Ok, this is getting clearer to me. So when the MRIdian system delivers the photon beams to the tumor they are then stopped upon reaching the 2mm margin? Also, is this 2mm margin established at any given point around the entire tumor via the mapping process? Then there's the subject of fiducial markers. I've read that sometimes they are used and sometimes not. One article even mentioned the use of permanent ink markers (a black Hilighter pen??) On the mskcc.org website it describes the entire nasty procedure. Sounds like a probe with a needle is inserted into the rectum and then the needle passes through the rectal wall to access the prostate to place the markers. Is this your understanding? Seems like it would make more sense to make the trip up through the perineum to avoid the chances of infection in the rectum. Then don't forget the SpaceOar hydrogel which may be given using a needle which is inserted up through the perineum. After all of this rooting around prep work will there be anything left of my prostate? Just give me a silver bullet to bite down on!!