Hi Claire,
That list at Kate's link has lots of good questions.
I am amused at the idea of asking what version of treatment planning software they use; what sort of answer might you get? "Oh, we are using Microsoft Radiation 2007", or perhaps something like "RADFactor 5.6". Um, okay.
I'm curious which questions you consider are the obvious ones. I think my advice would be to try and ask the questions that you will care about the most later, as you think it all over and try to make a decision. Things like: Is this going to work? Have you done this before? What sort of post-treatment symptoms will I get, and for how long? Can I drive home, or should someone pick me up?
Technical questions may not help much, if you are not prepared to make sense of the answers. The practical questions are the ones that bring it home to you. Can you picture yourself doing this treatment? What would it take to make you feel it is a good choice, and that you are comfortable with it?
Steve