1. Department of Radiation Oncology, Hokkaido Cancer Centre, Sapporo
2. Medical Image Laboratory, Sapporo
3. Department of Radiation Oncology, Kushiro Municipal General Hospital, Shunkodai Kushiro
4. Varian Medical Systems Japan, Nihonbashi Tokyo
5. Department of Radiation Oncology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan