• Core needle biopsy demonstrating DCIS (ductal carcinoma in situ) of non-palpable, image-detected breast abnormality

• Signed and dated IRB-approved written informed consent

• Women 18 years of age or older

• Mammographic calcifications or MRI non-mass enhancement measuring 4 cm or less in greatest dimension, including multifocal disease

• Estrogen receptor positive or negative, progesterone receptor positive or negative DCIS; HER2 positive, negative or unknown DCIS is allowed.

• Diagnostic needle biopsy within 16 weeks of randomization

• Patients must have a biopsy marker placed within the tumor bed confirmed on post biopsy imaging and evidence of residual radiographic abnormality. Confirmation of residual imaging abnormality is required within 6 weeks of randomization.

• Placement of Savi scout optical reflectance marker in tumor bed area as a wireless guide for surgery and for neoRT treatment planning is preferred but not required if anatomic metallic markers are sufficient for radiation planning. Placement does not have to occur before randomization. Additionally, wire localization before surgery is permissible.

• Planned lumpectomy. Mastectomy will be acceptable if lumpectomy fails by virtue of involved margins or size of lesion, or patient chooses this approach after randomization

• Radiation Oncologist to ascertain feasibility of PBI prior to randomization - based on their estimation that 30% or less of the breast volume will be encompassed in the radiation fields

• Patients who had a prior contralateral invasive or non-invasive (DCIS) cancer are eligible

• ECOG performance status 0, 1, or 2

• Concurrent foci of atypia or lobular carcinoma in situ in the ipsilateral or contralateral breast are allowed