Purpose. The objective of this study was to determine the estimated effective radiation dose of pulmonary CT angiography (CTA) for suspected pulmonary embolism (PE) contributing to total medical radiation exposure over a 4-year period. Materials and Methods. This investigation retrospectively reviewed 300 patients who presented to the emergency department and received a pulmonary CTA scan for suspected PE. We evaluated these patients' electronic medical record to determine their estimated radiation exposure to CT scans during the following four years. Using DLP to E conversion coefficients, we calculated the cumulative effective radiation dose each subject received. Results. A total of 900 CT scans were reviewed in this study. Pulmonary CTA delivered an average effective radiation dose of 10.7 ± 2.5？mSv and accounted for approximately 65% of subjects' 4-year cumulative medical radiation dose. Only 6.3% of subjects had a positive acute PE according to their radiology report. Conclusion. Pulmonary CTA accounted for the majority of subjects’ medically related effective radiation dose over a 4-year period. With only a minority of subjects having positive findings for acute PE, increased efforts should be made to clinically assess pretest probability before the consideration of imaging. 1. Introduction Pulmonary embolism (PE) is a significant cause of morbidity and mortality. In the United States, PE affects nearly 600,000 individuals and may result in approximately 100,000 deaths per year [1]. Presently, computed tomography (CT) angiography (CTA) has largely replaced the ventilation/perfusion (V/Q) lung scan and catheter pulmonary angiography for the diagnosis of PE due to its accessibility, reliability, and noninvasiveness [2–5]. However, only a minority of CTA scans ordered for suspected PE yield positive findings [1, 5–7]. The PIOPED II multicenter trial has also shown that this test is not as sensitive or specific as previously reported [8]. The health risks associated with medical imaging may increase as the cumulative radiation dose accumulates over a lifetime. Certain factors such as patient age, gender, and fractionation of radiation impact the potential injury from radiographic imaging. A CTA scan delivers an effective radiation dose of approximately 10？mSv [9]. Several controversial studies have attempted to estimate the cumulative carcinogenic risk from medical imaging. Exposure to ionizing radiation from CT has been estimated to be responsible for as many as 29,000 malignancies in the United States annually [10]. Brenner et al. report that a
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