Tokyo - People who survived the atomic bombings of Hiroshima and Nagasaki as children continue to have a higher-than-normal risk of thyroid cancer more than 50 years after radiation exposure, according to a US study.
Thyroid cells are particularly vulnerable to ionising radiation, the kind produced by the Chernobyl nuclear meltdown or the atomic bombings in Japan.
The study published in the International Journal of Cancer tracked new cancer diagnoses in people who were in Japan during the bombings in 1945 and those who were not.
In total, there were 371 thyroid cancers diagnosed between 1958 and 2005 in about 105,000 atomic bomb survivors.
The study found little evidence that adults exposed to the radiation were more likely to develop thyroid cancer later on.
However, for children exposed to the radiation, the result was different. The study found 36 percent of 191 thyroid cancers in people who were children or teens at the time was likely due to radiation exposure.
“Thyroid cancer is one of the most radio sensitive cancers,” said Kiyohiko Mabuchi at the National Cancer Institute in Bethesda, Maryland, who worked on the study.
“Younger (thyroid) tissue may be more sensitive to radiation - that's one of the hypotheses.”
The thyroid releases hormones that help regulate the body's metabolism. The gland works especially hard during times of fast growth and development in children and teens.
The researchers said it was not clear whether the findings have implications for Japanese children who were living near the Fukushima nuclear plant, which suffered a meltdown last March following an earthquake and tsunami.
In the case of Fukushima, quick evacuations may have minimised the exposure risk, said radiation researcher John Boice from Vanderbilt University in Nashville, Tennessee.
Boice pointed out that even among atomic bomb survivors, the risk of thyroid cancer was very low for people who only got a small dose of radiation.
“And, it appears around Fukushima and in Japan that the exposures to kids were below a level where there's been any detectable increase (in cancer risk),” Boice added.
Researchers are still calculating radiation exposures after Fukushima. A typical head CT scan delivers about 2 millisieverts (mSv) worth of radiation, compared to 350 mSv and higher exposures among people who were evacuated after Chernobyl. - Reuters