hi oscar. it's good that you're starting early. i'm just about done with my interviews, and having been on 10, here's what i've encountered.
In general, radonc interviews are exhausting. As opposed to the 1 or 2 that you may have at a prelim interview, i've probably averaged around 7-8 30 minute interviews at each institution. most interviews consist of your standard questions...tell me about yourself *since i haven't read anything about you*, why radonc, what questions do you have for me, etc, etc... It is not unheard of to encounter pimping type questions, although it's rare.
You'll interview with:
1. Chairman (if they have one...)
2. Program Director
3. Physicist (or panel of physicists i.e. loyola)
4. Radiobiologist
5-X. Rad Onc Faculty
6. Residents (largely informal, but at some i.e. UC-irvine, formal interviews with residents)
Some programs will ask you to present your research, or to present a case. Be prepared.
Some programs have two days scheduled. The first day usu for an overview of the program, tour, and dinner. Highly recommended.
Hopefully you'll see a lot of the same faces. It's a tough match, but a wonderful field. Be sincere and thoughtful. Interviews count. I'm sure more people will contribute to your thread once ROL's are in. Best of luck.