My situation was not exactly like your husband's, but here's my experience. After prostate surgery, I underwent 35 radiation treatments. My doctors were concerned about how the IMRT would affect my rectal fissue. Had to come prepared with a full bladder each session, (which is sort of a cruelty joke for one who just underwent a radical prostatectomy). All that is to say, yes, the doctors want to "fry" the bad cells, but walk a fine line in protecting the good stuff (which include the small intestine of course). Seems to me that your hubby's small intestine is extremely low to be a concern in that region. I'm one month past my last treatment, and dispite some relatively minor side effects, all seems well. Bets of luck to you and your hubby.
Bill in San Diego