One thing you will find during this process is that most of the people you know or have met in your daily life have never had radiation to the head and neck...however they will be quick to add their opinion on how to handle it.

Last I checked, Oil of Cloves mouthwash isn't standard in our treatment protocol, however I'd have your father talk to his "medical team" on how to handle the physical discomfort he's experiencing. This will probably cut down the chances of infection as well and probably his pain to boot.