?? i don't understand the catheter, or any other prep, also don't understand the need for a DRE, but maybe that's just my experience...
i got to the office, with no preparations at all. dude came over and gave me a liter of stuff, cooled down, and i drank it in the waiting room...the coolness of the solution, plus nerves, got me pretty shaky chilled by the end of the bottle....the solution fills your bladder, plus it has a chemical to make the bladder stand out more in the CT scan
the dude laid me down on the CT scan table. and then they do two things to help with your positioning. they make a rough foamy mold that holds your feet still, and prick you in 4 places (these make permanent dot "tatoos"). when they position you in all the next SRT procedures, they can put your feet in the molds, and line your tattos up with the laser scanners coming from the ceiling and walls, and they feel confident that you are in exactly the same orientation, time after time.
you then go through a CT scan, and the rad doctors use that 3D information to set up the radiation machine to blast where the prostate used to be, and try to hit where the cancerous cells would be, and minimize damage to bladder and rectum.
absolutely no pain or discomfort, except full bladder, nerves, and a guy poking you real quick with a point, to make your tatoos. you leave there thinking: what was i worrying about?? (oh, yeah, cancer....)
i don't like wishing you LUCK, but i'll join you in wishing/hoping that the doctors are able to knock it all down and you have many years of peaceful, low PSA's !
bob