S3040
Invited Speaker
ESTRO 2026
supports the integration of low-dose radiotherapy (LDRT) as a complementary approach to enhance tumor control and modulate the tumor microenvironment. In addition, LDRT and low doses associated with radon exposure are used to treat benign diseases that are often characterized by chronic inflammation. Current knowledge is presented in this work, with particular emphasis on immunomodulatory mechanisms. Mostly preclinical and, if available, clinical studies on the role of LDRT in oncology and benign disease management are considered, including radon treatment of autoimmune and chronic inflammatory disorders. Methods For preclinical studies, cells, co-cultures and tissue equivalents are typically employed. In addition, mouse models for various types of tumors or those with chronic inflammatory background, such as rheumatoid arthritis, psoriasis and pneumonia are used. Analysis of cells and tissue is performed with state-of-the-art methods, such as transcriptomics, multiplex-ELISA and multiplex-immune fluorescence. Some clinical studies are explorative, but others are conducted as controlled trials. Results LDRT induces a spectrum of biological responses that differ qualitatively and quantitatively from high-dose RT. In oncology, low-dose fractions can reprogram the tumor microenvironment by modified polarization of immune cells and reducing immune-suppressive signaling and thus enhancing anti-tumor immune responses. These effects can potentiate the efficacy of subsequent high-dose RT or systemic therapies. In benign and inflammatory diseases, LDRT using both photons and radon exposure have demonstrated anti- inflammatory benefits, including downregulation of adhesion molecules, suppression of macrophage activation, and modulation of lymphocyte subsets toward regulatory phenotypes. Conclusions LDRT represents a versatile therapeutic tool with dual relevance in oncology and chronic inflammatory disease management. Its capacity to shape the tumor microenvironment and modulate immune responses offers a rationale for its integration into multimodal cancer therapy. Furthermore, the anti-inflammatory and immunoregulatory effects observed in benign conditions, including those achieved through radon therapy ( α -particles at low doses), highlight its broader clinical potential. Future research should prioritize mechanistic studies, dose optimization, and controlled clinical trials to refine patient selection and maximize therapeutic benefit while minimizing risk.
multi-centre benchmarking study. Phys Imaging Radiat Oncol. 2026;37:100913. [3] Hoffmann L, et al. Development of a treatment planning protocol for the multi-centre reirradiation CURE Lung trial. Radiother Oncol. 2026;214:111293. [4] Nielsen M, et al. A comprehensive national audit of radiotherapy retreatment numbers, sites and indications. Acta Oncol. 2025;64:872-878. 5439 Roadmap to RTT led target definition Lisa Wiersema Radiation Oncology, Netherlands Cancer Institute (NKI- AvL), Amsterdam, Netherlands Target definition is an evolving new skill for RTTs. This has been deployed offline in some institutes, but for online adaptive setting it has become even more important/relevant. This teaching lecture will give an overview of the experience so far, including training programs, responsibility, challenges and how it can improve efficiency. What is the current status for RTT led target definition in an online adaptive setting? What is the effect on quality and consistencies of RTT led target definition? What do RTTs think of being responsible for target definition online? Are training programs sufficient enough? What are the benefits of RTT led target definition? Which legal challenges do we encounter? And what will the future bring with AI? Target definition is an upcoming new skill of RTTs that will be more common, a skill that needs to be introduced in standard education of RTTs and could be beneficial in various ways. Clear guidelines and protocols need to be available to support all clinicians, so everyone will feel confident. 5440 Low-dose radiation biology: perspectives for treatment of cancer and benign diseases Claudia Fournier Biophysics, GSI Helmholtz Center, Darmstadt, Germany Background Low doses of ionizing radiation, typically defined as exposures below 0.5 Gy, exert biological effects distinct from those induced by high-dose regimens. The interaction of sparsely ionizing radiation (e.g., X- rays, γ -rays) and densely ionizing radiation (e.g., α - particles, heavy ions) with biological tissues can modulate cellular and immune responses in ways that are increasingly recognized as therapeutically relevant. While high-dose radiotherapy (RT) remains a cornerstone in cancer treatment, emerging evidence
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