Moreover, they say, the science behind other more accepted types of screening, such as mammograms and PSA tests for prostate cancer, remains controversial. Many often have high rates of false positives. Plus, certain tests notoriously fail to catch large percentages of people who are at high risk for disease. A high cholesterol score, for instance, clearly indicates a higher risk for heart attacks, but half of all people who have a heart attack don't have high cholesterol. Isn't it better to be safe than sorry, they ask.
"We shouldn't wait 20 years to help those that can benefit from this if we know now this can save lives," says Dr. Matthew Budoff, assistant professor of radiology at Harbor-UCLA Medical Center.
A doctor's obligation
Others see the issue as a bit more complex. After all, how does a doctor proceed with a terrified patient whose screening results have shown an abnormality? Dr. Douglas Souvignier, chairman of internal medicine at Camino Medical Group in Sunnyvale, says doctors have an ethical and perhaps legal responsibility to make sure nothing is wrong, even if they strongly believe there isn't. That can sometimes involve invasive procedures, including potentially dangerous biopsies.
Souvignier recently had a patient who was "extremely upset" about a scan that showed a small spot on her kidney. After doing an ultrasound, he discovered it was just a benign cyst. It's a scenario that happens several times a year in his department, which he estimates costs insurance companies thousands of dollars in unneeded costs. "These exams open up a can of worms, and almost always it's for nothing," he says.
Last year, researchers at UC San Diego questioned 1,192 patients, ages 22 to 85, who had undergone a scan. Nearly 46% of those studied had an abnormality (which is typical, doctors say) and more than a third were told to go for a follow-up with their own doctor. In one out of 10 cases, patients had a mass that could have been either a cancer or another life-threatening illness such as an aortic aneurysm. In the end, however, just 1% of them were believed to have a major life-threatening condition. A separate study on CT lung cancer screenings released by Johns Hopkins University in January, also found more costs than benefits arose from elective screens.
In July, a study by researchers at Stanford University Medical Center published in the Journal of Radiology called for increased regulations for scanning centers. One major concern: The study found radiation from CT scans could be as high as 2 rads, or 250 times that of a normal chest X-ray and 30 times more than a mammogram. While the chance of getting cancer from the radiation is relatively low, doctors say it's possible. Radiation exposure is cumulative over a person's lifetime, so the risk is higher for younger patients or those who've had many previous X-rays.
"These centers are proliferating very quickly, but most people don't know or aren't paying attention to the risks that are involved," says Dr. Judy Illes, the study's lead author and a senior researcher at Stanford University Medical Center's department of radiology.
Still, doubts about certain CT tests, especially those that focus on specific organs rather than the whole body, increasingly fall on a sliding scale. Heart scans, for instance, are gaining more converts particularly if they're performed with a newer type of CT scan known as EBT, or electron beam tomography. Both machines look alike, but the EBT scan is much faster (an all-important difference when photographing a beating heart) and therefore takes better images and emits less radiation than traditional CT scans.
A recent article in the New England Journal of Medicine suggested that preventive EBT scans might be beneficial for high-risk groups, such as smokers and those with a family history of heart disease.
Preventive lung scans are also moving onto increasingly solid -- though still somewhat shaky -- scientific grounds especially for those at high risk, such as current and former smokers. Several studies, including the 1999 Lancet study and others, have shown that CT scans may be better at finding early tumors than traditional X-rays because they can scan areas up to 10 times smaller than X-rays.
Beyond that, most other CT screening tests remain largely dismissed. Elective virtual colonoscopies and CT brain scans may ultimately prove beneficial, but for now they have relatively little research behind them, radiologists say. And CT images don't work well on breast tissue or for spotting prostate cancer, so most doctors recommend staying away from scans in those areas. "Beyond [hearts and lungs], the science is extremely sketchy," says Budoff of Harbor-UCLA.
More study warranted