1. Medical Physics and Informatics Laboratory, Department of Electronics Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan
2. Department of Radiation Oncology, Institute for Advanced Radiation Oncology, Monmouth Medical Center, Barnabas Health, Long Branch, NJ 07740, USA
3. Department of Radiation Oncology, Kaohsiung Chang Gung Memorial Hospital, Chang Gung University, College of Medicine, Kaohsiung 833, Taiwan
4. Department of Medical Imaging and Radiological Sciences, Chang Gung University, Taoyuan 333, Taiwan
5. Medical Physics Department, Memorial Sloan-Kettering Cancer Center, 136 Mountain View Boulevard, Basking Ridge, NJ 07920, USA
6. Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA 91010, USA