As with any radiation risk, it's really a matter of minimizing exposure. Getting an x-ray isn't that bad because you aren't...or at least shouldn't be getting an x-ray all the time. It's a spike in your exposure but it shouldn't be happening often enough to start creating cumulative effects. And that's really the main issue of long term manned space flight. Can we keep the levels of exposure low enough to not have any detrimental cumulative effects.
"Don't confuse facts with reality."
-Robert D. Ballard