Well breast surgeon's rely on experience also. I would trust them. I know the biopsy says no cancer but they are working on years of knowledge that more than likely it is. I don't believe they would do the surgery otherwise.
Now as to radiotherapy ...that will depend on final pathology. Also if a significant amount of tissue is being taken is it worth saving tbe breast?. A mastectomy sometimes negates the need for radiotherapy but not always. ..especially if near chest wall.
Your breast csre nurse might he able to help with some answers if you have one.
Lots of unknowns. I probably haven't helped you at all...except to say...trust your surgeon. Kath x