1. Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
2. Department of Health Sciences, Faculty of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
3. Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
4. Ion Beam Therapy Center, SAGA HIMAT Foundation, 3049 Harakogamachi, Tosu-shi 841-0071, Japan
5. Department of Medical Radiation Physics, Lund University, SE-221 85 Lund, Sweden