My radiation oncologist told me that even though I had chemo and surgery, there could still be a stray cancer cell... and radiation is further insurance that they are all gone. I didn't find radiation to be all that terrible, and I had 33 sessions. To me, I'd rather have radiation than have the cancer return and have to go through more chemo later. I felt that I was just increasing my odds of it not returning with the radiation.
Good luck with whatever you decide.

There is no way for them to tell you that your cancer is "gone". Stray cancer cells are always a concern and do not show up on scans and tests. If you look at the statistics, radiation greatly increases survival rates. Breast cancer is a chronic disease, which means you are never considered "cured". I would definitely do the radiation. The worst part for me was the inconvenience of going every day for 6 weeks. Chemo was waaaay worse.

Me too, i had my surgery and reconstruction on dec 1. Healing well, got all my drains out then heavens. On my way to recovery!!!!

I had a lumpectomy, chemo, and radiation. My radiation oncologist also said radiation will get any stray cells. Radiation was not too bad for me. Some very red skin, a few tired days, but really not bad, especially compared to chemo. Today was my last day!

If the cancer is gone after the chemo, then why would you still need to have the mastectomy? That being asked, if you do still need the surgery and you don't have radiation, your skin will be in better shape for healing. I had radiation in 2008 following a lumpectomy and chemo. Then I had a recurrence last year and had a BMX with tissue expanders. Within about 2 weeks of my surgery, I had to have the TE's removed because the side where I had the radiation would not heal. If I could do it all over again, I would have had the BMX the first time I was diagnosed. Best of luck to you!