[1] QST Hosp, Natl Inst Quantum Sci & Technol, Chiba, Japan
[2] Univ Tsukuba, Dept Radiat Oncol, Fac Med, Tsukuba, Japan
[3] Univ Tsukuba, Proton Med Res Ctr, Fac Med, Tsukuba, Japan
[4] Yamagata Univ, Dept Radiat Oncol, Fac Med, Yamagata, Japan
[5] Chiba Rosai Hosp, Dept Radiat Oncol, Chiba, Japan
[6] Naomi Clin, Tokyo, Japan