1 Department of Heavy Particles & Radiation Oncology, Taipei Veterans General Hospital, Taipei, Taiwan.
2 Department of Heavy Particles & Radiation Oncology, Taipei Veterans General Hospital, Taipei, Taiwan; School of Medicine, National Yang Ming Chao Tung University, Taipei, Taiwan; Institute of Public Health, National Yang Ming Chao Tung University, Taipei, Taiwan. Electronic address: tylai@vghtpe.gov.tw.