Post-Chornobyl Thyroid Cancers in Ukraine. Report 1: Estimation of Thyroid Doses

Abstract

About 1.8 EBq of 131I was released into the atmosphere during the Chornobyl accident that occurred in Ukraine on April 26, 1986. More than 10% of this activity was deposited on the territory of Ukraine. Beginning 4-5 years after the accident, an increase in the incidence of thyroid cancer among children, believed to be caused in part by exposure to 131I, has been observed in different regions of Ukraine. A three-level system of thyroid dose estimation was developed for the reconstruction of thyroid doses from 131I for the entire population of Ukrainian children aged 1 to 18 at the time of accident: (1) At the first level, individual doses were estimated for the approximately 99,000 children and adolescents with direct measurements of radioactivity in the thyroid (so-called direct thyroid measurements) performed in May-June of 1986; (2) at the second level, group doses by year of age and by gender were estimated for the population of 748 localities (with 208,400 children aged 1-18 in 1986) where direct thyroid measurements of good quality were performed on some of the residents; and (3) at the third level, group doses by age and by gender were estimated for the population of the localities where no thyroid measurements were made in 1986. The third-level doses were then aggregated over the population of each oblast. Data, models and procedures required for each level of thyroid dose estimation are described in the paper. At the first level, individual doses were found to range up to 27,000 mGy, with geometric and arithmetic means of 100 and 300 mGy, respectively. At the second level, group doses were found to be highest for the younger children (aged 1 to 4 years); doses for the older children (aged 16 to 18 years) were 3.5 times smaller. At the third level, average population-weighted doses were found to exceed 35 mGy in the five northern oblasts closer to the Chornobyl reactor site; to be in the 14- to 34-mGy range in seven other oblasts, Kyiv city and Crimea; and to be less than 13 mGy in all other oblasts.

The epidemiology of thyroid cancer in the Czech Republic in comparison with other countries

“…The highest incidence was found in children, who were in 1986 ≤ 5 years of age and who lived in areas where the radiation doses reached ≥ 0.50 Gy (gray). Iodine deficiency made the situation even worse 21,22 . During the first 4 years after the Chernobyl disaster, an increase of newly diagnosed DTC from 2 to 4.6% was found in the Czech Republic.…”

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

“…According to the dosimetric model described by Likhtarev et al (2005Likhtarev et al ( , 2006b, the calculated thyroid dose of person i is expressed as Likhtarev et al, 2003Likhtarev et al, , 2006b) and will be ignored in this analysis. In principle, the uncertainty in f i can be included in the evaluation in many ways, using for example the shared parameter methods of Stram and Kopecky (2003).…”

“…We performed a simulation study based on data from epidemiological investigations (see Jacob, et al, 2006;Likhtarev, et al, 2005;Likhtarev, et al, 2006a;Likhtarev, et al, 2006b). For the simulation of doses a real subpopulation of 7077 children and teenagers up to 18 years was used; these persons resided in settlements of Zhitomir, Kyiv, and Chernigov Oblasts of Ukraine at the time of the Chornobyl accident and had direct measurements of thyroid activity in May-June 1986.…”

“…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.…”

Estimating Thyroid Masses for Children, Infants, and Fetuses in Ukraine Exposed to 131I From the Chernobyl Accident

“…Because the thyroid dose is inversely proportional to the mass of this organ, any error in the estimate of the thyroid mass is directly reflected in the error of the estimate of the thyroid dose. Up to a few years ago, the age-dependent thyroid masses recommended in ICRP Publications 23 and 56 (ICRP 1975(ICRP , 1989 for reference persons were used for thyroid dose estimation (Likhtarov et al 2005(Likhtarov et al , 2006. These values were based on a rather limited number of measurements of thyroid mass among the residents of the U.S. (ICRP 1975), where the dietary intake of iodine is very different from that in Ukraine.…”