1. Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill, NC, USA
2. Department of Radiation Medicine, MedStar Georgetown University Hospital, Washington, DC, USA
3. Merck & Co, Rahway, NJ, USA
4. Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA
5. Department of Radiation Oncology, Valley Mount Sinai Comprehensive Cancer Care, Paramus, NJ, USA