ESTRO 2025 - Abstract Book

S2807

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

ESTRO 2025

highest MU for lowest density on the order 575MU/Gy and Monaco provided lowest values. The effect of lung density beyond 0.1g/cm 3 has minimal effect. Most system are unstable in low density for small tumors giving variable results when plans are repeated multiple time. Similarly, maximum dose is also variable in most TPS.

Conclusion: There are significant variations in dosimetric variates for small lesion receiving lung SBRT. This poses challenges in multi-institutional clinical trials where maximum dose, MU, GI and HI could be discrepant with reported values.

Keywords: Lung cancer, SBRT, Algorithm

References: 1. Yadav P, Desrosiers CM, Mitra RK, Srivastava SP, Das IJ. Variability of Low-Z Inhomogeneity Correction in IMRT/SBRT: A Multi-Institutional Collaborative Study. J Clin Med. 2023;12(3):906. 2. Das IJ, Ding GX, Ahnesjö A. Small fields: Non-equilibrium radiation dosimetry. Med Phys. 2008;35(1):206-15. 3. Das IJ, Yadav P, Andersen AD, Chen ZJ, Huang L, Langer MP, et al. Dose prescription and reporting in stereotactic body radiotherapy: A multi-institutional study. Radiother Oncol. 2023;182:109571. 4. Moiseenko V, Grimm J, Yorke E, Jackson A, Yip A, Huynh-Le MP, et al. Dose-Volume Predictors of Radiation Pneumonitis After Lung Stereotactic Body Radiation Therapy (SBRT): Implications for Practice and Trial Design. Cureus. 2020;12(10):e10808.

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Digital Poster Improved Hippocampal Sparing in Whole Brain Radiotherapy using VMAT with optimized Dynamic Collimator Rotation and Modulated Ports Grace Gwe-Ya Kim, Kelly Kisling, Xenia Ray Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, USA Purpose/Objective: This study examines the enhancements in plan quality for Hippocampal Sparing in Whole Brain radiotherapy that can be achieved through a novel solution, RapidArc Dynamic - VMATp (Varian Medical Systems, Palo Alto, USA) that employs dynamic collimator rotation and integrates static angle modulated ports (STAMPs) in VMAT treatments. Material/Methods: For this study, hippocampal avoidance regions were added to 10 previously treated brain patients by contouring the hippocampus and adding a 5mm margin. Structure and clinical goal templates were established using the NRG-