Proton radiation has a few theoretic benefits over the standard photo or gamma radiation. It can limit the radiation dose to the normal tissue better and should have less long term side effects.
If a tumor is up against the optic nerve, Proton radiation can hit the tumor without hurting the optic nerve.
The downside is most brain tumors are diffuse and you need to treat a border around the tumor anyway, and it is more expensive and harder to find a facility.
More studies need to be done to prove an advantage.