Inclusion Criteria:

• Age ≥ 18 years old.
• Histological confirmation of breast cancer.
• Clinical Stage T0-T2 N0 M0.
• ECOG Performance Status (PS) 0 to 2.
• Able to and provides IRB approved study specific written informed consent.
• Study entry must be within 120 days of last biopsy (breast).         
• Able to complete all mandatory tests listed in section 4.0.
• Willing to return to enrolling institution for follow-up (during the active monitoring phase of the study).
• Planned breast surgery and indications for whole breast radiotherapy.
• No neo-adjuvant therapy.

Exclusion Criteria:

• Medical contraindication to receipt of radiotherapy.
• Severe active co-morbid systemic illnesses or other severe concurrent disease which, in the judgment of the investigator, would make the patient inappropriate for entry into this study or interfere significantly with the proper assessment of safety and toxicity of the prescribed regimens.
• Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements or providing informed consent.
• Active systemic lupus or scleroderma.
• Pregnancy.
• Women of childbearing potential who are unwilling to employ adequate contraception.
• Prior receipt of ipsilateral breast or chest wall radiation.
• Recurrent breast cancer.
• Indications for comprehensive regional nodal irradiation.