Inclusion Criteria:

- DCIS or invasive ductal, medullary, papillary, mucinous (colloid), or tubular
histologies.

- Eligible patients must have appropriate staging studies identifying them as AJCC
stage T1 or T2 (≤3 cm) treated with lumpectomy and axillary node dissection with at
least 6 nodes sampled or sentinel node biopsy. Patients with up to 3 positive nodes
without microscopic or macroscopic evidence of extracapsular extension are eligible.

- The patient's Zubrod performance status must be 0-2.

- Patients must be ≥ 18 years of age.

- If chemotherapy is planned, it must begin no earlier than two weeks following
completion of radiation therapy.

- Unifocal breast cancer (no evidence of gross multifocal disease, multicentric, or
bilateral disease.

- Negative margins after lumpectomy (re-excision for initial positive margins is
allowed-negative margins defined as >2 mm clear of tumor in all directions).

- Negative post- lumpectomy mammography if malignancy-associated microcalcifications
were initially present.

- The target lumpectomy cavity must be clearly delineated.

- Patients must complete appropriate pretreatment evaluation, including post-lumpectomy
mammogram if microcalcifications were initially present to confirm complete removal.

Exclusion Criteria:

- Evidence of suspicious microcalcifications in the breast prior to start of radiation.

- Patients with history of collagen vascular disease, specifically dermatomyositis with
a CPK level above normal or active skin rash, systemic lupus erythematosis, or
scleroderma.

- Patients with 4 or more histologically positive axillary nodes if axillary dissection
is performed.

- Patients with distant metastases.

- Patients with invasive or extensive in-situ lobular carcinoma or non-epithelial
breast malignancies such as sarcoma or lymphoma.

- Patients with multicentric gross disease defined as tumors in different quadrants of
the breast or tumor separated by at least 4 cm or other clinically or
radiographically suspicious areas in the ipsilateral breast unless confirmed to be
negative for malignancy or biopsy.

- Patients must not have any palpable or radiographically suspicious ipsilateral or
contralateral axillary, supraclavicular, infraclavicular, or internal mammary nodes
unless there is histologic confirmation that these nodes are negative for tumor.

- Any previously treated contralateral invasive breast carcinoma or synchronous
contralateral breast carcinoma.

- Prior non-hormonal therapy or radiation therapy for the current breast cancer or
hormonal therapy for > 28 days after diagnosis or refusal to discontinue hormonal
therapy.

- Patients with Paget's disease of the nipple

- Patients with prior invasive malignancy (except non-melanomatous skin cancer) unless
disease free for a minimum of 3 years (e.g., carcinoma in situ of the breast, oral
cavity, or cervix are all permissible).

- Patients with severe, active co-morbidity.

- Patients with psychiatric or addictive disorders that, in the opinion of the
investigator, would preclude obtaining informed consent.

- Patients who are pregnant or lactating.

- Previous breast radiation on either side or thoracic radiation on the ipsilateral
side..