Stefan Both received his PhD degree from the Babes-Bolyai University, in 2005. His Physicist career started at the Kiricuta Oncology Institute, Romania, in 1996. He immigrated to the US in 2000 and worked in private and academic radiation oncology. In 2008, Dr Both became a faculty member at the University of Pennsylvania, Philadelphia, where he was able to advance treatment programs in conventional radiotherapy, establish and lead the physics residency programs, and spearhead technical advances, including proton therapy. In 2015, he joined Memorial SloanKettering Cancer Center, New York, as an Associate Attending and Lead Physicist. Currently, Dr. Both is the Professor and Head of Medical Physics and Instrumentation in the Department of Radiation Oncology at the Groningen University Medical Center, Netherlands. He is board certified by the American Board of Radiology in Therapeutic Radiological Physics, a Fellow of the American Association of Physicists in Medicine and an Extraordinary Member of the Dutch Medical Physics Society. He serves on committees of the American Association of Physicists in Medicine, Particle Therapy Co-Operative Group, Commission on Accreditation of Medical Physics Programs and American Board of Radiology. Dr. Both has been an invited speaker and committee member at conferences, published over 70 papers in peer reviewed journals, has more than 140 conference contributions, participates to editorial and advisory boards and edited and coauthored books. His main research interests are advanced treatment planning, motion and range uncertainty management, biological guided adaptive radiotherapy and atomization in proton therapy.