How Important Is Having A Full Bladder During Radiation Treatment?

My worse nightmare happened right on the radiation table a week ago. I'd drank down two 16 oz bottles of water back-to-back (something I never normally do), encouraged by the techs, trying to ready myself for the procedure. Near 30 minutes later when I got on the table to be pre-scanned, then zapped, my bladder felt full, very full.

Right in the middle of the procedure, I had an extreme urge to "turn on the fire hose" and had to strain fiercely to control myself. Unable to control the urge any longer, I yelled out "I need help!" The three technicians doing the procedure in a different room showed up asking what the problem was. I told them and they gave me a urinal. I walked to the bathroom to empty it and returned to re-do the procedure.

The biggest thing that shocked me about the entire ordeal though, was me being told by the lead technician that my "bladder was not full." She said it in a "disappointing way," as if to say "it was not full enough to do the treatment in a proper way."

If that's the case, it may never be, given that I tend to have "low bladder capacity" that feels like it fills quickly and then wants to empty. I'm afraid the same thing's going to happen on my next round of radiation.

It's my understanding that a "full bladder" helps shield the small intestines from radiation. With this in mind, is it almost absolutely necessary to have one during the procedure?