I wouldnt be so harsh as to suggest someone should reconsider their interest in treating cancer because they dont know what hematology is. I can easily envision someone not yet in medicine who wants to go into it in order to treat cancer, and so who may not know what hematology is. I know I got into the field to treat cancer, but not hematological issues per se.
I wont bother talking about surgical or medical oncology (hematology-oncology) as they aren't my field and the folks in those fields can enlighten you.
Radiation Oncology is the treatment of cancer (and some benign conditions) with the use of ionizing radiation. The radiation oncologist has a very *very* deep and wide fund of knowledge on cancer, anatomy, imaging, and procedural issues; the technical aspect is indeed very procedural in nature in that your treatment plan will consider things like the given case's stage, surgery, extent of disease, extent of resection (if any) and proximity of normal tissues. To name a few relevant issues. Like a surgeon who must approach a case oriented in space, so too do radiation oncologists who develop three dimentional thinking. Technology is rapid and evolves fast. An understand of medical physics and radiobiology is gained during residency. We work with patients generally over a 5-8 week period of treatment (shorter usually in palliative cases) and then see them in the long term for follow-up. Its very satisfying. People can specialize in organ systems (ie prostate or breast), procedures (radiosurgery or brachytherapy) or populations (peds, gyne).
It's great!