ESTRO 2025 - Abstract Book

S136

Invited Speaker

ESTRO 2025

4878

Speaker Abstracts Low dose radiation as an immuno-modulatory approach in cancer Fernanda G Herrera Radiation Oncology, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland

Abstract:

Low-dose radiotherapy (LDRT) has emerged as a potential therapeutic strategy for its ability to modulate the immune response. Traditionally, high-dose radiotherapy has been used to treat various malignancies by inducing DNA damage in tumor cells, but recent studies have indicated that low doses of radiation can enhance immune system function and provoke anti-tumor immune responses in some cases when combined with immunotherapy. This immune-modulatory effect of LDRT is characterized by the activation of innate immune cells, such as dendritic cells and macrophages, and the promotion of adaptive immune responses, including the stimulation of T cells and the production of pro-inflammatory cytokines. This presentation explores the mechanisms underlying the immune modulatory properties of low-dose radiotherapy, its clinical implications, and the potential for combining LDRT with immunotherapies to optimize cancer treatment outcomes. Understanding how LDRT influences immune cell-tumor interactions and the broader immune landscape offers opportunities for improving the efficacy of cancer immunotherapies and enhancing patient responses

4879

Speaker Abstracts Development of radiotherapy utilizing autoactivation of cancer immune system Hitoshi Ishikawa 1,2 , Masatoshi Nakamura 2 , Taisuke Sumiya 2 , Hideyuki Sakurai 2 , Masaru Wakatsuki 1 , Noriyuki Okonogi 3,1 , Kazutoshi Murata 1 , Yoshiyuki Nagumo 4 , Hiroyuki Nishiyama 4 1 QST Hospital, National Institutes for Quantum Science and Technology, Chiba, Japan. 2 Radiation Oncology, University of Tsukuba, Faculty of Medicine, Tsukuba, Japan. 3 Radiation Oncology, Juntendo University Graduate School of Medicine, Tokyo, Japan. 4 Urology, University of Tsukuba, Faculty of Medicine, Tsukuba, Japan

Abstract:

Radiation therapy is thought to have immunosuppressive but immunostimulatory effects, because lots of studies have shown that ionizing irradiation induces activation of immune response to tumor cells via cancer cell death and various immune reactions such as cytokine releases and dendric cell maturation. Our previous study revealed that some cytokines were upregulated or downregulated by stereotactic body radiotherapy (SBRT) for metastatic breast cancer patients, and upregulation of interferon gamma and granulocyte macrophage colony stimulating factors by SBRT were favorable predictors for overall survival (OS) of them. Recent studies demonstrated that lymphopenia during curative radiotherapy were closely correlated with OS of patients with various cancers especially in the treatment for thoracic cancers such as locally advanced esophageal cancer (EC) and non-small cell lung cancer (NSCLC). Our studies also showed that grade 4 lymphopenia during concurrent chemoradiotherapy for EC and NSCLC were associated with OS after chemoradiotherapy and with dose volume histogram parameters of the lung, heart, and bone marrow known as organs of circulating blood pool and proton therapy was able to reduce doses and volumes irradiated at these organs. Our previous systematic review also showed the superiority of proton therapy to intensity-modulated radiotherapy by photons. Furthermore, even in proton therapy, irradiated doses and volumes at the organs should be reduced by optimizing the number and angle of proton beams in treatment planning.