Well, you'd be in the same boat as any other student who doesn't get into to his or her graduate school of choice... in which case it would mean that you either apply again the next year (presumably after doing something to strengthen your application) or you move on to something else.
If you're still interested in the field you might want to look into becoming a radiation therapist or dosimetrist, or perhaps getting involved in the technical side of sales or promotions with one of the larger commercial medical devices companies like Phillips. Otherwise you could look at the skills that you've picked up with your coursework and figure out how to market yourself with those - there are a lot of threads around here with advice on how to do that.