Department of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA. Electronic address: Nikhil.Rao@moffitt.org. Department of Radiation Oncology, Moffitt Cancer Center, Tampa, FL, USA. Department of Biostatistics, Moffitt Cancer Center, Tampa, FL, USA. Department of Radiation Oncology, University of Florida, Gainsville, FL, USA. Department of Radiation Oncology, Duke University Cancer Center, Durham, NC, USA. Department of Onc Dentistry Prosthodontics, MD Anderson Cancer Center, Houston, TX, USA. Department of Radiation Oncology, Temple University Cancer Center, Philadelphia, PA, USA. Department of Radiation Oncology, MD Anderson Cancer Center, Houston, TX, USA.