CT SCANS: Reducing Radiation Risk from Medical Imaging

Marc Gelman, MD, and Prasad Murthy, MD

Over the past few years, the media have brought a great deal of attention to radiation exposure from medical imaging and the associated risk for developing cancer. As a result there is now much greater awareness, among both physicians and patients, of the potential risks of medical imaging. Patients want to know if radiation from mammograms, x-rays and computed tomography (CT) will increase their risk of developing cancer. They have only to look at the Internet, sometimes obtaining information of questionable reliability that may create unfounded concerns and unnecessary stress. Clinicians often do not know how to address these concerns.

There is clearly a need for education in this area--for patients, clinicians and imaging professionals. This article looks at the extent of the problem, discusses steps clinicians can take to reduce imaging referrals, and highlights what Kaiser Permanente is doing to reduce radiation exposure and the need for CT scans.

Scope of the problem

What exactly is the extent of the problem? A recent report found that the per capita dose of radiation from medical imaging in the United States has increased by a factor of nearly six since the early 1980s.[1] The report also noted that medical imaging was responsible for almost 50% of all radiation exposure by Americans, and that CT scans were responsible for half this total.

Another recent study found that the use of CT scans in hospital emergency rooms has boomed, rising 330% in 12 years.[2] About one in seven patients in the ER gets a CT scan, and a quarter of all CT scans are performed through the ER. A related significant issue is the rise of “incidentalomas” in imaging, defined as findings that are unrelated to the clinical indication for the exam performed. Further imaging evaluation of these incidentalomas (most of which are benign) adds significantly to the number of CT scans performed.

The effects of radiation are dependent on sex and age at the time of exposure, and the risks are additive over time. CT scans have been shown to increase the risk of three types of cancers: breast cancer in women (CTs of chests being presumably the worst because of direct breast exposure), lung cancer and leukemia. Young age at time of exposure is a significant risk factor, as there is more time for the biologic action of the ionizing radiation to cause damage. For example, a 5-year-old female child undergoing a CT scan for possible appendicitis has a 1:296 risk of lifetime cancer vs. a risk of only 1:5747 for an 80-year-old male undergoing the same scan.

Background radiation from cosmic, industrial and consumer sources accounts for 3 millisieverts (mSv) on average per person per year.[3] (The millisievert quantifies the biologic effects of ionizing radiation.) To put radiation from medical imaging in perspective, just one CT chest scan equals 10 mSv of radiation. Other scans that equal 10 mSv include one CT scan of the abdomen or pelvis; five CT head scans; 1/2 of a bone scan; 5/6 of a myocardial profusion scan; and 5/8 of a PET scan. These numbers indicate the scope of the problem--one that will escalate unless corrective actions are taken on multiple fronts.

Choose wisely

Referring clinicians can do several things to mitigate radiation exposure and the need for CT scans. Two key recommendations are to (1) avoid ordering the test using ionizing radiation when feasible and (2) have the imaging center use protocols that minimize the dose of radiation.

Listed below are some specific guidelines drawn from multiple sources.[4,5]

 

Right upper quadrant (RUQ) pain. First consider the history and diagnostic labs. Ultrasound is the diagnostic imaging modality of choice, with higher sensitivity for biliary disease than CT. Transaminase and total bilirubin are good surrogate markers for obstruction that may not be seen on ultrasound.

Epigastric pain. Ultrasound is the best initial test for pancreatitis, though CT is more sensitive and specific after lab evaluation. A differential diagnosis needs to be considered to properly workup this symptom: consider dyspepsia, GERD, gall bladder disease, pancreatitis, myocardial infarction, pneumonia, pulmonary infarction and pleural effusions. Upper endoscopy is the test of choice if there are red flags suggesting gastric malignancy, which is generally seen in patients greater than age 50. Red flags include unintended weight loss, persistent vomiting, progressive dysphagia, odynophagia, unexplained anemia or iron deficiency, hematemesis, palpable abdominal mass or adenopathy, previous gastric surgery, or jaundice.

Lower abdominal pain/diarrhea. Abdominal pain associated with diarrhea of less than seven days can be managed expectantly with labs and stool tests as indicated. Symptoms lasting more than four weeks may require upper and lower endoscopy. Ileal pathology may present with both acute and chronic diarrhea. Lower abdominal pain in women requires a different approach to avoid pelvic radiation exposure, and it also begins with a differential diagnosis: consider pregnancy, adnexal cysts or masses with torsion or bleeding, endometriosis, and leiomyomas. Ultrasound is the preferred imaging test for a woman with a positive pregnancy and an uncertain diagnosis after labs and a positive physical examination.

Ongoing abdominal pain. For patients 50 years or older, ongoing abdominal pain can be evaluated with a single CT scan, not multiple scans. Check to make sure previous scans cannot be repurposed to answer a clinical question and avoid a repeat scan. Abdominal CT scanning for patients under age 50 should only be undertaken in the setting of red flags. Alternating diarrhea and constipation is reassuring. Symptoms of concern are fever, weight loss and chronic diarrhea. Physical exam and labs should be used. An unremarkable workup can be managed without further imaging. Testing should focus on a specific disease and not a general screen.

Vertigo. CT scanning for dizziness is not a good test, except for cerebellar hemorrhage, which only presents as isolated peripheral vestibular disease 10% of the time. Almost all vertigo symptoms (94%) are generated from peripheral disease. Physical examination may have more diagnostic accuracy than MRI imaging.

Headache. Don’t image for uncomplicated headache (see Choosing Wisely guidelines).[4]

Left lower quadrant pain and diarrhea. CT to confirm presumed acute diverticulitis is not routinely needed unless clinical sepsis is present or medical management is failing.

Chest nodules. CT chest scanning for nodules less than 4 mm (if not ground glass) in patients under 35 years old is low yield.[6]

Low back pain. Don’t obtain imaging for nonspecific low back pain that cannot be attributed to a specific disease or spinal abnormality following a history and physical examination. HEDIS guidelines consider ordering such a test in patients 18-50 to be a non-quality indicator within 28 days of presentation of symptoms.

Appendicitis. Acute appendicitis in patients less than age 40 with typical history and physical examination can proceed to surgery without CT. Older patients can present with a more confusing history and physical examination.

Pulmonary embolism. Low clinical probability and negative D-dimer are sufficient to avoid the CT scan.

Minor head injuries. The Canadian CT Head Rule should be applied to patients who meet certain risk criteria for minor head injuries (see Figure 1).[7]

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Figure 1. Canadian CT Head Rule

CT Head Rule is only required for patients with minor head injuries with any one of the following:

High risk (for neurological intervention)

• Glasgow Coma Score <15 at 2 hours after injury

• Suspected open or depressed skull fracture

• Any sign of basal skull fracture

• Vomiting (2 or more episodes)

• Age 65 years or older

Medium risk (for brain injury on CT)

• Amnesia before impact >30 min

• Dangerous mechanism (pedestrian struck by motor vehicle, occupant ejected from motor vehicle, fall from height >3 feet or five stairs)

Minor head injury is defined as witnessed loss of consciousness, definite amnesia, or witnessed disorientation in patients with a GCS score of 13-15.

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Image wisely

Awareness of the dangers of medical imaging has led to significant action in recent years, on multiple fronts. In 2010, the FDA launched a new Radiation Safety Initiative adopting two principles of radiation protection: (1) appropriate justification for each procedure ordered and (2) careful optimization of the radiation dose used during each procedure.[8]

The FDA initiative includes mandatory accreditation of CT scanners; appropriateness criteria for physician decision-making; creation of a national dose registry; and standardized reporting of medical imaging errors. Accreditation ensures that every CT scanner in use is optimized to achieve CT scan doses within specific recommended ranges. Beginning in July, a new California law will require mandatory reporting of CT dose in the radiology report. The law also requires accreditation by July 2013 of all facilities that perform CT for diagnostic purposes. In addition, there are initiatives to establish a patient dose record that will track total radiation exposure and assist clinicians in the decision-making process.

The medical imaging community has been proactive in responding to the outcry about radiation risk and in making changes to reduce the risk. The American College of Radiology and the Radiological Society of North America joined forces to create a website, RadiologyInfo.org, which provides extensive resources to help patients understand the risks and benefits of imaging tests and procedures. A second major initiative is the Image Wisely campaign (imagewisely.org), which asks imaging professionals and referring clinicians to take a pledge to reduce the amount of radiation used in medically necessary imaging studies and to eliminate unnecessary procedures.

CT protocols at Kaiser

At Kaiser Permanente, our CT Protocol Optimization Committee overhauled our protocols two years ago with the specific goal of reducing radiation dose. Protocols have been optimized to take advantage of vendor-provided dose reduction techniques and current research. Our average doses for exams have decreased more than 25%, and new dose-reduction techniques promise to reduce doses even more without significantly compromising image quality.

More recently, our radiologists have been addressing the incidentaloma issue. We are conducting a multidisciplinary review of guidelines for reporting and managing incidentalomas, and we are distributing specific guidelines to our physicians for use in daily practice. The goal is to reduce the number of CT and other imaging exams performed to evaluate incidentalomas, most of which have a high likelihood of being benign. Such reductions will lessen overall radiation exposure, patient anxiety and health care costs.

We are starting to see results from our new protocols, but we can do much better in two specific areas. First, we need to move from fear to education. The recent talk of imaging-related radiation risk has scared patients and created a mistrust of medical imaging. Referring clinicians and imaging professionals must be prepared to have informed, realistic conversations with patients about the true relative risks (as opposed to the absolute risks, which can confuse patients) and benefits of imaging studies. When used judiciously, medical imaging--particularly CT scans--can be lifesaving and actually reduce overall health care costs.

Second, both referring clinicians and imaging professionals have to do a better job of communicating and working together to minimize unnecessary imaging. Common scenarios that need to be eliminated include (1) radiologists protocoling and performing exams without relevant history and (2) referring clinicians having to order follow-up exams “on their own” without appropriate direction from the radiologist.

It is encouraging to see the improving alignment of radiologist, clinicians, patient perception and public policy. We should be proud of the progress we have made over the past few years on this significant medical issue, but we cannot afford to lose momentum.

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Dr. Gelman is an internist at Kaiser San Rafael whose administrative duties include access oversight for the hospital’s radiology department. Dr. Murthy, a radiologist at Kaiser San Rafael, serves on the Kaiser Northern California Regional CT Protocol Committee.

Emails: marc.gelman@kp.org, prasad.murthy@kp.org

References

1. National Council on Radiation Protection and Measurements, “Ionizing radiation exposure of the population of the United States,” NCRP Report No. 160 (2009).

2. Kocher KE, et al, “National trends in use of computed tomography in the emergency department,” Ann Emerg Med, 58:452-262 (2011).

 

3. Stabin MG, “Doses from medical radiation sources,” Health Physics Society website, hps.org (2011).

4. American College of Radiology, “Choosing wisely: Five things physicians and patients should question,” choosingwisely.org (2012).

5. Penner RC, Majumdar S, “Approach to abdominal pain in adults,” UpToDate (Jan 17, 2012).

6. Weinberger SE,” Diagnostic evaluation and management of the solitary pulmonary nodule. UpToDate (August 2011).

7. Stiell IG, et al, “Canadian CT head rule for patients with minor head injury,” Lancet, 357:1391-96 (2001).

8. U.S. Food & Drug Administration, “White paper: Initiative to reduce unnecessary radiation exposure from medical imaging,” fda.gov (2010).

Additional Reading

Brenner DJ, Hall EJ, “Computed tomography--an increasing source of radiation exposure,” NEJM, 357:2277-84 (2007).

Fazel R, et al, “Exposure to low-dose ionizing radiation from medical imaging procedures,” NEJM, 361:849-857 (2009).

Hendee WR, et al, “Addressing overutilization in medical imaging,” Radiology, 257:240-245 (2010).

Rabin RC, “Doctor panels recommend fewer tests for patients,” New York Times (April 4, 2012).