H/T Daring Fireball, from MSNBC Chance of Dying From Airport Backscatter Radiation About the Same as Chance of Getting Killed by Terrorists
"Peter Rez, a physics professor at Arizona State University in Tempe, did his own calculations and found the exposure to be about one-fiftieth to one-hundredth the amount of a standard chest X-ray. He calculated the risk of getting cancer from a single scan at about 1 in 30 million, "which puts it somewhat less than being killed by being struck by lightning in any one year," he told me.
While the risk of getting a fatal cancer from the screening is minuscule, it's about equal to the probability that an airplane will get blown up by a terrorist, he added. "So my view is there is not a case to be made for deploying them to prevent such a low probability event.""