Hypofractionated Partial Breast Irradiation in Treating Patients With Early Stage Breast Cancer

Inclusion Criteria: * Diagnosis of pathologically-confirmed invasive breast cancer or ductal carcinoma in situ * Pathologic T stage of Tis, T1, or T2 with total size of tumor =\< 3 cm (this size criteria applies to both pure DCIS and invasive tumors) * For patients with invasive breast cancer, pathologic N stage of N0, N0 (i-), or N0 (i+); pathologic staging of the axilla is not required for patients with pure DCIS * Treatment with breast conserving surgery * Unifocal primary tumor based on imaging and clinical assessment; microscopic multifocality is allowed * Final surgical margins negative defined as no tumor on ink; lobular carcinoma in situ involving the final surgical margin will be disregarded * For invasive cancers, the tumor must be estrogen receptor positive (defined as 10% or greater expression of estrogen receptor) * If the patient has a history of a prior non-breast cancer, all treatment for this cancer must have been completed at least one month 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 12 weeks of the later of two dates: the final breast conserving surgical procedure or administration of the last cycle of cytotoxic chemotherapy * Final criteria for eligibility established after simulation: The tumor bed can be readily visualized on simulation computed tomography (CT) and is localized to one quadrant or region of the breast that is amenable to par…