Im not an expert, so take these comments as such.

Post-prostatectomy salvage radiation is not the quite the same as initial prostate radiation. Typically, salvage is radiating the entire pelvic bed and the lymph nodes. Its a much larger area. Precision is still critically important, as you are getting very close to the bladder and the rectum. But it is my understanding there are no gold markers like there are when radiating the prostate. All the fun side effects apply. Often, hormones are included as part of salvage if you are high risk.

The arguments for type of radiation are the same. Photon-based IMRT is precise, IGRT complements IMRT by adding targeting precision that incorporates body movement and breathing. Proton is also an option. Proton offers the same benefit as it does for initial prostate radiation - in theory, anyway - using precise pencil-beam radiation that only "activates" when it reaches the target areas, and does not impact the areas going in or coming out. However, recent studies have indicated that proton is no more effective than photon.

Keep in mind that you will have 25-39 treatments, 5 days a week, so proximity is another factor to consider.

Ultimately, those decisions are up to you and your RO. There is lots of info online on salvage.......