Professor Kristian Berg has been head of the Department of Radiation Biology for 13 years and leader of the PCI-group for more than 25 years. After his MSc in biochemistry he has more than 30 years of experience in experimental and preclinical research within the field photodynamic therapy (PDT). A major focus of his research has been to reveal the mechanisms involved in the therapeutic effects of PDT and implementing such knowledge towards clinical utilization. These studies has influenced on the development of 5-aminolevulinic acid esters into clinical use. Since 1995 the focus has been to utilize PDT as a platform, named photochemical internalization (PCI), for inducing intracellular delivery and activation of drugs that accumulate in endocytic vesicles. This includes macromolecular therapeutics under development for clinical use in e.g. recombinant immunotoxin therapy, antigens for cancer vaccination, gene therapy and oligonucleotides for inhibition of gene expression, nanotechnology as well as some  chemotherapetics. Several clinical trials have been carried out on the PCI technology. This research has resulted in approx. 120 publication with Berg as coauthor and more than 400 peer-reviewed publications worldwide focusing on the PCI technology. In total, he has published more than 250 scientific publications on photobiological topics as well as 11 patents.

Kristian has been the President of the European Society for Photobiology (ESP) and involved in various commitments in ESP for more than 20 years, Board Member of IPA, Founder and Director of the ESP Photobiology School since its start in 2010 till 2020 and contributed to establishment of the photomedical companies Photocure and PCI Biotech. Kristian has also been associated editor of the journal Photochemical & Photobiological Sciences since 2008 and member of the advisory board of the journal Photodiagnosis and Photodynamic Sciences since 2007. He has received several awards including most recently the Lifetime Achievement Award of the International Photodynamic Association (2023), European Commissions Innovation Radar Prize for Innovative Science (2019), European Society for Photobiology Award for Excellence in Photobiological Research (2013), He is also elected Member of the Norwegian Academy of Science and Letters and the Royal Norwegian Society of Sciences and Letters.