ESTRO 2025 - Abstract Book

S2390

Interdisciplinary – Other

ESTRO 2025

radiation oncology community. This platform paves the way for new research questions and supports methodological innovation in radiotherapy.

Keywords: real-world evidence, multi-cohort study

References 1. Lievens Y et al, Lancet Oncol 2019. doi:10.1016/S1470-2045(18)30917-3. 2. Burock S et al, Eur J Cancer 2013. doi.org/10.1016/j.ejca.2013.05.016 3. Christ SM et al, Radiother Oncol 2024. doi.org/10.1016/j.radonc.2024.110235. 4. Alongi F et al, Radiother Oncol 2024. doi.org/10.1016/j.radonc.2024.110466 5. Bultijnck R et al, Clin Transl Radiat Oncol 2023. doi:10.1016/j.ctro.2023.100715.

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Digital Poster Systemic effects of local radiation in metastatic cancer: Characterization with a mathematical model calibrated with experimental data Pirmin Schlicke 1,2 , Preethi Korangath 3 , Robert Ivkov 3,4,5 , Heiko Enderling 1,2 1 Department of Radiation Oncology, MD Anderson Cancer Center, Houston, USA. 2 Institute for Data Science in Oncology, MD Anderson Cancer Center, Houston, USA. 3 Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University School of Medicine, Baltimore, USA. 4 Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, USA. 5 Department of Mechanical Engineering, and Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, USA Purpose/Objective For patients with metastatic cancerous diseases, successful management of the systemic disease is of utmost importance. About 90% of all cancer-related deaths are due to the presence of metastases. A common therapeutic approach is radiation: more than 50% of all cancer patients receive a form of radiotherapy during their treatment course [1,2]. There are several dynamics that feature both challenges and opportunities as well as pose fundamental questions on current knowledge and understanding of radiation biology [3]: Clinical case reports of observed regression or progression of metastatic lesions distant from the irradiation site following local radiation on the primary tumor have been increasing in recent years. This phenomenon is sometimes referred to as the abscopal effect and has been claimed to stem from immune activation as a potential result of radiation therapy [4,5]. However, these effects are, to date, unpredictable. Material/Methods We propose a mechanistic mathematical model based on a McKendrick-von Foerster transport equation with a global carrying capacity shared by all tumors. We examine the interaction dynamics of primary tumor and metastases in an untreated pan-cancer, pan-mouse setting. We calibrate the model to experimental data of 4T1 tumors in BALB/c mice and Py230 tumors in C57BL/6 mice. We then simulate the local and global effects of radiotherapy applied to the primary tumor and calibrate and validate the effects of different radiation schedules. Results Simulation results demonstrate that local and systemic tumor control depends on reliable activation of the immune system. Different pre-radiation immune environments may need different treatment protocols to achieve local and systemic control. This motivates pre-treatment in silico trials with different radiation dose and dose fractionation schedules for individual patients. This helps identify the conditions needed for a systemic response of local radiation, and helps understanding of the abscopal effect on a quantitative basis.