This study will evaluate the technical feasibility and reproducibility, cosmetic results, complication rates, and local control rate of 3D-CRT confined to the region of the lumpectomy cavity for patients with Stage I and II (= < 3 cm) carcinoma of the breast (non-lobular histology) treated with tylectomy with histologically assessed negative surgical margins (> 2 mm), up to 3 nodes positive at axillary dissection or sentinel lymph node biopsy, with no extensive intraductal component (EIC) by the Harvard definition.

Invasive ductal, medullary, papillary, colloid (mucinous), tubular histologies. AJCC Stage I or II (T1N0, T1N1, T2N0, T2N1); lesion <= 3 cm.