CT scans: 'A very high-dose' diagnosis
http://cgi.usatoday.com/usatonline/20001120/2852070s.htm
By Steve Sternberg

When most people think of nuclear radiation, they think of atom bombs and fallout, not medical tests. Yet more patients are exposed to radiation from CT scans than any other source, says physicist Fred Mettler of the University of New Mexico.

Though CT scans account for 11% of procedures done by the university's radiology department, those tests account for 60% to 70% of the total radiation dose delivered to patients, Mettler says.

CT -- computed tomography -- scans are essentially rapid-fire X-rays that spin around the human body, producing detailed images of internal organs. Each scan delivers 2 to 3 rads of radiation. A chest X-ray, by comparison, delivers 15 millirads of radiation; each millirad equals one-thousandth of a rad.

More energy is needed to penetrate thicker regions of the body than thinner ones. But most CT scans are designed to automatically deliver the amount of radiation needed to penetrate thick regions of the body.

''You're giving a higher dose than you need to,'' Mettler says. ''A lot of places use the same dose on kids as they do on adults,'' he says, though children are more prone to radiation-induced cancers than adults.

Mettler notes that CT scans have become an essential tool of medical practice, essential for diagnosing cancer, traumatic injuries in emergency rooms and other potentially life-threatening conditions. ''Surgeons love it, but they have to realize this is a very high-dose procedure for diagnosis.''

Some doctors even use CT scanning for general health screening, which Mettler says is ''incredibly stupid.''

''If you're a woman,'' he says, ''the dose to the breast from a CT scan is about the same as 10 mammograms. But you're not going to find breast cancer with a CT scan. It's nowhere as sensitive as a mammogram, and the dose is 10 to 15 times higher.

''In the belly, you can find metastases from liver cancer, but by then it's too late, the patient has metastatic cancer. It's almost impossible to pick up prostate cancer with a CT scan. A PSA (blood) test is much better.''

Harvey Eisenberg, a Newport Beach, Calif., radiologist, advocates what Mettler abhors. For $716 per scan, Eisenberg screens healthy people (other than pregnant women) at his HealthView Center for Preventive Medicine, looking for everything from heart disease to cancer. Eisenberg says Mettler is right that excess radiation can be dangerous, but he downplays the perceived level of risk, asserting that millions of scans have yielded no appreciable increase in cancer cases.

''It's pretty clear,'' Mettler counters, ''that . . . above 5 rad, there's a statistically significant increase in cancer. A whole bunch of people will say that, since you can't see an increase below 5 rad, it makes no difference. But if you get two CT scans, you're above the limit.''