Inclusion Criteria:

• Histological confirmation of breast cancer.
• Pathologic Stage T0-T3N0-N1M0.
• ECOG Performance Status (PS) 0 to 2. (Appendix I).
• Able to and provides IRB approved study specific written informed consent.
• Study entry must be within 12 weeks of last surgery (breast or axilla) or last chemotherapy (if applicable).
• 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).
• Fair, good or excellent cosmesis, as determined by trained nurse assessment using the Harvard Cosmetic Scale.
• Radiotherapy must begin within 12 weeks of the last breast cancer surgery or the last dose of adjuvant chemotherapy.
• Breast conserving surgery and indications for whole breast radiotherapy.

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.
• Women of childbearing potential who are sexually active and not willing/able to use medically acceptable forms of contraception
• Prior receipt of ipsilateral breast or chest wall radiation.
• Positive margins on ink after definitive surgery either for DCIS or invasive cancer.
• History of non-breast malignancies (except for in situ cancers treated only by local excision and basal cell and squamous cell carcinomas of the skin) within 5 years prior study entry.
• Recurrent breast cancer.
• Indications for comprehensive regional nodal irradiation.
• Male subjects.
• Patient requires bilateral breast radiation treatment.