A 2009 report, “Ionizing Radiation Exposure of the Population of the United States,” found that Americans were exposed to seven times as much ionizing radiation from medical procedures than they were in the 1980s. (www.ncrponline.org.) A large part of this increased radiation has come from the use of computed tomography. About three million CTs were done in the United States in 1980, and more than 85 million were being performed annually by 2010. (www.imvinfo.com.) The rate of increase each year seems to be slowing, but purported breakthroughs such as virtual colonoscopy, coronary CT angiograms, and peace-of-mind whole body scans threaten to increase this radiation exposure even more, perhaps even before these procedures have clear indications or established benefit.
Approaches to limit diagnostic imaging with ionizing radiation in our daily practice should always be considered, especially in more vulnerable populations such as children. Children's DNA is particularly sensitive to damage from ionizing radiation because of more rapid cell turnover. Unlike elderly patients, children will live for many decades after their CT radiation exposure, increasing the chance that damaged DNA will eventually express itself as a malignancy.
Steadfast efforts have been made to limit medical imaging with ionizing radiation whenever possible, but CTs are still clearly indicated and unavoidable in many cases. Investigators are now looking at other means to reduce radiation exposure even when a CT is absolutely necessary.
Low-Dose Abdominal CT for Evaluating Suspected Appendicitis
Kim K, Kim YH, et al
N Engl J Med
This trial took place at a single institution in South Korea. Emergency department patients 15 to 44 who had a CT ordered to rule out appendicitis by their emergency physician were randomized to receive a standard-dose radiation CT or a low-dose radiation CT protocol. Obvious differences in image quality, treating physicians, surgeons, and radiologists could not be blinded to the assigned study arm.
Patients were reasonably excluded from the study if they had received prior cross-sectional imaging for their acute presentation, had contraindications to IV contrast, or had already had an appendectomy. When surgical specimens were obtained, a pathologist blinded to the study arm was used to determine the final diagnosis. Independent study assessors also blinded to study arm used medical records and phone interviews to establish the final diagnosis in nonsurgical cases.
The primary endpoint in this study was the percentage of negative appendectomies, and it was not different in the two groups: 3.5 percent low-dose CT vs. 3.2 percent standard-dose CT; difference 0.3 percent (95% CI, -3.8 to 4.6). A secondary endpoint of perforation rate was also not statistically significant: 26.5 percent low-dose CT vs. 23.3 percent standard-dose CT (p=0.46). A slight increase, however, was seen in the need for secondary imaging in the study group: 3.2 percent low-dose CT vs. 1.6 percent standard-dose CT (p=0.09).
The study concluded that low-dose CT was not inferior to standard dose CT for ruling out appendicitis. The implications here are tremendous given that the median radiation dose-length product in the low-dose group (116 mGy·cm) was almost 80 percent less than the standard-dose group (521 mGy·cm).
Unfortunately, some significant limitations potentially affect this study's applicability to other patients and other environments. The study used a small group of specially trained radiologists not blinded to the study arm who were extremely comfortable and confident in their ability to read low-dose CT images. Low-dose CT images have less detailed images and more artifact in them, which an untrained radiologist might be more likely to misinterpret.
That means more unnecessary operations or more delayed diagnoses could easily overshadow any potential benefits from lowering the radiation dose. Clearly, this study involved emergency physicians, radiologists, and consulting surgeons comfortable with the low-dose CT protocol, but a similar alignment of goals might be more difficult to achieve in a non-research environment. Physicians practicing in litigious environments like the United States also might be more inclined to declare the low-dose images unreadable and insist on repeat images using standard dose radiation “just to be certain.” Patients in this situation might have the most to lose, ultimately enduring the highest radiation exposure, a repeat contrast load, and a delay in diagnosis.
This study opens the door for many future areas of research despite these limitations, and should stimulate further discussion about methods to lower radiation exposure for our patients. Perhaps similar changes can be made for other frequent indications for CT like head trauma or flank pain.
The single best way for emergency physicians to limit exposing patients to ionizing radiation is by making a conscious effort to avoid unnecessary CT in the first place. Sometimes other options do not exist and ionizing radiation is indeed the best option, but at least we can now consider turning down the dial.
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* Read an abstract of the New England Journal of Medicine article at http://bit.ly/Kwt7GQ.
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© 2012 Lippincott Williams & Wilkins, Inc.