Questions about breast-sparing surgery with radiation

If I choose breast-sparing surgery, how much of my breast has to be taken out?

In a lumpectomy the surgeon removes the cancer and a small amount of surrounding normal tissue but leaves most of the breast intact. With other types of breast-sparing surgery, somewhat larger areas of the healthy breast are removed. This distance between the outer edge of the tumor and outer edge of the normal tissue surrounding it is known as the margin. The goal of breast-sparing surgery is to obtain clear, or clean, margins — that is, a band of normal breast tissue around the entire tumor that is completely free of cancer. This dictates how much breast is ultimately removed.