Could radiation from mobile phones can cause brain tumor 10 or 20 years later? what about a ct scan its much more radiation?

No and probably no: Cell phones don't cause brain tumors. There's no biological basis, it's not the kind of radiation that mutates genes, the ongoing talk is driven by politicians, and the studies are such junk that one even had significantly more tumors on the opposite side. Ct scans may make a tiny contribution to glioma incidence but there's no proving in an individual case.