Doctors have long known that CT scans can be a double-edged sword. Their diagnostic power is pivotal in modern-day medicine, but their inherent cancer risks leave both physicians and patients wary.
Now, a new study presented at a major scientific meeting may alleviate some CT cancer fears -- but it may also fuel the controversy surrounding the tests.
The study of more than 10 million Medicare patient records suggests that the cancer risks from the scans are much smaller than past studies claim. Prior research estimated radiation-induced cancer rates associated with these scans around 1.5 to 2 percent, but results from the Stanford study found that CT scans were only associated with a 0.02 to .04 percent higher risk of cancer in its study population.
"The bottom line here is that not enough work has been done in this area yet," said Dr. Pat Basu, faculty radiologist at Stanford University and co-author of the study. "We need to be sure not to over-scan people, but not forget the tremendous benefits from CT scans; they can save lives and make medical care cheaper."
Researchers studied data from more than 5 million Medicare data records from 1998 to 2001 and more than another 5 million records from 2002 through 2005.
CT scans of the head were found to be the most common examination from the data, but abdominal CT scans brought on the highest amount of radiation for patients.
"CT scans do put you at risk of cancer, the question is how much," said Dr. Carl Schultz, professor of emergency medicine at UC Irvine School of Medicine and director of research at the Center for Disaster Medical Sciences. "This seems to be a more accurate estimation of the population's risk because it takes into account how CT scans are used in the population."
But, Dr. David J. Brenner, professor of radiation oncology at Columbia University, takes issue with the methodology of the study. Only patients who had received no less than the radiation of about four or five CT scans were included in the final risk results. Those patients who had only a few CT scans in the years studied were not included in the final results.
"They're saying, let's exclude the majority of CT scans by making an assumption that they're safe," said Brenner. "This methodology is not compatible with national or international agencies. One can do that, but it's certainly not the standard way, and not the technically correct way.
Basu, however, said there was a reason for leaving out that data.
"Below that number of radiation exposure, there is no conclusive data at that low level," said Basu. "Right now no physician can successfully argue both sides of cancer risk in regards to one or two CT scans."
A CT, or computed tomography, uses multiple images to create cross-section pictures of tissue, bone and blood vessels.
Today, more than 62 million CT scans are performed in the United States, compared with 3 million in 1980. A CT scan can have 50 to 250 times more radiation than a conventional X-ray.
For this reason, some doctors have raised alarm on unnecessary CT scans. Indeed, many studies have shown that patients are unnecessarily getting CT scans, exposing themselves to radiation.
Dr. Len Lichtenfeld, deputy chief medical officer for the American Cancer Society in Atlanta, agreed that the issue is in the amount of CT scans used on patients.