Charles B. Simone, MD 
The New York Proton Center, Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY 10035, USA
Stephen J. Hunt, MTR, MD, PhD 
Penn Image-Guided Interventions (PIGI) Laboratory, Department of Radiology, Perelman School of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA
Abass Alavi, MD, MD (Hon), PhD (Hon), DSc (Hon) 
Division of Nuclear Medicine, Department of Radiology, Perelman School of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA
Steven J. Feigenberg, MD 
Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA