Brian O’Sullivan is Professor of Radiation Oncology at the University of Toronto, Princess Margaret Hospital (PMH) Toronto, Canada. He received his medical degree in Dublin, Ireland and completed oncology training at PMH. He has almost 450 peer-reviewed publications and written numerous additional textbooks and articles. He is Chair of the UICC Prognostic Factors Committee of the Union for International Cancer Control (UICC). He has received numerous honours including the American Society of Radiation Oncology (ASTRO) Gold Medal in 2020.