Childhood Thyroid Cancer, Radiation Dose from Chernobyl, and Dose Uncertainties in Bryansk Oblast, Russia: A Population-Based Case-Control Study

Abstract

A population-based case-control study was conducted to estimate the radiation-related risk of thyroid cancer in persons who were exposed in childhood to (131)I from the Chernobyl accident of April 26, 1986 and to investigate the impact of uncertainties in individual dose estimates. Included were all 66 confirmed cases of primary thyroid cancer diagnosed from April 26, 1986 through September 1998 in residents of Bryansk Oblast, Russia, who were 0-19 years old at the time of the accident, along with two individually matched controls for each case. Thyroid radiation doses, estimated using a semi-empirical model based on environmental contamination data and individual characteristics, ranged from 0.00014 Gy to 2.73 Gy and had large uncertainties (median geometric standard deviation 2.2). The estimated excess relative risk (ERR) associated with radiation exposure, 48.7/Gy, was significantly greater than 0 (P = 0.00013) but had an extremely wide 95% confidence interval (4.8 to 1151/Gy). Adjusting for dose uncertainty nearly tripled the ERR to 138/Gy, although this was likely an overestimate due to limitations in the modeling of dose uncertainties. The radiation-related excess risk observed in this study is quite large, especially if the uncertainty of dose estimation is taken into account, but is not inconsistent with estimates previously reported for risk after (131)I exposure or acute irradiation from external sources.

ret/PTC Activation Is Not Associated with Individual Radiation Dose Estimates in a Pilot Study of Neoplastic Thyroid Nodules Arising in Russian Children and Adults Exposed to Chernobyl Fallout

“…One, based on 107 cases diagnosed in Belarus, found a strong relationship between estimated radiation dose and thyroid cancer, but thyroid doses were inferred for children from estimates for adults who lived in the same villages (16). Two studies, based on a total of 66 cases and individual estimates of thyroid radiation dose, found that the risk of thyroid cancer was significantly increased in a dose-dependent manner among residents of Bryansk Oblast of the Russian Federation who were exposed as children and adolescents to radiation fallout from the Chernobyl accident (17,18). Finally, a fourth case-control study of 276 patients less than 15 years of age at the time of the accident in Belarus and the Russian Federation matched with 1300 control subjects showed a strong dose-response relationship between childhood thyroid radiation dose and thyroid cancer risk (19).…”

Methods for Estimation of Radiation Risk in Epidemiological Studies Accounting for Classical and Berkson Errors in Doses

“…A similar method of risk parameters estimation was used in Kopecky et al (2006), but the approach proposed below makes it possible to give proper weight to the structure of measured doses. Note that the SIMEX method does not require the knowledge of the probability distribution for the true activity Q tr i .…”

“…The current methods of risk estimation (see Health Risks from Exposure to Low Levels of Ionizing Radiation, 2006;Jacob et al, 2006;Likhtarev et al, 2006a) take into account uncertainties related to health effects, but assume that the doses are known with perfect precision and accuracy, something that is not true (Kopecky et al, 2006;Likhtarev et al, 1993;Likhtarev et al, 2003;Ron and Hoffman, 1999). Although many attempts have been made to develop mathematical tools which take into account the dose uncertainty (see Carroll et al, 2006;Hofer, 2008;Kopecky et al, 2006;Li et al, 2007;Masiuk et al, 2008), the problem has yet to be solved in a satisfactory manner.…”

“…Although many attempts have been made to develop mathematical tools which take into account the dose uncertainty (see Carroll et al, 2006;Hofer, 2008;Kopecky et al, 2006;Li et al, 2007;Masiuk et al, 2008), the problem has yet to be solved in a satisfactory manner. It is our opinion that one of the reasons an accurate model is so hard to create is because the dose estimates are almost inevitably associated with a mixture of classical and Berkson errors (Reeves et al, 1998;Carroll et al, 2006;Li et al, 2007), which leads to difficulties in evaluating the influence of the mixed errors in the estimated dose on risk analysis, which is usually expressed in terms of relative (ERR) or absolute (EAR) risk (see Health Risks from Exposure to Low Levels of Ionizing Radiation, 2006).…”

“…Though in the simulations and analysis of the source of uncertainty induced by Berkson and classical measurement errors we used the dose estimate and its uncertainty related to the thyroid exposure (Likhtarev et al, 1993;Likhtarev et al, 2003;Likhtarev et al, 2005), the main goal of the present paper is to study the possibility to apply in the risk analysis the most popular methods of regression analysis, e.g., Simulation-Extrapolation (SIMEX), Maximum Likelihood and Regression Calibration (see Carroll et al, 2006;Kopecky et al, 2006;Masiuk et al, 2008;Kukush and Schneeweiss, 2005). Those methods take into account the presence of measurement errors (classical, Berkson and mixed) in regressors.…”