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      I-131 Dose Response for Incident Thyroid Cancers in Ukraine Related to the Chornobyl Accident

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          Abstract

          Background: Current knowledge about Chornobyl-related thyroid cancer risks comes from ecological studies based on grouped doses, case–control studies, and studies of prevalent cancers.

          Objective: To address this limitation, we evaluated the dose–response relationship for incident thyroid cancers using measurement-based individual iodine-131 (I-131) thyroid dose estimates in a prospective analytic cohort study.

          Methods: The cohort consists of individuals < 18 years of age on 26 April 1986 who resided in three contaminated oblasts (states) of Ukraine and underwent up to four thyroid screening examinations between 1998 and 2007 ( n = 12,514). Thyroid doses of I-131 were estimated based on individual radioactivity measurements taken within 2 months after the accident, environmental transport models, and interview data. Excess radiation risks were estimated using Poisson regression models.

          Results: Sixty-five incident thyroid cancers were diagnosed during the second through fourth screenings and 73,004 person-years (PY) of observation. The dose–response relationship was consistent with linearity on relative and absolute scales, although the excess relative risk (ERR) model described data better than did the excess absolute risk (EAR) model. The ERR per gray was 1.91 [95% confidence interval (CI), 0.43–6.34], and the EAR per 10 4 PY/Gy was 2.21 (95% CI, 0.04–5.78). The ERR per gray varied significantly by oblast of residence but not by time since exposure, use of iodine prophylaxis, iodine status, sex, age, or tumor size.

          Conclusions: I-131–related thyroid cancer risks persisted for two decades after exposure, with no evidence of decrease during the observation period. The radiation risks, although smaller, are compatible with those of retrospective and ecological post-Chornobyl studies.

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          Most cited references 46

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          Thyroid Cancer after Exposure to External Radiation: A Pooled Analysis of Seven Studies

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            Risk of thyroid cancer after exposure to 131I in childhood.

            After the Chernobyl nuclear power plant accident in April 1986, a large increase in the incidence of childhood thyroid cancer was reported in contaminated areas. Most of the radiation exposure to the thyroid was from iodine isotopes, especially 131I. We carried out a population-based case-control study of thyroid cancer in Belarus and the Russian Federation to evaluate the risk of thyroid cancer after exposure to radioactive iodine in childhood and to investigate environmental and host factors that may modify this risk. We studied 276 case patients with thyroid cancer through 1998 and 1300 matched control subjects, all aged younger than 15 years at the time of the accident. Individual doses were estimated for each subject based on their whereabouts and dietary habits at the time of the accident and in following days, weeks, and years; their likely stable iodine status at the time of the accident was also evaluated. Data were analyzed by conditional logistic regression using several different models. All statistical tests were two-sided. A strong dose-response relationship was observed between radiation dose to the thyroid received in childhood and thyroid cancer risk (P<.001). For a dose of 1 Gy, the estimated odds ratio of thyroid cancer varied from 5.5 (95% confidence interval [CI] = 3.1 to 9.5) to 8.4 (95% CI = 4.1 to 17.3), depending on the risk model. A linear dose-response relationship was observed up to 1.5-2 Gy. The risk of radiation-related thyroid cancer was three times higher in iodine-deficient areas (relative risk [RR]= 3.2, 95% CI = 1.9 to 5.5) than elsewhere. Administration of potassium iodide as a dietary supplement reduced this risk of radiation-related thyroid cancer by a factor of 3 (RR = 0.34, 95% CI = 0.1 to 0.9, for consumption of potassium iodide versus no consumption). Exposure to (131)I in childhood is associated with an increased risk of thyroid cancer. Both iodine deficiency and iodine supplementation appear to modify this risk. These results have important public health implications: stable iodine supplementation in iodine-deficient populations may substantially reduce the risk of thyroid cancer related to radioactive iodines in case of exposure to radioactive iodines in childhood that may occur after radiation accidents or during medical diagnostic and therapeutic procedures.
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              [Volumetric analysis of thyroid lobes by real-time ultrasound (author's transl)].

              Thyroid volume as measured by real-time ultrasound in cadavers was compared with direct measurements obtained by submersion. Length X width X thickness of the thyroid lobe multiplied by factor pi/6, correspond to a rotation ellipsoid, while the best calculated volume of the lobe is obtained by multiplying with the optimised correction factor f = 0.479. The correctness of this calculation is, by definition, 100%; average error of the method is 16%. The measurements are easy to do and require no additional equipment for planimetry or calculations. Volumetric analysis of the thyroid gland is especially necessary in assessing results of treatment and for measuring dosage in connection with radioiodine therapy.
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                Author and article information

                Journal
                Environ Health Perspect
                EHP
                Environmental Health Perspectives
                National Institute of Environmental Health Sciences
                0091-6765
                1552-9924
                17 March 2011
                01 July 2011
                : 119
                : 7
                : 933-939
                Affiliations
                [1 ]Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA
                [2 ]Institute of Endocrinology and Metabolism, Kyiv, Ukraine
                [3 ]Department of Epidemiology and Biostatistics, University of California–San Francisco, San Francisco, California, USA
                [4 ]Department of Medicine, The Thyroid Clinic, College of Physicians and Surgeons, Columbia University, New York, New York, USA
                [5 ]Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, USA
                [6 ]Department of Pathology, College of Physicians and Surgeons, Columbia University, New York, New York, USA
                Author notes
                Address correspondence to A.V. Brenner, Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, DHHS, MS 7238, 6120 Executive Blvd., Bethesda, MD 20892-7238 USA. Telephone: (301) 402-8680. Fax: (301) 402-0207. E-mail: brennera@ 123456mail.nih.gov

                It is with great sadness that we report the death of our colleague Elaine Ron while the manuscript was under review.

                1002674
                10.1289/ehp.1002674
                3222994
                21406336

                This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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