Contemporary radiotherapy (RT) planning utilizes both a computed tomography (CT) scan either in prone or supine position with no breast compression or magnetic resonance imaging (MRI). The application of MRI is limited by image distortion and a lack of electron density information. The standard supine position not only exposes the tumor to RT non-homogenously, it can cause damage to the neighboring benign tissues. Here, we compare the effectiveness of both the prone and supine positions in breast cancer RT and various aspects of breast cancer treatment planning using MRI and CT.