CT Scanning of the Paranasal Sinuses: Indications, Utilization, and Radiation Risks

Dr. Chandra noted that CT loosely correlates with symptom severity, it probably correlates with response to medical treatment (but he questioned whether serial CTs change management), and CT correlates poorly with surgical outcomes. As for polyposis, mucocele, and AFS, he said, initial CT helps define disease extent for surgical planning and patient counseling and a follow-up CT might be needed to confirm the response to medication if surgery is to be deferred.

Radiation Exposure Risk

Rounding up the panel presentation with a discussion of radiation exposure risk was Ramon E. Figueroa, MD, Professor and Chief of the Neuroradiology Service at Medical College of Georgia in Augusta. Noting a 10-fold increase in the annual number of CT examinations in the United States in less than two decades, he said the numbers have gone from 3.6 million a year to 33 million a year. Of these, 2.7 million CT studies per year are performed on children, who are more susceptible to radiation.

Although CT accounts for only 11% of X-ray-based exams in the United States, it delivers two-thirds of the total radiation dose associated with medical imaging, Dr. Figueroa said. The impact is much greater in the US than the rest of the world.

Noting raised concerns about mounting radiation exposure to the general population, Dr. Figueroa called for appropriate strategies to optimize and, if possible, reduce radiation dose due to CT usage.

How can we do this? he asked. We need to look at our utilization patterns and try to establish guidelines by which we decide which examination we really need to have, and what we can get by without.

The goal, he said, is to acquire diagnostic quality images by using radiation doses that are reduced to the lowest levels possible. Called as low as reasonably achievable (ALARA), this concept is the responsibility of radiologists, radiologic technologists, and all supervising physicians, he commented.

There are two types of radiation exposure risk, Dr. Figueroa said:

• Direct effect risks-typically radiation producing direct cell injury or death due to radiation exposure, such as from an industrial accident
• Indirect effects-those that produce a subclinical genetic injury and result in cumulative increased risk of cancer, with the probability of increased risk depending on the amount of absorbed radiation dose.

We can impact the probability of genetic injury that accumulates in our patient population, Dr. Figueroa said.

Utilizing a dose comparison chart, he illustrated how one typical-dose chest X-ray provides the equivalent dose of 2.4 days of radiation from natural background sources that normally occur. For one head CT, with a typical dose of 2 mSv, the equivalent dose from natural background radiation is 243 days. And, there are techniques in our medical imaging that even go beyond that, he said.