Soaring CT use may prompt need for long-term dose monitoring

Radiation dose concerns, long a major issue in Europe, are moving up the ladder of interest among U.S. radiologists. If you have any doubts, just look at the programs from this spring's crop of radiology meetings. They featured plenty of presentations on dose-reduction strategies, nine of which are highlighted in this issue.

Dose considerations have been a gathering storm in radiology for some time. CT has pushed radiation concerns to the forefront. Various studies have documented growing use of the modality as the number of slices and its clinical utility have increased. Our business newsletter, SCAN, reports that there were about 400 64-slice scanners sold in 2005 and, in that same year, about 210 sales of 32- and 40-slice scanners. Right now, probably 60 million CT scans are performed annually in the U.S., and that number seems destined to grow.

Vendors are aware of dose issues and have stepped up to the plate with technologies like automatic exposure control that can reduce dose without compromising image quality. And continuing research efforts such as those detailed in this issue will produce ways to reduce per-exam dose exposures even more.

But some big holes in the process remain. Principal among them is the lack of a patient continuity record that shows cumulative radiation exposure from diagnostic scans. Consider the following: A fall at four years, a soccer injury at 10, suspected appendicitis at 16, and a motorcycle crash at 21 could send one unfortunate individual to the ER four times and result in four CT scans before the age of 25.

We can't be absolutely sure that those scans will significantly boost this patient's chances of cancer later in life, but available evidence suggests we have a reason to be concerned. Most experts believe that dose is cumulative and exposure to ionizing radiation in medical settings can cause cancer. Further, the National Toxicology Program last year added x-ray and gamma radiation to its list of human carcinogens.

Even though we don't know the precise risk for this particular person, prudence suggests that we should begin tracking accumulated radiation dose in medical settings so we can at least better understand the relationship between low-dose scans and future medical consequences.

Right now that's impossible. Under our current disjointed and essentially local care system, radiation dose exposure is measured (or perhaps not) on a case-by-case basis. There are no standards for collecting it, much less aggregating it in a way that would help individual patients or groups of patients.

This type of monitoring is already an accepted fact in other settings. People with occupational exposure to ionizing radiation have long participated in registries designed to track their dose exposure. Extending this practice to those who undergo ionizing radiation medical scans would be a far greater task, but it should be considered.

At this point, we can't say that collecting this type of information would change practice patterns. Indeed, one argument against instituting such a complex program is that every scan should follow the ALARA principle-as low as reasonably achievable-and be performed only when indicated after balancing risks against benefits. But we might find that accumulated lifetime data alter the risk side of the equation and that practices would indeed change.

This information might also be used prescriptively. Suppose it was found that people with x number of head CT scans have a higher risk of thyroid cancer. This group might be periodically given ultrasound thyroid scans.

Like individual determinations for the use of CT and x-ray, the idea of lifetime radiation monitoring needs to be part of a cost (risk) benefit calculation, and it may not prove worth it. But with soaring use, this discussion needs to take place.