Just saw this interesting story in the Observer: Cancer scientists to classify gut bacteria to prevent the side-effects of radiotherapy | Science | The Observer. It discusses an effort to give more consideration to protecting and / or repopulating the microbiome in relation to radiation therapy. I think this is critically important. I want to note - people should give some credit to DARPA for being ahead of their time on this issue. I went to a workshop in 2004 organized by Brett Giroir and Manley Heather. The topic was "Radiation Protection" and one of the points of discussion was the gut microbiome and the effect of radiation on it.
Anyway - since that meeting I have been following this topic on and off. And I do think thinking about the microbiome in relation to radiation therapy (and any radiation exposure) is critically important.