I had the classic silver/mercury amalgam fillings throughout my mouth throughout the entire first 72GY of radiation. My oconological dentist did recommend that I wear the flouride trays during treatment. Why: he was concerned about potential heating or redirected radiation from the fillings. It gave me a sense of comfort but perhaps that was just because it did keep my tongue off the extensive fillings and the teeth themselves. I know when I posted this earlier that the "science" behind that was questioned. The issue was moot to me by then.
I do know there was extensive artifact splatters on my original CT that discovered the cancer which was attributed to my metal fillings in the radiologist's report.
Months after TX was over, I did get four crowns and three root canals (including a cracked wisdom tooth) and the new fillings are plastic and didn't need HBO or anything special.
So bottom line: my metal fillings didn't negatively impact my TX and I did wear my flouride trays during radiation TX with certainly no ill effects or discomfort.