Inclusion Criteria:

- Women,age of at least 45 years

- Zubrod performance status of 0-2

- AJCC Stage I-II (T1-T2, N0 M0) breast cancer

- Maximum tumor dimension < 3 cm

- Invasive ductal, medullary, papillary, tubular, colloid (mucinous) histologies

- Unifocal breast cancer

- Unilateral breast cancer (no synchronous or previous contralateral breast cancer)

- Lumpectomy with negative surgical margins by at least 2 mm or re-excision specimen
with negative surgical margins by at least 2 mm

- Ductal Carcinoma In-Situ

- Negative axillary lymph nodes for invasive breast cancer (sentinel node biopsy or
standard level I-II dissection with > 6 nodes removed)

- Time interval from final breast surgery to brachytherapy loading less than 8 weeks

- At least 2 mm of breast tissue between the skin and the MammoSite® balloon
surface(prefer > 5 mm)

- If chemotherapy is planned, it must begin no earlier that 2 weeks following
completion of radiation therapy. If chemotherapy is first, a minimum of 2 weeks from
the last cycle must elapse prior to the start of radiation therapy.

- Signed study-specific consent form

Exclusion Criteria:

- Invasive lobular histology

- Non-epithelial breast malignancies such as sarcoma or lymphoma

- Multifocal or multicentric invasive carcinoma

- Extensive intraductal component (EIC)

- Paget's disease of the nipple

- Skin involvement by tumor, regardless of tumor size

- Positive axillary lymph nodes

- Distant metastases

- Collagen vascular disease (scleroderma)

- Pregnant or lactating women, due to potential exposure of the fetus to RT and unknown
effects of RT on lactating females (negative pregnancy test for women of
child-bearing age)

- Any previously treated or synchronous contralateral breast carcinoma

- Patients with psychiatric or addictive disorder that would preclude obtaining
informed Consent

- Men