Hypofractionated Radiation Therapy or Standard Radiation Therapy in Treating Patients With Ductal Breast Carcinoma In Situ or Early Invasive Breast Cancer

Inclusion Criteria: * Pathologically confirmed ductal carcinoma in situ of the breast or early invasive breast cancer defined as pathologic stage Tis, T1, or T2, N0, N1mic, or N1a (pathologic staging of the axilla is required for all patients with invasive disease but is not required for patients with ductal carcinoma in situ \[DCIS\] only); (upfront pathologic stage cannot be assigned to patients treated with neoadjuvant chemotherapy; for such patients, the criteria for pathologic stage shall be applied to the initial clinical stage) * Treatment with breast conserving surgery * Final surgical margins must be negative, defined as no evidence for ductal carcinoma in situ or invasive breast cancer touching the inked surgical margin; if the invasive or in situ breast cancer approaches within less than 1 mm of the final surgical margin, then a re-excision is strongly encouraged; lobular carcinoma in situ at the final surgical margin will be disregarded * Age 40 years or older. This age cutoff is justified because breast cancers in women under the age of 40 are known to have a significantly higher risk of IBTR presumably due to underlying biologic differences. * Female sex. * Attending radiation oncologist declares intention to treat the whole breast only and that a third radiation field to treat regional lymph nodes is not planned (radiation of the undissected level I/II axilla with high tangents is allowed) * If the patient has a history of a prior non-breast cancer, all treatm…