DISEASE CHARACTERISTICS:

• Histologically confirmed ductal carcinoma in situ (DCIS*) or invasive* adenocarcinoma of the breast

  • Stage 0, I, or II disease

    • Stage II tumors must be ≤ 3 cm

  • Gross disease must be unifocal

    • Microscopic multifocality allowed provided total pathological tumor size is ≤ 3 cm
  • No proven multicentric carcinoma in more than 1 quadrant or separated by ≥ 4 cm
  • No non-epithelial breast malignancies (e.g., sarcoma or lymphoma) NOTE: *Patients who are 50 years of age and over with DCIS regardless of hormone receptor status AND patients with invasive breast cancer meeting all of the following criteria: ≥ 50 years of age, node-negative, and hormone-receptor positive status will not be enrolled in study after 12/30/2006

• Prior axillary staging required for patients with invasive breast cancer, including 1 of the following:

  • Sentinel node biopsy alone (if sentinel node is negative)
  • Sentinel node biopsy followed by axillary dissection or sampling with ≥ 6 axillary nodes (if sentinel node is positive)
  • Axillary dissection alone with ≥ 6 axillary nodes

• No more than 3 positive axillary nodes

  • No axillary nodes with definite evidence of microscopic or macroscopic extracapsular extension
  • No positive non-axillary sentinel nodes (intramammary nodes are staged as axillary nodes)
  • No 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

• Must have undergone lumpectomy

  • Resected margins histologically free of tumor
  • Re-excision of surgical margins allowed
  • Target lumpectomy cavity clearly delineated AND target lumpectomy/whole breast reference volume ≤ 30% based on postoperative pre-randomization CT scan
  • Final surgery (i.e., lumpectomy, re-excision of margins, or axillary staging procedure) within the past 42 days
• No suspicious microcalcifications, densities, or palpable abnormalities in the ipsilateral or contralateral breast unless biopsied and found to be benign
• No Paget's disease of the nipple

• No history of invasive breast cancer or DCIS

  • Prior lobular carcinoma in situ treated by surgery alone allowed
• No synchronous bilateral invasive or non-invasive breast cancer
• Partial breast irradiation deemed technically deliverable by radiation oncologist at a credentialed facility
• Must have undergone a history and physical exam within the past 4 months AND a bilateral mammogram within the past 6 months

• Hormone receptor status:

  • Estrogen receptor (ER) status known
  • Progesterone status known if ER analysis is negative
  • Marginal or borderline results are considered positive

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Female

Menopausal status

• Premenopausal or postmenopausal

Performance status

• Not specified

Life expectancy

• At least 10 years, excluding diagnosis of breast cancer

Hematopoietic

• Not specified

Hepatic

• Not specified

Renal

• Not specified

Other

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective non-hormonal contraception

• No other malignancy within the past 5 years except previously treated carcinoma in situ of the cervix or colon, melanoma in situ, or basal cell or squamous cell skin cancer

  • Deemed to be at low risk for recurrence
• No collagen vascular disease (e.g., systemic lupus erythematosus or scleroderma), specifically dermatomyositis with a CPK level above normal, or active skin rash
• No psychiatric or addictive disorder that would preclude study therapy

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No prior biologic therapy for this malignancy

Chemotherapy

• No prior chemotherapy for this malignancy
• No concurrent chemotherapy during study radiotherapy

Endocrine therapy

• No prior hormonal therapy for this malignancy unless total duration of hormonal therapy was no more than 28 days before randomization
• Concurrent hormonal therapy allowed provided it is not administered during chemotherapy
• No concurrent raloxifene, tamoxifen, or other selective estrogen receptor modulating drugs
• No concurrent hormone replacement therapy
• No concurrent Femring^®

Radiotherapy

• No prior radiotherapy for this malignancy
• No prior breast or thoracic radiotherapy
• No concurrent brachytherapy boosts
• No concurrent intensity modulated radiotherapy
• No concurrent regional nodal irradiation

Surgery

• See Disease Characteristics

• No prior breast implants

  • Patients who have had implants removed are eligible

Other

• No other concurrent anticancer therapy