Scientific Protocol for the Study of Thyroid Cancer and Other Thyroid Disease in Belarus Following the Chernobyl Accident
Condition: Thyroid Cancer; Non-Cancer Thyroid Disease; Non Thyroid Cancer
MeSH terms: Thyroid Neoplasms; Thyroid Diseases
Study type: Observational

Summary: 
      Iodine-131(131I) and other radioisotopes of Iodine are contained in fallout from atmospheric
      nuclear weapons tests and are among the radionuclides most likely to be released in a nuclear
      reactor accident. In spite of nearly 50 years of experience, the risk of thyroid disease,
      especially thyroid cancer, attributable to exposure to 131I remains unknown, although the
      carcinogenic potential of x-ray and gamma-ray exposure of the thyroid is reasonably well
      known. The available data also indicate that children face greater risks of radiation-induced
      thyroid cancer than do adults.

      The nuclear power plant accident at Chernobyl released large quantities of 131I and other
      radioisotopes of iodine into the atmosphere, contaminating thousands of square kilometers and
      exposing millions of people. It is proposed that a well-defined subset of Belarussian
      children aged 0-18 years at the time of the accident be examined by well-trained specialists
      for thyroid disease at least biennially for up to 30 years. A cohort of 15,000 children has
      been identified, all of whom had their thyroids measured for radioactivity during the weeks
      immediately following the accident. Under a rigid research protocol these children will
      receive complete diagnostic thyroid examinations, including palpation, ultrasound scanning,
      thyroid hormone and other laboratory tests, and fine-needle aspiration, as appropriate.
      Cancer will be determined by expert pathology examination of tissue. In addition to the
      analysis of thyroid radiation measurements made in May-June, 1986, efforts will be made to
      reconstruct each person's exposure and to estimate the radiation doses to the thyroid. This
      will involve 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.

      The data will be analyzed to evaluate the relationship, if any, between thyroid disease,
      especially cancer, and the radiation dose to the thyroid, with emphasis on the dose from
      131I. The primary focus will be on dose-response analyses of person-year incidence data with
      stratification by sex, age at exposure, geographic area, time, and age at risk. Confounding
      factors, e.g., use of potassium iodide (KI) as a prophylactic measure, will be evaluated and
      controlled in the analysis, and the uncertainty of the dose estimates will be taken into
      account.

      In addition to producing risk coefficients for thyroid cancer and other thyroid diseases in
      children as a function of sex and age at the time of exposure, it is expected that the
      analyses will contribute new knowledge of the carcinogenic effectiveness of 131I in
      comparison with that of x-ray and gamma radiation. This information will fill a major gap in
      the world's knowledge of radiation effects, and will provide guidance for radiation
      protection and public health policies wherever nuclear reactors are in operation.
    

Detailed description: 
      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
      Belarusian children under age 18 years at the time of the accident were identified and
      examined by well-trained specialists for thyroid disease every two years for three cycles.
      The study is a collaborative effort of researchers in Belarus and the United States.

      <TAB>

      The cohort includes approximately 12,000 persons who were children in 1986, all 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 are also collected. All
      subjects were followed for thyroid cancer morbidity and mortality. Overall, 163 cancers were
      identified. Interviews with mothers of the subjects who were less than 10 years of age at the
      time of the accident whose memory of events proved inadequate increased the total accrual to
      13,552.

      Based on thyroid radiation measurements made in May-June, 1986, and other information
      (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), each person s radiation dose to the thyroid was estimated.

      The aim of the study is to assess the early and late morphologic and functional changes in
      the thyroid glands of young persons exposed to radiation from radioactive materials released
      as a consequence of the Chornobyl nuclear power plant accident, with emphasis on dose- and
      time-specific changes.

      Active screening for thyroid cancers ended in September 2006. The third and final thyroid
      screening examinations were completed in September 2006, identifying 163 cases of thyroid
      cancer during the examination period. Subject accrual through screening is no longer ongoing.
      Thyroid and other cancer case ascertainment is underway by linkage to the Belarusian Cancer
      Registry. A paper has been published on the radiation dose response for prevalent thyroid
      cancer and analyses of incident cancer cases and other thyroid disease are ongoing.
    

Observational model: Cohort
Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Subjects exposed to I131 at age less than 18 years, and subjects exposed to I131 in utero
      
Keywords: Cohort; Radiation; In Utero