Hypofractionated Irradiation At Regional Nodal Area for Breast Cancer Vs Existed Standard Treatment

This study is comparing two ways of delivering radiation therapy after breast cancer surgery — a shorter, more intense schedule (fewer but higher-dose sessions) versus the standard longer schedule — to see which is safer and more effective at treating the underarm lymph node area. **You may be eligible if...** - You are between 18 and 75 years old - You have been diagnosed with invasive breast cancer in one breast (confirmed by biopsy) - You have had breast-conserving surgery (lumpectomy) or a full mastectomy - Cancer was found in your underarm (axillary) lymph nodes - Your surgical margins were clear (at least 2mm) - You are in generally good health and expected to live more than 5 years - You have not had prior radiation to the chest or underarm area **You may NOT be eligible if...** - Cancer has spread to distant parts of the body (metastatic disease) - You are pregnant or breastfeeding - You have cancer in both breasts at the same time - You have had previous radiation to the chest, underarm, or neck area - You have a serious connective tissue disease (such as lupus or scleroderma) - You have severe heart disease, serious arrhythmia, or severe lung disease that would prevent radiation treatment Talk to your doctor to see if this trial is right for you.