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zoom RSS 放射能汚染による甲状腺ガンのリスクは長期にわたる/チェルノブイリ原発事故 放射性ヨウ素

<<   作成日時 : 2011/03/20 20:58   >>

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 木曜日に国立がん研究所が発表した研究によると、ウクライナのチェルノブイリ原子力発電所の事故後約25年経過したが、汚染された牛乳を飲んだりチーズを食べた子供やティーンエイジャーの甲状腺癌のリスク増加は続いている。
 この結果は、甲状腺の中で蓄積し後でガンを発症する放射性ヨウ素のリスクについての以前の研究結果を立証している。ヨウ化カリウムは、甲状腺の放射性の蓄積を防止するためにしばしば与えられるが、ロシア当局は、危険な状態の人たちへ提供しなかった。放射性ヨウ素はちょうど8日の半減期であり、発電所の外では直ちに健康上の問題を起こすほど高濃度に存在すると考えられていなかった。しかし、雌牛により牛乳に集積され、乳製品を摂った子どもが危険な状態となる。
 国立がん研究所が組織する国際チームが何年もの間チェルノブイリ事故の健康に及ぼす影響を監視している。
 1986年の事故当時近くの3地域に住む18歳以下の12,500人をスクリーニングし、事故後2ヶ月以内に放射能測定をした。被曝量が最も高かった子ども達に甲状腺ガンの発病も最も高率だった。10年間で65人が甲状腺ガンになった。発病リスクは減少していない。
 第二次世界大戦後の日本での研究は、甲状腺癌のリスク増加が、原子爆弾の爆発の30年後に下落しはじめたが、40年後も通常より高率であり続けたことを示していた。

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Chernobyl Study Says Health Risks Linger
By GARDINER HARRIS
Published: March 17, 2011
http://www.nytimes.com/2011/03/18/health/research/18cancer.html

画像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.

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Embargoed For Release
Thursday, March 17, 2011
12:01 am EDT
http://www.nih.gov/news/health/mar2011/nci-17.htm

Higher cancer risk continues after Chernobyl

NIH study finds that thyroid cancer risk for those who were children and adolescents when they were 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.
Chernobyl powerplant
Recent photo of the Chernobyl nuclear power plant in Ukraine

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.
Map of radiation levels around Chernobyl
Map of Radiation Levels near Chernobyl in 1996. Source: CIA Factbook, Eric Gabba (vectorisation), Matthew Truch (English Translation) [CC-BY-SA-2.5], via Wikimedia Commons. Click to enlarge.

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.

* For more information about the NCI’s research related to the Chernobyl Accident, please visit: http://chernobyl.cancer.gov
* For more information about radioactive I-131 from fallout, please visit: http://www.cancer.gov/cancertopics/causes/i131
* For more information about measure radiation dose, please visit: http://www.bt.cdc.gov/radiation/pdf/measurement.pdf
* For more information about NCI’s Division of Cancer Epidemiology and Genetics, please visit: http://dceg.cancer.gov

NCI leads the National Cancer Program and the NIH effort to dramatically reduce the burden of cancer and improve the lives of cancer patients and their families, through research into prevention and cancer biology, the development of new interventions, and the training and mentoring of new researchers. For more information about cancer, please visit the NCI Web site at www.cancer.gov or call NCI's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237).

The National Institutes of Health (NIH) ― The Nation's Medical Research Agency ― includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. It is the primary federal agency for conducting and supporting basic, clinical and translational medical research, and it investigates the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit www.nih.gov.
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 Chernobyl Accident. Mar 17, 2011, EHP, Vol. 119.

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放射能汚染による甲状腺ガンのリスクは長期にわたる/チェルノブイリ原発事故 放射性ヨウ素 医師の一分/BIGLOBEウェブリブログ
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