Childhood exposure due to the Chernobyl accident and thyroid cancer risk in contaminated areas of Belarus and Russia

Abstract

The thyroid dose due to 131 I releases during the Chernobyl accident was reconstructed for children and adolescents in two cities and 2122 settlements in Belarus, and in one city and 607 settlements in the Bryansk district of the Russian Federation. In this area, which covers the two high contamination spots in the two countries following the accident, data on thyroid cancer incidence during the period 1991–1995 were analysed in the light of possible increased thyroid surveillance. Two methods of risk analysis were applied: Poisson regression with results for the single settlements and Monte Carlo (MC) calculations for results in larger areas or sub-populations. Best estimates of both methods agreed well. Poisson regression estimates of 95% confidence intervals (CIs) were considerably smaller than the MC results, which allow for extra-Poisson uncertainties due to reconstructed doses and the background thyroid cancer incidence. The excess absolute risk per unit thyroid dose (EARPD) for the birth cohort 1971–1985 by the MC analysis was 2.1 (95% CI 1.0–4.5) cases per 10 4 person-year Gy. The point estimate is lower by a factor of two than that observed in a pooled study of thyroid cancer risk after external exposures. The excess relative risk per unit thyroid dose was 23 (95% CI 8.6–82) Gy −1 . No significant differences between countries or cities and rural areas were found. In the lowest dose group of the settlements with an average thyroid dose of 0.05 Gy the risk was statistically significantly elevated. Dependencies of risks on age-at-exposure and on gender are consistent with findings after external exposures. © 1999 Cancer Research Campaign

Recent Epidemiological Results of Thyroid Cancer in the Most Radiated Territory in Poland

“…For example, Jacob (5) shows that the excess absolute risk per unit thyroid dose for the birth cohort 1971-1985 by the Monte Carlo analysis was 2.1 cases per 104 person-year Gy, and the excess relative risk per unit thyroid dose was 23 Gy-1. Reports on a great increase in the frequency of thyroid cancer in children in Belarus, where incidence started to rise in 1990 and continues in some regions of Belarus, can be found in (6), or in (7).…”

Increasing world incidence of thyroid cancer: Increased detection or higher radiation exposure?

“…Focal micropapillary hyperplasia has been found in the thyroids of children exposed at Chernobyl, likely representing a histopathologic precursor of carcinoma, and it is the children's exposure to fallout that constitutes the most logical explanation. General aspects of radiation injury to the thyroid gland, and the well documented history of the Chernobyl accident in April 1986 and its consequences, have been extensively reviewed 31,32 and will not be discussed at any significant length here. Suffice it to say that a strong dose response curve has been observed based upon reconstructions of estimated radiation dosage exposure and dietary iodine intake.…”

RET/PTC rearrangement in benign and malignant thyroid diseases: a clinical standpoint

“…These studies evidenced that the Chernobyl accident resulted in a dramatic increase in the number of thyroid cancers of PTC type with a frequency of rearrangements of the RET proto-oncogene higher than that in sporadic PTC (45,46). The association of RET rearrangements with radiation exposure was sustained by the observation that the incidence of PTCs is severely increased in radiocontaminated areas following a linear relationship with dose exposition (47). In the comparative analysis of RET rearrangements in sporadic and radiation-induced thyroid tumors performed by Nikiforov et al (45), RET/PTC1 was shown to be the dominant type within sporadic carcinomas and was strongly related to the classic variant, while RET/PTC3 was predominant among radiation-induced carcinomas and more frequent in the solid PTC variant.…”