Ultra Hypo-fractionated Adjuvant Whole Breast Radiation Therapy With Simultaneous Integrated Boost for Early-Stage Breast Cancer (H-ASSIST)

In order to participate in this study a subject must meet all of the eligibility criteria outlined below. Inclusion Criteria: * Willing and able to provide written informed consent obtained to participate in the study and HIPAA authorization for release of personal health information. * Women ≥ 50 years of age with confirmed de novo invasive carcinoma of breast or ductal carcinoma in situ. * Subjects with completed breast-conserving surgery (BCS) with or without sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND). * Subjects planned to receive either SOC whole breast 3D conformal radiation therapy (3D CRT) or SOC whole breast intensity modulated radiation therapy (IMRT) with standard dose tumor bed boost. * Subjects with a prior or concurrent malignancy whose natural history or treatment does not have the potential to interfere with the safety or efficacy assessment of the investigational regimen are eligible for this trial, per the discretion of the treating radiation oncologist. * Enrollment in another clinical trial is allowed if there is no interference with interventions on this trial per discretion of the Principal Investigator. Exclusion Criteria: * Receipt of concurrent breast reduction involving tissue rearrangement in the lumpectomy cavity (so that boost cannot be accurately targeted). * Synchronous bilateral breast cancer requiring bilateral radiation therapy. * Clinical or imaging evidence of distant metastases. * Prior ipsilateral breast or thoracic radiation. * Autoimmune conditions * Collagen Vascular Disease (such as systemic lupus erythematosus, scleroderma, dermatomyositis, among others) * Patients with pT4 tumors. * Patients recommended to receive regional nodal irradiation with associated radiation risks