Trial Information

Study to Improve Thyroid Doses From Fallout Exposure in Kazakhstan

The proposed work will improve our understanding of historical, fallout-related radiation
doses received by residents of villages in Kazakhstan immediately downwind from the
Semipalatinsk Nuclear Test Site (SNTS), where multiple nuclear test explosions were carried
out between 1949 and 1962. In collaboration with scientists at the Institute for Biophysics
in Moscow, NCI has developed a combined bi-national dose reconstruction methodology based on
lessons learned from studying radioactive fallout from tests at the SNTS in Kazakhstan, the
Nevada Test Site in the United States, and other test sites. Gamma rays from radionuclides
such as cesium 137 in fallout are highly penetrating and can affect all organs even when the
radioactive source is outside the body, whereas less-penetrating beta particles from iodine
131, also plentiful in fallout, mainly affect the thyroid gland when ingested in milk from
dairy animals grazing on contaminated pasture. We are particularly interested in both kinds
of radiation doses to children, because their thyroid glands are small and very active, tend
to concentrate ingested iodine, and are highly sensitive to radiation carcinogenesis. The
conditions of fallout exposure in Kazakhstan are directly relevant to those following a
hypothetical nuclear accident or radiation terrorism incident involving high levels of local
fallout.

We propose a field study in Kazakhstan to investigate aspects of typical daily village life
in areas affected by fallout that might influence individual radiation doses to the thyroid
gland. Using focus group interviews, we will collect retrospective information about factors
influencing radiation dose to the thyroid gland in children of two distinct ethnic groups
(Kazakh and European). These factors include milk and milk product consumption, dependence
on different species of dairy animals known to differ with respect to concentration of
iodine in milk, seasonal practices of pasturing and supplemental feeding of dairy animals at
the time of the nuclear tests, time children typically spent outdoors, and radiation
shielding provided by dwellings and other buildings. We will also ask about protective
measures taken at the time, such as details of temporary evacuations of villages predicted
to be in the fallout paths from particular tests. These data will fill key gaps in the
current dose-reconstruction methodology and should result in improved dose estimates, as
well as a basis for evaluating and quantifying dosimetric uncertainty and related biases in
risk estimates.