1. Department of Radiation Oncology Graduate School of Medicine Hokkaido University Sapporo 060‐8638 Japan
2. Global Station for Quantum Medical Science and Engineering Global Institution for Collaborative Research and Education (GI‐CoRE) Hokkaido University Sapporo 060‐8648 Japan
3. Department of Radiation Oncology Stanford University Stanford CA 94305‐5847 USA
4. Department of Radiation Oncology Hokkaido University Hospital Sapporo 060‐8648 Japan
5. Department of Radiation Medical Science and Engineering Faculty of Medicine and Graduate School of Medicine Hokkaido University Sapporo 060‐8638 Japan
6. Department of Proton Beam Therapy Research Center for Cooperative Projects Faculty of Medicine Hokkaido University Sapporo 060‐8638 Japan