belated hello alexander.
There is so much reading its hard to imagine actually; unlike medicine and surgery which are primarily learning by doing and reading up on what you see, rad onc is extremely academic; you must not only learn the techniques, but read and master the literature on all relevant topics: gyn, cns, peds, GI, GU, breast, head and neck, lung, sarcoma, lymphoma, and some more minor things. And remember, there are many permutations of every malignancy so this adds up to a lot of information. This is what makes the boards so challenging. They love to ask about specific studies and have you use them to defend your approach to treatment-which means you've got to know the details of what was compared, who was included, what techniques were done and what the shortcomings of the articles were. Its a lot but if you dedicate yourself to study you can pass on the first go.