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more photosAdvanced imaging equipment, such as this computed tomography (CT) scanner at Bend Memorial Clinic, has allowed doctors to make quick and accurate diagnoses of diseases. But experts are concerned that the growth in imaging use could be exposing patients to too much radiation and raising a small but real risk of cancer.
Andy Tullis / The Bulletin file photo
Radiation overload?
Medical imaging usage has grown, and some are concerned it's too much
By Markian Hawryluk / The Bulletin
Published: October 29. 2009 4:00AM PSTOne of the great advances in the practice of medicine has been the development of increasingly sophisticated ways of looking into the human body. Imaging technology, from X-rays to ultrasound to computed tomography (CT), has allowed doctors to see what was once visible only by cutting into the body. And as the machines have become more powerful, scores of new uses have been found.
As a result, the number of CT scans performed in the United States has risen from 3 million in 1980 to 62 million in 2006. Undoubtedly, many of the scans have allowed for quick diagnosis and treatment that has saved patients' lives.
But there is a growing worry among many doctors that the cavalier use of these imaging tests, driven by convenience, utility and economics, may be needlessly exposing patients to radiation and increasing their risk of cancer.
“There's a shift in the general culture of medicine where it's so easy to do these tests, we go to these tests even before getting a thorough history and physical exam,” said Dr. Reza Fazel, a medical professor at Emory University in Atlanta. “It's just easier to order these tests.”
Radiation risk
CT scans are of particular concern because of the amount of ionizing radiation they emit. Such radiation can damage cellular DNA in the body, giving rise to cancerous tumors or leukemia. X-rays also emit ionizing radiation but at much lower doses. Magnetic resonance imaging (MRI) and ultrasound emit no radiation.
The question of how much radiation, measured in millisieverts (msv), is too much is still a matter for debate. Most people are exposed to 3 msv of radiation from natural sources over the course of a year. A standard chest X-ray emits about 0.1 msv, while a mammogram about 0.7 msv. A CT scan, on the other hand, can expose an individual to 10 to 20 msv in a matter of seconds.
Studies of atomic bomb survivors in Japan have shown an increase in cancers in the people farthest from the epicenter, who were exposed to between 5 msv and 150 msv during the bombings, with a mean dose of about 40 msv. That's comparable to the doses involved in just two or three CT scans.
The risk is small, accounting for only a handful of additional cancers in every 100,000 patients exposed. But the risk is real.
Based on the Japanese data, researchers from Columbia University were able to estimate that 1.5 percent to 2 percent of cancers in the U.S. might be directly attributable to radiation from CT scans.
“When a CT scan is justified by medical need, the associated risk is small relative to the diagnostic information obtained,” lead author Dr. David Brenner and his colleagues wrote in the New England Journal of Medicine in 2007. “However, if it is true that about one-third of all CT scans are not justified by medical need, and it appears to be likely, perhaps 20 million adults and, crucially more than 1 million children per year in the United States, are being irradiated unnecessarily.”
Brenner's findings were provocative to say the least. Many questioned whether the full-body radiation experienced by survivors was comparable to the more targeted radiation of CT scans, or whether it was appropriate to consider the cumulative effects of multiple lower-dose scans to a single higher-dose exposure. Yet it remains the first and best estimate of the risk.
“That's still very controversial,” said Dr. Archie Bleyer, a pediatric oncologist in Bend. “It's generally accepted that some of the cancer problem is caused by a history of multiple scans of individuals. I think the controversy is to what extent? Is it a major problem or a trivial problem?”
If Brenner's numbers are correct, it would represent 15,000 to 30,000 new cases of cancer caused by imaging in the U.S. each year.
“Some of those are occurring here in Central Oregon,” Bleyer said. “Since we're avid users of CT scanners — we've put in more than we probably need to serve our community — we're probably overrepresented in what that estimate is. I really worry about that.”
Multiple scans
Doctors are careful to put the risk into perspective, to avoid scaring people away from needed imaging tests. On its own, an individual scan might be easily justified by medical need, and the benefits may far outweigh the risks. But many doctors are worried about the cumulative effects of relying so heavily on CT scans for diagnostic purposes.
In an article published earlier this year, Fazel and his colleagues examined insurance billing records for more than 952,000 patients younger than 65. About 70 percent of those patients underwent an imaging test involving radiation, accounting for a combined 3.4 million scans over a three-year period. One in five were exposed to at least 20 msv of radiation, and 2 percent to more than 50 msv.
“A lot of time these tests cluster in patients, where they get one thing and it leads to another thing, and it keeps going,” Fazel said. “It turned out about two percent of the population were getting high doses, because of repetitive testing. That's sounds like a small proportion, but when you translate that to the U.S. population, you have about 4 million people getting these high doses.”
And that was for only one year of their lives. Over their lifetimes, it's likely they'll be exposed to much more radiation, he said.
Much of the growth in imaging has been for the purpose of screening, whether mammography for breast cancer, virtual colonoscopies for colorectal cancer or coronary calcium screening for heart disease. Central Oregon was an early adopter of coronary calcium screening, which initially used electron beam tomography, to measure how much calcification there was in a patient's coronary arteries. The extent of the calcification is thought to better predict a patient's risk of a heart attack than other screening methods and helps doctors to determine how aggressively to treat heart disease.
Eventually, local providers switched to newer models of CT scanners that could provide clear images of coronary arteries but could also be used for other purposes. The switch represented a slight increase in radiation but still within acceptable limits.
“The radiation dose with a calcium score is very small. It's about 1 msv,” said Dr. Bruce Brundage, a pioneer of coronary calcium screening and now director of the Heart Institute of the Cascades in Bend. “That's about three plane rides across the United States at 35,000 feet. It's not huge.”
But some researchers question whether coronary calcium screening is being used appropriately to identify at-risk individuals who would otherwise not be treated.
Dr. Richard Koch, a cardiologist with Bend Memorial Clinic, conducts both coronary calcium screening and lung cancer screening using CT scans. The clinic was one of the first to receive a variance from the state allowing them to do the calcium and lung screening tests for individuals without a doctor's order as long as the patient met certain criteria. For calcium scoring, that includes men older than 45 and women older than 55 who had at least one risk factor for cardiac disease.
Such patients are considered at intermediate risk for heart disease and a calcium score can help doctors determine how to treat them.
For patients initially deemed at low risk, there's little reason to treat even if they had a high calcium score, and if they're at high risk, doctors would treat them aggressively regardless of their calcium score.
“In my mind, there's no value in that test, and at the front, they'd tell them, ‘You shouldn't get the test,'” Koch said. “It's about picking the right people.”
Reducing risk
Brundage said there's more concern over CT angiograms, a procedure that uses a CT scan to map the arteries of the heart to identify blockages. Traditional angiograms require doctors to snake a catheter through an artery in the patient's groin and into the heart to deliver a contrast dye that can be picked by an X-ray. But many doctors have been excited about the prospects of angiograms with CT scans because they are less invasive. Standard angiograms carry a longer recovery period and a greater risk of complication. But CT angiograms involve more radiation, 15 to 20 msv, than a traditional angiogram at 5 to 7 msv.
“Because it's easier and theoretically less dangerous to do, that lowers the threshold probably for doctors ordering it,” Brundage said. “The less dangerous the exam, they're a little quicker to pull the trigger.”
Now that concerns about radiation in imaging have been raised, cardiologists are developing new ways of doing CT angiograms to reduce the overall radiation involved. Better technology and protocols have brought the radiation level down nearly to the level of an invasive angiogram.
“If you've got a potentially serious problem, it's well worth the radiation exposure to get to the bottom of the problem,” Brundage said. “If it's being used a little willy-nilly, then you're exposing the patient to unnecessary radiation.”
The tremendous growth in imaging has many believing that a good number of scans aren't truly necessary. When a recent report found that the per capita dose of radiation from medical imaging has increased seven-fold since 1980, the American College of Radiology blamed the increase on doctors who purchased imaging equipment for their clinic and then stood to profit from referring patients. Others blame the current malpractice environment that encourages overtesting to protect against patient lawsuits.
“When you look at the area of coronary disease, 80 percent of malpractice dollars given out for emergency room visits are for missed myocardial infarctions,” Koch said.
Doctors have little to lose by ordering the scan that can provide a definitive answer rather than relying on their medical judgment and risking a lawsuit. And many doctors just aren't aware of the risk. One study found that 50 percent of radiologists and 91 percent of emergency department physicians were unaware that CT was associated with an increased risk of cancer. Many just didn't encounter that in their medical training.
Koch, for example, is board-certified in nuclear cardiology and cardiac CT, so he's undergone substantial training and testing on the risk of imaging-related radiation. But primary care and emergency room doctors who might be sending patients for such tests may not realize the risks.
“The people who are reading the scans are educated, but the people who are ordering them have not been formally educated,” Koch said.
Safe limits
The problem with such overuse is that no one knows how much total radiation the human body can handle, and for the most part, nobody is tracking how much radiation a patient is getting. Health and nuclear industry workers are routinely monitored for radiation exposure, and restricted to 100 msv every 5 years, with a maximum of 50 msv in any given year.
A number of hospitals and clinics have now started to track their patients' exposure to radiation in their medical records. But so far, that's occurring solely by institution and so records can't account for scans performed at other locations.
Some institutions have incorporated flags in their computer systems that inform doctors of the radiation levels of the tests as they order them. Fazel said efforts to reduce exposure will likely focus on technological and protocol improvements that cut radiation levels as well as ensuring that scans are done for the right reasons.
“I think it's completely fair and reasonable for a patient to have a frank discussion with their doctor and ask, ‘Why do you think we need to do this test, how is it going to help me, and what are the alternatives?'” he said. “The best patients are the informed patients.”
Bleyer, the pediatric oncologist, maintains there are almost always alternatives that involve less radiation. Often, doctors can use ultrasound, MRI or X-ray instead. There are times when only a CT scan will do, but that only underscores the need for not accumulating radiation when other alternatives exist.
“We still don't know the critical level that is the threshold above which that risk ratio leads to the point of finding some other way because that next scan is going to induce cancer,” he said. “Maybe this scan won't be the one that trips me over, but if it's one of the next few I'm going to get, maybe I should not get this one. It all adds up.”
Bleyer recalled how soon after Seattle Children's Hospital installed its first CT scanner in the 1970s, doctors noticed a rise in the incidence of brain tumors. An analysis conducted in 1997 showed that indeed after the introduction of CT scanners, brain tumor diagnoses went up. But doctors couldn't be sure whether CT scanners were simply better at detecting brain tumors caused by other factors or were causing those brain tumors themselves.
Bleyer recently updated that data to see whether brain tumor rates fell back down to previous levels after the CT scanners helped to uncover the previously undiagnosed tumors. Rates fell somewhat but not back down to original levels.
“That pattern seemed to me to affirm that some of the brain tumors that we diagnosed after the advent of CT scanners were caused by the CT scans,” he said. “I don't know that for a fact, nor does anybody, but it certainly raises the issue.”
Critics counter that if CT scans are indeed causing and not simply uncovering more brain tumors in kids, we should be seeing more brain tumor deaths. But we're not. Pediatric deaths from brain tumors have not gone up since the 1980s.
“That's the current interpretation, but I'm not entirely convinced,” Bleyer said. “We're preventing death. We're doing a better job treating those cancers that were caused by it.”
Protecting kids
Children are at higher risk of complications from radiation exposure because their organs and tissues are still developing. And because cancers often take decades to emerge, the younger the patient exposed to radiation the greater the chance of incurring a cancer in his or her lifetime.
That's why initial efforts to reduce exposure to imaging radiation have focused on children. Bleyer participated in an effort called As Low As Reasonably Achievable (ALARA) that worked to reduce radiation levels to the lowest levels that would still give reasonable results. It led to the Image Gently campaign that has called greater attention to the imaging risks for children.
CT scans, however, have gained in popularity among physicians treating children because they don't require anesthesia or sedation. Now doctors are urged to consider other alternatives and to limit the cumulative radiation exposure for kids. The Alliance for Radiation Safety in Pediatric Imaging has developed a card that parents can download from its Web site and use to track a child's exposure over his or her lifetime.
“We were trying to use the lowest dose reasonably possible. There's been a lot of effort to reduce it and we've done it well in Oregon,” Bleyer said. “We don't know if we've gone down enough, if we've reduced the number of scans enough.”
Bleyer is also concerned that children might be exposed to radiation even before they're born.
“The highest incidence of cancer during childhood and adolescence is in the first year of life. There's more cancer diagnoses in the first 12 months of life than in any other 12-month interval after that,” he said. “And I worry that some of those cancers are caused by abdominal X-rays or CT scans (of pregnant women).”
Studies have shown the risk of childhood cancer is 40 percent to 50 percent higher when a pregnant woman received a single abdominal CT scan. Yet CT scans in pregnant women have increased by 25 percent per year from 1997 to 2007.
Bleyer said many of those scans might occur in the six to eight weeks before a woman even knows she's pregnant. But others might involve situations where doctors had no other choice or did not know the risks involved.
“There is still unawareness among our medical professionals and certainly in the community about this risk,” he said. “There's still too much ignorance.”
Markian Hawryluk can be reached at 541-617-7814 or mhawryluk@bendbulletin.com.
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