is a Professor of Radiation Oncology at Harvard Medical School and Director of Physics Research for the Department of Radiation Oncology at Massachusetts General Hospital. He received his PhD in experimental nuclear physics in 1992 from the Rheinische-Friedrich-Wilhelms University in Bonn, Germany. He has been working in radiation therapy research since 1994 and has made many significant contributions to the field of radiation oncology physics and biology, specifically in proton therapy. He has published about 300 peer-reviewed publications and numerous book chapters and edited three books on proton radiation therapy. His research interests include planning and delivery uncertainties in radiation therapy, biological effect modeling, Monte Carlo dose calculation, advanced optimization and imaging techniques as well as understanding radiation induced toxicities and systemic effects on the immune system. His work has been funded mostly by the National Institute of Health, including seven R01 grant awards as Principal Investigator throughout his career. In 2022 he received the Particle Therapy Co-Operative Group (PTCOG) Robert R. Wilson Award for significant contributions to the field of particle therapy. For his efforts in mentoring junior faculty he received the A. Clifford Barger Excellence in Mentoring Award by Harvard Medical School in 2012.

In addition to his research, he has been involved in numerous task groups and committees for organizations such as PTCOG, International Atomic Energy Agency, International Commission on Radiation Units and Measurements, International Commission on Radiological Protection, International Organization for Medical Physics, American Association of Physicists in Medicine (AAPM), and American Society for Radiation Oncology (ASTRO) and served, for instance, as the Physics Track Chair of ASTRO as well as Therapy Program Director for AAPM. He currently serves on ASTRO’s Research Grants Evaluation Subcommittee is an elected member of NCRP.