Inclusion Criteria

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