Intensity Modulated Accelerated Partial Breast Irradiation Before Surgery in Treating Older Patients With Hormone Responsive Stage 0-I Breast Cancer

PRIMARY OBJECTIVES: Establish the feasibility for preoperative APBI delivered with IMRT in the prone position using daily CT guidance for Stage I breast cancer patients who are intended to undergo a lumpectomy for breast conserving therapy. SECONDARY OBJECTIVES: 1. To determine the acute and late surgical and radiation toxicity of preoperative APBI delivered with IMRT in the prone position. 2. To document the cosmetic appearance of the breast when treated with preoperative APBI IMRT in the prone position. 3. Establish the percentage of patients that can meet dosimetric goals and normal tissue constraints if treated with preoperative APBI IMRT in the prone position. 4. Evaluate molecular changes in breast cancer and/or stroma before and after preoperative APBI OUTLINE: Patients undergo image-guided intensity-modulated APBI twice daily (BID) in the prone position over a period of 5-10 days for a total of 10 treatment. Within 4-6 weeks post-APBI, patients undergo lumpectomy. After completion of treatment, patients are followed up at 4 weeks and then every 6 months for 5 years.