Patient description: The patient is a 42 year-old postmenopausal woman who had a screening sonogram which revealed an abnormality in the right breast. She had no palpable masses on breast exam. Core biopsy was done and revealed a 1.8 cm infiltrating ductal breast carcinoma in the left upper outer quadrant. Lumpectomy was done and the surgical margins were clear. The tumor was HER2-positive and ER/PR negative. Axillary sampling revealed 1 positive lymph node out of 12 sampled. CXR was unremarkable. She is using “well women” multivitamins daily and no other medication. She smokes frequently and consumes alcohol occasionally. She is in a relation with only one partner and has a history of 3 pregnancies and live births. She breastfed all three children.

Clinical trial eligibility criteria: eligible ages (years): 18.0-999.0,  Early Stage Breast Cancer Ductal carcinoma in situ (DCIS) or invasive epithelial (ductal, medullary, papillary, mucinous (colloid), or tubular histologies Willing and able to provide consent Age >=18 years Performance status Eastern Cooperative Oncology Group (ECOG) 0-2 Women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, for the duration of study participation, and for 90 days following completion of therapy. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her treating physician immediately Appropriate staging studies identifying as American Joint Committee on Cancer (AJCC) stage 0, I, or II breast cancer. If stage II, the tumor size must be 3 cm or less Surgical treatment of the breast with lumpectomy Clinical Target Volume (CTV) margin up to 5 cm in maximum dimension with histologically confirmed margins free of tumor (negative margins defined as no tumor on ink in all directions). Re-excision of surgical margins is permitted Gross disease within the breast must be unifocal. (Patients with microscopic multifocality are eligible as long as the total extent of tumor, gross and microscopic, occupies a volume with greatest dimension 3 cm or less) Patients with invasive disease are required to have axillary staging including: sentinel node biopsy alone if sentinel node is negative, sentinel node biopsy followed by axillary dissection with a minimum of 6 axillary nodes sampled if sentinel node is positive, or axillary dissection alone (with a minimum of 6 axillary nodes). Patients with DCIS are not required to have axillary staging Patients with a history of non-breast invasive malignancies are eligible if they have been disease-free for 3 or more years prior to entry into the study  T2 (>3.0 cm), T3, stage III, or stage IV breast cancer More than 3 histologically positive axillary lymph nodes or axillary lymph nodes with microscopic or macroscopic extracapsular extension Positive non-axillary sentinel nodes or evidence of suspicious supraclavicular, infraclavicular, or internal mammary nodes by imaging or physical exam, unless biopsied and found to be negative for tumor Evidence by physical examination or mammography of other suspicious masses, densities, or microcalcifications in either breast, unless biopsied and found to be benign Non epithelial breast malignancies such as sarcoma or lymphoma Multicentric gross breast carcinoma (either DCIS or invasive cancer) or microscopic breast carcinoma occupying a volume with maximum dimensions of more than 3 centimeters Synchronous bilateral invasive or non-invasive breast cancer Paget's disease of the nipple Previous breast radiation on ipsilateral side or thoracic radiation on the ipsilateral side Treatment plan that includes regional nodal irradiation