Increased Risk Of Thyroid Diseases Linked To Exposure At Chernobyl, Study Shows
     ScienceDaily (Feb. 19, 2008) — Persons exposed to radioactive fallout from the Chernobyl accident as children and adolescents have an increased risk of follicular adenoma or benign tumor of the thyroid gland, according to researchers at Columbia University Mailman School of Public Health. Results of the study further suggest that age at exposure, history of thyroid diseases, and location of residence do not modify its risk. This is the first epidemiologic study of the association between radiation exposure from radioactive iodine fallout from the Chernobyl accident and subsequent risk of follicular adenoma in those exposed at 18 years old or younger.
     The Chernobyl accident in 1986 was the largest nuclear accident ever and exposed many individuals to radioactive iodines. Thyroid cancer is one of the most radiosensitive tumors when exposure occurs at young ages. Previous studies showed that the risk of thyroid cancer increased with radiation dose from radioactive iodines, but the effects of radiation on benign thyroid diseases has been largely unknown.
     Researchers selected a random sample of 32,385 persons from a database of more than 75,000 records of thyroid radioactivity measurements taken within two months after the incident in those under the age of 18 who resided in three heavily contaminated areas in Ukraine. Various methods were used to trace these subjects and invite them for screening which consisted of an examination of the thyroid gland and sonogram, blood and urine tests, a detailed questionnaire, and an independent clinical examination by an endocrinologist.
     Those with suspicious findings were further referred for fine-needle biopsy and surgery as needed. The scientists reported a significant three-fold increase in risk for those exposed to the standard measure of 1 gray of radiation compared to those with zero dose. The study further indicates that women had a notably higher risk of follicular adenoma compared with men.
     "The Chernobyl accident presented an unparalleled opportunity to study the association between radioactive iodines and a spectrum of thyroid diseases," said Lydia B. Zablotska, MD, PhD, principal investigator of the project and assistant professor of Epidemiology at the Mailman School of Public Health. 
     "While there have been several analytical epidemiologic studies of thyroid cancer following the Chernobyl accident, none had evaluated follicular adenoma in particular. This paper presents risk estimates of follicular adenoma in relation to individual thyroid doses as well as the effects of gender, age at exposure, iodine deficiency, and other possible effect-modifying factors."
     The researchers note that the radioactive iodines accumulated in the human thyroid gland via the consumption of contaminated milk and other food items. Various earlier studies have shown that the populations of Ukraine, Belarus, and the Russian Federation experienced large increases of thyroid cancer in those exposed to the fallout before the age of 18 years. This increase became apparent 4--5 years after the accident and confirmed previous suggestions.
Also among the major strengths of the Mailman School study are the availability of individual thyroid doses based on thyroid radioactivity measurements made within two months after the accident and the data collected during screening. While the researchers caution that these results are based on a small number of cases, "our findings are further strengthened by the high fine-needle biopsy compliance rate of 93%. Because all those referred for surgery following fine-needle aspiration biopsy have been operated upon, it is unlikely that follicular adenoma was underdiagnosed," Dr. Zablotska said.
     Ukraine is known to have a mild to moderate iodine deficiency previously shown to affect radiation-related risks of thyroid cancer. In this study several indicators of iodine deficiency such as place of residence, history of thyroid diseases, and current urinary iodine excretion did not modify the risk of follicular adenoma.
     "Our findings confirm that follicular adenoma is strongly related to exposure from radioactive iodines, and while we found that the risk is modified by gender, age at exposure, place of residence, and personal history of thyroid diseases do not affect its subsequent development," said Dr. Zablotska.
     The paper is published in the February 2008 issue of the American Journal of Epidemiology. The research was supported by funding from the National Cancer Institute.
     Adapted from materials provided by Columbia University's Mailman School of Public Health.
Pour information... "contradictoire" en français, une publication de l'IRSN:
Les retombées radioactives de l'accident de Tchernobyl sur le territoire français.
Conséquences environnementales et exposition des personnes.
     Le vingtième anniversaire de la catastrophe nucléaire de Tchernobyl a été l'occasion, pour l'IRSN, de dresser un nouveau bilan des retombées radioactives dues à l'accident sur le territoire français. Ce livre rend notamment compte des connaissances acquises grâce aux nombreux travaux scientifiques réalisés en France depuis la première édition de l'ouvrage en 1999.
     Cette nouvelle édition fournit les connaissances et les interprétations les plus actuelles sur le transfert des substances radioactives rejetées par l'accident dans l'air, dans les sols et dans les aliments.
Cet état des lieux permet d'expliquer les niveaux de contamination radioactive observés en France de 1986 à 2006, puis d'évaluer l'exposition de la population française aux retombées de l'accident.
     L'analyse de l'accident de Tchernobyl illustre ainsi la multitude et la complexité des phénomènes de contamination et de transfert des substances radioactives dans l'environnement jusqu'à l'homme.
     Enfin, ce livre présente les enseignements tirés de la catastrophe en termes de connaissances et de développement de programmes scientifiques, de surveillance radiologique et de gestion d'une crise nucléaire en France.

Dossier Tchernobyl