Hi Terry,
When I was about to start radiation, someone on this board suggested going out and trying to gain 10-15 pounds before treatments begin. It was very good advice which I followed. I still lost 45 pounds but that 15 pound cushion made a difference.
While everyone has different experiences with radiation and feeding tubes, I found the PEG to be critical to getting nutrients into my system when I had absolutely no appetite. The problem I think is that once the treatments begin and the radiation effects kick in, the actual procedure for installing the feeding tube is more painful than it would be if installed beforehand. Further, it often takes a week or so to schedule the PEG installation, a time during which it is more difficult to remain hydrated and nourished.
Good luck with your treatments.
Best wishes, Sheldon