Ok, so since there seem to be very few actual rad-onc jokes, I guess I can tell my one general doctor joke. We can make the patient a cancer patient if you want.
So this doctor is seeing a 95 year-old lady in the office when she, rather embarrassed, brings up a problem she has been having.
"Doc, I just have so much gas, it's simply unbelieveable. I'm just farting ALL THE TIME. Fortunately they are always silent and they don't stink, but I'm worried just by the sheer frequency of it. Why, since we've been here talking I must have farted over a dozen times."
The doctor scratches his chin for a minute and says, "I think I can help." He writes her a prescription and instructs her to come back in a week to see if she notices any difference.
She comes back the following week and says, in exasperation, "Doc, that prescription you gave me just made things much worse! I'm still farting just as much as before, but now they smell TERRIBLE!"
The doctor smiles and says to her, "Okay, now that we've cleared up your sinuses, let's see what we can do about your hearing."