Concerned

I start radiation on Monday and its the one where I hold my breath - left breast with left lung and heart damage already- but I wonder what the protective film radiation is.  I feel like I'm very trusting of my oncologist and presume because the place is new and gear seems new all is well and they are using the latest.  But maybe not.  Can someone please enlighten me on what I should be asking about the radiation....  Im receiving it in a square of about 8" X 8" across breast and slightly into armpit to get breast and one lymph node that was 1/1mm but had cancer.