Cat Scans and Cancer

The recent news about the study indicating that about 30,000 extra cases of cancer may be caused by CT scans (audio version from WBUR here, silly shallow TV version below) didn't surprise me much. I have yet to read the study, so I cannot speak to its methods and whether I agree with its conclusions, but it certainly sounds plausible. After all, a CT scan provides a relatively large dose of radiation...I was told by a radiologist during my residency to think of it as the equivalent of 300 x-rays, although according to the news stories this number is at the high end of the estimate, noting that most scans are equivalent to about 100 x-rays. The sicker you are, the more likely you are to get more than one cat scan; some patients that I admit have had dozens of cat scans in a time span of only a few years. Because dividing cells are exquisitely sensitive to radiation and can more easily become cancerous, a few CT scans won't make much difference if the patient is 60 or 70 because most of the cells in their bodies don't actively replicate. But in a 30 year-old--or even one cat scan in a child, whose cells will divide multiple times over the span of their life--this dose of radiation is not without its risks.

So like I said, not a major surprise. Also not surprising is that a good number of these scans were unnecessary: the link above to Toronto's Globe and Mail is useful because it approaches the study from a Canadian perspective, and helpfully points out that Canadian MDs order about half the number of cat scans than their American counterparts, and even then Canadian health experts believe that about a third of those are unnecessary. From a systems perspective on how docs utilize these tests, it's a problem.

How big a problem is an open question. I don't want to sound like an apologist for radiation or to soft-peddle the serious problems raised by this study, but there has been a fair amount of context missing from the news stories and a not-insubstantial amount of fear-mongering to boot. Take a listen to WBUR's Robin Young as she practically jumps out of her seat from fear of getting cancer by just talking about the subject with radiologist Donald Frush of Duke:

"Well, let's get to some of these scary and startling statistics. We understand that some of the highest doses of radiation are routinely used for coronary angiography [to look for blocked arteries in the heart]...the Los Angeles Times writes that according to the [study]...1 in 270 women and 1 in 600 men, at the age of forty, just one [scan], might be at risk to develop cancer as a result. That's a pretty startling conclusion." [my emphasis]

Scary, startling...and Dr. Frush to his great credit gave some critical context to the statistic: that this looks at people who are getting very high levels of radiation, that not all experts agree with the calculations and that the risk may in fact be lower, and most importantly that it ignores the benefit derived from the patients who receive an accurate diagnosis as a result of such a test.

For instance: I admitted a patient recently and was told by the ER physician that "this guy's got community acquired pneumonia, couldn't hack it as an outpatient, he just needs pain control." The patient, a relatively young man in his 30s, had been feeling lousy for a few days and saw his primary care doc, who ordered some blood tests and a standard, low-radiation dose chest x-ray, which I could see in the ER clearly showed an "infiltrate"--a hazy spot on the film that certainly looked just like pneumonia. His blood test showed a high white count indicating an infection, and so before I even saw the patient it seemed like the diagnosis was gift-wrapped: game, set, match. Give the guy antibiotics and some morphine and move on to the next patient.

Only problem was that as soon as I started talking to the patient things weren't making sense in the nice, clear way the labs and film suggested. I found out that he had had these symptoms a few times in the last six months; the symptoms included coughing up blood and night sweats. Can regular old pneumonia cause someone to have night sweats and cough up blood? Sure, but in an otherwise healthy guy in his 30s who just recovered from a similar bout two months ago? That was weird. I mulled it over and after talking about other things like recent travel, his family background, and his job, I realized he could have one of many different things and "community acquired pneumonia" was now about the fifth or sixth most-likely diagnosis. I was worried that he might have had undiagnosed HIV, or tuberculosis, or a pulmonary embolism (a "PE," which is a blood clot in the lungs), or lymphoma, or even lung cancer...plus a few other more zebra-like diagnoses. To rule out each of these things would require different tests, but the first place to start was by getting a cat scan to rule out cancer and that blood clot. An hour later, I had my answer: he had several PEs in his lungs. The treatment he needed was blood thinners, not antibiotics. It wouldn't be too melodramatic to suggest that the cat scan--which delivered that radiation that so spooked Robin Young of WBUR--may well have saved his life.

It's that kind of nuance that requires emphasis every time one of these studies comes out. Indeed, the study estimated that unnecessary radiation from cat scans accounted for only 2 percent of all cancers. Will that be taken into account by every current cancer patient who has undergone a CT scan when they hear the story, or will they assume that their cancer was without doubt cause by a careless doc or hospital or CT scan manufacturer? Will she be like Connie Barton, the woman recently featured in the Sunday NYT who believes that her breast cancer diagnosis was, without question, due to the hormone replacement therapy that was prescribed by her doctor and made by Wyeth, Inc.? At least in the Barton case I'm sympathetic: Wyeth, as the Times notes, "oversold the benefits of menopausal hormones and failed to properly warn of [its] risks." But docs aren't cashing in on thousands of useless tests: if anything, the problem is often the reverse based on my experience, namely that we order tests defensively, fearing that if we don't get a cat scan for something we're pretty confident doesn't require one, we could find ourselves in court having to defend not ordering the test sometime down the line.

--br

In other news, Season's Greetings! In the Rubin household this means "Happy Hanukkah." Billy notes this truly weird article in the Times about how the Very Mormon Senator Orrin Hatch (R) of Utah wrote a little Hanukkah jingle and even did a little bopping (ahem, the musical variety) in the studio. Quoth the Senator, "Anything I can do for the Jewish people, I will do." All Billy can say is: please don't do much! (Though thanks for the sentiment.) And, of course, Billy thanks the Lord that his last name is Rubin and not, say, Hatch. Hat Tip to the Professor of Rhode Island.