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Radiat Res. 2016 May;185(5):473-84. doi: 10.1667/RR14213.1. Epub 2016 Apr 29.

Thyroid Cancer after Childhood Exposure to External Radiation: An Updated Pooled Analysis of 12 Studies.

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a   Divisions of Cancer Epidemiology and Genetics and.
c   Institute for Radiation Protection and Dosimetry, Brazilian Nuclear Energy Commission, Rio de Janeiro, Brazil;
d   Department of Oncology and Radiation Physics and the Oncological Centre, Sahlgrenska University Hospital, Goteborg, Sweden;
e   Department of Cancer Epidemiology, Lund University, Lund, Sweden;
f   Representing the Nordic Countries Childhood Cancer Survival Group;
g   Captain, United States Public Health Service (retired), Bethesda, Maryland;
h   Cancer and Radiation Epidemiology Unit, The Gertner Institute, Chaim Sheba Medical Center and Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel;
i   University of Rochester School of Medicine and Dentistry, Department of Public Health Sciences, Rochester, New York;
j   Radiation Effects Research Foundation, Hiroshima, Japan (retired);
k   University of Illinois College of Medicine, Section of Endocrinology, Diabetes and Metabolism, Chicago, Illinois;
l   Program in Epidemiology, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington;
m   Oncology, Department of Radiation Sciences, Umeå University, Umeå, Sweden;
b   Cancer Control and Population Sciences, National Cancer Institute, NIH, DHHS, Bethesda, Maryland;
n   Cancer Epidemiology Research Unit, National Institute for Health and Medical Research-Institut Gustave Roussy, Villejuif, France;
Centre for Childhood Cancer Survivor Studies, Department of Public Health and Epidemiology, University of Birmingham, Birmingham, United Kingdom; and.
p   Department of Medical Physics, Radiumhemmet, Karolinska University Hospital and Karolinska Institute, Stockholm, Sweden.


Studies have causally linked external thyroid radiation exposure in childhood with thyroid cancer. In 1995, investigators conducted relative risk analyses of pooled data from seven epidemiologic studies. Doses were mostly <10 Gy, although childhood cancer therapies can result in thyroid doses >50 Gy. We pooled data from 12 studies of thyroid cancer patients who were exposed to radiation in childhood (ages <20 years), more than doubling the data, including 1,070 (927 exposed) thyroid cancers and 5.3 million (3.4 million exposed) person-years. Relative risks increased supralinearly through 2-4 Gy, leveled off between 10-30 Gy and declined thereafter, remaining significantly elevated above 50 Gy. There was a significant relative risk trend for doses <0.10 Gy (P < 0.01), with no departure from linearity (P = 0.36). We observed radiogenic effects for both papillary and nonpapillary tumors. Estimates of excess relative risk per Gy (ERR/Gy) were homogeneous by sex (P = 0.35) and number of radiation treatments (P = 0.84) and increased with decreasing age at the time of exposure. The ERR/Gy estimate was significant within ten years of radiation exposure, 2.76 (95% CI, 0.94-4.98), based on 42 exposed cases, and remained elevated 50 years and more after exposure. Finally, exposure to chemotherapy was significantly associated with thyroid cancer, with results supporting a nonsynergistic (additive) association with radiation.

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