Algorithm May Reduce CT Radiation Exposure in Patients With Suspected Pulmonary Embolism

Laurie Barclay, MD

January 21, 2010

January 21, 2010 — An educational intervention and algorithm may reduce computed tomography (CT) radiation exposure in patients with suspected pulmonary embolism (PE), according to the results of a study reported in the February issue of the American Journal of Roentgenology.

"Recently, there has been a rise in physician and public awareness of radiation exposure in diagnostic radiology," write Evan G. Stein, MD, PhD, from Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, New York, and colleagues.

"In the 1980s and early 1990s, ventilation–perfusion (V/Q) scanning was the main imaging technique for the detection of [PE]. However, with the increasing availability of CT pulmonary angiography (CTPA), there has been a rapid increase in the use of this technique for imaging patients with suspected PE and a concomitant decrease in the use of V/Q scanning."

The study goal was to determine whether an educational intervention could reduce radiation exposure for patients with suspected PE by safely increasing the use of V/Q scanning and decreasing the use of CTPA.

"The total effective radiation dose from CTPA is approximately five times greater than that from V/Q scanning, and the dose is 20 – 40 times greater to the female breast," senior author Linda B. Haramati, MD, MS, said in a news release. "Most physicians are not aware of these differences."

In December 2006 and January 2007, collaborative educational seminars for the radiology, nuclear medicine, and emergency medicine departments addressed the radiation dose and accuracies of V/Q scanning and CTPA for diagnosing PE.

These seminars also presented an imaging algorithm designed to reduce radiation exposure. Emergency department patients with a clinical suspicion of PE underwent chest radiography; if the results of the radiography were normal, V/Q scanning was recommended, otherwise CTPA was recommended. Before and after the intervention, the number and results of CTPA and V/Q scanning were recorded retrospectively, and mean radiation effective dose was calculated. False-negative results were defined as subsequent thromboembolism occurring within 90 days.

The number of CTPA tests decreased from 1234 in 2006 to 920 in 2007. During the same time period, the number of V/Q scans increased from 745 in 2006 to 1216 in 2007, and the mean effective radiation dose decreased by 20%, from 8.0 mSv in 2006 to 6.4 mSv in 2007 (P < .0001).

In 2006, patients who underwent CTPA and V/Q scanning were of similar age, whereas in 2007, patients who underwent V/Q scanning were significantly younger. The false-negative rate for CTPA and V/Q scanning was not significantly different in 2006 vs 2007 (range, 0.8 - 1.2%).

"The practice patterns of physicians changed in response to an educational intervention, resulting in a reduction in radiation exposure to emergency department patients with suspected PE without compromising patient safety," the study authors write. "Even though the 24-hour coverage provided by our nuclear medicine department is not widely available in other institutions, this radiation-reducing algorithm can be used at any institution during normal working hours."

Limitations of this study include its retrospective design, lack of requirement for objective clinical assessment and D-dimer before imaging, possible underestimation of recurrent thromboembolic disease, and modeling rather than measurement of radiation exposure for both CTPA and V/Q scanning.

"Our results show the success of this approach in the real-world setting of a large urban academic medical center," the study authors conclude. "In fact, our emergency department has become interested in further reducing patient radiation exposure and has recently instituted radiation reduction measures for other diagnoses, such as renal colic and hydrocephalus."

The study authors have disclosed no relevant financial relationships.

Am J Roentgenol. 2010;194:392-397.

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