Figure 1.

Schematic representation of the inline MRI-linac apparatus. The treatment beam is inline with the main magnetic field of the MRI magnet. The patient is positioned between the poles of the open bore MRI magnet in a perpendicular position with respect to the main magnetic field and the treatment beam. The x-ray source is placed 100 cm from the system isocenter, which defines the standard configuration of the MRI-linac system. Hence, for the standard configuration, the electron gun cathode position is approximately 130 cm from the MRI-linac isocenter. The linac is allowed to move along the system axis of symmetry with ±15 cm around the standard configuration position.