Questionnaire- and Measurement-Based Individual Thyroid Doses in Ukraine Resulting from the Chornobyl Nuclear Reactor Accident

Abstract

The U.S. National Cancer Institute (NCI), in cooperation with the Ministries of Health of Belarus and of Ukraine, is involved in epidemiological studies of thyroid diseases presumably related to the Chornobyl accident, which occurred in Ukraine on 26 April 1986. Within the framework of these studies, individual thyroid absorbed doses, as well as uncertainties, have been estimated for all members of the cohorts (13,215 Ukrainians and 11,918 Belarusians), who were selected from the large group of children aged 0 to 18 whose thyroids were monitored for gamma radiation within a few weeks after the accident. Information on the residence history and dietary habits of each cohort member was obtained during personal interviews. The methodology used to estimate the thyroid absorbed doses resulting from intakes of (131)I by the Ukrainian cohort subjects is described. The model of thyroid dose estimation is run in two modes: deterministic and stochastic. In the stochastic mode, the model is run 1,000 times for each subject using a Monte Carlo procedure. The geometric means of the individual thyroid absorbed doses obtained in the stochastic mode range from 0.0006 to 42 Gy. The arithmetic and geometric means of these individual thyroid absorbed doses over the entire cohort are 0.68 and 0.23 Gy, respectively. On average, the individual thyroid dose estimates obtained in the deterministic mode are about the same as the geometric mean doses obtained in the stochastic mode, while the arithmetic mean thyroid absorbed doses obtained in the stochastic mode are about 20% higher than those obtained in the deterministic mode. The distributions of the 1000 values of the individual thyroid absorbed dose estimates are found to be approximately lognormal, with geometric standard deviations ranging from 1.6 to 5.0 for most cohort subjects. For the time being, only the thyroid doses resulting from intakes of (131)I have been estimated for all subjects. Future work will include the estimation of the contributions to the thyroid doses resulting from external irradiation and from intakes of short-lived ((133)I and (132)Te) and long-lived ((134)Cs and (137)Cs) radionuclides, as well as efforts to reduce the uncertainties.

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

“…• In the second scenario, at the preliminary stage the cutoff was not performed, and the subpopulation was artificially enlarged to N = 70 770 persons (see Figure 2). The true parameters of the absolute risk model (1) were given by the values close to the estimates obtained in the epidemiological studies of the thyroid cancers in Ukraine (Jacob, et al, 2006;Likhtarev, et al, 2006a • f i is the estimate from the ecological dosimetric model, see Likhtarev et al (2006b), • for Q tr i we took the thyroid activity measured in 1986, see Likhtarev et al (1993), • and M mes i is the median of the thyroid mass distribution for corresponding age-sex-region group, see Chornobyl: A Decade (1997).…”

“…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.…”

“…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. The thyroid doses for this subpopulation were reconstructed in the framework of the Ukrainian-American project on the investigation of Post-Chornobyl thyroid cancers in Ukraine (Likhtarev, et al, 2006b). …”

“…In the epidemiologic study of thyroid cancer conducted in Ukraine (Likhtarev et al, 2006b), the thyroid dose estimates are based on the measurements of Iodine-131 ( 131 I) that were performed on all subjects, and the uncertainties in the thyroid dose estimates are mainly due to those in the measured activities and in the thyroid mass (Likhtarev et al, 2003).…”