Assessing the RISK of Thyroid Cancer after Fukushima Crisis

In the year and a half since the Fukushima Daiichi Nuclear Power Plant disaster following the March 2011 earthquake and tsunami in Japan, residents near the site have become increasingly concerned about the potential long-term effects to their health from radioactive contamination.

More than 100,000 people were evacuated after the meltdown, and significant radiation spread across 700 square miles of land, prompting health officials to make care and treatment of those exposed to radiation a top priority.

Monitoring such residents is “an unprecedented health management program for a two-million population for almost a whole lifespan,” said Shunichi Yamashita, M.D., vice president of Fukushima Medical University, during a presentation at ENDO 2012.

The organ most at risk from radioactive iodine is the thyroid gland, according to the American Thyroid Association (ATA). The thyroid absorbs iodine from the bloodstream and uses it to create energy-regulating hormones. The gland cannot, however, distinguish between regular iodine and the radioactive type and will absorb whatever it can. When thyroid cells absorb too much radioactive iodine, it can cause DNA damage, leading to the development of thyroid cancer several years after the exposure. Babies and young children are at highest risk.

Valuable lessons have been learned from past nuclear accidents, such as the 1986 disaster at Chernobyl in Ukraine that led to huge releases of radioactive materials into the atmosphere, Yamashita said in his lecture. The average thyroid “effective dose”— the amount of risk—to children at Chernobyl was 490 mSv (millisieverts), whereas children in Fukushima averaged a thyroid effective dose of less than 50 mSv, he said. A typical CT head scan delivers 2 mSv. The effective dose of radiation exposure takes into account the amount of ionizing radiation energy absorbed, the type of radiation, and the likelihood of organ damage.

“The dose of thyroid exposure in children in Fukushima is much lower compared to those in Chernobyl,” Yamashita told Endocrine News. “We do not expect any significant increase of childhood thyroid cancer, but it is our responsibility to pay special attention and care to those suffering from the Fukushima nuclear disaster for a long time.”

Yamashita reported that medical surveys have been shipped to more than two million people to determine the whereabouts of every resident from the time of the March 11 accident onward. So far, about 430,000 surveys have been returned (21 percent response rate). In an effort to examine target populations, more than 360,000 thyroid ultrasound exams have been conducted on residents under age 18 in the last year. Residents’ mental health and lifestyle will also require lifelong monitoring.

Reports of the lasting health damage to Chernobyl residents spurred some of the concern in Fukushima. According the World Health Organization (WHO), nearly 5,000 cases of thyroid cancer have been diagnosed to date among children who were 18 years old or younger at the time of the accident and lived in the most contaminated areas of Belarus, the Russian Federation, and Ukraine. A lot of the exposure occurred from the radioactive iodine deposited in pastures where cows grazed; children later consumed the contaminated milk. The health risks from the two disasters, however, are far apart, experts said.

“Comparing the health consequences of Fukushima to Chernobyl is a bit like comparing a mouse to an elephant,” said Thomas McKone, Ph.D., deputy for research at the Lawrence Berkeley National Laboratory and adjunct professor in the School of Public Health at the University of California, Berkeley.

Unlike Chernobyl, there were fewer radioactive elements and significantly less total radiation released at Fukushima, he said.

“Residents near Fukushima were monitored, evacuated, and given potassium iodide to minimize doses from iodine isotopes, while in Chernobyl the authorities delayed evacuations for many days and didn’t use potassium iodide, which resulted in significant population exposures and health consequences,” McKone explained.

Potassium iodide floods the thyroid with iodine thus preventing radioactive iodine from being absorbed. According to the ATA, if taken at the proper time, the potassium iodide can protect the thyroid from radioactive iodine from all sources, including air, food, milk, and water.

Despite these optimistic reports, the Japanese government and the nuclear operator Tokyo Electric Power Co. (Tepco) were recently criticized harshly for the Fukushima Daiichi plant disaster. A 641-page report released in July by an independent parliamentary panel found that regulators and nuclear operators disregarded warnings that the plant was a safety risk because of its vulnerability to earthquake damage. The panel further accused Tepco and government officials of slow and faulty communication after the disaster, which hindered emergency response.

The officials, the report said, “effectively betrayed the nation’s right to be safe from nuclear accidents.”

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