RATIONALE: Radiation therapy uses high-energy x-rays to kill tumor cells. Giving radiation therapy during and after surgery may kill any tumor cells that remain after surgery.

PURPOSE: This phase II trial is studying the side effects of giving radiation therapy during and after lumpectomy and to see how well it works in treating women with stage I or stage II breast cancer.

OBJECTIVES:

• To determine the feasibility and acute tolerability of intraoperative electron radiotherapy (IOERT) and external-beam radiotherapy (EBRT) after lumpectomy in women with stage I or II breast cancer treated with breast conservation therapy.
• To determine the local tumor control and distant tumor control rates in these patients.
• To determine the long-term side effects and cosmetic outcome of IOERT to the tumor bed and EBRT after lumpectomy in these patients.

OUTLINE: Patients undergo standard lumpectomy. Patients with negative lymph nodes undergo intraoperative electron radiotherapy to the tumor bed. Beginning 2-8 weeks after surgery, patients undergo whole breast external beam radiotherapy once daily for 24-27 fractions.

After completion of study treatment, patients are followed periodically for up to 8 years.

DISEASE CHARACTERISTICS:

• Histologically confirmed primary invasive breast carcinoma, meeting the following criteria:

  • Stage I or II disease (T1-T2, N0, M0)
  • Tumor pathologically determined to be ≤ 5 cm in diameter
  • Single, discrete, well-defined primary tumor

• No multicentric disease and/or diffuse malignant appearing microcalcifications

  • Any microcalcifications must be focal

    • Specimen radiograph is required after lumpectomy to assure removal of all malignant appearing calcifications

• No axillary lymph node involvement

  • Axillary lymph node status can be determined by level I and II lymph node dissection or sentinel lymph node sampling

• Must have pathologically negative surgical margins

• No evidence of metastatic breast cancer

• Hormone receptor status not specified

PATIENT CHARACTERISTICS:

• ECOG performance status 0-2
• Menopausal status not specified
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• No pre-existing collagen vascular disease except rheumatoid arthritis that does not require immunosuppressive therapy

PRIOR CONCURRENT THERAPY:

• No prior irradiation to the area of planned radiation field
• Concurrent hormone therapy allowed