Study of a Shortened Radiation Therapy Schedule in People With Breast Cancer

Inclusion Criteria: * Female or male patients with invasive breast cancer who have had mastectomy and have a chest wall reconstruction in progress or completed. * Age ≥ 30 years * Final AJCC Stage IIa - IIIa (pathologic stage T0N1a-2a, T1N1a-2a, T2N1a-2a, T3N0-2a, all M0 status). Pathological stage for all patients not receiving neoadjuvant chemotherapy. Higher of the clinical or pathological T and N stage, if receiving neoadjuvant chemotherapy. T3N0 patients, either clinically by imaging before neoadjuvant chemotherapy, or by pathological stage at the time of surgery, are eligible. Exceptions to these criteria (e.g. for T4 or N3 patients) are possible after discussion with PI. * Histologically negative tumor margin. * ECOG Performance Status of 0 or 1 Exclusion Criteria: * Patients with distant metastasis. * Patients who are pregnant or breastfeeding. * Prior radiation therapy to the ipsilateral or contralateral breast or thorax. * All patients with clinical, radiographic or pathological T4, N3 or involved internal mammary disease (N1b, N1c, and N2b) will not be eligible to enroll. * Medical condition such as uncontrolled infection (including HIV), uncontrolled diabetes mellitus, or connective tissue diseases (lupus, systemic sclerosis, or other collagen vascular diseases) that, in the opinion of the treating physician, would make this protocol unreasonably hazardous for the patient. * Patients with a "currently active" second malignancy other than non-melanoma skin cance…