ESTRO 2025 - Abstract Book

S3197

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

Results: The patient agnostic workflow resulted in an average total of 16.7 minutes (ranging from 15 to 18 minutes) for the first adaptation fraction, while fractions 2-5 took an average of 10.5 minutes (ranging from 6.5 to 15.6 minutes). All patient agnostic plans reached sufficient PTV coverage (V3444cGy > 99%). For evaluating the OAR dose, the patient agnostic plans were evaluated using the clinical contours. Table 1 presents average dose parameters and interquartile range (IQR) on the clinical constraints.

Conclusion: High quality plans were achieved with just 6 minutes extra time during fraction 1 using patient-agnostic reference plans with only a slight increase in dose to some OARs. Abolishing patient-specific offline treatment preparation would potentially present a huge and safe efficiency improvement.

Keywords: simulation-free, adaptive radiotherapy, efficiency

References: [1]: Towards simulation-free MR-linac treatment: utilizing male pelvis PSMA-PET/CT and population-based electron density assignments, Carr et al, Phys. Med. Biol. 68 (2023) 195012 [2]: Adaptive radiotherapy: The Elekta Unity MR-linac concept, Winkel et al, Clin Transl Radiat Oncol. 2019 Apr 2;18:54–59

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Digital Poster Quantifying CNR Effects on CyberKnife® Xsight® Lung Tracking: A Motion Phantom Analysis Tsz Yan Lee, Bin Yang, Siu Ki Yu Medical Physics Department, Hong Kong Sanatorium & Hospital, Hong Kong, China Purpose/Objective: The aim of this study is to evaluate the impact of varying contrast-to-noise ratio (CNR) on the tracking performance of the fiducial-free lung tumour in the CyberKnife ® Xsight ® Lung Tracking (XLT) system using an anthropomorphic respiratory motion phantom. Material/Methods: A customised insert containing Gammex density plugs was fabricated and integrated into the CIRS Phantom Kit (Model 18023-08A) for XLT delivery. The density plugs measured 2.8cm in diameter and 7cm in length, with densities of 0.29, 0.45, 0.935, 0.978, 1.051 g/cm 3 . Phantom motion was driven by a sinusoidal pattern and a respiratory waveform extracted from a 4DCT scan, as shown in Figure 1(a).