@robertov I think there are some subtle issues here. First, a well done gel spacer is protective. I believe that with IMRT it makes the treatment safer. I think with Proton it makes it much safer , meaning, if the spacer has a lower quality placement there may be more risk with proton. I agree with most that the proton beam is more accurate, there is in my mind a challenge though. If it is positioned via CT , you have a highly accurate beam with a targeting system that is no better than IMRT say 4-5 mm. In your case you likely had control like Cyberknife fiducial implant feedback that would shut Proton streams off if it sensed an out of position prostate. That is not the case with 28 or 44 session proton to my knowledge. There is a 2 axis alignment prior to each treatment then no active feedback for position. My personal issues are not so bad , they have improved over time but it has caused me to explore this. I think proton has the potential to be extraordinarily accurate and is in fact gaining ground in many areas. It seems prostate treatment has a different set of variables than some other cancers. In the end it may be the premier treatment but I think it has a few iterations to go.