Prior to radiotherapy planning, breast conserving surgery in the form of lumpectomy will be carried out in the department of surgery under general anaesthesia. Patients will be recruited 2-3 weeks after lumpectomy. A planning CT scan will be made for each patient. The patients will be positioned on a breast board with sternum parallel to the table, and the ipsilateral arm abducted above the head. Before the CT scan skin marks would be placed to enable the patient repositioning during treatment. Radioopaque markers will be placed to locate the whole breast and lumpectomy cavity on CT images.