Trial to Compare MRI-guided Precision Prone Irradiation (PPI) Versus CT-guided Breast Irradiation

The Investigators are investigating the potential role of MRI-guided Radiation Therapy for patients receiving breast radiotherapy in the prone position with a MRI-Linac radiotherapy system, the Precision Prone Irradiation (PPI) technique. Hypothesis: The investigators would like to hypothesize that breast radiation therapy using MRI-guided system including the MRI-Linac (Arm 2) is comparable to the current standard of treatment using conventional CT-based system (Arm 1), in terms of local control of the disease at 2 year time point.