1. Department of Radiology, Perelman School of Medicine, University of Pennsylvania, 3620 Hamilton Walk, Philadelphia, Pennsylvania 19104, United States
2. Department of Radiation Oncology, Perelman School of Medicine, University of Pennsylvania, 3400 Civic Center Boulevard, Bldg 421, Philadelphia, Pennsylvania 19104, United States
3. Department of Physics and Astronomy, University of Pennsylvania, 3231 Walnut Street, Philadelphia, Pennsylvania 19104, United States
4. Department of Microbiology and Immunology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, United States