Verification and optimization of the optical parameters for slow extracted beam

Control of the beam size and position for three-dimensional pencil-beam scanning is important. We have developed a simple procedure for the optimization of the optical parameters and the beam alignment. Verification of the beam optics is performed by the measured beam size and variation of the beam position along the beam transfer line. Optimization of the beam optics is performed with the measured optical parameters at the extraction point. After the optimization, beamline tuning is performed with steering magnet and fluorescent screen. The misalignment between the beam position and reference axis in the treatment room is checked by the verification system, which consists of the screen monitor and an acrylic phantom. If the beam position is deviated from the reference axis, two pairs of steering magnets that are placed downstream of the beam transport line will correct the beam. These adjustments are iterated until the deviations for 11 energies of the beam are within 0.5 mm of the reference axis. To indicate the success of our procedure, we performed experiment at the Kanagawa Cancer Center using our procedure. (author)