Health experts are at odds on whether radiation from the Fukushima nuclear accident led to an unexpectedly high occurrence rate of thyroid gland cancer among children in Fukushima Prefecture.
The prefectural government has been conducting thyroid gland tests on all children in the prefecture who were 18 or younger when the nuclear crisis began to unfold in March 2011.
Twelve of the 174,000 children who have undergone the comprehensive checkups have been found with thyroid gland cancer, with an additional 16 suspected of having the disease.
A majority of radiologists, as well as the prefectural government, have dismissed speculation that radiation from the Fukushima No. 1 nuclear power plant had any role in the numbers. But others said it is premature to make any assessment based on the currently available data.
The figures mean about one in every 15,000 children in Fukushima Prefecture has thyroid gland cancer. The rate soars to one in every 6,000 if the suspected cases are included.
Those figures are higher than the thyroid gland cancer occurrence rate of 1.7 in every 100,000 individuals between the ages 15 and 19 in Miyagi and three other prefectures in 2007.
The Fukushima prefectural government has attributed the higher rate to the fact that a large number of children have been subjected to exhaustive, high-precision tests, which are able to detect cancer more accurately than conventional tests.
Shinichi Suzuki, a Fukushima Medical University professor involved in the tests, denies that radiation has had any impact on the occurrence rate.
He said thyroid gland cancer only began to emerge four or five years after the Chernobyl nuclear accident of 1986, and most of the patients were infants when they were exposed to radiation. By contrast, only two years have passed since the Fukushima nuclear disaster, and thyroid gland cancer has been found in children 9 years old or older, Suzuki said.
Kazuo Shimizu, a Nippon Medical School professor who was recently appointed to a prefectural government panel to discuss the test results, takes a more cautious stance.
"With the data we currently have, there is no way of telling if radiation has had any impact," Shimizu said. "A large-scale study is necessary to test the thyroid glands of children in similar age brackets who were never exposed to radiation."
Shimizu said the different scales of the Chernobyl and Fukushima disasters and the different situations of food-derived iodine intake preclude a simple comparison between the two cases.
Many experts have pointed out that an assessment remains difficult as long as little data is available on radiation doses in thyroid glands.
"Comparison with doses is essential, so there should be more research emphasis on that front," said Fumiko Kasuga, another member of the prefectural government panel, who is also a vice president of the Science Council of Japan.
(This article was written by Yuri Oiwa and Teruhiko Nose.)
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