Here's wishing your dad (and you!) well.
Knowing the relationship (all too well) between MEEI and MGH (heck, even on the same properties), I am surprised that they would note the Proton, even vs. the FSR at Brigham/Womans for your dad's facial neuroma. We have come to learn that if there are certain "financial considerations" of one recommendation, then my suggestion is to carefully view all options in Boston (Metro). Being here also here in town, there are many options:
Barker/McKenna at MGH (as you know, some of the best surgeons in town, as well as Dr. Peter Black at Brigham Woman's)
GammaKnife at Tufts, as well as in Providence (Dr. Noren)
Cyberknife at Beth Israel (more than happy to discuss with you if you want, as I had my treatment there over 5 mos ago)
FSR (Novalis) at B/W
Proton at MGH
We live in a terrific medical mecca, as you know and since many of these facilities are all in one way or another affilliated with Harvard Medical School, the expertise of the treating professionals will be key.
Hang in there. You will read many opinions, thoughts and thought processing in decision making. For your dad, if you all just take a deep breath and take each protocol research step by step, you all will be fine!