[1] Natl Inst Quantum & Radiol Sci & Technol, Hosp Natl Inst Radiol Sci, Chiba, Japan
[2] Brown Univ, Alpert Med Sch, Providence, RI 02912 USA
[3] SAGA HIMAT Fdn, Ion Beam Therapy Ctr, Tosu, Saga, Japan
[4] Yamagata Univ, Fac Med, Dept Radiat Oncol, Yamagata, Japan