The purpose of this study is to determine if lumpectomy followed by Intraoperative Electron Radiation Therapy (IOeRT) as a single, full dose partial breast irradiation will have as good or better results in preventing recurrence of local breast cancer, cosmetic appearance and early and late side effects.

See points VIII inclusion/exclusion criteria

Operation:

• Lumpectomy, steninal node biopsy
• IOeRT

After Surgery:

• Meet with a medical oncologist and discuss if chemotherapy and/or hormone therapy is recommended as part of your treatment course. In some cases, pathology results may indicate the need for removal of additional lymph nodes. The doctor will review pathology and discuss if additional surgery is required.
• Chemotherapy (if indicated)
• Hormone therapy (if indicated)

Follow-Up

• Visits will be completed with the surgeon, radiation oncologist and research staff as the protocol indicates.
• Assessements of acute toxicity according to CTC-toxicity scoring system
• Assessments of late toxicity according to LENT-SOMA scoring systems
• Assessment of cosmetic outcome according to scoring system and photo documentation in standardized positions.

Inclusion Criteria:

• Patient agrees to breast conservation therapy (segmental resection, partial mastectomy, and radiation therapy) as the treatment for their breast cancer
• Patient agrees to evaluation of the axilla with sentinel lymph node biopsy
• Post-menopausal women age > 60, defined as women who have experienced no menstrual period in the past 12 months.
• BRCA1 and 2 gene mutation negative, if tested. [genetic testing is NOT required based upon personal or family history]
• Unifocal (unicentric), invasive ductal carcinoma or favorable sub-types (mucinous, tubular, colloid) < 2.0 cm in diameter, primary T-stage of T1 (AJCC criteria)
• Grade 1, 2 acceptable
• Associated LCIS is allowed
• Estrogen receptor (ER) status of positive
• Negative margins at ink on gross pathologic examination
• Patient is node-negative, defined as N0 (i-) or N0 (i+)
• Patient must be deemed functionally and mentally competent to understand and sign the informed consent

Exclusion Criteria:

• Prior breast malignancy or other malignancy if metastatic, or with expected survival of < 5 years
• Immuno-compromised status
• Pregnancy
• Women with an active connective tissue disorder (i.e. scleroderma, lupus and others)
• Breast cancer that involves the skin or chest wall, locally advanced breast cancer
• Pure DCIS, all grades
• Invasive lobular carcinoma
• Evidence of lymphovascular invasion (LVI)
• Invasive carcinoma with extensive intraductal component (EIC)
• Neoadjuvant chemotherapy indicated
• Patients with 1 or more positive lymph node determined during surgery with sentinel node and/or axillary dissection
• Not eligible for breast conserving management, i.e., prior whole breast radiation therapy
• Estrogen receptor negative
• Her2 positive
• Grade 3