IOERT is no longer an experimental treatment and was now offered as SOC to patients experiencing IBC. As this therapy is being offered to them regardless of study participation at numerous institutions across the country.

The overall objective of this study is to determine the feasibility and tolerability of single dose Intraoperative Electron Radiation Treatment ("IOERT") as definitive therapy when administered at the time of breast conserving surgery for patients with early stage breast cancer.

Evaluate local and distant recurrence rates and cosmetic outcomes. Both clinical evaluation of cosmetic outcome by the Surgeon, and subjective impression of cosmetic outcome by the patient, are evaluated using questionnaire.

Local recurrence is evaluated under the same imaging protocol used for Whole breast radiation.

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
• Peri or post-menopausal women age > 50, defined as women who have experienced no menstrual period in the past 6 months or more
• 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 Tis or T1 (AJCC criteria)
• Grade 1, 2, or 3 acceptable
• Associated LCIS is allowed
• Pure DCIS allowed if <2.5 cm, low to intermediate nuclear grade and resected margins negative at > 3 mm (per ASTRO criteria)
• Estrogen receptor (ER) status of positive
• Patient has clear margins >2 mm 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
• Neoadjuvant hormonal therapy is allowed if all other ASTRO suitable criteria have been met prior to onset of hormonal therapy

Exclusion Criteria:

• Prior breast malignancy or other malignancy if metastatic, or with expected survival of < 5 years
• Immunocompromised 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
• Invasive lobular carcinoma
• Evidence of lymphovascular invasion (LVI)
• Invasive carcinoma with extensive intraductal component (EIC)
• Neoadjuvant chemotherapy
• Patients with 1 or more positive lymph node determined during surgery with sentinel node and/or axillary dissection
• Someone who is not a candidate for breast conserving management, i.e., prior whole breast radiation therapy