@saraheja

I'm not sure where you are getting your information.
There is, I agree, the risk of still needing some external beam radiation if the cancer is likely to have already spread (e.g., no clear margins or extensive lymph-node involvement), but the information that I have found says in early stage breast cancer IORT is just as effective as external radiation, and safer for the heart and lungs. I didn't want to attach 1 million websites and studies here, so here is simply one summary from the surgical breast care group at Columbia University, who presumably know the research so far…
https://columbiasurgery.org/conditions-and-treatments/intraoperative-radiation-therapy-breast-cancer