Hypofractionated Regional Nodal Irradiation in Breast Cancer

Inclusion Criteria: * Female * Age ≥ 18 years old * Life expectancy of \>5 years * ECOG (Zubrod) performance status 0-1 * Histologically confirmed invasive carcinoma of the breast, including ductal, lobular, mammary, medullary, and tubular histologies * Clinical T stage of cT0, cT1, cT2, or cT3 * Clinical N stage of cN0, cN1, or cN2a * Clinical M stage of cM0Definitive surgery must be performed (either partial mastectomy or mastectomy without immediate reconstruction) with negative surgical margins (defined as no invasive tumor or DCIS on ink). * Must have pathologic T stage of pT1, pT2, or pT3, or if receiving neoadjuvant chemotherapy, ypT0, ypTis, ypT1, ypT2, or ypT3 * Pathologic N stage of pN0, pN1, pN2a, or pN3a, or if receiving neoadjuvant chemotherapy, ypN0,ypN1, ypN2, or ypN3a) NOTE: any patient with clinically involved but undissected lymph nodes that would require a radiation boost will not be eligible. * The radiation oncologist is planning to treat the breast/chest wall and ipsilateral regional lymphatics (including the axillary, supraclavicular, and internal mammary chains) * Patient is able to understand and willing to sign an IRB approved written informed consent document * All dosimetric constraints outlined in protocol section 3.5 can be met Exclusion Criteria: * Clinical or pathologic T4 disease, including inflammatory breast cancer * Clinical N stage of cN2b, cN3 disease, pathologic N stage of pN2b, pN3b, or pN3c disease, or if receiving neoadjuvant chemo…