X-Ray scans are just russian roulette. It is legtime to imagine radiation like a particle (also like waves, both models are legitim, see wave-particle duality). To get cancer it is necessary that this particle hits your cell in a certain way, such the cell will malfunction. The intensities of x-rays are just the amount of this particles.
There is not really a difference between radiation at medical scans and the background radiation. This is just an extra opportunity to get cancer.
Also remember, if you get older, the chance to get cancer by radiation is less, because your cell division slows down.
