Radiation, like alcohol, is a double-edged sword. It has indisputable medical advantages: Radiation can reveal hidden problems, from broken bones and lung lesions to heart defects and tumors. And it can be used to treat and sometimes cure certain cancers.
But it also has a potentially serious medical downside: the ability to damage DNA and, 10 to 20 years later, to cause cancer. CT scans alone, which deliver 100 to 500 times the radiation associated with an ordinary X-ray and now provide three-fourths of Americans' radiation exposure, are believed to account for 1.5 percent of all cancers that occur in the United States.
但它同时亦藏有严重的安全隐患：损伤病人的DNA，在10～20年后诱发癌症。单独一项CT（Computed Tomography，计算机断层摄影）扫描，其放射性就是普通X射线的100-500倍。而CT已成为全美四分之三放射暴露(radiation exposure)的来源。据估计，美国有1.5%的癌症都因它而起。
Recognition of this hazard and alarm over recent increases in radiological imaging have prompted numerous experts, including some radiologists, to call for more careful consideration before ordering tests that involve radiation.
"All imaging has increased, but CTs account for the bulk of it," said Dr. Rebecca Smith-Bindman, a specialist in radiology and biomedical imaging at the University of California, San Francisco. "There's clearly widespread overuse. More than 10 percent of patients each year are receiving very high radiation exposures."
“所有放射成像技术都用得越来越多了，不过CT仍占绝大多数。”加州大学旧金山分校(University of California, San Francisco)放射与生物医学成像专家丽贝卡∙史密斯-宾德曼(Rebecca Smith-Bindman)医生说：“这显然是一种大范围的滥用。每年有10%以上的病人都在接受很高的放射暴露。”
The trick to using medical radiation appropriately, experts say, is to balance the potential risks against known benefits. But despite the astronomical rise in recent years in the use of radiation to obtain medical images, this balancing act is too often ignored. The consequences include unnecessary medical costs and risks to the future health of patients.
Both doctors and patients have a responsibility to better understand the benefits and risks and to consider them carefully before doctors order and patients undergo a radiation-based procedure.
Patients may be surprised to learn that some of the newest uses of radiological imaging, including CT scans of coronary arteries to look for calcium buildup, have not yet been shown in scientifically designed clinical trials to lead to better outcomes than tests that do not involve radiation exposure, and thus their true benefits are at best a guess. Experts have estimated that widespread use of coronary artery scans, which deliver 50 to 150 times the radiation of a chest X-ray, could result in 42 additional cases of cancer for every 100,000 men who have the procedure, and 62 cases for every 100,000 women who do.
For every 1,000 people undergoing a cardiac CT scan, the radiation adds one extra case of cancer to the 420 that would normally occur. This risk may seem inconsequential, but not to someone who gets a cancer that could have been prevented.
Complicating the matter is the enormous variation - sometimes tenfold or more - in the amounts of radiation to which patients are exposed from the same procedure at different institutions, or even at the same institution at different times.
Although the cancer-causing effects of radiation are cumulative, no one keeps track of how much radiation patients have already been exposed to when a new imaging exam is ordered. Even when patients are asked about earlier exams, the goal is nearly always to compare new findings with old ones, not to estimate the risks of additional radiation.
As Dr. Michael S. Lauer of the National Heart, Lung and Blood Institute wrote in The New England Journal of Medicine three years ago, "The issue of radiation exposure is unlikely to come up because each procedure is considered in isolation, the risks posed by each procedure are low and seemingly unmeasurable, and any radiation-induced cancer won't appear for years and cannot easily be linked to past imaging procedures."
三年前，美国国家心肺血液研究所(National Heart, Lung and Blood Institute)的迈克尔·S·劳尔(Michael S. Lauer)医生在《新英格兰医学期刊》(The New England Journal of Medicine)上撰文称：“放射暴露带来的问题不太容易被发现，其原因是每次放射都被认为是孤立的，每一回的风险都很低、几乎无法测量，而且任何放射诱发的癌症都是多年后才浮出水面，很难与从前做过的医学成像检查联系起来。”
After an extensive review of the environmental causes and risk factors for breast cancer, the Institute of Medicine reported last year that sufficient evidence of risk was found only for combined hormone therapy used by postmenopausal women and exposure to ionizing radiation, at doses much higher than those received during a mammogram.
医学研究所(Institute of Medicine)在广泛地分析了环境及其他危险因素与乳腺癌的关系之后，在去年发布了一份报告，当中指出，唯一有足够证据证明有损健康的举措是：停经女性采用激素疗法，同时暴露在比一般乳房X光摄影剂量高得多的电离辐射中。
Everyone is exposed to a certain amount of background radiation - about three millisieverts a year from cosmic rays, radon gas and the earth's radioactive elements. By 1980, according to The Harvard Health Letter, various introduced sources, like medical tests, nuclear power plants, nuclear fallout, television sets, computer monitors, smoke detectors and airport security scanners, added another 0.5 millisieverts per year.
实际上我们每个人都处在来自宇宙射线、氡气和地球上放射性元素的背景辐射中，大约每年3毫希（millisieverts,辐射剂量单位）。根据《哈佛健康通讯》(The Harvard Health Letter)报道，至1980年，随着各种新辐射来源进入人们的生活，如医疗检测、核电站、放射性沉降物、电视机、电脑显示器、烟雾探测器以及机场安检，每年人们接受的辐射量增加了0.5毫希。
Now, however, the amount of radiation used medically rivals that of the background radiation, adding three millisieverts each year to the average person's exposure. (A mammogram involves 0.7 millisieverts, a dose that is doubled with a 3-D mammogram.)
There are many reasons for this increase. Doctors in private practice who have bought imaging equipment tend to use it liberally to recoup the expense. The same goes for hospitals just a few miles apart that needlessly duplicate certain equipment so they can boast of having the latest and greatest capacity to detect disease. Doctors ordering tests suffer no adverse effects, and patients feel they are getting the most that modern medicine can offer.
Dr. Lauer wrote in a commentary about cardiac tests, "Most physicians who order imaging tests experience no consequences for incurring costs for procedures of unproven value. On the contrary, they or their colleagues are paid for their services, and their patients don't complain because the costs are covered by third parties. Patients are pleased to receive thorough evaluations that involve the best cutting-edge technologies."
According to a new study, the rise in medical imaging clearly goes beyond financial motives. Dr. Smith-Bindman and her colleagues reported in June in The Journal of the American Medical Association that a dramatic rise in imaging rates from 1996 to 2010, including a tripling of CT scans, occurred in six large prepaid health systems where the financial incentive ought to have encouraged fewer, not more, tests. The increased testing doubled the proportion of patients who received high or very high radiation exposures.
一项新的研究显示，医学成像的大量应用早已超过了原始的经济动机。史密斯-宾德曼医生及同事在6月刊的《美国医学协会杂志》(The Journal of the American Medical Association)上发表了一篇文章：1996～2010年间，6家大型预付型卫生系统的成像技术使用度飞速上涨，其中CT扫描的次数增加了两倍。然而从财政刺激的方面来讲，本应是鼓励少做，而非多做成像类检查的。这样大量地应用放射技术让接受高度甚至超高度放射暴露的病人比从前多出一倍。
By 2010, the researchers reported, 20 CT scans were performed for every 100 adult patients; for every 100 patients ages 65 to 75, about 35 CT scans were done. And among the 10 to 20 percent of children in the study who underwent a single CT scan of the head, radiation doses were in the range previously shown to triple the risk of later developing brain cancer or leukemia.
Dr. Smith-Bindman urged patients to participate in the decision to undergo medical imaging. She said, "Patients should ask, 'What is this test for? Do I need it? Why? Do I need it now?' "
Legislation can help curtail, or at least monitor, radiation doses, she said, citing a California law that took effect in July requiring that the dose used for CT scans be recorded in every patient's medical record and that inadvertent overdoses be reported to the state immediately.
If such recording were to become a national mandate, electronic medical records could help doctors and patients keep track of radiation exposures and provide further incentive to avoid unnecessary imaging.
Sidebar: Limiting the Fallout of Cancer Treatment
Radiation therapy to treat cancer depends on much higher doses than are used in imaging, and these treatments have long been known to increase a patient's risk of later developing another cancer. Doctors consider this risk of radiation therapy reasonable when the goal is to prevent death from the original cancer.
Last year in a report in The Lancet Oncology researchers from the National Cancer Institute and M.D. Anderson Cancer Center in Houston reported that among 647,672 adult cancer patients treated five or more years earlier, about one half of 1 percent developed a second cancer years later related to radiation treatment of the first cancer. More than half of the second cancers occurred in survivors of breast and prostate cancers.
去年，国家癌症研究所(National Cancer Institute)和休斯顿M.D.安德森癌症中心(M.D. Anderson Cancer Center)的研究人员在《柳叶刀肿瘤》(The Lancet Oncology)上发表了一篇报道：在过去的五年及以上时间里进行过癌症治疗的647672名成年病人中，约8%都因放疗而得了第二种癌症。这些人里有一半以上都曾是乳腺癌和前列腺癌的幸存者。
As expected, the risk of developing a second cancer was highest among those originally treated at younger ages and most often involved organs exposed to the highest doses of radiation.
In recent years, radiologists have taken great pains to limit radiation exposure to nontarget organs - for example, by using a cone beam when treating breast cancer - which should reduce the risk of radiation-induced second cancers.