Bugging me: cancer risks of smoking and x-rays

[bktheirregular]

Having been through a large battery of medical tests sparked by a legally mandated chest X-ray, and having had my body photographed by X-rays a number of times in the last month, I'm trying to remember: didn't someone, somewhere, run a comparison between a chest X-ray and X number of cigarettes, concerning the likelihood of causing cancer?

I suppose I'm getting morbid, but I keep wondering how much time got shaved off my life from all the zapping. (And how many cigarettes I just smoked, which is depressing considering I'm a rather vehement non-smoker...)