This invention relates to a design of a floor stand structure to be used in conjunction with stereotactic radiosurgery or radiotherapy with a linear accelerator (LINAC). The floor stand is typically mounted on the floor bearing of the LINAC and rotates about a vertical axis. It has a contoured shape, which might be C-shaped, so that the gantry of the LINAC can swing by the floor stand in its lowest position. This is enabled by the contoured shape of the floor stand structure. The floor stand is used to stabilize the positioning of a patient's anatomy relative to the isocenter of the LINAC. It is typically attached to the rotating portion of the LINAC floor bearing, or could be self-standing with its own vertical bearing system to make it independent of the LINAC floor bearing.