3-Dimensional Conformal Radiation Therapy In Treating Women With Stage I or Stage II Breast Cancer Previously Treated With Lumpectomy and Axillary Node Dissection

DISEASE CHARACTERISTICS: * Histologically confirmed invasive breast cancer * Stage I or II (T1, N0; T1, N1; T2, N0; or T2, N1) * Unifocal disease (single focus that can be encompassed by one lumpectomy) * The following histologies are eligible: * Invasive ductal * Medullary * Papillary * Colloid (mucinous) * Tubular * No invasive or extensive in situ lobular carcinoma or pure ductal carcinoma in situ (DCIS) * No nonepithelial breast malignancies such as sarcoma or lymphoma * Previously treated with lumpectomy of a lesion no greater than 3 cm and axillary dissection of at least 6 lymph nodes or a sentinel node biopsy * Six surgical clips in place delineating the margins of the tylectomy cavity * Negative, inked histologic margins of lumpectomy (greater than 2 mm) OR re-excision specimen available for confirmation * Negative mammography post-lumpectomy or post-excision if malignancy-associated microcalcifications were initially present * No prior lumpectomy so extensive that the cosmetic result is low or poor prior to radiotherapy * No more than 3 positive axillary nodes * No 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 negative by biopsy * No palpable or radiographically suspicious contralateral axillary, supraclavicular, infraclavicular, or internal mammary nodes unless nodes are histologically negative * No extensive intraductal carcinoma, indicated by one of the following according to the Harvard definition: * More than 25 % of invasive tumor is DCIS and DCIS is in adjacent breast tissue * Intraductal carcinoma with microinvasion * No previously treated contralateral breast cancer or synchronous ipsilateral breast cancer * No evidence of suspicious microcalcifications * No Paget's disease of the nipple * No skin involvement by disease, regardless of tumor size * No distant metastases * Hormone receptor status: * Not specified PATIENT CHARACTERISTICS: Age * 18 and over Sex * Female Menopausal status * Not specified Performance status * Not specified Life expectancy * At least 2 years Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception * Technically suitable for breast radiotherapy * No collagenous diseases (e.g., systemic lupus erythematosus, scleroderma, or dermatomyositis) * No other medical condition that would limit life expectancy * No psychiatric or addictive disorders that would preclude giving informed consent * No other malignancy within the past 5 years except nonmelanoma skin cancer PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * At least 2 weeks since prior chemotherapy * No concurrent chemotherapy during and for at least 2 weeks after completion of study therapy Endocrine therapy * Concurrent anastrozole or tamoxifen allowed Radiotherapy * No prior radiotherapy for the current malignancy Surgery * See Disease Characteristics Other * No prior nonhormonal therapy for the current malignancy