Eh, for viral infections, a chest X-ray is usually not necessary; for bacterial TB and SOME pneumonia, it's needed, but viral? I'd steer clear if I were you.

Cannabis doesn't have any known links to lung cancer; its effects seem to be almost protective for the lungs. There might be a minor bit of barely perceptible difference (I don't want to say damage because at the rate you're smoking, there isn't likely to be any perceivable damage) but if anything does show up, the radiologist's report won't mention anything about smoking (cigarettes or weed). It's up to your own doctor to look at your patient history (what you have told him-or not told him- about your smoking habits) and decide what it looks like. I work in healthcare- you've really got nothing to worry about as far as your dad finding out.

Feel better!