Hypofractionated vs. Conventional Regional Nodal Radiation Therapy for Patients With Invasive Breast Cancer

Inclusion Criteria, if receiving postoperative radiation therapy * Radiation oncologist recommends radiation treatment to the supraclavicular and infraclavicular fossa (i.e. RNI). * Pathologically-confirmed invasive breast cancer. If patients undergo upfront surgery, the pathologic stage must be T0-T3, N0-N2a or N3a. If patients receive neoadjuvant chemotherapy prior to surgery, the clinical stage must be T0-T3, N0-N2a or N3a. T4b disease is permitted if the patient undergoes breast conserving surgery. * Treatment with mastectomy or segmental mastectomy and axillary evaluation (sentinel node evaluation, axillary sampling, or axillary lymph node dissection). If the patient has T0 disease, breast surgery is not required. * Age 18 years or older. * If enrolling on in the arm lymphedema assessment cohort, documentation of arm volume measurement by perometer prior to axillary surgery. * If the patient has a history of a prior non-breast cancer, all treatment for this cancer must have been completed prior to study registration, and the patient must have no evidence of disease for this prior non-breast cancer. * Patients must be enrolled on the trial within 24 weeks of the later of two dates: the final breast cancer surgical procedure or administration of the last cycle of cytotoxic chemotherapy. If after trial enrollment it is determined the patient requires additional cytotoxic chemotherapy or additional breast cancer surgery prior to radiation therapy the patient may stay on tri…