1. Department of Radiation Medicine, Faculty of Medicine, Hokkaido University, North-15 West-7, Kita-ku, 0608638, Sapporo, Hokkaido, Japan
2. Global Station for Quantum Medical Science and Engineering, Global Institute for Cooperative Research and Education, Hokkaido University, North-15 West-7, Kita-ku, 0608638, Sapporo, Hokkaido, Japan
3. Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA, USA
4. Department of Medical Physics, Hokkaido University Hospital, Sapporo, Japan