Beam position alignment and its verification for rotating-gantry

Control of the beam position is important for three-dimensional pencil-beam scanning. In the rotating-gantry, the beam alignment with each gantry angle is required for delivering high-stabilized beam. We have developed a simple procedure for the beam alignment to shorten the adjustment time. Firstly, beamline tuning is performed with steering magnets and beam profile monitors in the beam transport line. After the beamline tuning, the misalignment between the beam position and reference point in the treatment room is checked by the beam alignment verification system, which consists of the beam profile monitor and an acrylic phantom. If the beam position deviates from the reference point, the correction kick angle of steering magnet is calculated from the deviation of beam position at reference point. This adjustment is performed for the beam with different 201 energies at some gantry angles, the setting of the steering magnet current is interpolated at the different gantry angles. Finally, the beam alignment with the interpolated magnet's current is confirmed. In this report, we will report the result of our beam alignment method in the gantry at NIRS. (author)