Many years ago, radiation for breast cancer was only used for large tumors that were considered inoperable. Now it is a part of the local therapy in lumpectomy cases. Radiation can be administered to the entire breast or just to the area where the tumor existed (where the risk of recurrence is highest). Each method has advantages and disadvantages, but both seem equally effective.
Overall, though, the biggest change in radiation is the increased precision with which it is delivered, thereby minimizing damage to adjacent normal tissues.