CAT Scans Cause Cancer
The big "oops" of the week in the medical community concerns CT scanning, otherwise known as computed tomography or CAT Scaning (computer aided tomography). Touted as miracle technology when it first hit the scene in the 1970s (in fact, the developers of modern CT scan technology shared the Nobel Prize in 1979), CT scans provide three-dimensional images far more detailed and flexible than normal X-rays. Doctors love to rely on them, and so the number of CT scans performed in the US increased 23-fold from three million in 1980 to about 70 million by 2007. At a typical cost of $500 and up to $1500 per scan, which can mean $6000 or more for diagnostic scans of several body parts, it's been a profitable addition to the medical bag of tricks.
Despite assurances from doctors that the benefits of getting such accurate diagnostic images outweigh the risks, new evidence indicates that the radiation received from CT scans increases cancer risk…by a substantial margin. A study just completed at four San Francisco hospitals found the median dose of radiation delivered during CT scans was higher than previously thought. Also, the radiation levels varied wildly for the same procedure from hospital to hospital and even within the same institution. In fact, there was a 13-fold difference between the highest and lowest doses of radiation for identical procedures.
To put the radiation exposure in perspective, a complete set of dental x-rays (about 18 exposures) provides an effective dose of about 1.5 mrem (or .015 mSv). The average person absorbs one millisiervert (mSv) of background radiation annually just from routine living. A single pelvic/abdominal CT scan, on the other hand, exposes the patient to an average of 31 mSv while a typical head scan puts out an average of two mSv. But those are just averages. The researchers discovered that while a head scan at one hospital exposed patients to only 0.3 mSv, the same procedure at another hosptial exposed patients to six mSv (about 400 times the exposure of a complete set of dental x-rays). The deviations become startling when considering variations in the radiation for the abdominal/pelvic series, where researchers found radiation as high as 90 mSv at one hospital -- almost 60 units above the average. This represents a 13-fold variation in dose and means that some patients are getting far more exposure than necessary for an adequate image. Consider that the survivors of Hiroshima suffered increased cancer risk from radiation exposures estimated to be as low as 10 mSv, and that the typical CT scan delivers as much radiation as 74 mammograms and 442 chest X-rays.
Given these figures, it's no wonder that a second study published in the Archives of Internal Medicine concluded that 29,000 new cancers would result from CT scans performed in 2007 alone. The majority of those cancers (14,000), not surprisingly, would result from scans of the abdomen and pelvis, according to the projections. Another 4,100 would come from chest scans; 4,000 from head scans; and 2,700 from CT angiograms. The most vulnerable populations include younger adults and women. The researchers project that those aged 35-54 would develop one-third of the projected cancers while women would develop two-thirds of those incipient cancers.
Viewed through another lens, researchers estimate that one out of every 270 women and one of every 600 men who received a CT coronary angiogram at age 40 would develop cancer from that scan, while one in 8,100 women and one in 11,080 men who had a routine head CT scan at age 40 would develop cancer. The researchers also expect 2000 extra breast cancers to develop just from CT scans in 2007. These figures don't account for those at far higher risk after receiving an abdominal/pelvic scan. They also don't consider the cumulative effect exerted on those who had multiple CT scans, including repeat and follow-up scans, or for the factor of age, which doubles the risk for 20-year-olds and halves it for those 60 and older.
Certainly one heart-breaking reality here is that many of the CT scans performed on patients never needed to be performed in the first place. "CT is generally considered to have a very favorable risk-to-benefit profile among symptomatic patients," said study director Dr. Rebecca Smith-Bindman of the University of California San Francisco. "However, the threshold for using CT has declined so that it is no longer used only in very sick patients, but also in those with mild, self-limited illness who are otherwise healthy. In these patients, the value of CT needs to be balanced against this small but real risk of carcinogenesis resulting from its use."
While Dr. Smith-Bindman is right about the need for caution, "the small but real risk" part of her statement needs a reality-check. A one in 270 chance of getting cancer for a superfluous procedure in an otherwise healthy individual seems not-so-small at all, and remember, that's just the tip of the iceberg. The odds go way up for young patients who have had several abdominal scans. Anyway, why should any otherwise healthy individual risk getting cancer to have a fancy diagnostic procedure done when other options exist? A more on-target viewpoint is the one expressed by the editor of the Archives of Internal Medicine, Dr. Rita Redber, who wrote that the study results "make us question if we have gotten carried away in our enthusiasm" for the use of CT.
The researchers suggest that practitioners exercise more restraint in prescribing CT scans in the first place, that radiation doses become standardized across institutions, and that medical institutions and practitioners track how many CT scans an individual has already had before wantonly assigning new ones -- something that apparently (and appallingly) isn't done. Also, in most cases, MRI or ultrasound or even simple X-ray procedures can get the same results as some very high-dose CT procedures that take multiple images of "slices" throughout the body.
Supposedly, the FDA is on the case after 260 patients at Cedars-Sinai Hospital in Los Angeles filed a class action suit after being exposed to eight-times the required dose of radiation during CT scans. Patients lost hair, suffered burns, and are at risk for forming cataracts as well as cancers. A class-action suit in Alabama claims patients there received 14-times the necessary dose. Investigators have found similar violations in other hospitals.
Lest you despair because you've submitted to a CT scan in the past, the good news is it could be worse. At least in some cases, CT scans do catch deadly problems that otherwise couldn't be detected. So, maybe in a few cases, the risks really are worth it. Compare that to the nuclear stress test -- where you ride a stationary bike or run on a treadmill while radioactive material lights up your heart to show how it's functioning. Although doctors like to give those stress tests to patients as soon as they sprout a few gray hairs, the test delivers a huge dose of radiation with, as yet, no real evidence that the procedure offers any benefit at all. According to Dr. Michael S. Lauer of the National Institutes of Health, "The imaging technology today is amazing, it's amazing how quickly it's advanced, yet we haven't answered the fundamental question of whether we're actually helping people by doing this."
The bottom line, it seems, is beware of doctors bearing imaging procedures. Do your homework, ask questions, and always go for the least amount of radiation necessary to find out what's going on inside of you -- which means preferably no radiation at all.