinoma was noted in children and adolescents in Ukraine; the group most affected was comprised of the individuals who were age < or = 5 years in 1986 (the year of the Chernobyl nuclear accident). The largest number of cases occurred in patients living in areas of thyroid radiation doses of > or =0.50 grays. The morphologic features of those thyroid tumors suggest that they are aggressive tumors with a high frequency of lymph node metastases, venous invasion, and extrathyroidal spread.

Thyroid dose and thyroid cancer incidence after the Chernobyl accident: assessments for the Zhytomyr region (Ukraine).

In the Zhytomyr region, about 52,000 measurements of the 131I activity in thyroids were performed. On the basis of these measurements, individual doses have been assessed for the people monitored and age-dependent average doses have been estimated for those settlements with more than 11 direct measurements. In order to estimate the pattern of thyroid exposure in the Zhytomyr region, these doses have been interpolated or extrapolated to population groups who were not monitored during May-June 1986. For this purpose, a model has been developed based on a correlation between thyroid dose estimates with the 137Cs deposition and the co-ordinates of the settlements relative to Chernobyl. Collective doses of people who were born in the years 1968 to 1986 were calculated. The radiation-induced thyroid cancer incidence in the period 1991 to 1995 was assessed by subtracting the spontaneous incidence from the observed incidence. The result is considerably lower than that observed in longer periods after external exposures. Possible reasons for this difference are discussed.

Emerging technological bases for retrospective dosimetry.

In this article we discuss examples of challenging problems in retrospective dosimetry and describe some promising solutions. The ability to make measurements by accelerator mass spectrometry and luminescence techniques promises to provide improved dosimetry for regions of Belarus, Ukraine and Russian Federation contaminated by radionuclides from the Chernobyl accident. In addition, it may soon be possible to resolve the large neutron discrepancy in the dosimetry system for Hiroshima through novel measurement techniques that can be used to reconstruct the fast-neutron fluence emitted by the bomb some 51 years ago. Important advances in molecular cytogenetics and electron paramagnetic resonance measurements have produced biodosimeters that show potential in retrospective dosimetry. The most promising of these are the frequency of reciprocal translocations measured in chromosomes of blood lymphocytes using fluorescence in situ hybridization and the electron paramagnetic resonance signal in tooth enamel.

Estimation of 131I thyroid doses for the evacuees from Pripjat.

The thyroid doses of 49,360 inhabitants of Pripjat evacuated after the accident at Chernobyl were reconstructed. During their evacuation most of the evacuees passed through highly contaminated territories. The evaluation of a large-scale public survey showed that only about 50% of the evacuees had left the contaminated areas within 5 days and that 30% of them stayed there for more than 30 days. As a first step, the model of dose estimations was improved, and thyroid doses were assessed for the group of evacuees for whom the 131I activity in the thyroids was measured. The 131I incorporation during the first 5 days after the accident was described by a single-intake model (inhalation); later incorporations were assumed to be proportional to the radioiodine activity in milk. As a second step, the correlation between the calculated doses and individual parameters (place of residence in Pripjat, intake of stable iodine, and age at the time of the accident) was described by an empirical equation. This equation was applied to all evacuees who completed the questionnaires of the public survey. Previous dose assessments were found to overestimate the thyroid doses especially for the younger evacuees. On the basis of these estimations, collective doses and the resulting radiation risks for thyroid cancer were assessed for different age groups.

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.

Dosimetric support of the International Programme on the Health Effects of the Chernobyl Accident (IPHECA) pilot project: main results and problems.

The problem of post-Chernobyl dosimetry is unique in its complexity in the history of radiation medicine and radiation protection. This is because the early experience of mass exposure of people (bombing of Hiroshima and Nagasaki, Windscale and South-Ural accidents, exposure of inhabitants of Nevada in the United States of America, the Semipalatinsk area in the former USSR, the Marshall Islands, and the Goiånia accident in Brazil, and others) differed both in the much simpler structure of the irradiation source and in the number and characteristics of exposed persons. It is obvious that post-Chernobyl dosimetry, both as an independent problem, and as a tool for epidemiological studies, requires significant expertise and economic and technical expenditures. Extensive and deep research has been carried out in Ukraine for the past 10 years. This article reviews the main results of these studies.

Evaluation of the 131I thyroid-monitoring measurements performed in Ukraine during May and June of 1986.

After the Chernobyl accident in 1986, about 150,000 monitoring measurements were performed in Ukraine. From this data base, 40,000 measurements were selected for which the results of the reference-source measurements could be analyzed by statistical means. The majority of these measurements are of high quality. In this paper, the uncertainties introduced due to the variabilities of anatomic parameters and the measurement geometry are quantified by measurements using a thyroid-neck phantom. Parameters considered are the thyroid mass, the thickness of the tissue overlying the thyroid as well as the detector-neck distance, the orientation, and the horizontal and vertical position of the detector. The uncertainty introduced due to the variability of these factors corresponds to a coefficient of variation in the range of 25-40% for the measured activity.

Analysis of the effectiveness of emergency countermeasures in the 30-km zone during the early phase of the Chernobyl accident.

Some radiation-emergency countermeasures, including evacuation, were implemented in the settlements of the 30-km zone during the early phase of the accident at the Chernobyl Nuclear Power Plant. These countermeasures are described and compared with the international recommendations. An analysis of the effectiveness of the emergency countermeasures was conducted based upon the results of a wide-scale public survey. Quantitative assessments of the effectiveness (dose reduction) of the countermeasures were derived.

Retrospective reconstruction of individual and collective external gamma doses of population evacuated after the Chernobyl accident.

About 90,000 citizens of Ukraine, who were residents of the near zone of the Chernobyl nuclear power plant were evacuated during the first weeks after the accident due to the heavy contamination of the environment. Doses of this cohort were unknown. Retrospective reconstruction of external gamma exposure doses, based on the results of direct dose rate measurements performed during the accident and individual behavior/migration histories of the evacuees, was performed. Individual doses were reconstructed for 30,586 evacuees from the city of Prip'at and the settlements of the 30-km zone. The average effective dose H(E) due to external irradiation for this cohort was estimated to be 15 mSv, although individual values vary in an extremely wide range from 0.1 to 383 mSv. The collective dose of the whole evacuated population was found to be 1,300 person-Sv.

Thyroid doses resulting from the Ukraine Chernobyl accident--Part I: Dose estimates for the population of Kiev.

In the context of the radiation exposure of the Ukrainian population resulting from the Chernobyl accident, the quantification of the thyroid doses due to iodine incorporation is of special interest. This first part of a series of planned publications deals with the dose and risk estimation for Kiev citizens. Although these doses are expected to be considerably lower than those for some other regions of Ukraine, the investigations started with this population because the quantification of the thyroid doses due to iodine incorporation is of special interest. This first part of a series of planned publications deals with the dose and risk estimation for Kiev citizens. Although these doses are expected to be considerably lower than those for some other regions of Ukraine, the investigations started with this population because of the availability of rather reliable measurements and because of the size of this population. The methods developed allowed the estimation of individual thyroid doses. The average values of individual thyroid doses for five age groups (birth years 1983-1986, 1979-1982, 1975-1978, 1971-1974, and < 1971) are 104, 62, 19, 18, and 41 mGy, respectively. The collective thyroid doses were estimated as 83 x 10(3) person-Gy for those born before 1971 and as 38 x 10(3) person-Gy for younger inhabitants. The numbers of expected thyroid cancers in the whole Kiev population are 66 and 130, respectively.

Thyroid dose assessment for the Chernigov region (Ukraine): estimation based on 131I thyroid measurements and extrapolation of the results to districts without monitoring.

Based on the results of 131I thyroid activity measurements in three districts of the Chernigov region (Ukraine), individual doses were calculated and an approach of the age dependence of the average thyroid exposure was derived. Using the relationships between the thyroid doses and the 137Cs deposition as well as the location relative to the Chernobyl Nuclear Power Plant (NPP), age-dependent average thyroid doses were extrapolated also for those settlements of this region where no monitoring measurements have been carried out. The highest doses were found in the west of the region with the lowest distance to the Chernobyl NPP. In this part, the highest mean of the thyroid dose in a settlement was 3.3 Gy for infants and 0.5 Gy for adults. The collective thyroid dose was 31,000 and 27,000 person-Gy for children and adults, respectively. Based on this assessment, 140 and 21 excess thyroid cancer cases are predicted for children and adults, respectively. In the years 1989 to 1991, in the whole contaminated territory of the Ukraine 0.4-1.2 cases per 100,000 children were observed. Although the absolute numbers are very small, this indicates the possibility of an increase in thyroid cancer morbidity among children. The same trend also seems to be indicated in the Chernigov region. A careful epidemiological study in the future is necessary to enable a final evaluation of radioinduced cancers in this region.

Ukrainian thyroid doses after the Chernobyl accident.

To estimate thyroid radioactivity in the Ukrainian population from May-June 1986, more than 150,000 individual examinations were carried out by special dosimetric teams. The results of these total measurements were approved to be a basis for assessing individual absorbed doses of infant and adult thyroid irradiation associated with the 131I exposure. The dosimetric radioiodine data bank of thyroid irradiation of the Ukrainian population was created to analyze these measurements. The analysis was performed using the data for eight Ukrainian districts and the town of Pripjat, which were all heavily contaminated due to radioiodine exposure. Results of the dose assessments are given using two models: the more conservative model of "single radioiodine intake" and a more realistic model that considers the individual duration of radioiodine intake. In accordance with the more realistic model, the predictions of late effects have shown that a collective thyro-oncogenic dose is equal to 64,000 person-Gy, stimulating the possibility of the emergence of 300 cases (30 incurable) of thyrocancers. Considering this information for the next 35 y (1991-2026), it is possible to predict a 1.4-fold increase over spontaneous thyroid cancer morbidity for children who lived in the heavily contaminated regions of the Ukraine in 1986 (spontaneous and radiogenic to spontaneous).