Statement: histologically confirmed invasive ductal breast cancer would result in exclusion from the primary trial, but not from the secondary trial.
Primary_evidence: Inclusion Criteria:   Unicentric Stage I invasive ductal breast cancer or Grade I or II DCIS measuring less than or equal to 2cm on pathology and/or mammography   Histologically negative tumor margin 2 mm or more from any inked edges, or no tumor in a re-excision specimen or final shaved specimen   Clips must be placed in the lumpectomy cavity at the time of final excision in order to aid in the delineation of the tumor cavity at the time of simulation and radiation delivery Exclusion Criteria:   No distant metastasis   Not pregnant or breastfeeding   No diffuse suspicious microcalcifications   No prior radiation therapy to the ipsilateral or contralateral breast or thorax   No histologic evidence of lymphovascular invasion (LVI)   No histologic evidence of EIC   No history of cosmetic or reconstructive breast surgery   No psychiatric illness that would prevent the patient from giving informed consent   No medical conditions that, in the opinion of the treating physician would make this protocol unreasonably hazardous for the patient   No other currently active second malignancy other than non-melanoma skin cancers