Although the medical profession has been harming unlucky patients for centuries, the patient safety movement didn’t take flight until 1999, when the Institute of Medicine published its seminal report, To Err is Human. And that report would have ended up as just another doorstop if not for its estimate that 44,000-98,000 Americans each year die from medical mistakes, the equivalent of a jumbo jet crashing each day.

Come to think of it, the quality movement also gelled after the publication of Beth McGlynn’s 2003 NEJM study, which produced its own statistical blockbuster: American medical care comports with evidence-based practice 54% of the time, a number close enough to a coin flip to be unforgettably disturbing.

These two examples demonstrate the unique power of a memorable statistic to catalyze a movement.

Recently, my colleague Rebecca Smith-Bindman, professor of radiology, epidemiology, and ob/gyn at UCSF and one of the nation’s experts in the risks of radiographs, gave Medical Grand Rounds at UCSF. Her talk was brimming with amazing statistics, but this is the one that took my breath away:

A 20-year old woman who gets an abdominal-pelvic CT scan (i.e., just about any young woman coming to the ED with belly pain) has a 1 in 250 chance of getting cancer from that single scan.

Did that fully register? One CAT scan, which until recently most of us ordered with no more restraint than we exhibit when asking the Starbucks barista for a tall latte, will cause cancer in one out of every 250 patients. Two-hundred fifty: that’s the number of students in my college Bio 101 class. Wow.

This is particularly scary given the remarkable increase in the use of this technology. Get this:

• Three million CT scans were performed in the U.S. in 1980. In 2011, there will be 72 million, an average of 19,500 every day.
• One in five Americans will receive a CT scan in any given year; some experts suggest that at least one-third of those scans are unnecessary.
• Between 2000 and 2005, Medicare spending for imaging studies more than doubled, from $6.6 billion to $13.7 billion, twice the rate of growth of physician fees.

And, although none of these examples has quite the impact of the 1-in-250 statistic, there are lots of other scary risk data, such as:

• The best estimates are that radiation from CT scans causes 29,000 excess cancers each year in the U.S., mostly in women.
• Researchers estimate that 15,000 people will die from the direct effects of the 72 million CT scans performed in 2007 alone.
• A 2004 study found that less than 50 percent of radiologists, and 9 percent of ER docs, were aware that CT scans could increase the subsequent risk of cancer.
• A multiphase abdominal/pelvic CT scan has the same radiation wallop as 500 transcontinental flights, 450 chest radiographs, and 74 mammograms.
• And those airport body scanners you’ve been so worried about? You’d need to be scanned 200,000 times in order to accumulate the radiation that you get from a single CT scan. I’m a 1K United flyer, but I won’t close in on 200,000 scans for the next couple of centuries.

In her grand rounds, Rebecca walked us through the multiple lines of evidence on the risks of radiation from CT scans, particularly those drawn from studies of Japanese A-bomb survivors and individuals who received radiation for both malignant (i.e., lymphoma) and non-malignant (i.e., acne) disease. All pointed to the conclusion that doses in the range of those delivered by CT scans are fully capable of causing cancer.

Remarkably, with all the attention given to regulating food and drugs, the radiation delivered by CT scanners has gone largely unregulated. (If you ask me, I’d rather receive a precise and predictable dose of radiation than of Vitamin D or Azithromycin.) Rebecca found that CT scanners at four Bay area hospitals delivered radiation doses 66% higher than the usually-quoted doses, and that there were staggering variations (up to 13-fold) among different scanners performing precisely the same test. In her talk, she blamed the lax regulations on radiation physicists, fastidious types who have been reluctant to take a stand on maximum radiation doses since they can’t define those doses precisely.

While I’m sure that’s true, I have to believe that some of the reluctance to blow the whistle can be traced to the usual Medical-Industrial Complex: scanning equipment manufacturers, radiologists, and hospitals who have no particular interest in killing this particular egg-laying goose. If you doubt that these forces are at play, witness the billboards for $1000 total body scans that line Florida’s highways (scans that, when performed in healthy people searching for asymptomatic tumors, undoubtedly cause more cancers than they cure). Even now, despite powerful evidence of the risks, there are some in the radiology community who don’t find the science compelling enough to alter their practice. The parallels to the Global Warming debate are eerie, and troubling.

Even if the risks turn out to be less than we fear, most skeptics now agree that we’re causing a lot of cancers, and that many could be prevented if we took a few sensible steps. Manufacturers, hospitals, and radiology facilities should test the radiation exposure of their scanners, with the goal of decreasing the variation and delivering the minimum dose that creates an acceptable image. Ultrasounds should be substituted for CTs when possible, such as in follow-up of patients with documented kidney stones. There is evidence from Mass General that the use of computerized appropriateness protocols can markedly cut down on the number of CT scans, and thus the cancer risk. And, if we need to obtain the patient’s informed consent before transfusing a unit of blood, we should also do so before ordering a CT scan, since the latter is a far riskier procedure.

But changing culture will be more important, and harder, than changing protocols. We physicians have become so accustomed to saying “Get the scan” that we have turned our brains off. Several months ago, I cared for a woman with a painful lumbar compression fracture of unknown duration. We asked the orthopedic surgery service to see her in consultation, and the resident’s recommendation – made without a hint of self-awareness or irony – was that we obtain both a CT and an MRI. I was dumbfounded. Yes, each test can provide slightly different information, but I don’t believe that both were absolutely necessary; nor did a couple of experts I later spoke with. (We ended up getting the MRI only, which produced all the information we needed.) Somehow, we must find a way to break our reflexive radiographic profligacy.

As we struggle as a nation to “bend the cost curve” and we grapple with the nexus of low yield and expensive medicine (the dreaded “R word”), let us all agree that when we have an issue like this – an overused technology that harms or kills thousands of patients each year – we come together to do the right thing. CT scans can be immensely helpful, even miraculous, at times, but there is no question that the right thing is to Just Say No far more often than we ever have before.

Bob Wachter is chair, American Board of Internal Medicine and professor of medicine, University of California, San Francisco. He coined the term “hospitalist” and is one of the nation’s leading experts in health care quality and patient safety. He is author of Understanding Patient Safety, Second Edition, and blogs at Wachter’s World, where this post originally appeared.