Thyroid Cancer Incidence Among People Living in Areas Contaminated by Radiation From the Chernobyl Accident

Abstract

As a result of the Chernobyl nuclear power plant accident, massive amounts of radioactive materials were released into the environment and large numbers of individuals living in Belarus, Russia, and Ukraine were exposed to radioactive iodines, primarily 131I. Iodine-131 concentrated in the thyroid gland of residents of the contaminated areas, with children and adolescents being particularly affected. In the decade after the accident, a substantial increase in thyroid cancer incidence was observed among exposed children in the three affected countries, and compelling evidence of an association between pediatric thyroid cancer incidence and radiation exposure to the thyroid gland accumulated. The data currently available suggest that both the magnitude and patterns of thyroid cancer risk are generally consistent with those reported following external exposure. Based on data from case-control studies, iodine deficiency appeared to enhance the risk of developing thyroid cancer following exposure from Chernobyl. Results from a recent large cohort study, however, did not support these findings. Data on adult exposure are limited and not entirely consistent. Similarly, information on thyroid cancer risks associated with in utero exposure is insufficient to draw conclusions. The lack of information on these two population groups indicates an important gap that needs to be filled. Twenty years after the accident, excess thyroid cancers are still occurring among persons exposed as children or adolescents, and, if external radiation can be used as a guide, we can expect an excess of radiation-associated thyroid cancers for several more decades. Since considerable uncertainties about the long-term health effects from Chernobyl remain, continued follow-up of the exposed populations should provide valuable information.

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

“…Alternatively, dose fractionation may be important only at very low doses, <0.10 Gy, a range at which the pooled data have little power to examine this effect (36). Nonetheless, our findings were consistent with dose rate having no effect or at best a weak effect on thyroid cell line survival (37) and largely compatible with results from studies of persons receiving 131 I radiation during childhood from the Chernobyl accident (38). …”

Occupation and thyroid cancer

“…Much has been learned about the mechanism of radiation-induced thyroid cancer from the Chernobyl accident19 and prior atomic bomb studies17 18; however, potential mechanisms for other environmental causes of thyroid cancer are currently unknown. Thyroid function is controlled by dynamic inter-relationships between the hypothalamus, the pituitary and the thyroid, which maintain circulating levels of the thyroid hormones, triiodothyronine (T 3 ) and thyroxine (T 4 ), within a narrow range under normal conditions.…”

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

“…Studies conducted approximately a decade after the Chornobyl nuclear power plant accident among individuals exposed as children or adolescents have demonstrated strong, consistent associations between radiation dose and risk of thyroid cancer with estimated odds ratios of approximately 5 at 1 Gy of exposure (Cardis et al 2005; Davis et al 2004; Ron 2007; Tronko et al 2006a). The estimates of relative risk (RR) per gray from ecological studies are even higher (Jacob et al 1999, 2006; Likhtarov et al 2006).…”