Scientific Protocol for the Study of Thyroid Cancer and Other Thyroid Disease in Ukraine Following the Chernobyl Accident

The nuclear power plant accident at Chornobyl released large quantities of Iodine-131 and other radioisotopes of iodine into the atmosphere, contaminating thousands of square kilometers and exposing millions of people. For this study, a well-defined subset of Ukrainian children aged less than 18 years or in utero at the time of the accident were identified and have been examined by well-trained specialists. The main cohort was screened for thyroid disease every two years for 4 cycles ending in April, 2007. The in utero cohort was screened once, between 2003-2006. The study is a collaborative effort of researchers in Ukraine and the United States.

The main cohort includes approximately 13,000 persons who were children in 1986, all or most of whom had their thyroids measured for radioactivity during the weeks immediately following the accident. Under a rigid research protocol, these subjects received diagnostic thyroid examinations, including palpation, ultrasound scanning, thyroid hormone and other laboratory tests. If indicated, they were referred for a fine-needle aspiration biopsy. Interview information regarding residential, health, diet and lifestyle history will also be collected. All subjects are followed for thyroid cancer morbidity and mortality. Thyroid cancers are confirmed by expert pathology examination of tissue obtained during surgery. The in utero cohort includes a total of 2,582 individuals. In addition starting in 2003, ~ 7,000 parents of members of the main cohort who were under age 10 y at the time of the accident were interviewed in order to increase the accuracy of recall. These individuals were listed as new subjects. Altogether, 23,143 individuals have been accrued in this study.

In addition to the analysis of thyroid radiation measurements made in May-June, 1986, radiation dose to the thyroid was estimated drawing on such data as the reconstruction of deposition patterns and environmental pathways of the radioiodines, and of the location, dietary characteristics, and lifestyle of each person throughout the exposure period. For in utero subjects, fetal dose was estimated based on the mother's thyroid dose.

The aim of the study is to assess the early and late morphologic and functional changes in the thyroid glands of persons exposed at young ages to radiation from radioactive materials released as a consequence of the Chornobyl nuclear power plant accident, with emphasis on dose-and time-specific changes. 110 cancers were identified in the main cohort, and 8 confirmed or suspect cases were diagnosed among those exposed in utero. Active thyroid screening ended in April, 2007, but data analyses are being actively pursued.

There have been three scientific amendments to the protocol: transition cancer case ascertainment to a passive form of follow-up based on linkage to the National Cancer Registry of Ukraine (NCRU); a sub-study involving an additional follow-up examination of those cohort members who were diagnosed with benign nodular thyroid pathology during one of the earlier four active screening cycles; and genetic studies (gene expression and germline SNP studies) of thyroid cancer in this Ukrainian cohort exposed to radioiodines from Chornobyl fallout as children or adolescents. Work is continuing to complete the linkage follow-up, nodule follow-up and blood sample collection.