Risk of Thyroid Cancer After Exposure to 131 I in Childhood

Abstract

Background: 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 131 I. We carried out a populationbased 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. Methods: 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. Results: 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% confi dence 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-defi cient 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). Conclusion: Exposure to 131 I in childhood is associated with an increased risk of thyroid cancer. Both iodine defi ciency and iodine supplementation appear to modify this risk. These results have important public health implications: stable iodine supplementation in iodine-defi cient 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

The Chernobyl Accident and its Consequences

“…Individual thyroid doses were reconstructed and used to estimate dose-response relationship. It was found to be significant and linear up to 1.5-2 Gy [41]. The odds ratio for thyroid cancer varied from 5.5 to 8.4 for a dose of 1 Gy according to different risk models; this was generally comparable with risk estimates for external exposures [42].…”

Clinical Behavior of Radiation-Induced Thyroid Cancer: Factors Related to Recurrence

“…Iodine deficiency has been welldocumented in the affected areas and has only been partially corrected over time (25,26). The resulting TSH stimulation, even by TSH levels within the reference range, may promote cancer development and progression (27,28). The Chernobylrelated cases identified so far have been in pediatric and young adult patients where aggressive characteristics are more commonly seen than in older patients.…”

Polymorphisms of DNA damage response genes in radiation-related and sporadic papillary thyroid carcinoma

“…Although radiation thyroid doses in Chernobyl PTC cases are generally greater than in controls in epidemiological studies (Cardis et al 2005, Jacob et al 2006, Likhtarev et al 2006, thus confirming radiation to be a risk factor for thyroid cancer, those in controls are non-zero. Furthermore, there were some 14 million residents in the contaminated territories at the time of exposure (Bennett et al 2006).…”