Impact of Uncertainties in Exposure Assessment on Estimates of Thyroid Cancer Risk among Ukrainian Children and Adolescents Exposed from the Chernobyl Accident

Abstract

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.

Thyroid Dose Estimates for a Cohort of Belarusian Children Exposed to131I from the Chernobyl Accident: Assessment of Uncertainties

“…The current state-of-the-art approach in dosimetry is to document sources and quality of all input data, to establish a dosimetry error structure and to characterize each parameter used in dose calculations as a source of shared or unshared error (5, 6). These data may then be used in a probabilistic dose calculation to generate multiple sets of dose estimates for the entire study population, so that dose-response analyses can be performed using multiple sets of doses (7–9). …”

Low dose radiation risks for women surviving the a-bombs in Japan: generalized additive model

“…The results from GAM models applied to relevant subcohorts are compatible with [6, 11, 13, 15, 34, 35]. They are higher than extrapolations from [1, 36, 37], which concerned higher dose ranges.…”

“…Additional file 1: Table S9 shows some results from [1, 6, 7, 11, 13, 15, 34–37]. In each case, an appropriate subcohort of the female incidence data was analysed for comparison, using the simplest quasipoisson dose model Q2d and the preferred quasi model for the subcohort, chosen to approximate the dose and agex range in the study, or with mean dose close to that at which risk was reported.…”

“…For Chernobyl survivors with agex < 18, Little [6] considered a linear-exponential model with low-dose asymptote ERR = α D, estimating α = 9.72 (2.67, 94.31) 95% . At the geometric mean dose as reported in [38], this gives an asymptotic RR | 190 mGy = 2.85 (1.51, 18.92) 95% .…”

30 years After the Chernobyl Nuclear Accident: Time for Reflection and Re-evaluation of Current Disaster Preparedness Plans

“…29 The cohorts have undergone periodic standardized screening for thyroid cancer and nonmalignant diseases of the thyroid. The Ukranian [30][31][32] and Belarusian 33 studies have shown a significantly increased risk of thyroid cancer which was similar in magnitude to the risk associated with external radiation exposure. 4,28 Evidence from other smaller population-based case-control studies confirms a causal relationship between the observed increase in thyroid cancer risk and exposure to 131 I from the Chernobyl fall out.…”