The IGRT could (read could, not definitely will) cause your white blood cell count to drop, which might cause you to have some more infection issues.
My WBC dropped to almost zero for over a year after RT. I was seriously warned by my GP to stay away from groups, sick people, walk the other way if someone sneezed, no movie theaters, fly only if essential (GFMPH qualified as I saw it), etc. Now at 2 years out I am back above the minimums by a hair.
The issue is that IMRT/IGRT hits the bone marrow in your hips, which is a big WBC creation area. Mine was devastated, others have less or no problems.
I kept a bottle of levaquin in my pocket the whole time - hear a sneeze, 10 day dose. On doctor's orders, of course.