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): 20.0-65.0,  Breast Cancer ECOG. (Eastern Cooperative Oncology Group): 0-2 2. Histologic documentation of invasive duct or lobular adenocarcinoma of the breast 3. If neoadjuvant chemotherapy was NOT administered: pathologic T1-3, N1-2 following definitive surgery 4. If neoadjuvant chemotherapy was administered, pathology from the definitive surgery must confirm pathologic T1-3, N1-2 disease and also meet one of the following Clinical T1-3, N1-2 or Pathologic confirmation of axillary nodal involvement at presentation (ie, before neoadjuvant therapy) based on any of the following: Positive fine-needle aspiration (FNA), Positive core needle biopsy. 5. Complete resection of known breast disease by one of the following surgeries Lumpectomy with axillary lymph node dissection with no more than 12 resected lymph nodes. Mastectomy and axillary lymph node dissection with no more than 12 resected lymph nodes. 5 ER(estrogen-receptor), PR (progesterone-receptor), and HER2(human epidermal growth factor receptor 2) testing performed on the primary breast tumor; when applicable, testing must have been performed before receiving neoadjuvant chemotherapy. 6-Margins of the resected specimen must be histologically free of invasive tumor and ductal carcinoma in situ (DCIS) as determined by the pathologist. 7-The surgical wound should be completely healed without any signs of infection. 8-Interval between the last surgery for breast cancer or the completion of adjuvant chemotherapy and study enrollment must be ≤ 56 days (ie, a maximum of 8 weeks). 9-If adjuvant chemotherapy is received there should be at least 10 days gap between the last day of chemotherapy and the enrollment in the study to avoid skin toxicity. 10-Women of child-bearing potential must agree to use a medically accepted form of pregnancy prevention for the duration of study treatment 11-Ability to understand and willingness to sign the consent form written in Arabic  Patients with surgical margins less than or equal to 2mm. 2. Patients with axillary dissection of more than 12 lymph nodes due to high incidence of arm lymphedema. 3. Women with Huge pendulous breast. 4. Patients with bad breast conservative surgery ( Surgery that impair the cosmetic outcome before starting radiotherapy). 5. T4 tumors including inflammatory breast cancer. 6. Known definitive clinical or radiologic evidence of metastatic disease. 7. Patients re operated for microscopic positive margins after definitive surgery. 8. Previous radiation therapy for the currently diagnosed breast cancer prior to study enrollment 9. History of ipsilateral or contralateral breast or thoracic radiotherapy for any condition 10. History of ipsilateral or contralateral axillary surgery for any condition 11. History of lymphedema involving the ipsilateral or contralateral arm at present or at any time in the past 12. Active collagen vascular disease, specifically dermatomyositis with a creatine phosphokinase (CPK) level above normal or with an active skin rash, systemic lupus erythematosis, or scleroderma. 13. Pregnancy or breastfeeding 14. Second primary cancer