Higher Per Daily Treatment-Dose Radiation Therapy or Standard Per Daily Treatment Radiation Therapy in Treating Patients With Early-Stage Breast Cancer That Was Removed by Surgery

OBJECTIVES: Primary * To determine whether an accelerated course of hypofractionated whole-breast irradiation (WBI) including a concomitant boost to the tumor bed in 15 fractions following lumpectomy will prove to be non-inferior in local control to a regimen of standard WBI with a sequential boost following lumpectomy for early-stage breast cancer patients. Secondary * To determine whether breast-related symptoms and cosmesis from accelerated WBI that is hypofractionated (in only 3 weeks) with a concomitant boost is non-inferior to standard WBI with sequential boost. * To determine whether the risk of late cardiac toxicity in patients with left-sided breast cancer treated with hypofractionation will be non-inferior to conventional fractionated radiation therapy (RT) based upon analysis of radiation dosimetry from CT-based treatment planning and normal tissue complication probability (NTCP) calculations. * To determine whether CT-based conformal methods intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiotherapy (3D-CRT) for WBI are feasible in a multi-institutional setting following lumpectomy in early-stage breast cancer patients and whether dose-volume analyses can be established to assess treatment adequacy and likelihood of toxicity. * To determine that cosmetic results and breast-related symptoms 3 years after hypofractionated breast radiation with concomitant boost will not be inferior to that obtained 3 years after WBI with sequential boost. * To determine whether future correlative studies can identify individual gene expressions and biological host factors associated with toxicity and/or local recurrence from standard and hypofractionated WBI. * If shown to be non-inferior, to then determine if accelerated course of hypofractionated WBI including a concomitant boost to the tumor bed in 15 fractions following lumpectomy will prove to be superior in local control to a regimen of standard WBI with a sequential boost following lumpectomy for early-stage breast cancer patients. * To determine whether treatment costs for hypofractionated WBI with concomitant boost are not higher than WBI with sequential boost. OUTLINE: This is a multicenter study. Patients are stratified according to age (\< 50 vs. ≥ 50 years), prior chemotherapy (yes vs. no), estrogen-receptor status (+ vs. -), and histology grade (1-2 vs. 3). Patients are randomized to 1 of 2 treatment arms. Treatment begins within 9 weeks of last surgery or chemotherapy delivery. After completion of study therapy, patients are followed at 1 month, at 6 months, and then yearly.