Results of the analysis of our own and literature data on the occurrence and development of radiation-induced thyroid cancer are presented. The analysis involved the distribution of the thyroid cancer incidence among 1 million children and 3 million adults, by age and sex, living in the radioactively contaminated territories of Russia; published data of the United Thyroid Cancer Registry of Russia and Byelorussia; results of medical examinations of the populations; and other information. Main attention was paid to the understanding of the latency period of spontaneous and radiation-induced cancers, comparison of oncopathology features in children and adults, and the role of screening in the increase of incidence rate parameters. The analysis permitted an offering of a new interpretation of several previously known facts and the developing of new explanations regarding the induction and development of radiogenic thyroid cancer, particularly regarding a far more significant increase of the thyroid cancer incidence in adults, living in the contaminated territories, than has been considered earlier.

The level of iodine consumption of the population living at a territory contaminated by the Chernobyl accident is evaluated for the Bryansk region (more than 30,000 km2). Analysis of iodine concentrations in the urine, carried out in 6750 children and adolescents from 125 settlements indicates that the level of iodine supply at the studied territory varies from normal to medium low iodine insufficiency. Age and sex did not affect renal excretion of iodine. An algorithm is suggested for detailed assessment of iodine consumption at large territories.

Ultrasonic examination of thyroid and determination of the median of iodine excretion with urine form a necessary part of prophylactic thyroid examination of people living in ecologically unsafe regions or in regions exposed to the radioactive trail.

The paper discusses a methodological approach developed for reconstruction of thyroid doses from internal exposure to 131I and prospects of future works in this field. Estimated levels of thyroid irradiation for the population of Russia after the accident are presented. These results have been obtained based on the retrospective analysis using the developed approach. Also, long-term health consequences of thyroid irradiation in the population of Russia have been predicted. Retrospective estimates have been made for individual thyroid doses for children and adolescents with the diagnosis of thyroid cancer living on the contaminated areas.

The developed standardized procedure of individual accumulated dose estimation based on ESR-spectroscopy of tooth enamel samples was applied to large-scale dosimetric study. Measurements of over 2000 individual accumulated doses in residents of the southwest areas of Bryansk region with radio-contamination density between 5 and 30 Ci/km2 and in clean (control) territories were made. Teeth extracted according to medical prescription were collected in dentist outpatients. Dose values were estimated with the use of calibration relationships obtained after exposure of tooth enamel samples to the direct beam of gamma-radiation of a 137Cs source. Measured dose values were put into computer data bank and underwent statistical analysis. Dose value patterns for population of various areas were satisfactory described by log-normal functions. With accounting for the systematic correction value of the methodical approach used the average dose values for clean territories equal to 3-5 cGy. For residents of 137Cs contaminated areas the averaged dose values are in the range up to 12 cGy. Persons with accumulated doses essentially exceeding the above mentioned averaged values are included into groups of risk. They are subjected to compulsory medical examination and follow up as well as medical and dosimetric investigation. The clear correlation between the measured by ESR and averaged dose values and the level of ra-diocontamination of certain territories was found. The slope of the appropriate linear regression was 2 found equal to 0.24 ± 0.08 cGy/(Ci/km ). The dependence of individual doses on age of patients is described by linear regression with the slope of 0.14 ± 0.05 cGy/year. The mentioned relationships are in agreement with results obtained using calculations models of retrospective estimation of accumulated doses.

137 Cs source. The statistical analysis of the meas- urement results has shown that dose distribution is adequately described by the log-normal function for the population of dif- ferent territories. With allowance for a fixed error, the aver- age doses range from 3 to 5 cGy for the uncontaminated areas and about 12 cGy for the contaminated ones. Residents having accumulated doses much higher the average ones are referred to a risk group and have to be followed up and subjected to dosi- metric investigation. It has been established that there is a clear correlation between the average individual accumulated doses measured by EPR and the level of radioactive contamination of the area. The linear regression coefficient has been found to be 0.24 0.08 cGy (Ci/km 2 ). The dependence of individual doses on age is given by a linear regression with the slope of 0.14 0.05 cGy/year. The indicated relationships are in agreement with re- sults obtained with the models estimating retrospectively the accumulated doses.

In presented paper the problem of thyroid cancer following the ChNPP accident is considered for the first time on the basis of system approach. The three main tasks are solved: prognostication of immediate and later effects of radiation action comments with the induction of malignant thyroid tumors; determination of radiation risks of non-cancer thyroid diseases; estimation of radiation risks of cancer thyroid diseases. As a result of conducted prognostication estimates it is shown, in particular, that the attributive life time risk for children from the territories of Bryansk oblast contaminated by radionuclides will constitute 44% (i.e., nearly each second cancer will be conditioned by radiation), for children of Kaluga oblast this coefficient will amount to 26%. In the cohort of children and adolescents of Kaluga oblast (5694 people) with individual radiation dose of thyroid gland based on direct radiometry carried out in 1986 the radiation risk estimates of non-cancer thyroid diseases were obtained. In particular, estimation of excess relative risk coefficient at the dose of 1 Gy equal to 0,2 (0,06; 0,34) is in a good agreement with the data published on the basis of AHS-cohort (Japan). The technology case-control is realized first for determination of radiation risks of thyroid cancer diseases by children and adolescent (at the moment of the accident) living in Bryansk oblast. The relative risk coefficient of thyroid cancer diseases in the western rayons of Bryansk oblast contaminated by radionuclides at the dose of 1 Gy is equal 7,15 (1,52; 33,8). The principal radiation epidemiological data obtained evidence the necessity of conducting the long-term monitoring the persons exposed to radiation action due to the ChNNP accident.

This work presents results of complex studying the morbidity and mortality from malignant neoplasms on the territories of Bryansk, Kaluga, Orel and Ryazan oblasts most radiocontami-nated after the ChNPP accident. Complexity of the approach was provided by solving the three basic tasks: assessment of possible contribution of radiation factor into oncomorbidity, i.e. prognostication of mortality and morbidity conditioned by radiogenic cancers; analyzing the development of oncoepidemiological situation (dynamics of morbidity indices) during the period from 1981 till 1994; assessment of relative risks of arising malignant neoplasms among population of indicated oblasts as compared to Russia before and after the ChNPP accident. Calculations models and risk coefficients recommended by the International Commission on Radiological Protection (ICRP) and the Committee on Biological Effects of Ionizing Radiation of USA (BEIR-V) as well as medico-demographic and dosimetric data on studied regions are used in the prognostication. In consequence of the prognostication the life attributive risk for the majority of oncodiseases was demonstrated not to exceed 5%, except thyroid cancer for which the attributive risk is expected to peak in Bryansk oblast and to reach 18-20% for adults and 45-50% for children. By this is meant that each fifth thyroid cancer among adults and each second cancer among children will be radiation-induced. Analysis of risks and oncomorbidity indices among residents of contaminated territories before and after the accident allows to conclude that the forming the levels of oncomorbidity available at present, their structure and dynamics occurred primarily under influence of factors existing before the accident. As a result of the analysis of all three aspects of given problem the conclusion about the lack of statistically reliable effect of radiation factor on oncomorbidity is made. Levels of onco-morbidity and oncomortality in contaminated regions reflect mainly the common tendency of changing these indices on Russia as a whole. The conclusion made is generally in agreement with the data of world practice on latent periods of induction of radiogenic cancers and values of radiation effects for levels of irradiation to which the population living on contaminated territories is exposed.