Radiation Therapy in Treating Women With Early Stage Breast Cancer

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