Can you provide additional information? Was the tumor removal complete, radical subtotal, or subtotal? Or if not certain of how the removal was characterized, was tumor left behind? In my case, some slivers were left on the facial nerve and brain stem as the tumor was adhesive in those places and there was no plane to dissect along. The sliver on the brain stem died and and is no longer MRI enhancing, probably because it had no blood supply. The facial nerve remnant did regrow 5 years later and I had GK in Oct 2016
My surgeon in 2011 said it was more probable than not that growth would recur, but advised against GK immediately on the remnant because regrowth was not guaranteed, nor could it be predicted when it may happen. No treatment is 100% safe, so he advised waiting until it was necessary. As it turned out I did develop complications from the GK which is rare, but not not unheard of. On Jan 24th this year I developed Grade 4 facial paralysis which has improved some in the past months, probably grade 3 at this point as I can now close my affected eye with little effort. Other symptoms remain. I also have tumor and brain swelling with edema in the brain adjacent to the tumor.
My personal preference was to wait until I knew I had regrowth before undergoing more treatment, your particular situation may be different. Did your surgeons at USC discuss GK?