Radiation Therapy (WBI Versus PBI) in Treating Women Who Have Undergone Surgery For Ductal Carcinoma In Situ or Stage I or Stage II Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed ductal carcinoma in situ (DCIS\*) or invasive\* adenocarcinoma of the breast * Stage 0, I, or II disease * Stage II tumors must be ≤ 3 cm * Gross disease must be unifocal * Microscopic multifocality allowed provided total pathological tumor size is ≤ 3 cm * No proven multicentric carcinoma in more than 1 quadrant or separated by ≥ 4 cm * No non-epithelial breast malignancies (e.g., sarcoma or lymphoma) NOTE: \*Patients who are 50 years of age and over with DCIS regardless of hormone receptor status AND patients with invasive breast cancer meeting all of the following criteria: ≥ 50 years of age, node-negative, and hormone-receptor positive status will not be enrolled in study after 12/30/2006 * Prior axillary staging required for patients with invasive breast cancer, including 1 of the following: * Sentinel node biopsy alone (if sentinel node is negative) * Sentinel node biopsy followed by axillary dissection or sampling with ≥ 6 axillary nodes (if sentinel node is positive) * Axillary dissection alone with ≥ 6 axillary nodes * No more than 3 positive axillary nodes * No axillary nodes with definite evidence of microscopic or macroscopic extracapsular extension * No positive non-axillary sentinel nodes (intramammary nodes are staged as axillary nodes) * No palpable or radiographically suspicious ipsilateral or contralateral axillary, supraclavicular, infraclavicular, or internal mammary nodes unless there is histologic confirmation that these nodes are negative for tumor * Must have undergone lumpectomy * Resected margins histologically free of tumor * Re-excision of surgical margins allowed * Target lumpectomy cavity clearly delineated AND target lumpectomy/whole breast reference volume ≤ 30% based on postoperative pre-randomization CT scan * Final surgery (i.e., lumpectomy, re-excision of margins, or axillary staging procedure) within the past 42 days * No suspicious microcalcifications, densities, or palpable abnormalities in the ipsilateral or contralateral breast unless biopsied and found to be benign * No Paget's disease of the nipple * No history of invasive breast cancer or DCIS * Prior lobular carcinoma in situ treated by surgery alone allowed * No synchronous bilateral invasive or non-invasive breast cancer * Partial breast irradiation deemed technically deliverable by radiation oncologist at a credentialed facility * Must have undergone a history and physical exam within the past 4 months AND a bilateral mammogram within the past 6 months * Hormone receptor status: * Estrogen receptor (ER) status known * Progesterone status known if ER analysis is negative * Marginal or borderline results are considered positive PATIENT CHARACTERISTICS: Age * 18 and over Sex * Female Menopausal status * Premenopausal or postmenopausal Performance status * Not specified Life expectancy * At least 10 years, excluding diagnosis of breast cancer Hematopoietic * Not specified Hepatic * Not specified Renal * Not specified Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective non-hormonal contraception * No other malignancy within the past 5 years except previously treated carcinoma in situ of the cervix or colon, melanoma in situ, or basal cell or squamous cell skin cancer * Deemed to be at low risk for recurrence * No collagen vascular disease (e.g., systemic lupus erythematosus or scleroderma), specifically dermatomyositis with a creatine phosphokinase (CPK) level above normal, or active skin rash * No psychiatric or addictive disorder that would preclude study therapy PRIOR CONCURRENT THERAPY: Biologic therapy * No prior biologic therapy for this malignancy Chemotherapy * No prior chemotherapy for this malignancy * No concurrent chemotherapy during study radiotherapy Endocrine therapy * No prior hormonal therapy for this malignancy unless total duration of hormonal therapy was no more than 28 days before randomization * Concurrent hormonal therapy allowed provided it is not administered during chemotherapy * No concurrent raloxifene, tamoxifen, or other selective estrogen receptor modulating drugs * No concurrent hormone replacement therapy * No concurrent Femring\^® Radiotherapy * No prior radiotherapy for this malignancy * No prior breast or thoracic radiotherapy * No concurrent brachytherapy boosts * No concurrent intensity modulated radiotherapy * No concurrent regional nodal irradiation Surgery * See Disease Characteristics * No prior breast implants * Patients who have had implants removed are eligible Other * No other concurrent anticancer therapy