RecruitingPhase 2Radiation therapyEMERALD: Endocrine Therapy oMission With Radiation in ER+ Breast Cancer: Assessing Quality of Life and Disease Control: a Prospective Phase II TrialThis clinical research study is to learn about the effects of giving radiotherapy alone after lumpectomy to patients who have early-stage, low-risk breast cancers and who are 60 years of age or older.