Thyroid Cancer Study among Ukrainian Children Exposed to Radiation after the Chornobyl Accident

Abstract

In collaboration with the Ukrainian Research Center for Radiation Medicine, the U.S. National Cancer Institute initiated a cohort study of children and adolescents exposed to Chornobyl fallout in Ukraine to better understand the long-term health effects of exposure to radioactive iodines. All 13,204 cohort members were subjected to at least one direct thyroid measurement between 30 April and 30 June 1986 and resided at the time of the accident in the northern part of Kyiv, Zhytomyr, or Chernihiv Oblasts, which were the most contaminated territories of Ukraine as a result of radioactive fallout from the Chornobyl accident. Thyroid doses for the cohort members, which had been estimated following the first round of interviews, were re-evaluated following the second round of interviews. The revised thyroid doses range from 0.35 mGy to 42 Gy, with 95 percent of the doses between 1 mGy and 4.2 Gy, an arithmetic mean of 0.65 Gy, and a geometric mean of 0.19 Gy. These means are 70% of the previous estimates, mainly because of the use of country-specific thyroid masses. Many of the individual thyroid dose estimates show substantial differences because of the use of an improved questionnaire for the second round of interviews. Limitations of the current set of thyroid dose estimates are discussed. For the epidemiologic study, the most notable improvement is a revised assessment of the uncertainties, as shared and unshared uncertainties in the parameter values were considered in the calculation of the 1,000 stochastic estimates of thyroid dose for each cohort member. This procedure makes it possible to perform a more realistic risk analysis.

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

“…The stochastic thyroid dose estimates from 131 I intakes that have been obtained in our study were compared with those from a study that was conducted in a Ukrainian cohort of 13,204 subjects using similar methodology (6). The results are similar in terms of the overall mean stochastic thyroid dose for the cohort (0.68 Gy in our study and 0.65 Gy in Ukraine) and geometric mean (0.27 Gy in our study and 0.19 Gy in Ukraine).…”

“…The uncertainties arise from, among other sources, stochastic variability of parameters used in exposure assessment, lack of knowledge about true values and low reliability of data on individual behavior during radiation exposures that occurred a long time ago. 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).…”

Factors associated with serum thyroglobulin in a Ukrainian cohort exposed to iodine-131 from the accident at the Chernobyl Nuclear Plant

“…Detailed methods for 131 I thyroid dose reconstruction have been described by Likhtarov and colleagues (Likhtarov et al, 2014). Briefly, assessment of thyroid doses from 131 I was based on direct readings (readings of gamma radiation from radiation detectors placed on the neck), age-and sex-specific thyroid masses derived for the Ukrainian population from the results of ultrasound measurements done in 1991-1996, questionnaires on residential history, dietary and lifestyle habits, and environmental transfer models.…”

“…One thousand individual stochastic doses were calculated for each cohort member accounting for shared and unshared errors. The distribution of dose estimates was close to lognormal with geometric standard deviations (GSD) ranging from 1.6 to 5.4 among cohort members (Likhtarov et al, 2014). The arithmetic mean of 1000 individual stochastic dose realizations was used for this analysis.…”

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

“…At the geometric mean dose as reported in [38], this gives an asymptotic RR | 190 mGy = 2.85 (1.51, 18.92) 95% . Fitting the quasi models over C + restricted to agex < 18, Q2d gives RR | 190 mGy = 2.62 (1.50, 4.57) 95% .…”