1. Graduate School of Engineering Hokkaido University Sapporo Hokkaido Japan
2. Hitachi Ltd. Hitachi Ibaraki Japan
3. Faculty of Engineering Hokkaido University Sapporo Hokkaido Japan
4. Proton Beam Therapy Center Hokkaido University Hospital Sapporo Hokkaido Japan
5. Department of Medical Physics Hokkaido University Hospital Sapporo Hokkaido Japan