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zoom RSS 40年後の長崎原爆の影響

<<   作成日時 : 2010/12/15 23:57   >>

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 第二次大戦で長崎に投下された原子爆弾の生存者は、放射能により今でも病気になり続けているという驚くべき日本の研究が明らかにされた。
 1985年〜2004年の間で生存者を検査している研究者は、原爆から高いレベルの放射線を受けた人々が、低いレベルにさらされた人より8倍も稀な血液疾患を発症しやすいと気づいた。10万人あたり10人の骨髄異形成症候群MDSの発症が8倍になっても、一般的な発癌リスクに比べれば小さなリスクである。
 しかし、CTスキャン検査などの現代の放射線源についての現在進行中の議論に問題点を追加することになる。米国人の3人に1人は一生の間にガンを発症し、CTスキャンの実施増がさらに増加させるのではないかと危惧される。
 新型のCTでは放射線量が減少しているが、平均的なスキャン5回で、原爆投下地点から2-3マイルにいた長崎の生存者と同じレベルの被曝量となる。それが病気のリスクを上昇させるのかどうかはまだわかっていない。
 国立がん研究所の2009年の研究によると、50歳で癌を発症させるにはコンピュータ断層撮影法が1,000回必要である。しかし専門家の間では、適切な状況の下では検査の利点が大きいと合意されている。
 新たな研究では、86,000人を超える長崎生存者の中で、1985年〜2004年の間で198人がMDSを発症した。爆心地からの距離が1km(0.6マイル)ごとに発症リスクが70〜88%上昇した。被曝量が多く1グレイ以上(CTスキャン数百回相当)の生存者は10万人あたり81人がMDSを発症した。1回のCTスキャン相当の被曝量では発症率は10万人あたり11であり、一般人の範囲内である。
 新たな研究で放射線により数十年後にMDSを発症することがわかった。MDSの人は白血病のリスクが非常に高いので注意が必要である。
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CTスキャンの放射線被曝によるガン発症/米国医療事情
http://kurie.at.webry.info/200912/article_24.html
医療画像検査による放射線被爆と発ガン性/米国医療事情 CTスキャン PET
http://kurie.at.webry.info/200908/article_41.html
米国人の放射線被曝は29年で6倍以上に増加/米国医療事情
http://kurie.at.webry.info/200903/article_6.html
CTスキャンによるガンの危険性
http://kurie.at.webry.info/200712/article_1.html
ビートルズとCTスキャンの関係
http://kurie.at.webry.info/200801/article_13.html
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40 years later, Nagasaki bomb still causes disease
http://www.reuters.com/article/idUSTRE6BD69Y20101214

By Frederik Joelving
NEW YORK | Tue Dec 14, 2010 5:16pm EST

NEW YORK (Reuters Health) - Survivors of the World War II atomic bomb dropped on Nagasaki continue to fall ill today as a result of the radiation they received, a surprising Japanese study shows.

Researchers testing survivors between 1985 and 2004 found people who had received high levels of radiation from the bomb blast were eight times more likely to develop a rare blood disease than those exposed to low levels.

"It adds evidence to the fact that radiation even at moderately low doses is hazardous, and the diseases you can get aren't only cancers," said David J. Brenner, who heads the Center for Radiological Research at Columbia University in New York, and was not involved in the study.

The Japanese researchers focused on so-called myelodysplastic syndromes, or MDS, in which damage to cells in the bone marrow prevents blood cells from developing properly.

With a baseline rate of only a dozen MDS cases per 100,000 survivors per year, Brenner added, even an eight-fold increase in risk doesn't amount to much.

"This is quite a small risk relative to getting the common cancers," he said.

The findings nevertheless may add to ongoing debate over modern radiation sources, such as computed-tomography (CT) scanning, a high-resolution form of x-ray.

About one in three Americans develop some type of cancer during their lives, and researchers have worried the recent upswing in CT scans performed for a variety of reasons could drive the number even higher.

Although newer CT machines have significantly reduced the amount of x-ray radiation patients receive, a handful of average scans is still enough to land patients in the same exposure category as Nagasaki survivors living a couple miles from where the bomb landed. Whether that raises their risk of disease remains unclear.

According to a 2009 study from the National Cancer Institute, it takes 1,000 CT scans to cause a case of cancer in a 50-year-old. So experts agree that under appropriate circumstances, the benefits far outweigh the harms.

The new study looked at more than 86,000 Nagasaki survivors, 198 of whom developed MDS between 1985 and 2004. However, the Japanese researchers couldn't pick up cases that happened before that.

They found the disease risk rose by between 70 and 88 percent for each kilometer (about 0.6 miles) closer the survivors had lived to the blast.

Among those survivors who had received the highest dose of radiation -- more than one gray, the equivalent of a few hundred standard CT scans -- 81 per 100,000 per year got MDS. Among those exposed to the equivalent of about one CT scan, the rate was about 11 MDS cases per 100,000. That's within the range in the general population.

Dr. Rebecca Smith-Bindman of the University of California, San Francisco, noted that people with MDS are at very high risk of developing leukemia, adding that the new study was the first to show radiation could cause MDS decades later.

"The work highlights another harm of radiation and should increase our efforts to reduce radiation exposure to the degree possible," she told Reuters Health in an e-mail.

SOURCE: link.reuters.com/sug22r Journal of Clinical Oncology, online December 13, 2010.

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Risk of Myelodysplastic Syndromes in People Exposed to Ionizing Radiation: A Retrospective Cohort Study of Nagasaki Atomic Bomb Survivors

1. Masako Iwanaga,
2. Wan-Ling Hsu,
3. Midori Soda,
4. Yumi Takasaki,
5. Masayuki Tawara,
6. Tatsuro Joh,
7. Tatsuhiko Amenomori,
8. Masaomi Yamamura,
9. Yoshiharu Yoshida,
10. Takashi Koba,
11. Yasushi Miyazaki,
12. Tatsuki Matsuo,
13. Dale L. Preston,
14. Akihiko Suyama,
15. Kazunori Kodama and
16. Masao Tomonaga

+ Author Affiliations

1. From the Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Science; Kwassui Women's College; Radiation Effects Research Foundation; Japanese Red Cross Nagasaki Genbaku Hospital; St. Francis Hospital; Nagasaki Municipal Hospital; Nagasaki Atomic Bomb Casualty Council Health Management Center; and Nagasaki Municipal Medical Center, Nagasaki; Radiation Effects Research Foundation, Hiroshima, Japan; and Hirosoft International, Seattle, WA.

1. Corresponding author: Masako Iwanaga, MD, MPH, Department of Hematology and Molecular Medicine, Atomic Bomb Disease Institute, Nagasaki University Graduate School of Biomedical Sciences, 1-12-4 Sakamoto, Nagasaki, 852-8523, Japan; e-mail: masakoiwng@gmail.com.

画像Abstract

Purpose The risk of myelodysplastic syndromes (MDS) has not been fully investigated among people exposed to ionizing radiation. We investigate MDS risk and radiation dose-response in Japanese atomic bomb survivors.

Patients and Methods We conducted a retrospective cohort study by using two databases of Nagasaki atomic bomb survivors: 64,026 people with known exposure distance in the database of Nagasaki University Atomic-Bomb Disease Institute (ABDI) and 22,245 people with estimated radiation dose in the Radiation Effects Research Foundation Life Span Study (LSS). Patients with MDS diagnosed from 1985 to 2004 were identified by record linkage between the cohorts and the Nagasaki Prefecture Cancer Registry. Cox and Poisson regression models were used to estimate relationships between exposure distance or dose and MDS risk.

Results There were 151 patients with MDS in the ABDI cohort and 47 patients with MDS in the LSS cohort. MDS rate increased inversely with exposure distance, with an excess relative risk (ERR) decay per km of 1.2 (95% CI, 0.4 to 3.0; P < .001) for ABDI. MDS risk also showed a significant linear response to exposure dose level (P < .001) with an ERR per Gy of 4.3 (95% CI, 1.6 to 9.5; P < .001). After adjustment for sex, attained age, and birth year, the MDS risk was significantly greater in those exposed when young.

Conclusion A significant linear radiation dose-response for MDS exists in atomic bomb survivors 40 to 60 years after radiation exposure. Clinicians should perform careful long-term follow-up of irradiated people to detect MDS as early as possible.

* Received June 28, 2010.
* Accepted October 15, 2010.

JCO published online on December 13, 2010; DOI:10.1200/JCO.2010.31.3080

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