MRI-Based Preoperative Accelerated Partial Breast Irradiation

Inclusion Criteria: * Pathologically proven diagnosis of invasive breast cancer, clinically stage I-II. * Female * Age ≥40 years * Estrogen receptor positive * Patients with both her2 positive and her2 negative tumors are eligible * Unifocal disease * Invasive ductal carcinoma diagnosed by core needle biopsy * Clinically node negative both by physical exam and by ultrasound. All enlarged or abnormal appearing lymph nodes must be biopsied. * Zubrod performance status 0-2 * Study entry must be within 120 days from initial diagnosis of breast cancer. * Complete blood count (CBC) /differential obtained within 14 days prior to study entry, with adequate bone marrow function defined as follows: Absolute neutrophil count ≥ 1,800 cells/mm\^3; Platelets ≥ 75,000 cells/mm\^3; Hemoglobin ≥8.0g/dl. * Not pregnant or lactating; willing to use acceptable forms of contraception during radiation therapy. * Prior breast augmentation, including breast implants, is allowed. * Patients with a prior history of contralateral breast cancer will be considered eligible if they completed all treatment (including anti-endocrine therapy) more than five years prior to registration. * Patients must not have a prior treatment of malignancy diagnosed or treated within the past five years, with the exception of non-melanomatous skin cancer, carcinoma in situ of the cervix and contralateral breast cancer. * Interested patients must meet with a medical oncologist prior to study entry to determine if Oncotype …