The use of computed tomography (CT) scans in medicine to diagnose disease, and in many cases save lives, has exploded in recent decades.
The down side, a new study concludes, is that the radiation US patients receive from these medical exams will eventually result in 29,000 new cancer cases and 15,000 new cancer deaths each year at current levels of CT usage and cancer cure rates.
Furthermore, the dose of radiation delivered during CT exams is wildly variable, the researchers found, even within the same type of exam. In general, the radiation dosages delivered to patients were substantially higher than expected. The research findings are published in the current issue of the Archives of Internal Medicine.
UCSF’s Rebecca Smith-Bindman, MD, a radiologist and epidemiologist, led the study. Smith-Bindman and her collaborators investigated radiation exposure to 1,119 patients resulting from 11 of the most commonly used types of diagnostic CT exams. The study was conducted using archived images and data from four San Francisco Bay Area hospitals.
The degree of variation in radiation delivered to patients sent to imaging for similar clinical indications was dramatic. On average, for the 11 study types the amount of radiation received during the highest-dose exam was 13 times greater than for the lowest-dose exam.
Smith-Bindman and colleagues examined the images, recorded all scanner settings used for the exams, and fed parameters into computer programs to gauge actual radiation exposure to patients. For each exam reviewed – including different types of chest (including coronary), head and neck, and abdomen and pelvis exams -- at least 100 patients were included in the study.
While physicians and patients alike may be reassured by the clarity of images obtainable through CT exams, it’s important to be aware of and to discuss potential risks as well as benefits, Smith-Bindman says.
“The doses are higher than we had appreciated, and I think we need to take into account that these CT exams are not harmless. As physicians we need to weigh the risks and benefits and ask ourselves what we are going to learn from each exam, and whether any information gained can be useful in guiding treatment decisions.
“If the CT scan is expected to change management or influence clinical decision making, then it should be used. If it is unlikely to change practice and is being obtained simply for reassurance, then perhaps it need not be obtained at all.”
Lifetime Cancer Risk
Smith-Bindman and colleagues estimated that there is up to a one-in-eighty lifetime cancer risk for a 20-year-old woman who receives either a CT exam for a suspected pulmonary embolism, a CT coronary angiography, or a multiphase abdomen and pelvis CT. Five percent of CT exams are performed in children, and 10 percent in adults 20 to 30 years of age, according to the researchers. The lifetime risk posed by each new exam declines with increasing age, but the effects of radiation exposures from multiple exams may be cumulative.
Researchers struggle with gauging the risks of low-dose radiation -- the amount that a woman would receive during a mammogram, for instance. In contrast, there is clear, observable data on excess cancers attributable to higher radiation exposures, such as those received during CT exams, Smith-Bindman says.
“We have observable data from several different sources where we see an association between exposure and cancer risk,” Smith-Bindman says. “The Nagasaki and Hiroshima survivors for example, had an average radiation dose of 40 millisieverts. That’s in the same ball park as one or two CTs.”
Overuse of CT Exams
Rita Redberg, MD, a UCSF cardiologist who closely tracks cost-benefit studies of imaging exams used to diagnose and evaluate heart disease, wrote an editorial to accompany the CT studies published in the current issue of the journal.
Redberg noted that a recent study of close to one million non-elderly adults found that 70 percent had received a CT scan during a three-year period from 2005 to 2007. The US total for CT scans was estimated to be 72 million for the year 2007. There is significant variation in the use of CT exams in different states, Redberg stated.
“Given the lack of data indicating that patients do better in states with more imaging and given the highly profitable nature of diagnostic imaging, the wide variation suggests that there may be significant overuse in parts of the country.”
During an interview, Redberg pointed out that a CT coronary angiogram – used to identify blood vessels with constrictions caused by heart disease – delivers radiation equal to more than 300 chest X-rays. “The growth in use of these exams greatly exceeds the evidence for their benefits,” she says. “There are many asymptomatic patients that now are getting cardiac CT angiograms.”
Redberg notes that emergency rooms often have CT scanners and conduct the exam on patients with chest pain. The American College of Cardiology has published a guide on appropriate criteria for CT use in cardiology, and has concluded that the highest potential value is in identifying congenital heart abnormalities, Redberg says.
CT Exams are Profitable
Steven Schroeder, MD, Distinguished Professor of Health and Health Care at UCSF and former President and CEO of the Robert Wood Johnson, notes that “CT is very seductive; it’s cutting edge; people ask for it; the risks are not very visible -- and very few physicians are censured for overdoing tests.”
According to Schroeder, insurance reimbursement for physician services favors the use of high technology. Medicare sets the standard for reimbursement, he says, but a committee established by the American Medical Association (AMA) is very influential on Medicare when it comes to deciding reimbursement rates for physician services, he says. The AMA/Specialty Society Relative Value Scale Update Committee (RUC) makes recommendations about valuing physician services to the Centers for Medicare and Medicaid Services (CMS).
The RUC committee includes few generalist physicians, Schroeder says, but includes many specialists, among them the types of specialists that often own scanning equipment and profit the most from its use. Unfortunately, unlike advances in personal computers, cost savings due to manufacturing advances in medical technology do not quickly translate into consumer price savings, Schroeder says.
According to Fergus Coakley, MD, vice chair of clinical services for the UCSF Department of Radiology, radiology practices sometimes profit from CT exams, but radiologists are not the ones ordering the exams, and not every ordering physician gives extensive background information on why the test has been ordered. In addition, a majority of scanners are not owned by self-referring specialty clinics, according to Coakley. Still, he adds, there is little incentive in the US health care system for radiologists to question a physician who orders an exam.
New Radiation Safety Committee at UCSF
At UCSF, Coakley says, radiologists are analyzing a way to use the radiology information system to flag some patients who have had multiple CT studies so that the radiologist can interact with the physician who orders the CT exam.
Smith-Bindman says there is a temptation to use high-dose studies to obtain desired information, rather than taking the time to carefully set-up lower dose studies that could be used to obtain the same information. "The default settings on these machines are not chosen to minimize dose," she says.
Some research suggests that in many cases CT exam protocols are being used for medical indications for which they are not the best choice. For instance, a University of Wisconsin study of abdomen and pelvis CT exams in 500 patients presented earlier this month at a Chicago meeting of the Radiological Society of North America found that a majority received at least one inappropriate exam, based on guidelines established by the American College of Radiology.
Coakley and Smith-Bindman are among the UCSF radiologists who have led efforts to establish a new Departmental Radiation Safety Committee to oversee radiation-intensive imaging protocols and to improve education of physicians and technicians within the Department of Radiology and in other departments. The committee also aims to develop strategies for reducing radiation doses delivered to patients, especially in high-volume practices such as abdominal imaging, thoracic imaging, neuroradiology, pediatric radiology and nuclear medicine.
Radiation Dose Associated With Common Computed Tomography Examinations
and the Associated Lifetime Attributable Risk of Cancer
Rebecca Smith-Bindman, Jafi Lipson, Ralph Marcus, Kwang-Pyo Kim, Mahadevappa Mahesh, Robert Gould, Amy Berrington de González, and Diana L. Miglioretti
Archives of Internal Medicine Internal Medicine
(December 14, 2009)
Editorial, Rita Redberg, MD
Archives of Internal Medicine (December 14, 2009):
Interim Recommendations to Address Concern of Excess Radiation Exposure
US Food and Drug Administration (December 7, 2009):
Unindicated CT Series Result in Unnecessary Radiation Exposure for Patients
Radiological Society of North America (December, 2009):
Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures
New England Journal of Medicine (August 27, 2009):