As the imaging world continues to seek optimal dose standards across all studies, patient groups, and modalities, questions remain about the cumulative body burden of ionizing radiation over a lifetime.
But at what point does the risk of contracting cancer assumed by getting an x-ray, mammogram, or CT outweigh the potential health benefits of the same?
According to R. Edward Hendrick, PhD, even the doctors who order and review these tests couldn’t necessarily tell you.
“There are dozens and dozens of tests and each has its own relative risk,” Hendrick says. “Previous surveys that have been published show that referring physicians—for example, ER physicians who order these tests—and even radiologists who interpret a lot of these tests aren’t that familiar with the risks involved."
That’s why Hendrick, a clinical professor at the University of Colorado-Denver and fellow at the American College of Radiology, developed the Adult Dose-Risk Smartcard, a quick reference guide for physicians that helps couch the risks of various imaging studies in terms that patients and their providers can understand.
Hendrick’s project was published in the current issue of the Journal of the American College of Radiology.
“It gives sort of a worst-case estimate of risk for all of these procedures,” Hendrick says. “We’re not trying to take this card and estimate that so many thousand people will die from these exams. The point is to give an idea of the relative risks of these exams as far as cancer inductions as compared to their benefit.”
The mathematical model behind the Adult Dose-Risk Smartcard assumes “a linear, no-threshold model between risk and radiation dose,” Hendricks says. Therefore, doubling any dose, no matter how low, doubles a patient’s risk of cancer induction.
“It’s saying a) there’s no threshold below which there is no likelihood of causing a cancer, and b) that the relationship between dose and risk is linear,” he says.
The Smartcard is meant to be used on an exam-by-exam basis, and calculates whole-body radiation doses in millisieverts (mSv) based on gender- and age-averaged estimates of adults aged 18 to 64. Best of all, it frames the level of comparative risk of developing cancer from undergoing an individual imaging study against, say, a debilitating bicycle accident.
“If you’re referring a 50 year-old woman for mammography, there’s less than a one in 125,000 chance of [that scan] causing breast cancer as compared with her one in eight lifetime chance of contracting breast cancer and her one in 40 chance of dying from breast cancer,” Hendrick says.
“That’s equivalent to your risk of being killed by lightning,” he says. “The radiation you’re going to get from a screening mammogram is about equal to the cancer risk you have from two months of natural background radiation.”
In addition to the Smartcard, Hendrick and his team have developed an accompanying PowerPoint presentation; they also hosted a conference about radiation dose and risks, “the aim of which was to encourage people to do everything they can to minimize risks and to correctly communicate what the risks are,” he says.
“The people who work with radiation on a regular basis liked it a lot because it puts things in concrete terms that are pretty easy to understand,” Hendrick says.