Dr Holmberg is the Head of the Radiation Protection of Patients Unit at the International Atomic Energy Agency (IAEA), Vienna, Austria - an organization within the United Nations family. He is a medical physicist from Sweden with radiotherapy experience from Skåne University Hospital, Malmö; Sweden, St. Luke's Hospital, Dublin, Ireland; and The Netherlands Cancer Institute, Amsterdam. Prior to his appointment at the IAEA he was the Chief Physicist at Copenhagen University Hospital, Herlev, Denmark.

He is a co-founder of the Radiation Oncology Safety Information System (ROSIS, 2001) an international voluntary safety reporting system for radiotherapy, and has also participated as a Task Group member for the International Commission on Radiological Protection (ICRP) on prevention of accidental exposures from new external beam radiation therapy technologies, which led to the ICRP Publication 112.

Dr Holmberg has published scientific papers on radiation protection of patients in journals such as The Lancet. He has served as Course Director for ESTRO on radiotherapy treatment planning. He is the Scientific Secretary for the Steering Panel of the International Action Plan for Radiation Protection of Patients, a body with participation of many international organizations, including the IAEA, WHO, UNSCEAR, ICRP and ICRU, and he was recently the Scientific Secretary for the International Conference on Radiation Protection in Medicine - Setting the Scene for the Next Decade, held in Bonn, Germany, in December 2012.