For comparison, a total body exposure of 5 rads of radiation increased the risk of cancer among survivors of the World War II atomic blasts in Hiroshima and Nagasaki. Radiation exposure from medical procedures can vary according to the different machines used across the nation. When most people think of nuclear radiation, they think of atom bombs and fallout, not medical tests. Yet more patients are exposed to radiation from CT scans than any other source, says physicist Fred Mettler of the University of New Mexico. Each scan delivers 2 to 3 rads of radiation.
More energy is needed to penetrate thicker regions of the body than thinner ones.
But most CT scans are designed to automatically deliver the amount of radiation needed to penetrate thick regions of the body. Mettler notes that CT scans have become an essential tool of medical practice, essential for diagnosing cancer, traumatic injuries in emergency rooms and other potentially life-threatening conditions. Surgeons love it, but they have to realize this is a very high-dose procedure for diagnosis. But you're not going to find breast cancer with a CT scan. It's nowhere as sensitive as a mammogram, and the dose is 10 to 15 times higher.