CT scans cause cancer - studies

Editor's note: Get to know the risk. Often times radiation-based diagnostic tools like CT scans are labeled as non-invasive. They are not actually!

By David Liu

Computed tomography scans or commonly known as CT scans each year may cause tens of thousands of future cancer cases, according to two studies in the Dec 14-28, 2009 issue of Archives of Internal Medicine.

CT scans are based on radiation which is the most studied carcinogen in history and recognized by the National Toxicology Program as a human carcinogen. Ionizing radiation causes DNA mutations that potentially lead to development of various cancers.

The first study led by Rebecca Smith-Bindman MD of the University of California, San Francisco and colleagues estimated that one in 270 women and one in 600 men who undergo CT coronary angiography or a heart CT scan at age 40 will develop cancer due to the exposure to the radiation from the device and one in every 8,100 women and one in 11,080 men who have a routine head CT scan at the same age will develop cancer.

Dr. Smith-Bindman and colleagues examined data from 1,119 patients undergoing the 11 most common types of diagnostic CT scans at 4 area institutions in 2008.  Based on the radiation dosage involved in each scan, they estimated lifetime risks of cancer.

"For 20-year-old patients, the risks were approximately doubled, and for 60-year-old patients, they were approximately 50 percent lower," the researchers wrote in their study report.

In another study, Amy Berrington de González, D. Phil., of the National Cancer Institute, Bethesda, Md., and colleagues built a mathematic model and estimated age-specific cancer risk for each type of CT scan based on previous reports on radiation-association cancer risks, national surveys and insurance claims.

The researchers found CT scans performed in 2007 could lead to development of about 29,000 future cancers including 14,000 cases from scans of the abdomen and pelvis which require higher dosages of radiation; 4100 from chest scans; 4,000 from head scans; and 2,700 from CT angiography.

One-third of the projected cancer cases would occur in individuals who received the radiation from the diagnostic tool at age 35 to 54, and 15 percent in children and teenagers. Two thirds of the cancers would occur in women.

There were an estimated 70 million scans performed in 2007 in the U.S. compared to 3 million in 1980.

"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," Dr. Smith-Bindman and colleagues wrote.

"Our detailed estimates highlight several areas of use in which the public health impact may be largest, specifically abdomen and pelvis and chest CT scans in adults aged 35 to 54 years," Dr Berrington de González et al wrote.

"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."

John Gofman, MD PhD, a distinguished nuclear physicist and medical physician, estimated that 75 percent of new cases actually have something to do with ionizing forms of medical radiation from all types of diagnostic tools including x-rays, CT scans, mammograms and fluoroscopy.  He said there is no zero risk from radiation and any tiny amount damages DNA.

David Brenner, a leading radiologist from Columbia University in New York, was cited in a report released in Feb 2008 as admitting that CT scans are likely to account for some 29,000 new cases of cancer every year in the US.

The most dangerous yet least valuable CT scan is probably the whole body scan.  The Food and Drug Administration warned in a statement published in 2002 against use of the whole body scan saying "At this time the FDA knows of no data demonstrating that whole-body CT screening is effective in detecting any particular disease early enough for the disease to be managed, treated, or cured and advantageously spare a person at least some of the detriment associated with serious illness or premature death"

Many medical associations including the American College of Radiology are cited by the FDA as saying that they do not recommend CT screening, which is not as common as diagnostic CT scans.

The FDA said children are more sensitive to radiation than adults and have a longer life expectancy and they are at higher risk of radiation-induced cancers in the future.