HI there... tongue cancer (I am assuming it is oral tongue cancer - not base of tongue - which is down the throat...) is normally treated by removing the tumor in the tongue surgically, then usually a neck dissection is added as a preventative to remove a certain number of nodes. Most drs can predict - for the most part - which nodes should be removed. This is what your father's dr. didn't do that he should have.

Radiation is very effective against HPV related BASE OF TONGUE cancer (the one that is found down his throat) But oral tongue cancer can be tricky. Radiation and chemo in this instance are usually used after surgery.

This is a moot point now as they have already done the radiation. I would first want to know if the radiation was to just his head only (just his tongue?) or if the neck was included in the spray radius. If it wasn't he could be re -radiated. However, Ideally they will remove the nodes by doing a neck dissection and wait and see if that does the trick. It's harder for radiated skin etc... to heal however, this surgedry is often done if there is a recurrence in the neck (generally called salvage surgery).

Chemo will NOT cure this cancer, he should have surgery or be re-radiated (with chemo).

He should also have a chest CT to see if there is anything in his lungs as this is where the cancer likes to travel to after the nodes. (not always but a lot of the time)

Hopefully, his chest is clear and they schedule him for surgery ASAP. Mind you at this point because of the radiation, there may be some hot spots on his CT or MRI.

How have they determined it's in his neck? Was it confirmed by biopsy?

best of luck.