more robust immune system activation, compared to conventional radiotherapy modalities [27, 29]. In our research, we investigate how CIRT can modulate radiation responses, tumor control and immune activation [...] supporting the killing of tumor cells by activating an immune response [16, 17]. In an in vivo model system (osteosarcoma, metastases in the lungs), we were able to demonstrate that carbon ions – in combination [...] which is not the case for conventional photon therapy (XRT), when compared to untreated negative controls (NC). Addition of immunotherapy (Figure 1: a mix checkpoint inhibitors, CPI) fosters the immunogenic