Radiation Therapy in Treating Patients With Stage 0-II Breast Cancer

PRIMARY OBJECTIVES: I. To assess the cosmesis, acute toxicity and late toxicity in patients treated with accelerated partial breast irradiation delivered with proton radiation. SECONDARY OBJECTIVES: I. To evaluate the convenience of accelerated partial breast irradiation and quality of life during accelerated partial breast irradiation. II. To estimate the in-breast tumor control rates in patients treated with accelerated partial breast irradiation delivered with proton radiation. III. Compare dosimetry to alternate treatment modalities. OUTLINE: Within 10 weeks of last breast cancer surgery, patients undergo accelerated partial breast irradiation (APBI) delivered with proton radiation twice daily (BID) for 5 days. After completion of study treatment, patients are followed up at 6 weeks, 6 months, 1 year, and 18 months, then annually for 10 years.