A new study confirms a substantially increased risk of thyroid cancer among people exposed to radiation during childhood and adolescence after the 1986 Chernobyl nuclear accident. A total of 13,127 of the 32,385 individuals living in the most contaminated area of the Ukraine during the nuclear plant meltdown and who were under 18 at the time were screened between 1998 and 2000, Dr. Geoffrey R. Howe of Columbia University in New York and colleagues report. They found that 45 cases of thyroid cancer occurred compared with 11.2 cases that would have been expected in the absence of radiation exposure. Plus, the higher the dosage of radioactive iodine, the greater the thyroid cancer risk.

The study is the first to measure the risk of thyroid cancer associated with specific radiation dosage, Howe and his team note in the Journal of the National Cancer Institute. Radioactive iodine and cesium were the main components of the Chernobyl fallout. Because radioactive iodine is used frequently in medicine -- and is also likely to be a chief contaminant released in any future nuclear emergency -- understanding the risk associated with exposure is a public health concern, as well as of scientific interest, the researchers point out.

A spike in thyroid cancer cases had already been observed among Ukraine residents who were children and adolescents when the Chernobyl accident occurred. However, the researchers note, increased rates of screening for thyroid cancer and a low dietary iodine intake, which increases the uptake of radioactive iodine by the thyroid gland, "almost certainly" were factors in this increase.

To investigate the specific risk associated with radiation exposure, the researchers estimated each persons radiation exposure using measurements made after the accident and from interviews. They found a "strong" relationship between radiation exposure and thyroid cancer risk. While there was a tendency for risk to be greater among people exposed at younger ages, as well as among females, neither was statistically significant.

"We estimate that 75 percent of the thyroid cancer cases would have been avoided in the absence of radiation," the researchers conclude. "This estimate demonstrates a substantial contribution of radioactive iodines to the excess of thyroid cancer that followed the Chernobyl accident."
(Com informações do Journal of the National Cancer Institute, Planet Ark, 07/07/2006)