Since your father is not having surgery, adding chemo to the radiation seems the wisest course. Yeah it is a pain to sit in the chair those hours and the IV insertions don't always go as smoothly as they should but as I've posted before:
In for a nickel, in for a dime.
My doctors did not use the term boost, but rather described it as an alternative attack on the cancer that also enhances the efficacy of the radiation.
I found the radiation had the most negative and permanent effects so since he is having that, go for the chemo.
Keep the Faith
Charm