The paper deals with one of the most urgent aspects of irradiation hygiene, namely assessment of risk for irradiation-induced cancers of the thyroid. A model is described to predict high mortality rates of thyroidal cancer in the population due to the catastrophe at the Chernobyl Atomic Power Station. With the model, life-time risk rates involving sex and age at the moment of irradiation, as well as an irradiation mode.
The estimation of the effective dose equivalents of exposure to accidental and non-accidental sources was made on the basis of the studying of radiation situation variations in Kiev after the Chernobyl accident in 1986-1989. The total annual effective dose equivalents to the Kiev population from all sources of exposure for 1986-1989 were 9.19, 7.29, 5.34 and 5.03 mSv, respectively. The necessity of radiation health measures aimed at limiting the intake of long-acting radionuclides of Chernobyl nature and reducing the exposure doses by optimizing the x-ray procedure and by regulating the natural radioactivity of building materials are under discussion.
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.
The paper considers the radiation doses of the thyroid gland in the inhabitants from the Ukrainian SSR areas (Kiev, Zhitomir, Chernigov, and Vinnitsa Regions), which have been obtained by instrumental studies of thyroidal radioactivity in May-June, 1986, and calculated by the most conservative single-dose administration model. A hygienic evaluation has been made of the findings, taking into account the age and residence. The cumulative irradiation doses of the thyroid have been estimated for children and adults. Possible late sequelae for the areas in question may account for 1060 and 300 thyroid carcinoma cases during the whole life for children and adults, respectively.
The paper is devoted to one of the most important aspects of the accident at the Chernobyl Nuclear Power Station: thyroid irradiation in the residents of 8 areas in the Ukrainian SSR and the town of Pripyat, affected with radioactive iodine. Irradiation doses, prognosis of medical effects of the accident, methods and practical measures for the organization of endocrinological monitoring of the affected population were thoroughly considered. The authors proposed a scheme of health care of the population in these areas. They also discussed the structure of data bases for analysis of medico-dosimetric information on "iodine" effects of the accident. The main trends in medico-dosimetric problems of the effects of thyroid irradiation were outlined.
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).