1 Division of Medical Radiation Physics, Department of Radiation Oncology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
2 Department of Radiation Oncology, University of Colorado School of Medicine, Aurora, Colorado.
3 Department of Radiation Oncology, Mayo Clinic Arizona, Phoenix, Arizona.
4 Department of Radiation Oncology, University of Pennsylvania, Philadelphia, Pennsylvania. Electronic address: david.carlson@pennmedicine.upenn.edu.