電腦斷層檢查

[Guest]

電腦斷層檢查 致癌率升高
中國時報【諶悠文、張翠芬／綜合報導】

醫師經常使用電腦斷層（掃描）（CT scan）診斷病情，但美國
兩項最新研究報告顯示，民眾接受電腦斷層檢查引發的致癌風險
大於原本認知，電腦斷層掃描與其他同樣使用放射線的醫學技術，
最好不要過度使用。

美國國家癌症研究院十四日發表研究指出，二○○七年美國人接受
電腦斷層檢查的次數，從一九八○年的三百萬人次暴增至逾七千萬
人次，美國國家癌症研究院岡薩雷茲女士與同事研發電腦模型，
評估其影響。

研究結果估測，二○○七年所做的電腦斷層檢查將導致兩萬九千人
罹患癌症，其中近一萬五千人有致命之虞。其中以年輕人的風險
最高，且有三分之二將發生在女性身上。另外，估計接受腹部與
骨盆電腦斷層檢查的民眾，以後致癌人數最多。

另一項由加州大學舊金山分校教授史密斯─賓德曼女士率領的團
隊，分析二○○八年在四所醫院接受十一種最常見電腦斷層檢查的
一一一九名患者數據。

研究人員指出，美國醫學界必須努力讓患者暴露在最低放射線劑
量之中，包括減少不必要的檢查、降低患者每次接受電腦斷層檢
查時的放射線劑量，並制定標準化劑量。這兩項研究報告都刊登
在最新一期美國《內科醫學檔案》（Annals of Internal Medicine）。

國內醫師也認為，電腦斷層雖是檢查利器，但對病人卻是兩面
刃，使用要更謹慎。台大外科教授張金堅指出，國外近年曾發
現，帶有ＢＲＣＡ１或ＢＲＣＡ２突變基因的婦女對輻射較為敏
感；東方女性乳房組織較緊密，對輻射敏感度也有加乘作用，都
容易導致乳癌發生率增加。

張金堅說，電腦斷層輻射劑量高，約八至十毫西弗，照一次等於
在自然環境中接受四至五年的輻射總劑量，除非特殊狀況，不要
常常進行這項檢查。

台北榮總核子醫學部主任王世楨表示，需要進行電腦斷層檢查的
民眾多半有些疾病、甚至是罹癌危險群，是否因此造成罹癌率升
高，值得探討。美國這項研究對醫界是一項警惕，電腦斷層檢查
會造成輻射劑量在體內累積，兒童和婦女使用應更謹慎。

健保局統計，國內一年約有一百多萬人次接受電腦斷層檢查，每
年以十％的速度成長。王世楨強調，傳統電腦斷層輻射劑量相當
高，只適合做局部不宜做全身檢查，醫界應為病患評估利弊，而
不是動不動就叫病人檢查。

New concerns about cancer risk from CT scans

Computed tomography scans (known as CT scans) use
computers to build detailed pictures of the inside of your
body, based on images taken using radiation. Because
of the level of detail, they can be good at picking up
small cancers, blood clots, or blockages in blood vessels
that might otherwise go unseen.

In recent years, there's been a trend towards using
these types of scan more widely, especially in the US.
For example, they might be used to investigate symptoms
such as blood in the urine, which could be a sign of renal
cancer but is much more likely to have a minor cause.
Some private companies have advertised CT scans for
healthy people, to pick up anything that might cause a
problem in future.

But every CT scan involves a dose of radiation, and
radiation can cause cancer. For most people, it's unlikely
that one scan would cause a cancer. But as CT scanning
becomes more widespread, more people will be put at
increased risk. Doctors wanted to know how much a
CT scan would increase the risk of cancer for people
having different types of scan, and at different ages.

The risk of getting cancer from a scan is higher in
younger people, because they have their whole lives
ahead in which a cancer may develop. For older people,
who have less of their lives left to live, the risk is lower,
because any changes to cells caused by radiation may
not have time to develop into cancer during their lifetime.

Also, women are at increased risk of cancer from chest
and abdomen scans, because of the risk of breast and
gynaecological cancers.

Two new studies have just been published. One looked
at the average amount of radiation people absorbed
while having CT scans at 4 hospitals or clinics in California.
They used this to calculate how much the scan would
increase people's lifetime risk of getting a cancer. The
second study looked at how many scans were done across t
he US in 2007, and calculated how many future cancers
might have been caused by those scans.

http://www.guardian.co.uk/lifeandstyle/besttreatments/2009/dec/15/new-concerns-about-cancer-risk-from-ct-scans