ESTRO 2021 Abstract Book

S192

ESTRO 2021

Conclusion We show that IACS-010759 decreases oxygen consumption in several tumor cell lines in vitro while it also causes energetic stress and growth inhibition. Moreover, IACS-010759 has an immunomodulatory effect on the TME in vivo . Changes in the TME are likely due to a decrease of oxygen consumption and subsequent relieve of tumor hypoxia. The observed change towards a more immune permissive TME suggests this new treatment strategy might be combined with immuno- and radiotherapy to enhance treatment efficacy.

Proffered papers: Proffered papers 15: Radiobiology of normal tissues

OC-0283 LET dependence of proton RBE in early normal tissue damage in vivo C. Overgaard 1 , M.K. Sitarz 2 , N. Bassler 3 , H. Spejlborg 4 , J.G. Johansen 2 , E. Kanouta 2 , C. Grau 2 , J. Overgaard 5 , P. Poulsen 2 , B.S. Sørensen 2 1 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus , Denmark; 2 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 3 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus , Denmark; 4 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 5 Aarhus University Hospital, Department of Experimental Clinical Oncology, Aarhus, Denmark Purpose or Objective Proton therapy can provide more favorable dose distributions than photon radiotherapy, but while the physical characteristics of proton radiation have been the aim of intense research, less focus has been on the actual biological response particle irradiation gives rise to. Protons radiation has a higher radiobiological effect (RBE) than photons, and current clinical practice uses a fixed RBE of 1.1, but RBE is a complex quantity, depending on both biological and physical parameters. In vitro studies and the few conducted in vivo show a varying biological effect across the Spread Out Bragg Peak (SOBP), especially at the distal end of the proton track due to the rapidly increasing linear energy transfer (LET). There is a need for in vivo data to link between the current in vitro studies and clinical considerations regarding proton RBE. The aim of this study is to quantify the distal edge RBE of normal tissue for acute skin damage in a mouse model. Materials and Methods In this study 362 12-14 week-old C 3 H/HeNRj mice were included. Mice were fixated in jigs and placed on top