Whole Body CT Radiation Concern

An Australian study of emergency department imaging practices has raised radiation safety concerns and new arguments about the clinical benefits of whole-body computed tomography (CT) imaging for the initial emergency department evaluation of critically injured patients.

Pan-scans, a wide field-of-view CT imaging protocol covering the body from the head to the pubic symphysis, stirred intensive debate when they were first introduced in the mid-2000s. A majority of academic authorities eventually accepted the high-speed application for diagnosing life-threatening, multifocal trauma in the emergency department, despite its propensity for exposing patients to levels of radiation of 20 mSv or more.

That single dose is double the amount of ionizing radiation the National Academy of Science's Seventh Assembly of the Committee on Biologic Effects of Ionizing Radiation says will give a 40-year-old adult a 1-in-1000 chance of future cancer.

Stephen Asha, MD, and colleagues from St. George Hospital, Sydney, Australia, have drawn additional attention to CT pan-scans with their study, which compares 656 severely injured patients who were evaluated with conventional imaging before the introduction of a pan-scan protocol at a level 1 trauma center with 624 patients with similar injuries who were examined after adoption of the technique.

Their study was
published online December 7, 2011, and in the February 2012 print issue of Emergency Medicine Australasia.

Participants were at least 18 years of age. To qualify for a pan-scan, they must have suffered 1 of 8 possible mechanisms of injury, such as a motor vehicle collision of at least 35 miles per hour, a bicycle accident of at least 18 miles per hour, or a fall of more than 10 feet.

Required vital signs included a respiratory rate between 10 and 30 breaths per minute, an oxygen saturation rate of less than 90%, a heart rate less than 50 beats per minute or greater than 120 beats per minute, a Glasgow Coma Score less than 14, or pupil dilated or nonreactive.

The range of injuries included an obvious fracture of 2 or more long bones; suspected spinal cord injury; crush injury or limp amputation; penetrating injuries to the head, neck, torso, or groin; or burns to more than 20% of the body. Emergency department physicians also had the discretionary power to order CT pan-scans on the basis of their direct clinical examination.

The before-and-after study format confirmed that conversion to pan-scanning with a 64-detector CT system significantly increased the likelihood that a severely injured patient would be exposed to more than 20 mSv of ionizing radiation during initial injury assessment. About 12% of trauma patients were exposed to at least 20 mSv from conventional imaging before pan-scan implementation; 20% exceeded that threshold after the protocol was introduced.

Moreover, a multivariate analysis revealed that the odds of a high radiation dose after the introduction of CT pan-scanning were similar for varying patient age and injury severity.

"We basically increased radiation exposure across the board," Dr. Asha told Medscape Medical News.


Finding Raises Concern


This finding raises concern, according to Dr. Asha, because the protocol was designed to discourage the use of pan-scans for younger patients who are relatively more susceptible to the long-term effects of radiation. It was also geared toward encouraging the scan's use for more severely injured patients. Neither desired pattern emerged from the trial.

The diagnostic yield from pan-scans was also discouraging. Dr. Asha and colleagues identified slightly more incidences of missed injuries before pan-scan implementation than after. Six patients had missed head, neck, or torso injury (0.9%) before introduction, and 4 patients with such trauma (0.6%) were missed afterward.

In an accompanying editorial published online February 8 and in the February 2012 print issue of Emergency Medicine Australasia, Dirk Stengel, MD, PhD, director of the Center for Clinical Research at the Unfallkrankenhaus Trauma Center, Berlin, Germany, writes that the results cast doubt about whether multidetector CT technology can minimize radiation exposure while increasing the diagnostic yield.

According to Dr. Stengel, the findings suggest that pan-scanning may be 26 times as likely to harm patients in the long run as to immediately help them in the acute care setting. His conclusions are based on the increased probability a trauma patient will be exposed to at least 20 mSv from a pan-scan, and the protocol's limited ability to improve injury detection.

Possibly Little Effect on Outcomes

Results from an another study that was described in a letter to the editor also published online February 8 and in the February 2012 print issue of Emergency Medicine Australasia by radiologist Ian Cowan, MD, from the Radiology Department, Christchurch Hospital, New Zealand, and colleagues suggest pan-spanning has little effect on clinical outcomes when it does detect occult injuries.

The protocol was thought not to be indicated for 88 of 137 trauma patients. It actually uncovered occult injuries in 20% (18/88) of the patients, but the injuries were panel adjudicated as clinically significant for only 3.4% (3/88) of the patients, the authors write.

Dr. Asha's findings underscore the risk for overusing CT pan-scan, said Carlo L. Rosen, MD, vice chair for emergency medicine education at Beth Israel Deaconess Medical Center in Boston, Massachusetts.

"The trick with pan-scanning is to really think carefully about which patients should receive it, and to not necessarily make it an automatic order for all trauma patients who qualify for a major mechanism criteria," he told Medscape Medical News.

Despite exposing patients to high level of radiation, pan-scans still meet the emergency department physicians' need for speed in assessing suspected multitrauma patients for major, life-threatening, and limb-threatening injuries.

"The nice thing about pan-scans is you get a field of view covering the head to the pelvis very rapidly in a systematic fashion," Dr. Rosen said.

For Dr. Asha, the results should serve as warning for the emergency department physician against ordering pan-scans for lower-risk patients, especially ones who only meet the criteria by mechanism.

"I think we really need to reconsider [pan-scanning] that group of patients," he said.


By James Rice, Medscape
Reviewed / Posted by: Scott W. Yates, MD, MBA, MS, FAC

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