Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed breast cancer, including 1 of the following subtypes:

- Ductal carcinoma in situ

- Invasive ductal carcinoma

- Invasive lobular carcinoma

- Medullary carcinoma

- Papillary carcinoma

- Colloidal (mucinous) carcinoma

- Tubular carcinoma

- Pathological stage 0-IIIA disease (pTis; pT1-2, N0-N2a, M0)

- Tumor size ≤ 5 cm

- Breast considered technically satisfactory for radiotherapy

- Has undergone lumpectomy or mastectomy and either sentinel node biopsy or axillary
dissection (if invasive carcinoma is present)

- Negative inked histological margins (i.e., no invasive cells at surgical margin)
or confirmed negative re-excision specimen

- Unifocal or multifocal (confined to 1 quadrant; tumors < 4 cm apart) disease with 1
or 2 foci that can be encompassed by 1 lumpectomy

- No proven multicentric carcinoma (tumors in different quadrants of the breast or
tumor separated by ≥ 4 cm) with other clinically or radiographically suspicious areas
in the ipsilateral breast unless confirmed to be negative for malignancy by biopsy

- No evidence of suspicious microcalcifications in the breast before the start of
radiotherapy

- If malignancy-associated microcalcifications were initially present, the
post-excision mammography must be negative

- No more than 9 positive axillary lymph nodes

- No palpable or radiographically suspicious contralateral axillary, supraclavicular,
infraclavicular, or internal mammary nodes unless there is histologic confirmation
that these nodes are negative for tumor

- No previously treated contralateral breast cancer or synchronous ipsilateral breast
cancer

- No lobular carcinoma in situ alone (i.e., no invasive component) or non-epithelial
breast malignancies (e.g., sarcoma or lymphoma)

- No Paget disease of the nipple

- No skin involvement, regardless of tumor size

- No distant metastases

- Hormone receptor status not specified

PATIENT CHARACTERISTICS:

- Pre- or post-menopausal

- ECOG performance status 0-1

- No co-existing medical condition that would limit life expectancy to < 2 years

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- No other malignancy within the past 5 years except for nonmelanoma skin cancer (the
disease-free interval from any prior malignancy must be continuous)

- No collagen vascular disease, specifically systemic lupus erythematosus, scleroderma,
or dermatomyositis

- No psychiatric or addictive disorder that would preclude obtaining informed consent

PRIOR CONCURRENT THERAPY:

- See Disease Characteristics

- No prior radiotherapy for the current breast cancer

- No tylectomies so extensive that the cosmetic result is low or poor prior to
radiotherapy

- Chemotherapy allowed provided the following criteria are met:

- Chemotherapy is not administered prior to, during, and for ≥ 21 days after
completion of radiotherapy (for patients receiving brachytherapy boost)

- Chemotherapy is not administered for ≥ 21 days before, during, and for ≥ 21 days
after completion of radiotherapy (for patients receiving external beam
radiotherapy boost or chest wall irradiation)

- Concurrent tamoxifen, anastrozole, or other hormonal therapy allowed

- May be initiated before, during, or after radiotherapy

- No other concurrent chemotherapy, immunotherapy, or experimental medications