This probably does not apply in your father's case, but my son had a very bad reaction to medication after starting the Radiation treatments which caused his tongue to swell up and he had to go to the emergency room. They gave him Benadryl shots to counterract the swelling. Your father's surgery seems to be quite different from that of my son's and I only mention this as something to pehaps rule out and ask your doctor about in the event that medication could be contributing to the swelling.