1. Proton Medical Research Center, University of Tsukuba, 2-1-1 Amakubo, Tsukuba, Ibaraki 305-8576, Japan
2. Department of Radiation Oncology, Kobe Proton Center, 1-6-8, Minatoshima-minamimachi, Chuou-ku, Kobe, 650-0047, Japan
3. Obstetrics & Gynecology of University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan