Recently, some doctors and radiation biologists have expressed concern about the increase in the number of CT scans given to the general public and the increased dose that results. A 2007 paper by David Brenner and Eric Hall, two very highly respected experts in the biological effects of radiation, sparked a great deal of discussion in the media. Brenner and Hall used radiation risk data and applied it to the general public. They calculated that as much as 1.5 to 2 percent of cancers within the US may be due to the radiation from CT scans. To try and respond to those concerns and educate the public, three diagnostic radiology residents have created a website called X-Ray Risk that will tell you the added risk of cancer from various medical imaging procedures.
Estimating the risks due to low levels of radiation is a very difficult thing to do. Obviously, we cannot irradiate a human being to measure his or her increased chance of cancer, and animal models will only carry us so far. Most of our data comes from survivors of Hiroshima and Nagasaki and early radiation workers who were exposed to a significant dose. This data is summarized and turned into radiation risk parameters by a group called the Committee to Assess Health Risks From Exposure to Low Levels of Ionizing Radiation, a committee of the National Research Council. Their latest report, the Biological Effects of Ionizing Radiation (BEIR) VII, was published in 2005 and increased the previously estimated risk from radiation.
The radiation safety community is still coming to terms with the results of that study. The general consensus that is forming is that while the risk from diagnostic scans like CT is low, there is still some toxicity associated with it. Therefore, scans should only be ordered when medically necessary. There is an ongoing effort to educate physicians and the public to the risks of medical scans, which are often overprescribed as a result of defensive medicine. Because children can be most sensitive to the effects of radiation, a campaign called Image Gently has been formed. That being said, there is no doubt that CT imaging is of immense value in the diagnosis of patient disease and trauma, and the risks for most scans are well outweighed by the benefits, which can be literally life saving.
Hopefully, patients can use the information from X-Ray Risks to understand that the risk from a medically indicated scan is low compared to the benefits, and physicians can use it to determine whether the risk to the patient from a scan is justified.
