It's a "one-two" punch for the cancer cells. You are not sure, nor are the doctors that chemo has killed it. It is standard protocol to do both in many cancer treatments. I had it the first time I was diagnosed. I had chemo then was supposed to have 30 radiation treatments. They stopped the radiation treatments early because they thought I didn't need anymore. My cancer returned 6 months later. So what if I had completed the full radiation? Maybe it wouldn't have came back? No one knows, but I would have been good with finishing all of them.
After you finish chemo, radiation is a walk in the park (comparatively), but still hard on you. My personal opinion, I will take radiation any day over chemo.
My advice is take it and be extra assured you have done all you can do.