I'm Aliza, a BC patient and the site's unofficial resident Medical Librarian. I answer questions - usually non medical ones*, provide referrals to doctors, hospitals, institutions, agencies, websites, books, media, etc. I also do research when requested or required. (*Librarians tend to shy away from answering medical questions even if we know the answers because to do so is practicing medicine sans license which, of course, is illegal). I am however, allowed to speak from my own experience as a Cancer patient as well as those of my family and friends (we number too many).
I think perhaps in this situation that the best thing to do is contact the radiation oncologist asap and advise him of your Dad's condition and let him make him make the call of whether to delay treatment or not based on this "superbug". It just might be that waiting a week till he's over it might make a difference (or not). I'm not an oncologist -I'm a Librarian with a Master's degree...;) that's why I'm suggesting you call her/him.
I hope your Dad feels better soon from what ails him and hope for the best possible outcome from his radiation treatments, no matter when he starts them.
If there's anything I can do for you, please don't hesitate to ask. Contact me here or email me offsite.