1. Research Center for Charged Particle Therapy National Institute of Radiological Sciences Chiba 263‐8555 Japan
2. Research and Development Center Toshiba Corporation Kanagawa 212‐4582 Japan
3. Accelerator Engineering Corporation Chiba 263‐0043 Japan
4. Department of Radiation Oncology Yonsei University College of Medicine Seoul 03722 Korea
5. Toshiba Energy System & Solutions Corporation Kanagawa 212‐8585 Japan