I am currently going through the application process for Radiation Oncology residency. To answer some of the specific questions that have been raised. Radonc is a 5 year residency. A prelim year in Med, Surg, or a transitional followed by 4 years of radonc training. There are apparently fellowships available, but I don't actually know of any programs offering them. The fellowships are in peds, head & neck, brachytherapy, etc.
The work is primarily clinic based, working up new patients, developing treatment plans, which entails CT sim, designing ports, calculating isodose curves through target volumes as well as important normal structures (medical physicists do most of this). You see the patients receiving treatment and evaluate response and manage complications. There are some OR procedures involving brachytherapy. All in all it involves a little of everything which is one of the attractions. As to hours and compensation, the hours are pretty favorable with fairly benign call, as there are only a few radiation emergencies (SVC syndrome, cord compression, cervical hemorrhage). I don't know of anyone making 750k+ as one poster indicated, but most radonc docs are not impoverished. The most important thing is to base your decision on what you like to do at work rather than what your life outside of work will be like, because regardless of specialty you will spend more time working than not. Hope that helps somewhat. If you have any more questions feel free to ask.
Later.