Insurance coverage is a very complicated question. The companies provide bundles of services for specified costs. My (huge national) insurance company does not cover proton for PCa under any circumstances, period. They do cover it for a large number of other cancers that really need the precision. However, they see IGRT as being equivalent.
FDA approval means they can cover it if they want to, but there is no obligation.
You would be very surprised (possibly unpleasantly) about what policies do and do not cover. Just search for threads on ED meds and you'll find those who get nothing covered at all, many like me who get a counted number (5-8) of pills per month regardless of strength or need, and those who get enough for one a day. Then ask about costs / copays
Well, don't ask here. It will only cause a firestorm of posts.
It is no different from car insurance, but because most of us have insurance through an employer, we have a lot less choice.
But for everyone starting down the PCa road, my strongest suggestion on the insurance front is to get every pill, shot, test, and procedure pre-approved, and in writing if possible. Every single one.