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A new study offers the most solid evidence to date that radiation from CT scans increases children's risk of developing leukemia and head and neck cancer.
一項新研究提供了迄今為止最確鑿的證據，證明CT掃描產生的輻射將增加兒童罹患白血病和頭頸部癌癥的風險。
Children and adolescents who received two to three computed tomography scans of the head were three times as likely to develop brain cancer as those in the general population, according to the study of 176,587 children.
6月6日《柳葉刀》（Lancet）雜志網站發表了這項對176,587名兒童所進行研究的結果，研究顯示，接受過二至三次CT掃描的兒童和青少年患腦癌的概率是普通人的三倍，接受過五至10次頭部CT掃描的兒童患白血病的風險則是普通人的三倍。
The study, published online Wednesday in the journal Lancet, also said the risk of contracting leukemia was three times as great for children who received five to 10 CT scans of the head.
這項研究的作者強調，整體患癌概率仍然非常低，而且CT掃描的直接好處（例如檢查頭部損傷）仍然大于風險。
The study's authors emphasized that the overall likelihood of getting the cancers remained very small and that the immediate benefits of the scans, such as in detecting head injuries, still outweigh the risks.
這項研究發現，每接受一次CT掃描，患癌風險就隨之升高，即使對于只接受過一次CT掃描（以前被稱為CAT掃描）的人，風險也有升高。
The report found cancer risk grew with each scan received, and there was an elevated risk even in those who received only one CT, formerly called a CAT scan.
以前的研究提出了對于CT掃描增加致癌風險的擔憂；這份報告則提出了第一個關于這種聯系強度的直接證據。它研究了英國國民健康服務（National Health Service）對22歲前接受過一次CT掃描的病人記錄，并考察了他們平均10年后的病史。
Previous studies raised concerns about cancer risk from the scans; this report offers the first direct evidence of the magnitude of the link. It examined the U.K.'s National Health Service records of patients who had received a CT before age 22 and looked at their medical history for an average of 10 years afterward.
紐卡斯爾大學（Newcastle University）名譽主席、該論文的作者之一艾倫•克拉夫特（Alan Craft）稱，"這篇論文證實，輻射，即使是相對低劑量的輻射，也會導致"罹患特定癌癥的"風險。沒有安全劑量。"
"This paper confirms that radiation, even in relatively low doses, does lead to risk' of certain cancers, said Alan Craft, emeritus chair at Newcastle University and an author of the paper. 'There is no safe dose."
增加的風險意味著，每10,000個做過CT掃描的10歲以下的病人，在第一次做CT掃描10年后患白血病的病例將多出一例，或者每30,000個做過CT掃描的10歲以下的病人，在第一次做CT掃描10年后患腦癌的病例將多出一例。
The increased risk corresponded to one additional case of leukemia in the 10 years after the first scan for every 10,000 patients younger than 10 who were scanned, or to an extra case of brain cancer for every 30,000 such people scanned.
CT掃描結合了一系列不同角度的X光，以提供骨骼和軟組織的復合視圖。該研究的重點是頭部掃描，因為腦部被認為是對輻射高度敏感的部位。研究的考察對象是年輕人，因為他們的組織比成年人更易受影響，而且癌癥可能需要很長時間才會形成。
CT scans combine a sequence of X-rays from different angles to offer a composite view of bone and soft tissue. The study focused on head scans since the brain is believed to have heightened sensitivity to radiation. It looked at young people since their tissue is more susceptible than adults' and cancer can take a long time to develop.
克拉夫特博士稱，美國病人接受CT掃描的可能性是英國病人的五倍。在美國，2011年使用了8,530萬次CT掃描，是20世紀90年代初的四倍。
Patients are five times as likely to receive a CT scan in the U.S. as in the U.K., said Dr. Craft. In the U.S., use of CT scans quadrupled to 85.3 million in 2011 since the early 1990s.
美國放射學會兒科放射成像委員會（American College of Radiology Pediatric Imaging Commission）主席馬爾塔•舒爾曼（Marta Schulman）稱，該項研究進一步支持了病人只應在必要時進行CT掃描，并且盡可能使用最低劑量輻射的掃描。
Marta Schulman, chair of the American College of Radiology Pediatric Imaging Commission, said the study adds to the impetus that patients should be scanned only when necessary and with the lowest dose of radiation possible.
美國正在努力限制對兒童過度使用CT掃描，包括2009年8月發起的"溫柔成像"（Image Gently）倡議，該倡議由一個致力于改變醫療實踐的醫療組織聯盟牽頭。
Efforts are under way in the U.S. to curb overuse of CT scanning in children, including the Image Gently initiative, launched in August 2009 and spearheaded by a coalition of health-care organizations dedicated to changing medical practice.
在6月6日發表的這項研究中，已經被診斷出癌癥的病人或在做完CT掃描后二年內患上癌癥的病人被剔除，以降低不接受CT掃描也會得癌的病人虛增風險計算結果的可能。
In Wednesday's study, patients who already had cancer diagnoses or who developed cancer within two years of a CT scan were excluded, to decrease the likelihood that risk calculations would be inflated by patients who would have developed cancer without getting a CT scan.
這項研究是五國機構研究人員的合作，它由英國衛生部（U.K. Department of Health）和美國國家衛生研究院（National Institutes of Health）共同資助。
