A gantry configuration for a combined mobile radiation inspection system, comprising: a first arm frame configured to be movable along a first rail; a second arm frame, opposite to the first arm frame, configured to be movable along a second rail parallel to the first rail; and a horizontal third arm frame connecting the first and second arm frames (100, 200), so as to move with the first and second arm frames (100, 200), wherein the first, second and third arm frames (100, 200, 300) together define a scanning channel to allow an inspected object to pass therethrough, wherein the gantry configuration for the combined mobile radiation inspection system further comprising: a position sensing device (110, 210) configured to detect a position error (e) between the first arm frame and the second arm frame; a radiation source mounted on one of the first arm frame and the second arm frame and configured to emit a ray onto the inspected object passing through the scanning channel, and a radiation detector mounted on the other of the first arm frame and the second arm frame and configured to receive the ray emitted from the radiation source; and a controller configured to control a moving speed of at least one of the first arm frame and the second arm frame based on the position error (e) detected by the position sensing device (110, 210), so that the position error (e) between the first arm frame and the second arm frame is equal to zero, characterised in that the position sensing device comprises a deformation sensor configured for detecting a deformation of the horizontal third arm frame so as to determine the position error between the first arm frame and the second arm frame based on the deformation. a first arm frame configured to be movable along a first rail; a second arm frame, opposite to the first arm frame, configured to be movable along a second rail parallel to the first rail; and a horizontal third arm frame connecting the first and second arm frames (100, 200), so as to move with the first and second arm frames (100, 200), wherein the first, second and third arm frames (100, 200, 300) together define a scanning channel to allow an inspected object to pass therethrough, wherein the gantry configuration for the combined mobile radiation inspection system further comprising: a position sensing device (110, 210) configured to detect a position error (e) between the first arm frame and the second arm frame; a radiation source mounted on one of the first arm frame and the second arm frame and configured to emit a ray onto the inspected object passing through the scanning channel, and a radiation detector mounted on the other of the first arm frame and the second arm frame and configured to receive the ray emitted from the radiation source; and a position sensing device (110, 210) configured to detect a position error (e) between the first arm frame and the second arm frame; a radiation source mounted on one of the first arm frame and the second arm frame and configured to emit a ray onto the inspected object passing through the scanning channel, and a radiation detector mounted on the other of the first arm frame and the second arm frame and configured to receive the ray emitted from the radiation source; and a controller configured to control a moving speed of at least one of the first arm frame and the second arm frame based on the position error (e) detected by the position sensing device (110, 210), so that the position error (e) between the first arm frame and the second arm frame is equal to zero, characterised in that the position sensing device comprises a deformation sensor configured for detecting a deformation of the horizontal third arm frame so as to determine the position error between the first arm frame and the second arm frame based on the deformation.