Your dads situation sounds like mine. I had three of the best places in the US tell me the same thing with my tumor just below the ear and wrapped around the corotid artety. I found a place that does Stereotactic body radiation therapy SBRT. This allows them to hit the cancer with one more round of radiation (possibly 2). The results are mixed but we have had a few on this board who have had success with it and a few not.

It was successful for my last time but they nissed a spot so I am going in for one more set of treatments.

This regime is 5 teatments over ten days so not as bad as IMRT.

I would try to find a facitlity in Canada theat offers Stereotactic radiation and get them your fathers records. Ther may be a chance yet.