Image Gently

If Google led you here thinking this was a post about a lost sequel to Douglas Adams' holistic detective, turn back! Instead, it concerns a widespread movement to reduce radiation dosage in children.

A recent article by Brenner and Hall raised important concerns about safety in patients undergoing computed tomography (CT).

Brenner, D.J., Hall, E.J. (2007). Computed Tomography -- An Increasing Source of Radiation Exposure. New England Journal of Medicine, 357(22), 2277-2284. DOI: 10.1056/NEJMra072149

This paper is aimed primarily at non-radiologists. The authors give a nice review of CT, the radiation dose from CT scans, the biological effects of low doses of ionizing radiation and the cancer risks associated with CT scans.

The authors raise particular concern for pediatric CT use, which has increased sharply since 1990. One factor leading to this increased CT usage in children is the growing adoption of rapid multi-detector CT machines. Prior to the current generation of scanners, most children's imaging was performed under sedation. These speedy new MDCT units can complete an entire study in as little as one second, obviating the need for sedation in the majority of cases.


Most of the concern about radiation dose centers around cancer risk. Estimating this risk is not straightforward. As the authors point out:

No large-scale epidemiologic studies of the cancer risks associated with CT scans have been reported.

Therefore, estimates of the potential cancer risk from CT (and other diagnostic imaging procedures) are based upon studies of 25,000 Japanese atomic bomb survivors and 400,000 radiation workers in the nuclear industry. These studies show a significant increase in the overall cancer risk for radiation exposures in the ballpark of a patient receiving multiple CT scans.

The situation is even clearer for children, who are at greater risk than adults from a given dose of radiation, both because they are inherently more radiosensitive and because they have more remaining years of life during which a radiation-induced cancer could develop.

So far, the authors haven't presented anything too controversial. However, some might find one of their next statements a bit alarming:

On the basis of such risk estimates and data on CT use from 1991 through 1996, it has been estimated that about 0.4% of all cancers in the United States may be attributable to the radiation from CT studies. By adjusting this estimate for current CT use, this estimate might now be in the range of 1.5 to 2.0%.

They conclude:

Although the risks for any one person are not large, the increasing exposure to radiation in the population may be a public health issue in the future.

At this point, I'd like to add a bit of perspective -- a certain amount of radiation exposure is unavoidable. The U. S. Centers for Disease Control estimate that the average dose per person from natural background radiation in the United States is about 3 millisieverts (mSv) per person per year (largely from radon gas).


To put this in further perspective, the additional radiation dosage one gets from a roundtrip airplane flight from New York to Los Angeles is about 0.03 mSv. Doses received from a chest radiograph, an adult abdominal CT and a neonatal abdominal CT are respectively about .1 mSv, 10 mSv and 20 mSv.

Among these exposures, CT certainly stands out, particularly if a given patient needs to undergo several CT's as part of their care.

So, how are radiologists reacting to this study? Quite seriously, as summarized recently by Goske, et al.:

Goske, M.J., Applegate, K.E., Boylan, J., Butler, P.F., Callahan, M.J., Coley, B.D., Farley, S., Frush, D.P., Hernanz-Schulman, M., Jaramillo, D., Johnson, N.D., Kaste, S.C., Morrison, G., Strauss, K.J., Tuggle, N. (2008). The Image Gently Campaign: Working Together to Change Practice. American Journal of Roentgenology, 190(2), 273-274. DOI: 10.2214/AJR.07.3526

There may be disagreement within the medical community about the accuracy of the risk models or the degree to which the risks of radiation were emphasized by the authors. These arguments will not be settled in the near term. However, one fact is indisputable: We must continue our efforts to do a better job of reducing radiation dose to children if and when they need a CT scan.

Goske et al review the ALARA principle (as low as reasonably achievable) and describe recent work by the Alliance for Radiation Safety in Pediatric Imaging, an alliance of 13 major professional organizations. The Image Gently Campaign program by the Alliance is of particular interest.

"One size does not fit all" summarizes much of the Image Gently Campaign, which promotes 4 common sense precepts for pediatric imaging:

1. Reduce or "child-size" the amount of radiation used
2. Scan only when necessary
3. Scan only the indicated region
4. Multiphase scanning is usually not necessary in children

There is no question that CT is an extremely valuable diagnostic imaging tool in both adults and children. It has also been demonstrated quite well that the radiation dose of CT can be minimized in many cases without sacrificing significant image quality. Therefore, even with radiation risks in mind, I would not personally hesitate to have any member of my family undergo a needed CT. Hopefully, the development of sensible risk-reduction programs such as the Image Gently Campaign will help to make this decision easier for other parents as well.