UKRAINIAN-AMERICAN PROSPECTIVE COHORT STUDY OF THE STATE OF THYROID SYSTEM AFTER THE CHORNOBYL NPP ACCIDENT

Abstract

Epidemiological data regarding the effects of radioactive iodine and the risk of thyroid cancer in children are very limited. The exposure of large populations to radioactive fallout as a result of the Chornobyl nuclear power plant (ChNPP) accident in Ukraine on April 26, 1986 has become a serious public health, social and economic problem. The aim of the work is to characterize individuals in a prospective cohort study depending on the thyroid radiation dose, age at the time of the Chornobyl accident, gender and social status, analysis of migration and results of routine, additional and in-depth examination. Material and methods. In 1998, the
joint Ukrainian-American project «Scientific Project for the Study of Cancer and Other Thyroid Diseases in Ukraine as a Result of the Chornobyl Accident» (UAP) was launched, which provided a survey of residents of Ukraine: a) who at the time of the Chornobyl accident were permanent residents of the Kyiv and Chernihiv regions; b) who were under 18 years of age at the time of the accident; c) who underwent thyroid radiometry in the first weeks after the Chornobyl accident, and d) who were selected using a random sampling method. The examination procedure for UAP participants consisted of registration, thyroid ultrasound examination of the thyroid gland, blood analysis (determining levels of thyroid-stimulating hormone, free thyroxine, thyroglobulin, ionized calcium, antibodies to thyroid thyroperoxidase and thyroglobulin), determination of iodine levels in urine, and an endocrinologist consultation with palpation of the thyroid gland, as well as a survey to reconstruct the thyroid radiation doses. If necessary, additional in-depth examination was prescribed at the clinic of the State Institution «V.P. Komisarenko Institute of Endocrinology and Metabolism of the National Academy of Medical Sciences of Ukraine» (in particular, fine-needle aspiration puncture biopsy of the thyroid gland) and appropriate treatment. Results. During the period from April 1998 to December 2000 inclusive, 13,243 potential UAP participants underwent the first cycle of examination, of which 46.4% had a thyroid radiation dose of less than 0.3 Gy, 26.3% – from 0.3 to 1.0 Gy and 27.3% – more than 1.0 Gy (information was missing for 20 people); 50.8% of those examined were women, 49.2% were men; 34.2% of people were under 4 years of age at the time of the Chornobyl accident, 29.7% – from 5 to 9 years old, 29.9% – from 10 to 14 years old, 6.2% – from 15 to 18 years old inclusive. Subsequently, the second cycle of the examination (2001-2003) was completed by 12,419 Project participants, the third (2003-2005) – 11,745, the fourth (2005-2008) – 10,187 and the fifth (2012-2015) – 10,146. 26.7% of UAP participants changed their place of residence. The prevalence of thyroid diseases among UAP participants, depending on the screening cycle, was: malignant neoplasms – 4.38-16.77 cases per 1000 person-years, follicular adenomas – 0.51-3.65, diffuse non-toxic goiter – 200.44-225.80, diffuse toxic goiter – 0.60-1.87, non-toxic nodular goiter - 19.71-173.86, autoimmune thyroiditis – 4.61-14.14, postoperative hypothyroidism – 5.36-16.16 and acquired hypothyroidism – 0.81-1.28. In recent years, activities have been carried out to support the UAP cohort, reaching 12,274 cohort participants (92.7% of the total), 11,532 of whom (87.0%) agreed to continue participating in the Project. Conclusions. Over 17 years of UAP implementation, 76.5% of participants
were retained. The prevalence of malignant neoplasms, diffuse toxic goiter, nontoxic nodular goiter, autoimmune thyroiditis and postoperative hypothyroidism gradually increased. The prevalence of follicular adenoma and diffuse nontoxic goiter tended to decrease. The prevalence of acquired hypothyroidism remained unchanged. The prevalence of almost all thyroid diseases significantly exceeded official data for Ukraine and the northern regions of Ukraine (in particular, Zhytomyr, Kyiv, and Chernihiv oblast). Prospects. Resumption of active surveys after the lifting of martial law and normalization of the situation in Ukraine.