A robotic patient positioning assembly for therapeutic radiation treatment includes a robotic positioning device for moving and supporting the patient during treatment, a sensor system for detecting the position of the robotic positioning device, and a controller operatively connected with the sensor system for receiving position data of the robotic positioning device and operatively connected to the robotic positioning device for controlling the motions of the robotic positioning device. The controller is adapted for controlling the motion of the robotic positioning device in response to information representative of the position of the robotic positioning device received from the sensor system, so that the treatment target within a patient loaded on the robotic positioning device is properly aligned with a radiation source of a therapeutic radiation treatment system.