The breast quadrants division is established in upright position. However, according to the surgery simulator pipeline (Figure 2), the tumor is defined in the supine position. Therefore, in an attempt to define quadrants in the horizontal position which correctly correspond the upright ones, the nipple position (manually annotated) is used as a reference point to compute the vertical and horizontal planes that define the quadrants boundaries. Three main planes are then sequentially defined, as seen in Figure 5. The first plane corresponds to the one along the pectoral muscle (Figure 5a) and is defined by its normal which is computed by the cross product of two vectors, defined by three corner points of the pectoral muscle (two on the top and one on the bottom). The second plane sets the superior-inferior boundary (red plane in Figure 5b) and is defined as parallel to the xy-plane (taking into account that the direction of the MRI acquisition is perpendicular to this plane), crossing the nipple. Finally, the third plane sets the lateral-medial boundary (green plane in Figure 5c), being perpendicular to the pectoral plane and crossing the nipple too.