Impact of uncertainties in exposure assessment on estimates of thyroid cancer risk among Ukrainian children and adolescents exposed from the chernobyl accident

The 1986 accident at the Chernobyl nuclear power plant remains the most serious nuclear accident in history, and excess thyroid cancers, particularly among those exposed to releases of iodine-131 remain the best-documented sequelae. Failure to take dose-measurement error into account can lead to bias in assessments of dose-response slope. Although risks in the Ukrainian-US thyroid screening study have been previously evaluated, errors in dose assessments have not been addressed hitherto. Dose-response patterns were examined in a thyroid screening prevalence cohort of 13,127 persons aged <18 at the time of the accident who were resident in the most radioactively contaminated regions of Ukraine. We extended earlier analyses in this cohort by adjusting for dose error in the recently developed TD-10 dosimetry. Three methods of statistical correction, via two types of regression calibration, and Monte Carlo maximum-likelihood, were applied to the doses that can be derived from the ratio of thyroid activity to thyroid mass. The two components that make up this ratio have different types of error, Berkson error for thyroid mass and classical error for thyroid activity. The first regression-calibration method yielded estimates of excess odds ratio of 5.78 Gy-1 (95% CI 1.92, 27.04), about 7% higher than estimates unadjusted for dose error. The second regression-calibration method gave an excess odds ratio of 4.78 Gy-1 (95% CI 1.64, 19.69), about 11% lower than unadjusted analysis. The Monte Carlo maximum-likelihood method produced an excess odds ratio of 4.93 Gy-1 (95% CI 1.67, 19.90), about 8% lower than unadjusted analysis. There are borderline-significant (p= 0.101-0.112) indications of downward curvature in the dose response, allowing for which nearly doubled the low-dose linear coefficient. In conclusion, dose-error adjustment has comparatively modest effects on regression parameters, a consequence of the relatively small errors, of a mixture of Berkson and classical form, associated with thyroid dose assessment

Metamorphism of Paleoproterozoic paragneisses in the Belarus-Podlyasie granulite belt: Prograde-retrograde evolution

Metasedimentary granulites from the central portion of the Belarus-Podlyasie granulite belt were studied with the purpose to reproduce the Paleoproterozoic tectono-thermal evolution in the western part of the East European craton. The regularities identified in the compositional variations in minerals (particularly, garnet), textural relations between minerals, and thermobarometric data point to the complicated evolution of metamorphism with a well pronounced prograde stage. The latter is marked by the predominantly growth zoning of large garnet poikiloblasts from the paragneisses and corresponding variations in the composition of biotite and plagioclase inclusions in this garnet, which testify, when analyzed together with textural -structural relationships between minerals, to a temperature and pressure increase from 530-570degreesC, 3-4 kbar to 650-670degreesC, 6-7 kbar at similar to1870 Ma. The metamorphic peak is represented by the assemblages Grt +/- Crd + Sil + Bt +/- Spl +/- Ilm + Mag + Pl + Kfs + Qtz, occurred at T = 750-760degreesC, P = 7.5-8 kbar, at t similar to 1800 Ma and was coeval with intense bimodal magmatism during the postcollisional evolutionary stage of the granulite belt. Retrograde reactions proceeded as the temperature and pressure decreased from their peak values to 530-540degreesC, 3.5-4.5 kbar at 1780-1740 Ma. The fairly high uplift velocities and cooling rate of the rocks (1.4-0.2 mm/yr and 20-4degreesC/m.y., respectively), the preservation of garnet growth zoning, and a characteristic configuration of the P-T-t path suggest the relatively rapid exhumation of the granulites to upper crustal levels