S2697
RTT - Patient preparation, immobilisation, and verification protocols
ESTRO 2026
captured distinct, site-specific topography. 3D- rendered heat maps consistently emphasized the fold of the breast, the nasal bridge and the inguinal crease. The slope inter-quartile range(IQR) showed breast and pelvis demonstrated the largest range of available slopes, (IQR, p<0.001). Aspect showed limited contralateral directional dispersion in breast, consistent with unilateral occlusion, while pelvis and H&N crossed the midline, indicating a greater area of dominant surfaces facing each camera (IQR, breast(67.7°)<head(155.4°)<pelvis(193.2°); p<0.001). VRM highlighted small high-resolution features at the breast inframammary fold and H&N perioral region, with minimal (near-zero) values in pelvis (VRM median; p<0.001). There was clear separation between clinical sites for TRI with H&N showing the most local topography (pelvis<breast<H&N for mean/median/IQR; p<0.001). TPI dispersion also increased from Pelvis to H&N showing greater regional variation across the ROI(IQR: p<0.001).
Mini-Oral 264 Standardizing the Surface: application of a Novel Topographical Framework to Establishing Normative SGRT ROI Quality Metrics Ciaran Malone 1,2 , Samantha Ryan 1 , Jill Nicholson 1,3 , Frances Duane 1,3 , Claire Fitzpatrick 1 , Sinead Brennan 1,3 , Orla McArdle 1,4 , Ruth Woods 1 , Aodh MacGairbhith 1 , James Waldron 1 , Clodagh Callagh 1 , Rachel Harwood 1 , Paul O'Connor 1 , Brendan McClean 1,5 , Gerard G Hanna 1,3 1 Radiation Oncology, St.Luke's Radiation Oncology Network, Dublin, Ireland. 2 Department of Radiotherapy, Erasmus MC Cancer Institute, University Medical Center Rotterdam, Rotterdam, Netherlands. 3 Trinity St. James’s Cancer Institute, Trinity College Dublin, Dublin, Ireland. 4 Beaumont Cancer Institute, Royal College of Surgeons, Dublin, Ireland. 5 Centre for Physics in Health and Medicine, School of Physics, UCD, Dublin, Ireland Purpose/Objective: The quality of Surface-Guided Radiation Therapy (SGRT) Regions of Interest (ROIs) is crucial for accurate patient setup, yet the definition of “good topography” remains subjective. Two ROIs based on recommended landmark boundaries may have very different internal topographies. The feasibility of applying geography- derived topographical metrics (e.g., slope, ruggedness, aspect) to quantify ROI surface topography has been previously demonstrated (Malone et al., 2025). We aim to apply this novel concept to cohorts of clinical cases to establish normative metric ranges across common anatomical sites to enable objective evaluation and training. Material/Methods: We retrospectively analysed 60 patients treated using SGRT (VisionRT): 20 head & neck (H&N), 20 left breast, 20 pelvis using our previously published framework. External surface meshes were exported and loaded into an in-house Python application to draw ROIs and calculate metrics. ROIs followed vendor recommended anatomical boundaries. We computed: Slope(°), Aspect(°), Vector Ruggedness Measure (VRM, 5mm), Terrain Ruggedness Index (TRI, 15mm), and Topographic Position Index (TPI, 50mm). Kernel sizes were chosen to complement each metrics’ purpose to capture fine, local, and regional structure. 3D-renders were generated with colour wash to highlight the magnitude and location of metric values. For each anatomical site, we established normative ranges. For aspect we also reported the two dominant directions (°). Distributions were compared using Kruskal-Wallis with holm-bonferroni correction. Results: Normative ranges were established and metrics
Conclusion: This novel study establishes normative ranges of topographical metrics for SGRT ROI characterization,
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