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Posted: January 12, 2010

CT Scan Worries: Some Scans Double Cancer Risk

You might want to think twice about getting that CT scan your doctor ordered for you or a loved one.

Two reports in the journal Archives of Internal Medicine found that doses of radiation from the commonly performed procedure vary widely, they appear higher than generally believed and may contribute to an estimated tens of thousands of future cancer cases.


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CT, short for computed tomography, scans have become increasingly common in the United States, with about 70 million performed in 2007. "While CT scans can provide great medical benefits, there is concern about potential future cancer risks because they involve much higher radiation doses than conventional diagnostic X-rays," the authors of one report write. For example, a chest CT scan exposes the patient to more than 100 times the radiation dose of a routine chest X-ray.


The report says that while risks to individuals are likely to be small, "even small risks could translate to a considerable number of future cancers." The authors note that it is important to understand how much radiation medical imaging delivers to help balance benefits and risks.


Shawn Farley, a spokesman for the American College of Radiology (ACR), tells his organization believes there "probably are too many" CT scans being performed right now.


Farley recommends that patients considering CT scans ask their doctors such questions as, "Why do I need this exam; how will having this exam improve my health care; and are there alternatives that do not use radiation which are equally as good?"


In one paper, Dr. Rebecca Smith-Bindman and colleagues at the University of California, San Francisco studied 1,119 patients undergoing the 11 most common types of diagnostic CT scans at four area institutions in 2008. Using hospital records, they calculated the radiation dosage involved with each scan and then estimated lifetime risks of cancer that could be attributed to those scans.


Radiation dosage varied widely between different types of CT studies. Median (midpoint) doses ranged from 2 millisieverts for a routine head CT scan to 31 millisieverts for a multiphase abdomen and pelvis scan.


The estimated number of CT scans that would lead to the development of one cancer case also varied by type of CT scan and also by each patient's age and sex. For instance, an estimated one in 270 women and one in 600 men who undergo a heart scan at age 40 will develop cancer as a result. One cancer case will likely occur among every 8,100 women and 11,080 men who had a routine head CT scan at the same age. "For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50% lower," the authors write.


"The radiation exposure associated with CT has increased substantially over the past two decades, and efforts need to be undertaken to minimize radiation exposure from CT, including reducing unnecessary studies, reducing the dose per study and reducing the variation in dose across patients and facilities," they conclude.


In another paper, researchers at the National Cancer Institute constructed a risk model to estimate age-specific cancer risks for each scan type. Data were derived from previous reports of radiation-associated cancer risks, national surveys and insurance claims.


"Overall, we estimated that approximately 29,000 future cancers could be related to CT scans performed in the US in 2007," the authors write. This includes an estimated 14,000 cases resulting from scans of the abdomen and pelvis; 4,100 from chest scans; 4,000 from head scans; and 2,700 from CT angiography. One-third of these projected cancer cases would occur following scans performed on individuals age 35 to 54 years, compared with 15% due to scans performed in children and teens. Two-thirds of the cancers would be in women.


"Further work is needed to investigate the balance of the risks and benefits from CT scan use and to assess the potential for dose or exposure reduction," the authors conclude.


ACR says it supports the "as low as reasonably achievable" concept which urges providers to use the minimum level of radiation needed in imaging exams to achieve the necessary results.


(Article courtesy of

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