this chart makes it seem like the stuff we're worried about - x-rays, CT scans, etc. - give us only low dosages of radiation compared to typical background radiation that we're all exposed to, and much lower dosages compares to what radiation workers experience every year.

but what i want to know is, does radiation do its damage gradually over time, or is it more like a gamble with every scan you have? for example, an x-ray is apparently not very dangerous on average, but is it possible that you're unlucky and end up with cancer from a single chest x-ray?