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zoom RSS 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

<<   作成日時 : 2009/08/29 02:24   >>

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 少なくとも400万人の65才以下の米国人が医療画像検査による高い放射線被爆を毎年受けているという。
 そのうち約40万人は、原子力発電所や放射性物質取扱い事業所の従業員の年間被爆許容量を越える被爆を受けている。UnitedHealthcareの保険患者ほぼ100万人の2005-2007年調査による研究結果であるが、今後数十年の発がん効果は評価していない。カリフォルニア大サンフランシスコのRita Redberg博士によれば、数万人がんの発症が増加し、低レベルの放射能によるガンの増加は間違いないだろうという。
 最近20年間で心臓病の診断のための放射線診断が増加した。心臓病の徴候がなくても検査を勧められる。多くの医師がCTとPETスキャナーを購入設置し、使用量は20年で急増した。2007年保健福祉省は、1995-2005年でメディケア患者のCTスキャン実施数はほぼ4倍となり、PETはそれ以上であると概算した。
 新たな研究でEmory大のReza Fazel博士は、2005-2007で同様な増加をみせたようだという。米国人の平均被爆量は年間約3ミリシーベルトである。UnitedHealthcare患者の1.9%が3年のうちの1年で少なくとも20ミリシーベルト、平均の7倍を被爆した。そのうちの10%、患者全体の0.2%は、50ミリシーベルト以上を受けた。これらの数値から、約400万人の米国人が1年に20ミリシーベルト以上の累積線量を受け取ることを示唆している。
 人々が画像検査を要求する文化的な要因が大きい。ほとんどの場合は医師のより良い決定の手助けとなっている証拠がない。スキャンが治療改善に役立つ結果をもたらすかどうか査定する大規模な臨床試験が必要とされる。検査の危険性と全体の被爆量に常に注意すべきである。
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CTスキャンによるガンの危険性
http://kurie.at.webry.info/200712/article_1.html
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Study Finds Radiation Risk for Patients
http://www.nytimes.com/2009/08/27/health/research/27scan.html
By ALEX BERENSON
Published: August 26, 2009

At least four million Americans under age 65 are exposed to high doses of radiation each year from medical imaging tests, according to a new study in The New England Journal of Medicine.

About 400,000 of those patients receive very high doses, more than the maximum annual exposure allowed for nuclear power plant employees or anyone else who works with radioactive material.

The paper, being published on Thursday, was based on a survey from 2005 to 2007 covering almost one million patients insured by UnitedHealthcare.

It did not estimate the number of cancer cases that the radiation might cause over the next several decades. But Dr. Rita Redberg, a cardiologist and researcher at the University of California, San Francisco, who has extensively studied the use of medical imaging, said it would probably result in tens of thousands of additional cancers.

Each individual patient is at relatively minor additional risk from the tests, Dr. Redberg said, but because they are given to so many people, the cumulative risk is significant.

“It’s certain that there are increased rates of cancer at low levels of radiation, and as you increase the levels of radiation, you increase cancer,” said Dr. Redberg, who was not connected with the new study.

The radioactive tests are given for hundreds of purposes. In the last two decades, they have become especially common in cardiology, where physicians use them to check for the buildup of plaque in the arteries and the heart’s ability to pump blood.

Some cardiologists now encourage their patients to have routine heart scans even if they do not have clinical symptoms of heart disease, like chest pain or shortness of breath. The study did not examine what percentage of the tests were medically necessary.

The use of the tests has risen sharply in the last two decades, as more and more physicians have bought CT and PET scanners and installed them in or near their offices. In 2007, the Department of Health and Human Services estimated that the number of CT scans given to Medicare patients had almost quadrupled from 1995 to 2005, while the number of PET scans had risen even faster.

The new study’s lead author, Dr. Reza Fazel, a cardiologist at Emory University, said the use of scans appeared to have increased even from 2005 to 2007, the period covered by the paper.

“These procedures have a cost, not just in terms of dollars, but in terms of radiation risk,” Dr. Fazel said.

The researchers calculated the amount of radiation received by the patients by looking at insurance codes for various kinds of imaging tests. Exposure is measured in millisieverts; the average American receives about three millisieverts a year from all sources.

The paper found that in at least one of the three years, 1.9 percent of the UnitedHealthcare patients received at least 20 millisieverts of radiation, or nearly seven times the average. Of that group, about 10 percent, or 0.2 percent of all patients, received at least 50 millisieverts, more than the annual maximum that nuclear regulators allow.

Those figures suggest that about four million Americans receive cumulative doses exceeding 20 millisieverts a year.

Federal rules allow physicians to profit from the use of machines they own or lease. But Dr. Harlan M. Krumholz, a cardiologist at Yale and an author of the paper, said financial incentives were only part of the reason the number of tests had risen so fast.

“I think the central driver is more about culture than anything else,” Dr. Krumholz said. “People use imaging instead of examining the patient; they use imaging instead of talking to the patient.

“Patients should be asking the question: ‘Do I really need this test? Is the information in this test going to help in the decision-making process?’ ”

In many cases, there is little evidence that the routine use of scans helps physicians make better decisions, especially in cases where the treatments that follow are also of questionable efficacy.

In an editorial accompanying the paper, Dr. Michael S. Lauer, director of prevention and epidemiology at the National Heart, Lung and Blood Institute, called for large clinical trials that would assess whether the scans improve care and lead to better outcomes for patients.

“Were we to insist that all, or nearly all, procedures be studied in well-designed trials, we could answer many critical clinical questions,” Dr. Lauer wrote.

Until then, patients and physicians should discuss the risk of the tests and keep close track of the overall radiation dose that patients are receiving, he wrote, adding, “We have to think and talk explicitly about the elements of danger in exposing our patients to radiation.”

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NEJM Volume 361:849-857 August 27, 2009 Number 9
Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures

Reza Fazel, M.D., M.Sc., Harlan M. Krumholz, M.D., S.M., Yongfei Wang, M.S., Joseph S. Ross, M.D., Jersey Chen, M.D., M.P.H., Henry H. Ting, M.D., M.B.A., Nilay D. Shah, Ph.D., Khurram Nasir, M.D., M.P.H., Andrew J. Einstein, M.D., Ph.D., and Brahmajee K. Nallamothu, M.D., M.P.H.

ABSTRACT

Background The growing use of imaging procedures in the United States has raised concerns about exposure to low-dose ionizing radiation in the general population.

Methods We identified 952,420 nonelderly adults (between 18 and 64 years of age) in five health care markets across the United States between January 1, 2005, and December 31, 2007. Utilization data were used to estimate cumulative effective doses of radiation from imaging procedures and to calculate population-based rates of exposure, with annual effective doses defined as low (?3 mSv), moderate (>3 to 20 mSv), high (>20 to 50 mSv), or very high (>50 mSv).

Results During the study period, 655,613 enrollees (68.8%) underwent at least one imaging procedure associated with radiation exposure. The mean (±SD) cumulative effective dose from imaging procedures was 2.4±6.0 mSv per enrollee per year; however, a wide distribution was noted, with a median effective dose of 0.1 mSv per enrollee per year (interquartile range, 0.0 to 1.7). Overall, moderate effective doses of radiation were incurred in 193.8 enrollees per 1000 per year, whereas high and very high doses were incurred in 18.6 and 1.9 enrollees per 1000 per year, respectively. In general, cumulative effective doses of radiation from imaging procedures increased with advancing age and were higher in women than in men. Computed tomographic and nuclear imaging accounted for 75.4% of the cumulative effective dose, with 81.8% of the total administered in outpatient settings.

Conclusions Imaging procedures are an important source of exposure to ionizing radiation in the United States and can result in high cumulative effective doses of radiation.

Source Information

From the Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta (R.F.); the Section of Cardiovascular Medicine, Department of Medicine (H.M.K., Y.W., J.C.), the Robert Wood Johnson Clinical Scholars Program, Department of Medicine (H.M.K.), and the Section of Health Policy and Administration, School of Public Health (H.M.K.), Yale University School of Medicine; and the Center for Outcomes Research and Evaluation, Yale--New Haven Hospital (H.M.K.) ― both in New Haven, CT; the Mount Sinai School of Medicine and the James J. Peters Veterans Affairs Medical Center (J.S.R.); and the Department of Medicine, Cardiology Division, and the Department of Radiology, Columbia University Medical Center and New York Presbyterian Hospital (A.J.E.) ― all in New York; the Divisions of Cardiovascular Diseases (H.H.T.) and Health Care Policy and Research (N.D.S.), Mayo Clinic, Rochester, MN; the Johns Hopkins Ciccarone Preventive Cardiology Center, Baltimore (K.N.); the Department of Internal Medicine, Boston Medical Center, Boston (K.N.); and the Veterans Affairs Ann Arbor Health Services Research and Development Center of Excellence and the University of Michigan, Division of Cardiovascular Medicine (B.K.N.) ― both in Ann Arbor.

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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 医師の一分/BIGLOBEウェブリブログ
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