RECENTLY I HAD a barely perceptible symptom, but one that’s on the list for potential risk, which led my doctor to send me for a CT scan. What showed up was the tiniest mark on my lung, probably scarring from a teenage bout with pneumonia – something that would have never been seen without a CT scan, and was so small that it was probably of no significance.
BUT once the doctor had seen this, he felt obliged to require another CT scan a year later to make sure it hadn’t grown. I complied. There was no change. Then he told me he really wanted one more to be sure. At that point, I began checking out radiation risks.
A CT (computerized tomography) scan uses many 2-D x-ray images taken from different angles as the x-ray tube rotates around the patient’s body to create a single 3-D image. The rotating x-ray tube causes an overall higher dose of ionizing radiation to be absorbed by the irradiated parts of the body. Thus, a CT scan of the chest measures 7 to 8 mSv (milliseverts) versus .1 for a single chest x-ray. (Bone scans measure 4 mSv; mammograms, .7 mSv; and dental x-rays, .01)
Compared to the MRI — which uses magnets and radio waves, not x-rays — CT scans are better for looking at cancer, pneumonia and bleeding in the brain; broken bones and vertebrae; and lungs and organs in the chest cavity. Because CT scans show organ tear and injury more quickly, they are better for use on accident victims.
But with every CT scan and x-ray, added to the “natural background” radiation acquired daily, an individual’s lifetime “accumulated radiation dose” gets higher. Higher lifetime doses are linked to increased risk of cancer, more so for those who received x-rays at a younger age and more so for women.
My full-body scan measured 12 mSv. Although full-body scans are useful for patients already diagnosed with cancer, the National Cancer Institute recommends against using full body scans on those with no symptoms: “Most abnormal findings from this procedure do not indicate a serious health problem, but the tests that must be done to follow up and rule out a problem can be expensive, inconvenient and uncomfortable.”
And the risk of “false positive” results – that is, showing something that is never going to amount to anything – from full-body scans is “very high,” according to Roshini Rajapaksa, M.D., medical editor of Health magazine. My “focused” chest CT scan the following year measured 8 mSv, which, added to the full-body scan, brought me up to 20 mSv for diagnostic tests, not counting mammograms and bone scans.
No one seems to know exact numbers for quantifying risk, i.e., for deciding when to balk.
In the absence of symptoms or a diagnosed medical condition, I questioned the need for a second CT scan. When the second one showed no change and he recommended I have one more, I said yes again, because I believe in following your doctor’s advice.
After that one showed no change, he actually recommended a fourth CT scan. At that point, I became suspicious: Was the doctor merely covering himself instead of watching out for my radiation risks? That time I said no, to which he said, “okay, but just so you know, that my advice is to have one more.” I wished I’d balked sooner.