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zoom RSS 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

<<   作成日時 : 2009/03/05 21:09   >>

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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
 米国人は現在、1980年に比べて約7倍の放射線を浴びており、医療用のスキャンがその理由であると最近の研究でわかった。
 最近20年でCTスキャンの使用が劇的に増加しており放射線被曝も増加すると思われていた。ほとんどの専門家は画像診断の利点がリスクに勝るとしているが、将来のガン発症の増加を心配する人もいる。
 CTスキャンは患者を被爆させる全体の医学的処置のわずか17%を占めるのみだが、医療放射線被曝の約半分の49%を占め、全ての放射線被曝のほぼ1/4の24%を占めると報告された。
 低容量でも発癌リスクは増加する。放射線被曝による発癌リスクについての知見は、日本の1945年の原子爆弾投下の生存者の研究から導き出されたものである。2007年11月のNEMJで出された研究では、2-3回のCTスキャンに相当する低容量の被爆者の全体のガンのリスクが明らかに増加したとしている。
 米国放射線科医学会は、7200万CTスキャンが2006年に米国で実行されたと概算している。
 あまりに多くのCTスキャンがあり、多くの専門家が医師の検査乱用を心配している。患者と話すよりもスキャンをオーダーし読影することで利益を得る医療システムである。メディケア(高齢者公的医療保険)の統計では、自らの私的クリニックで検査を施行している医師の数が1998-2005年で3倍になった。
 別の要因として医師の訴訟に対する恐怖がある。訴えられないために画像検査を施行する傾向が強くなっている。
 更に別の要因として、一定のスクリーニングテストを行うための規格化したガイドラインが無いことがある。
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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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Americans' Radiation Exposure Rises 6-Fold in 29 Years
CT Scans and Other Radiation-Based Medical Tests May Be to Blame for Increase in Radiation Exposure
By AUDREY GRAYSON
ABC News Medical Unit
March 3, 2009
http://abcnews.go.com/Health/CancerPreventionAndTreatment/Story?id=6996192&page=1

画像Americans are now exposed to about seven times more radiation on average than they were in 1980, new research finds, and medical scans may be the reason.
Increased medical tests and CAT scans has exposed Americans to more radiation.

A report published by the National Council on Radiation Protection and Measurement examined radiation exposure in the U.S. population from all sources. The greatest increase in radiation exposure, it found, came from physicians having more and more patients undergo diagnostic imaging tests, which use radiation.

"The increase in medical [radiation] exposure was not a big surprise to anybody," said Kenneth Kase, executive vice president of NCRP. "We expected [radiation] exposures for medical uses to increase dramatically because of the increase in the use of CT scanning in the last 20 years."

While most experts believe that the benefits of diagnostic imaging tests such as CT scans far outweigh the risks, some worry the rise in radiation exposure could lead to many more cancer cases in the future.

"Radiation exposure from these scans is not inconsequential and can lead to later cancers," said Dr. Len Lichtenfeld, deputy chief medical officer for the national office of the American Cancer Society. "This doesn't mean people shouldn't get CT scans, but it does mean we need to be very careful in how we use these technologies in the future."

The report also found that while CT scans account for only 17 percent of the total medical procedures that expose patients to radiation, the CT scan accounts for nearly half (49 percent) of all medical radiation exposure and nearly a quarter (24 percent) of all sources of radiation exposure.

Even Low Doses Up Cancer Risk

A great deal of the current understanding of the risks associated with radiation-induced cancer stems from studies performed on the survivors of the 1945 atomic bombings on Japan.

A study published in the November 2007 issue of the New England Journal of Medicine notes that those survivors who were exposed to low doses of radiation -- about the equivalent of the dose administered to an adult patient undergoing two or three CT scans -- still experienced a significant increase in their overall cancer risk.

The American College of Radiology estimates that 72 million CT scans were performed in the United States in 2006.

Are There Too Many CT Scans?

Many experts are concerned that physicians are overusing such tests. An issue of particular concern is that some physicians may be referring more patients to undergo unnecessary medical tests because they are benefiting financially by offering these tests in their practices.

"Our medical care system is rewarding doctors much more for ordering and reading scans than for talking to a patient," Lichtenfeld said.

Medicare statistics show that the number of physicians referring patients for radiological testing in their private practices in which they have a financial stake grew at triple the rate of the same exams in other settings between 1998 and 2005.

"I think [this] is one of the reasons we have the problem with increased background radiation due to medical imaging," explained Dr. Stephen Amis, chairman of radiology at the Montefiore Medical Center in New York. "Physicians are trying to augment income in every way possible in this time of decreasing reimbursement. It's not too hard to come up with a reason to image patients while they're seeing you in the office, and that's an ongoing concern."
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Fear of Lawsuits

Another possible factor contributing to the increased use of these medical tests could be physicians' fear of being sued by patients who believe the doctors did not do everything in their power to successfully diagnose the patient's condition.

"Fear of litigation [is] prevalent throughout the medical community, and [physicians] figure if they get imaging [on a patient] it reduces their chances of being sued," Amis said. "Especially in an emergency room setting," where doctors use scans "to ... make absolutely certain someone doesn't have appendicitis before they throw them back on the street."

Lichtenfeld agreed. "More scans are being used now because it's almost routine to the point where my colleague in an emergency room tells me when a patient comes in complaining of something, instead of doing the standard physical to diagnose them they immediately send them for a CT scan," he said.

Re-Examining the Scan?

Experts noted that another contributing factor is a lack of standardized guidelines that outline the appropriate circumstances under which to use certain screening tests.

"We need more guidelines on whether a radiologist needs to do scan or not, and we need to do a better job teaching medical students about to go into primary care practices about the appropriate use of these technologies and the long-term risks of overuse of these screening tools," Lichtenfeld explained.

However, experts also pointed out that health care professionals are not the only ones to blame for the overuse of these tests.

"What patients shouldn't do is self-refer themselves for an imaging test," Kase said.

Amis explained that more and more patients are coming into their doctors' offices and demanding screening tests that are perhaps unnecessary or premature.

Still, radiation experts agreed that for the most part, these medical tests still provide more benefit than harm.

"It's important for people not to be afraid of getting radiation exposure for a medical condition that their physician thinks they need," Kase said. "I think we can state pretty certainly that for the most part, the benefit the patient will get from the exam will be greater than any harm that the radiation might deliver -- as long as the test has been prescribed by a physician and there's a clear reason for doing the test."

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NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States
http://www.ncrponline.org/Press_Rel/Rept_160_Press_Release.pdf

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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 医師の一分/BIGLOBEウェブリブログ
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