1. Department of Radiation Oncology; Tohoku University Graduate School of Medicine; Sendai 980-8574 Japan
2. Department of Bioengineering; Graduate School of Engineering Science; Osaka University; Osaka 565-0871 Japan
3. Department of Radiology; Tohoku University Hospital; Sendai 980-8574 Japan
4. Department of Therapeutic Radiology; Tohoku University School of Medicine; Miyagi 980-8574 Japan