DISEASE CHARACTERISTICS:

Inclusion criteria:

• Histologically confirmed ductal carcinoma in situ or invasive carcinoma of the breast (including ductal, medullary, papillary, colloid [mucinous], or tubular histologies) meeting all of the following criteria:

  • AJCC stage 0, I, or II (Tis, T1N0, or T2N0) disease with a lesion ≤ 3 cm treated with lumpectomy and either sentinel node biopsy or axillary dissection (if invasive carcinoma is present)
  • Unifocal breast cancer (i.e., single focus that can be encompassed by one lumpectomy)

• Underwent or plan to undergo lumpectomy with placement of gold fiducial markers (markers placed concurrently with the surgery or on a later date)

  • Patients who has underwent lumpectomy must meet all of the following criteria:

    • Must be enrolled between 14-60 days from date of last surgery, and radiation must start within 15-80 days of date of last surgery
    • Four to six gold fiducial markers placed in the tumor bed, delineating the margins of the lumpectomy cavity

    • Negative, inked histologic margins of lumpectomy (> 1 mm) or re-excision specimen to be confirmed prior to radiation

      • Margins are unacceptable if there is invasive or non-invasive tumor within 1 mm of the inked margin
• Negative post-excision mammography if malignancy-associated microcalcifications were initially present
• Hormone receptor status not specified

Exclusion criteria:

• Evidence of suspicious microcalcifications in the breast prior to the start of radiation
• One or more positive axillary nodes or positive sentinel biopsy
• Distant metastases
• Invasive or extensive in-situ lobular carcinoma or non-epithelial breast malignancies such as sarcoma or lymphoma
• Proven multicentric carcinoma (tumors in different quadrants of the breast or tumor separated by at least 4 cm) with other clinically or radiographically suspicious areas in the ipsilateral breast unless confirmed to be negative for malignancy by biopsy
• Palpable or radiographically suspicious contralateral axillary, supraclavicular, infraclavicular, or internal mammary nodes, unless there is histologic confirmation that these nodes are negative for tumor
• Paget's disease of the nipple
• Skin involvement, regardless of tumor size

PATIENT CHARACTERISTICS:

• Female
• Menopausal status not specified
• ECOG performance status 0-1
• Life expectancy ≥ 2 years
• Not pregnant or nursing
• No prior treated breast carcinoma within the past 5 years
• No collagen vascular diseases, specifically systemic lupus erythematosus, scleroderma, or dermatomyositis
• No co-existing medical conditions
• No patients with medical conditions that would preclude compliance with the trial, as determined by the investigator

• No other malignancy, except non-melanomatous skin cancer, within the past 5 years

  • Disease-free interval from any prior carcinoma must be continuous
• No breast technically unsuitable for radiotherapy

PRIOR CONCURRENT THERAPY:

• See Disease Characteristics
• Concurrent tamoxifen citrate, anastrozole, or other hormonal therapy allowed
• Future chemotherapy allowed provided it is administered after the APBI and begins no earlier than 2 weeks after completion of radiotherapy
• No tylectomies so extensive that the cosmetic result is low or poor prior to radiation
• No prior radiation to the ipsilateral breast
• No prior non-hormonal therapy or radiotherapy for this disease
• No chemotherapy in the past 2 weeks
• No concurrent chemotherapy, immunotherapy, or experimental medications