RadOnc is essentially an outpatient speciality. There are a lot of private practice guys who either have free-standing clinics (expensive b/c of the $$ of accelerators), clinics affiliated with community hospitals, or departments in major academic medical centers (where residents/attendings are on call for a week at a time to take care of inpatient problems).
So, in a nutshell, you can work in virtually any environment you'd like after graduation. Right now, most RadOnc grads (even from the "big name" places) are going into private practice b/c of the big bucks.