Computed tomography (CT or CAT) scans help doctors detect everything from cancer to kidney stones. But some physicians are raising concerns about the safety of such procedures — most notably, an increase in cancer risk. A CT scan packs a mega-dose of radiation — as much as 500 times that of a conventional X-ray. If your doctor orders a CT scan for you or your child, should you think twice?
计算机断层扫描(CT or CAT) 有助于医生检出从癌症到肾结石范围内的任何病变。然而有些医师正在提升对扫描过程的关注程度，特别是在癌症危险性的增加的方面。一次CT扫描说包含的射线剂量相当于500次普通X线照射。如果医生让你或你的孩子做一次CT扫描，你还想两次吗？
Absolutely, say researchers behind two recent studies that sound the alarm about the increased cancer risk associated with multiple CT scans. In the first study of its kind, physicians at hospitals in Florida and Washington, D.C., evaluated the medical-imaging records of 1,243 randomly selected patients to calculate just how much radiation each patient had sustained in the past five years. Although CT scans were the biggest source of radiation, other offenders included X-rays and mammograms. The results of the study, presented in May at the annual conference of the Society for Academic Emergency Medicine, were disturbing: the average patient had received 45 millisieverts (mSv) of radiation. (The typical chest X-ray dispatches 0.02 mSv of radiation.) And 12% of patients had gotten more than twice that amount — 100 mSv or more. "Our focus is to bring awareness to the fact that people are getting large doses of radiation and it's not innocuous," says Timothy Bullard, the study's lead author and chief medical officer at Orlando Regional Medical Center. "We want people to use the technology appropriately."
多数的研究者在近期的两项研究中，是关于多层螺旋CT扫描与增加癌症危险性方面的。在第一项研究中，佛罗里达和华盛顿医院的内科医生从1243名随机挑选的病人的影像资料里估计了在过去的5年里平均每个病人所接受辐射量。尽管，CT扫描是射线的最大的来源，也包括X线和乳腺钼靶。在五月份的急诊医学的年会上，以下的研究结果使人们不安，平均每个病人接受45mSv的射线量。（标准的胸部放射线释放0.02 mSv射线量）。12%的病人已经多遭受了两倍的射线量-100 mSv，甚至更多。奥兰多地区医疗中心的首席医官Timothy Bullard说：“我们的目的是让人们意识到这个事实：人们正在遭受大量的有害人体的射线，因此人们应当适当的使用这些设备”
"Appropriate" is the key word — especially since a review study published last November in the New England Journal of Medicine determined that as many as one-third of all CT scans performed in the United States are unnecessary. The authors take issue with the "perhaps 20 million adults and, crucially, more than 1 million children per year in the United States [who] are being irradiated unnecessarily." Part of the problem, the authors say, is that patients are being prescribed multiple, unneeded CT scans, a predicament that could be avoided with better communication between physicians. "Having the same CT scan twice is ridiculous," says David Brenner, the review's lead author and director of the Center for Radiological Research at Columbia University Medical Center. "There is no excuse." In one of the review's highlighted studies, among patients undergoing CT scans, 30% were on their third scan, 7% had five or more, and 4% had more than nine. Also to blame: doctors increasingly practicing defensive medicine. "There is an underlying philosophy that you're at fault if you miss anything," says Bullard. "The goal is to be perfect every time." Plus, he notes, CT scans have no immediate negative side effects. "They are quick, painless, and send patients away with the sense of satisfaction that everything's been done."
“适当”作为关键词，尤其是最近十一月份发表在《新英格兰医学杂志》上的回顾性文章表明全美已经施行的CT扫描中有将近三分之一的扫描是不必要的。作者撰文阐述“在美国每年有2000万成年人和多于100万儿童所遭受的辐射没必要的。作者认为诸如病患大处方和不需要的CT扫描的问题能够通过医生之间的沟通来更好的解决。David Brenner认为，“重复的CT扫描是荒谬可笑的”。回顾性文献也让作者和美国哥伦比亚医学中心的导师们认为“这是毫无理由的”。在一项回顾文献研究中突出表明，进行过CT扫描的病人中，30%的病人经历过三次扫描，7%的病人经历过五次或许更多，4%的病人经历过九次之多。并且谴责说:医师在实际工作中越来越采取保守治疗。Bullard说：“如果你做错了，那么你就是有过错的，这是医疗潜规则”。另外，他着重提到说：“CT扫描根本就没有副作用，它是快速，无痛苦，能让病人在任何方面都感到满意的检查方法”。
Exactly how much radiation is too much? Because CT scans came into vogue in the 1980s and radiation-induced cancer takes roughly 20 years to develop, long-term studies of CT scans and cancer are still under way. But scientists are already anticipating future health implications. Indeed, researchers found a population of 25,000 Japanese post-atomic-bomb survivors who were exposed to roughly the same amount of radiation as two CT scans. Based in part on those studies, the Food and Drug Administration estimates that an adult's lifetime risk of developing radiation-induced cancer from a CT scan is roughly 1 in 2,000. Worse, the risk for children is even higher.
准确的说，多少射线量才是多的呢？因为CT扫描在上个世纪80年代起才广泛使用，射线导致癌症大约需要20年的发展，CT扫描和癌症的关系这项长期的研究仍在进行中。但是科学家已经预测出未来健康的隐患。研究人员发现原子弹爆炸后的25000名日本受害者他们所遭受的射线量等同于两次CT扫描量。在那些研究的部分基础上，食品和药品管理局估计一个成年人的一生中有可能从CT 扫描中获得的辐射而诱发癌症的几率是1：2000。更糟糕的是，儿童的危险性更高。
Compared with adults, children are more sensitive to radiation because they have longer life expectancies and because their cells divide more rapidly, making their DNA more vulnerable to damage. A child's risk of developing a fatal cancer from one CT scan is as high as 1 in 500. Although newer machines can be adjusted to deliver up to 50% less radiation for children and small adults, a 2001 study published in the American Journal of Radiation showed that radiologic technologists (RT) rarely make those adjustments. "Changing technical factors is very easy. It just requires a little thought and a few extra seconds," says Michele Scoglietti, a spokesperson for the American Society of Radiologic Technologists. "But I think there are many RTs who are either not trained to vary the technique, don't know how, are in a hurry or are just lazy."
比较成年人而言，儿童对射线更为敏感。不仅因为儿童有更长的生命周期，还因为他们的细胞分裂更加快速，他们的DNA更容易受到损害。由于一次CT扫描导致儿童罹患癌症的风险性为五百分之一这么高。虽然新型仪器能够为儿童和幼儿将辐射剂量调整到50%，2001年美国放射学杂志发表的文章表明技术人员很少进行这种调整。美国放射技术协会发言人 Michele Scoglietti说：“改变这种技术因素很容易，仅仅需要闪念之间和些许时间。然而，我认为那些技术人员也不能够熟练掌握各种型号的机器设备的使用，不知道怎么使用，或是匆忙的工作或只是懒惰而已。”
When doctors first ordered a CT scan for Jen Houck's six-month-old daughter in 2003, the new mom was more worried about the risks of anesthesia (used to keep children from squirming in the machine) than of radiation exposure. In 2006 and 2007, her daughter, now 5, had two additional CT scans, 6 months apart, for what doctors initially thought was a growth abnormality. They've since determined the child was perfectly healthy. "All that, just to find out her head is bigger than normal," says the 27-year-old mother of two in Boone, North Carolina. In hindsight, Houck wishes she had done things a bit differently. "I would have asked more questions about the necessity for a third scan so soon after the second." She also says no one mentioned the option of a low-dose scan, and she has no idea how much radiation her daughter received. "I wish I'd known to ask the question."
当医生首次让Jen Houck的六个月大的女儿做CT扫描时，这位年轻的妈妈不是担忧射线照射的危险，而是更加担心麻醉的风险（麻醉是用来让儿童在仪器扫描是保持安静）。从2006年到2007年间，她五岁的女儿已经做了两次CT扫描，每扫描一次间隔六个月复查，因为医生初诊考虑异常新生物。这位27岁美国北卡罗来纳州原住民说医生们已经明确诊断孩子是健康的，只是孩子的头比正常的大些。事后表明，Houck希望她已经开始尝试不同的事情。“我就要去询问关于经历第二次扫描后不久就做第三次扫描的必要性的问题了",她也说没有人谈论关于低剂量扫描的问题，她也没有关于女儿接收多少辐射剂量问题的观念。她说：“但愿我能知道这些问题的答案。”
So what should you ask, if a doctor recommends a CT scan for you or your child?Brenner suggests the following: is a CT scan really necessary? Might a test that doesn't involve radiation, such as an ultrasound or MRI, do the job? In some cases, a CT scan is absolutely required — for example, for diagnosing severe head trauma or internal injuries, for acute abdominal pain, or to diagnose an existing cancer. If your doctor schedules you for a scan, call ahead to see if you can bring a flash drive. That way you can take an electronic copy of your CT scan to go, and may be able to avoid another scan later, should you move or change doctors. (A hard copy of the scan is bulkier, but may also be an option.) If your child needs a CT scan, ask the technologist to put the machine on pediatric-appropriate settings.
假如医生推荐你或你的孩子去做一次CT 扫描，你是否也要这样的询问呢？ Brenner提出下列观点：CT扫描真的是必要的吗？能否使用诸如超声与核磁共振这样的不含有辐射的仪器来检查病人呢？在有的病例中，CT扫描是绝对必要的，例如为了诊断严重的头部创伤或内部损伤，为了诊断急腹症或者癌症的进展判断。如果医生安排你去做一次CT扫描，你最好设法带进去CT扫描拷贝资料，可以避免多余的辐射，或许会改变医生的想法。（一个硬盘的存储量是巨大的，而且也是可以选择的）。假如，你的孩子需要CT扫描，那么就去咨询技术人员来设置适当的用于儿科的检测设备。
