SEISMES ET ENERGIE NUCLEAIRE
JAPON Fukushima Dai-Ichi (11 mars 2011)
Fukushima versus TCHERNOBYL
Higher cancer risk continues after Chernobyl
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http://chernobyl.cancer.gov/
For more information about radioactive I-131 from fallout, please visit:
http://www.cancer.gov/cancertopics/causes/i131
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http://www.bt.cdc.gov/radiation/pdf/measurement.pdf
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NIH study finds that thyroid cancer risk for those who were children and adolescents when exposed to fallout has not yet begun to decline
Nearly 25 years after the accident at the Chernobyl nuclear power plant in Ukraine, exposure to radioactive iodine-131(I-131, a radioactive isotope) from fallout may be responsible for thyroid cancers that are still occurring among people who lived in the Chernobyl area and were children or adolescents at the time of the accident, researchers say.
An international team of researchers led by the National Cancer Institute (NCI), part of the National Institutes of Health found a clear dose-response relationship, in which higher absorption of radiation from I-131 led to an increased risk for thyroid cancer that has not seemed to diminish over time.
The study, which represents the first prospective examination of thyroid cancer risk in relation to the I-131 doses received by Chernobyl-area children and adolescents, appeared March 17, 2011, in the journal Environmental Health Perspectives.
"This study is different from previous Chernobyl efforts in a number of important ways. First, we based radiation doses from I-131 on measurements of radioactivity in each individual's thyroid within two months of the accident," explained study author Alina Brenner, M.D., Ph.D., from NCI's Radiation Epidemiology Branch. "Second, we identified thyroid cancers using standardized examination methods. Everyone in the cohort was screened, irrespective of dose."
The study included over 12,500 participants who were under 18 years of age at the time of the Chernobyl accident on April 26, 1986, and lived in one of three Ukrainian oblasts, or provinces, near the accident site: Chernigov, Zhytomyr, and Kiev. Thyroid radioactivity levels were measured for each participant within two months of the accident, and were used to estimate each individual's I-131 dose. The participants were screened for thyroid cancer up to four times over 10 years, with the first screening occurring 12 to 14 years after the accident.
Standard screenings included feeling for growths in the thyroid glands and an ultrasonographic examination (a procedure that uses sound waves to image the thyroid gland within the body), and an independent clinical examination and thyroid exam by an endocrinologist. Participants were asked to complete a series of questionnaires including items specifically relevant to thyroid dose estimation. These items included residential history, milk consumption, and whether they were given preventive doses of non-radioactive iodine in the two months following the accident, to help lessen the amount of radioactive iodine that would be absorbed by the thyroid. Participants with a suspected thyroid cancer were referred for a biopsy to collect potentially cancerous cells for microscopic examination. If warranted, participants were also referred for surgery. In total, 65 of the study participants were diagnosed with thyroid cancer.
Researchers calculated cancer risk in relation to how much energy from I-131was absorbed by each person's thyroid, measured in grays. A gray is the International System of Units measure of absorbed radiation. Each additional gray was associated with a twofold increase in radiation-related thyroid cancer risk.
The researchers found no evidence, during the study time period, to indicate that the increased cancer risk to those who lived in the area at the time of the accident is decreasing over time. However, a separate, previous analysis of atomic bomb survivors and medically irradiated individuals found cancer risk began to decline about 30 years after exposure, but was still elevated 40 years later. The researchers believe that continued follow-up of the participants in the current study will be necessary to determine when an eventual decline in risk is likely to occur.
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REFERENCE: Brenner AV, Tronko MD, Hatch M, Bogdanova TI, Oliynik VA, Lubin JH, Zablotska LB, Tereschenko VP, McConnell RJ, Zamotaeva GA, O'Kane P, Bouville AC, Chaykovskaya LV, Greenebaum E, Paster IP, Shpak VM, Ron E. I-131 Dose-Response for Incident Thyroid Cancers in Ukraine Related to the Chornobyl Accident. Mar 17, 2011, EHP, Vol. 119.
Chernobyl Study Says Health Risks Linger
http://www.nytimes.com
Nearly 25 years after the accident at the Chernobyl nuclear power plant in Ukraine, children and teenagers who drank contaminated milk or ate affected cheese in the days and weeks after the explosion still suffer from an increased risk of thyroid cancer, according to a study released Thursday by the National Cancer Institute.
The study confirms earlier research about the risks of radioactive iodine, which can accumulate in the thyroid gland and lead to cancer later. Potassium iodide is often given as a supplement to prevent the accumulation of the radioactive type in thyroid glands, but Russian authorities failed to provide the supplement to all those at risk.
Radioactive iodine has a half-life of just eight days, and it was not thought to be present outside the power plant in concentrations high enough to cause immediate health problems. But the isotope was concentrated by cows in milk, and children who drank contaminated milk or ate affected dairy products are particularly at risk.
An international team of researchers led by the National Cancer Institute, a federal agency based in Bethesda, Md., has been monitoring the health effects of the Chernobyl accident for years. In the study released Thursday, the team screened 12,500 people who were under 18-years-old at the time of the 1986 accident and lived in one of three provinces near the accident site. The subjects' thyroid glands were measured for radioactivity within two months of the accident.
Those with the greatest exposures were at highest risk for developing thyroid cancer in later years, the researchers found. Sixty-five of the study's subjects developed thyroid cancer during the study's 10 years of screening.
Indeed, the increased risks associated with exposures to radioactive iodine have yet to show any sign of declining. Studies done in Japan after World War II suggested that the increased risks of thyroid cancer began to decline 30 years after the atomic explosions but remained above normal even 40 years later.
Some of the participants in the Chernobyl study lived as far as 90 miles from the accident site, demonstrating the risks of eating or drinking contaminated foods among people who were exposed to little or no radioactive iodine from the immediate fallout.
"This study confirms the risk of thyroid cancer from radioactive iodine," Dr. Alina V. Brenner, a radiation epidemiologist at the cancer institute and a co-author of the study, said in an interview. "But thyroid cancer is largely a nonlethal cancer. If detected and treated in a timely manner, they have a good prognosis."
That this study was released in the midst of the crisis at the stricken Fukushima Daiichi Nuclear Power Station in Japan was a coincidence. Indeed, government officials scheduled the release for Thursday because they feared weeks ago that the government might shut down on Friday as a result of a budget impasse on Capitol Hill.