ESTRO 2025 - Abstract Book

S3888

Radiobiology - Immuno-radiobiology

ESTRO 2025

Results: Of 70 patients enrolled, nineteen with 73 plasma samples were included in this analysis, of which 5 (26%), 9 (47%), 4 (21%) and 1 (5%) had a gastrointestinal (GI), hormone receptor positive breast, genito-urinary (GU) and skin cancer diagnosis respectively. Median progression free survival was 4.8 (IQR 3.2 – 7.7) mths, which did not differ between groups (Breast - 5.4 vs other 4.8mths, p=0.79), and median time to change in next line systemic therapy was 5.6 (IQR 4.6 – 10.3) mths. Among plasma samples (n=73), ctDNA levels were detectable in 49 (67%). Seventeen (89.5%) patients had detectable ctDNA in at least one TP. Median ctDNA level for patients with detectable ctDNA at each TP (1-5), respectively, was 2.4 (n=13), 5.1 (n=9), 0.6 (n=14), 0.6 (n=8), and 0.1 (n=5) MTM/mL. Of13 patients with detectable ctDNA at baseline, 2 (breast/GU) cleared by TP4, 1 (breast) cleared by TP5. Six patients had undetectable levels at baseline; 2/6 (Breast) never detectable, 1/6 (GU) experienced a small rise at TP2 (0.06MTM/Ml), and 3/6 patients at TP3 (0.38 [Breast], 0.45 [Prostate], 0.94 [Breast] MTM/mL), all returned to undetectable levels by 6 weeks post SBRT. GI cancers (N=5) had detectable ctDNA at each TP. Compared with other cancer types, GI cancers had significantly higher ctDNA levels at TP1 (14.9 vs 0.17, p=0.04) and TP3 (16.2 vs 0.33 p=0.04). Conclusion: Among patients with OP, ctDNA levels at each TP varied according to primary diagnosis, with lower median levels post SBRT completion. Patients with GI cancer had greater levels compared to other cancers. ctDNA holds promise as a non-invasive tool to guide treatment for patients with OP cancer. Its predictive and prognostic role in the OP setting warrants further investigations.

Keywords: ctDNA, oligoprogression, SBRT

References: 1. Schellenberg, D., et al., Stereotactic Ablative Radiation for Oligoprogressive Cancers: Results of the Randomized Phase 2 STOP Trial. Int J Radiat Oncol Biol Phys, 2024. 2. Glicksman, R.M., et al., The Role of Stereotactic Body Radiotherapy in Oligoprogressive Malignant Disease (RADIANT): Oncologic Outcomes From a Phase 2 Nonrandomized Controlled Trial. International Journal of Radiation Oncology, Biology, Physics.

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Digital Poster Multi lineage spheroid of glioblastoma to mimic in vivo effect of minibeam radiotherapy on immune system Macrina Milani Capialbi, Lisa Alborghetti, Maria Assunta Lacavalla, Stefano Pizzardi, Federica Vurro, Antonello Spinelli Experimental imaging centre, IRCCS San Raffaele Scientific Institute, Milan, Italy Purpose/Objective: The aim of the study is to analyze the effect of minibeam radiotherapy (MBRT) on macrophages behavior in a multi lineage model of glioblastoma. The model was developed to study macrophages localization, activation, differentiation and cytokine release before and after radiotherapy. Our final goal is to compare MBRT with conventional radiotherapy (CRT), to identify the advantages of MBRT 1 . Material/Methods: A co-culture system of GL261 and RAW264 migration was assessed as an initial step in understanding macrophages migration and activity 2 . Viability assays were performed in these cultures to evaluate cell survival and preliminary macrophage responses to irradiation with MBRT or CRT.