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