Marni,
Just jumping out of the clear blue sky here (and without a parachute even), most RO's don't want people on any supplements, antioxidants, etc., during radiation - whether that includes HRT, I don't know. Have you mentioned this to your RO yet?

You certainly don't want to take anything that would contraindicate the radiation therapy or worse yet act as a "bolus" (effect enhancer). Even if this were true you would probably only have to suspend the HRT during the 6 weeks of treatment.

Checking with your oncologist was a wise first step as they are usually the most in tune with body chemistry issues during cancer treatment. Mine managed virtually all of my medications during treatment and constantly monitored and ordered my lab tests, scans, etc.

Be sure to find a competent medical source if you want to seek a second opinion - and stay away from internet testimonials!