I went the same Viewray route as you but I'm one year behind you. My UCLA radiation oncologist, Dr. Reddy, employed the hydrogel spacer because my large prostate was pressed against the prostate (the pre-/post hydrogel images were dramatic.) I suffered zero colorectal post-radiation effects as a result. Five treatments (around 30 minutes) in 10 days was an amazing process. Excellent staff.
My gleason 9 disease has responded well by all markers and tests.
Good luck.