I think you will find that radiation definitely effects the chest muscles. I know my radiation was to the chest wall and the doctor told me that what we see on the surface, skin wise, is happening inside but even worse. I also had radiation to the axillary area and my neck. I have a lot of tighness in all of these areas and find I need to do a lot of stretching to keep it all operational. I actually got cording a few weeks after radiation finished and had to do a lot of stretching and massage to fix this. My radiation finished mid November last year. :) Deanne xxx