A cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: objectives, design and methods.

The thyroid gland in children is one of the organs that is most sensitive to external exposure to X and gamma rays. However, data on the risk of thyroid cancer in children after exposure to radioactive iodines are sparse. The Chornobyl accident in Ukraine in 1986 led to the exposure of large populations to radioactive iodines, particularly (131)I. This paper describes an ongoing cohort study being conducted in Belarus and Ukraine that includes 25,161 subjects under the age of 18 years in 1986 who are being screened for thyroid diseases every 2 years. Individual thyroid doses are being estimated for all study subjects based on measurement of the radioactivity of the thyroid gland made in 1986 together with a radioecological model and interview data. Approximately 100 histologically confirmed thyroid cancers were detected as a consequence of the first round of screening. The data will enable fitting appropriate dose-response models, which are important in both radiation epidemiology and public health for prediction of risks from exposure to radioactive iodines from medical sources and any future nuclear accidents. Plans are to continue to follow-up the cohort for at least three screening cycles, which will lead to more precise estimates of risk.

Histologic verification of leukemia, myelodysplasia, and multiple myeloma diagnoses in patients in Ukraine, 1987-1998.

In preparation for a possible large epidemiological study of radiation-related leukemia in Chernobyl clean-up workers of Ukraine, histologic evaluation of 62 cases of leukemia and related disorders was conducted by a panel of expert hematologists and hematopathologists from the United States, France, and Ukraine. All cases were randomly selected from a surrogate population of men in the general population of 6 regions of Ukraine who were between the ages of 20 and 60 years in 1986 and were reported to have developed leukemia, myelodysplasia, or multiple myeloma between the years 1987 and 1998. The hematologists and hematopathologists on the panel were in agreement with one another and with the previously reported diagnoses and classifications of about 90% of the cases of acute and chronic leukemia in the study. These results suggest that strong reliance can be placed on the clinical diagnoses of acute and chronic forms of leukemia and multiple myeloma that have occurred in Ukrainian Chernobyl clean-up workers providing that the diagnoses are supported by records of the patients having had adequate histologic bone marrow studies. The number of cases in this study with the diagnosis of myelodysplasia, however, was too small to draw firm conclusions.

A cohort study of thyroid cancer and other thyroid diseases after the chornobyl accident: thyroid cancer in Ukraine detected during first screening.

BACKGROUND: The Chornobyl accident in 1986 exposed thousands of people to radioactive iodine isotopes, particularly (131)I; this exposure was followed by a large increase in thyroid cancer among those exposed as children and adolescents, particularly in Belarus, the Russian Federation, and Ukraine. Here we report the results of the first cohort study of thyroid cancer among those exposed as children and adolescents following the Chornobyl accident. METHODS: A cohort of 32 385 individuals younger than 18 years of age and resident in the most heavily contaminated areas in Ukraine at the time of the accident was invited to be screened for any thyroid pathology by ultrasound and palpation between 1998 and 2000; 13 127 individuals (44%) were actually screened. Individual estimates of radiation dose to the thyroid were available for all screenees based on radioactivity measurements made shortly after the accident and on interview data. The excess relative risk per gray (Gy) was estimated using individual doses and a linear excess relative risk model. RESULTS: Forty-five pathologically confirmed cases of thyroid cancer were found during the 1998-2000 screening. Thyroid cancer showed a strong, monotonic, and approximately linear relationship with individual thyroid dose estimate (P<.001), yielding an estimated excess relative risk of 5.25 per Gy (95% confidence interval [CI] = 1.70 to 27.5). Greater age at exposure was associated with decreased risk of radiation-related thyroid cancer, although this interaction effect was not statistically significant. CONCLUSION: Exposure to radioactive iodine was strongly associated with increased risk of thyroid cancer among those exposed as children and adolescents. In the absence of Chornobyl radiation, 11.2 thyroid cancer cases would have been expected compared with the 45 observed, i.e., a reduction of 75% (95% CI = 50% to 93%). The study also provides quantitative risk estimates minimally confounded by any screening effects. Caution should be exercised in generalizing these results to any future similar accidents because of the potential differences in the nature of the radioactive iodines involved, the duration and temporal patterns of exposures, and the susceptibility of the exposed population.

Cancer in Korean war navy technicians: mortality survey after 40 years.

This study reports on over 40 years of mortality follow-up of 40,581 Navy veterans of the Korean War with potential exposure to high-intensity radar. The cohort death rates were compared with mortality rates for White US men using standardized mortality ratios, and the death rates for men in occupations considered a priori to have high radar exposure were compared with the rates for men in low-exposure occupations using Poisson regression. Deaths from all diseases and all cancers were significantly below expectation overall and for the 20,021 sailors with high radar exposure potential. There was no evidence of increased brain cancer in the entire cohort (standardized mortality ratio (SMR) = 0.9, 95% confidence interval (CI): 0.7, 1.1) or in high-exposure occupations (SMR = 0.7, 95% CI: 0.5, 1.0). Testicular cancer deaths also occurred less frequently than expected in the entire cohort and high-exposure occupations. Death rates for several smoking-related diseases were significantly lower in the high-exposure occupations. Nonlymphocytic leukemia was significantly elevated among men in high-exposure occupations but in only one of the three high-exposure occupations, namely, electronics technicians in aviation squadrons (SMR = 2.2, 95% CI: 1.3, 3.7). Radar exposure had little effect on mortality in this cohort of US Navy veterans.