Statement: Patients cannot be excluded from the primary trial on the basis of gender or ethnicity.
Primary_evidence: INCLUSION CRITERIA:   Patient must be 18 years of age or older   Patients must have histologically confirmed (by routine H&E staining) adenocarcinoma of the breast any T, any N, M0 disease   Patients must have undergone a segmental mastectomy (SM) with a level I and ll axillary dissection or sentinel lymph node biopsy. Surgical margins at time of local surgery must be negative greater or equal to 2mm for both invasive carcinoma and for non-invasive ductal carcinoma Patients who have post-operative margins which are negative but less than 2mm will be considered eligible if the surgeon states that the margin in question cannot be improved.   Patients must be registered such that radiation therapy begins within 10 weeks of last surgery   Patients must have a performance status 0 or 1 by Eastern Cooperative Oncology Group (ECOG) criteria or a 80-100 Karnofsky Performance Scale at time of consult   Women of all races and ethnic groups are eligible for this trial EXCLUSION CRITERIA:   Patients must not have received prior radiation therapy to the breast at any time for any reason   Patients with squamous carcinomas or sarcomas of the breast cancer are not eligible   Patients treated with a mastectomy are NOT eligible   Any patient with active local-regional disease prior to registration is not eligible   No other prior malignancy is allowed except for adequately treated basal cell or squamous cell skin cancer, in situ cervical cancer, or any other cancer from which the patient has been disease-free for at least 5 years   Patients must not be pregnant due to the potential for fetal harm as a result of this treatment regimen. Women of child-bearing potential must use effective non hormonal contraception while undergoing radiation therapy   Patients must not have a serious medical or psychiatric illness which prevents informed consent or compliance with treatment