Aug 20 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 U.S. study.
Thyroid cells are particularly vulnerable to ionizing
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
minimized 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.
(Reporting from New York by Genevra Pittman at Reuters Health;
Editing by Elaine Lies and Michael Perry)