Rad onc: Great board scores, lots of research, get people in the specialty to say you're great. pray really really hard (tough love: it's a hard field to get into and although possible, it's not likely to happen. it's best be open minded to other things, especially early in the game)
Oncology: Is a medical subspecialty, so you'd need to get into an academic medical program. better if it's a well-regarded one! good board scores, good clinical evaluations, good letters. research helps but is not absolutely necessary at the residency application stage, although I'm sure it becomes very important for fellowship applications. the field of cancer loves its research
Nobody will ever split hairs over osteopathic schools the way people do here, so don't make the school decision a totally agonizing one. I'd avoid schools that make you do 12 weeks of family practice or surgery, but that's a very personal preference