S2752
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
1. Christopher Mayhew; Jeyaanth Venkatasai; Marina Khan; Victoria Butterworth; Kasia Owczarczyk; George Ntentas. Effect of end expiration breath hold on target volumes and organ at risk doses for oesophageal cancer radiotherapy. Physics and Imaging in Radiation Oncology. 2025;33:100726.
doi:10.1016/j.phro.2025.100726 Keywords: DIBH, Liver, SGRT
Digital Poster 4495
The role of offline verification protocols in optimizing geometric safety margins: A retrospective multiregional analysis of 4,220 CBCT scans Filipe Cidade Moura Medical Imaging and Radiotherapy, Portuguese Red Cross Higher Health School, Lisboa, Portugal
Purpose/Objective: To be confident on the best available off-line
verification protocols and localization methods, clinical systematic and random errors have been studied for treatment quality improvement in different treatment sites. The geometric safety margins were calculated for each clinical protocol for optimal target volume coverage, according to the literature. This retrospective analysis intent to establish a ground knowledge for future application of online/realtime protocols compared to the existent off-line treatment The study was conducted during eight years (2008– 2016) according to pre-defined verification protocols (figure 1). The treatments were delivered in the ELEKTA Linear Accelerator coupled with kV-CBCT controlled by the integrated X-Ray Volumetric Imaging (XVI) software for tri-dimensional image acquisition and registration. Data has been collected through online and off-line correction protocols. Error analysis was performed and reported on a daily basis for further protocol development and continuous optimization. Patient comfort and privacy have been never compromised by the continuum data collection and processing. General data protection regulations were safely adhered to. verification methods. Material/Methods:
Results: The Systematic ( Σ ) and Random ( σ ) errors from different sites/protocols were combined and plotted together into cumulative frequency graphs (not shown here). Systematic and random errors for respective pair site/protocol is shown in figure 2, where the specific margin calculation is based on previously reported formalisms, hereby reported for further geometrical safety margin optimization.
Conclusion: The protocols evaluated in this study enabled the development of a comprehensive decision-making framework. Within this context, establishing probabilistic action levels for each patient category, relative to population-based distributions, supports
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