ESTRO 2025 - Abstract Book

S2917

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

Results: SPArc demonstrated superior sparing of critical OARs, reducing V30 for the brainstem and chiasm by 30.9% and 22.8%, respectively, compared to IMPT (Fig c). However, SPArc plans increased peripheral blood exposure V >0Gy to 27.5% ± 7.4% versus 16.2% ± 5.0% (µ±σ) for IMPT (Fig 1d, Fig 2a). The average D 2% index was lower for SPArc (1.9 cGy) compared to IMPT (2.2 cGy) (Fig 2b)). Despite irradiating a larger CL volume, SPArc plans resulted in a lower fraction of CL depletion (6.8% ± 3.4%) relative to IMPT (7.9% ± 4.3%) (Fig2 c)).

Conclusion: While SPArc plans irradiated a larger CL volume than IMPT, they demonstrated improved trade-offs between low dose exposure and effective CL depletion rates (effective CL killing rate = volume of killed cells/V >0Gy ). SPArc also improved sparing of adjacent OARs, suggesting its potential as a preferable treatment for glioblastoma, especially in the era of immunotherapy to improve the synergistic effect of radiation and immunotherapy.

Keywords: lymphopenia, glioblastoma, proton-arc

References: [1] Kleinberg, L. S. (2019). Radiotherapy, Lymphopenia, and Host Immune Capacity in Glioblastoma: A Potentially Actionable Toxicity Associated With Reduced Efficacy of Radiotherapy. Neurosurgery , 85:441–453. [2] Hammi. (2023). 4D dosimetric-blood flow model: impact of prolonged fraction delivery times of IMRT on the dose to the circulating lymphocytes. Physics in medicine and biology , 68(14), 10.1088/1361-6560/acdcdc. https://doi.org/10.1088/1361-6560/acdcdc. [3] ICRP89. (2002). Basic anatomical and physiological data for use in radiological protection reference values. Ann. ICRP 32 89.

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Digital Poster Integrating dose prediction into magnetic resonance-guided radiotherapy

Benjamin Tengler 1 , Marcel Nachbar 1 , Simon Böke 2 , Cihan Gani 2 , Maximilian Niyazi 2 , Daniela Thorwarth 1 1 Section for Biomedical Physics. Department of Radiation Oncology, University of Tübingen, Tübingen, Germany. 2 Department of Radiation Oncology, University of Tübingen, Tübingen, Germany Purpose/Objective: Magnetic resonance-guided radiation therapy (MRgRT) aims to improve treatment outcomes, but on the expense of long treatment times, due to daily contour and plan adaptations. Deep learning (DL) dose prediction models might