Whole Breast Irradiation vs Twice Daily vs. Once Daily Accelerated Partial Breast Irradiation

This is a randomized phase III trial in women with invasive carcinoma of the breast with negative axillary nodes treated by Breast Conserving Surgery (BCS). Eligible, patients will be randomly allocated to receive radiotherapy of 3 Dimensional Conformal Radiation Therapy (3DCRT) Whole Breast Irradiation (WBI) 50 Gray (Gy) in 25 daily fractions over 5 weeks or Accelerated Partial Breast Irradiation (APBI) 38.5 Gy in 10 daily fractions of 3.85Gy over two weeks or 38.5 Gy in 10 twice daily fractions of 3.85Gy over one week. Patients will be followed at 6, 12, 18 and 24 months post randomization. Cosmetic outcome will be measured using photographs and evaluated by a panel of trained radiation oncologists. Radiation toxicity will be assessed using National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE).