S2793
RTT - RTT contouring, target definition, and treatment planning
ESTRO 2026
Results: True collision alerts, ranges of machine rotation and ranges of detected collisions for both methods are reported per patient in Table 1. The (union) bounding box volume was on average 8315,531 cm3 with standard deviation of ± 3293,697 cm3 for the surrogate cylinder and external structures, and 81276,315 ± 10215,261 cm3 for the surface structure. The time required to run the check was 1,844 ± 0,309 seconds for the surrogate arm method, and 1,983 ± 0,334 seconds for the surface scan method. Table 1: Patient-wise collision detection data. Green indicates true positive detected collision, orange indicates false positive detected collision.
Purpose/Objective: The objective of this study was to evaluate performing collision detection for radiotherapy (RT) purposes when using patient surface scans, compared to representing patient geometry through added digital
surrogate structures. Material/Methods:
For a cohort of 14 breast cancer patients, a surface scan was acquired using SentinelTM 4DCT c4D version 6.5 (scanned volume 650x670x270 mm ³ ) during CT simulation. The 3D scan was converted to STL format using a C-RAD prototype tool, manually imported and registered to the patient external structure in the treatment planning system (TPS) (RayStation v2025- ReC). The TPS’ deep learning segmentation model was used to segment the humeral heads’ contours, one of which was manually completed until the end of the image stack. Through scripting, a cylinder (diameter 11 cm, length 29 cm) was positioned based on the humerus’ direction to resemble the contralateral arm. A collision detection script was run twice inside the TPS, once for a combination of the external and the surrogate arm, and once for the surface scan, against a machine model structure using a 0.1cm margin. Examples of all structures are depicted in Figure 1.
Conclusion: Performing collision detection inside the TPS enables creating collision checked plans without increasing planning time. In contrast to surrogate arm, using surface scans resulted in a more streamlined workflow as no additional contouring was required. The surfaces could be used without additional processing after format conversion, and automation of import and registration to patient external would result in a fully automized workflow. The surface scan method also enables collision detection for body sites where adding surrogate structures would be unfeasible in clinical practice. Keywords: Collision detection, surface scan MR-based dose planning for head and neck cancer using electron density estimation in photon and proton therapy: preliminary results Nils Tanneau 1 , Sebastian Tattenberg 1 , Charlène Bouyer 2 , Benjamin Leporq 1 , Frank Pilleul 1,3 , Vincent Grégoire 4 , Olivier Beuf 1 1 CREATIS, INSA-Lyon, Universite Claude Bernard Lyon 1, CNRS, Inserm, UMR 5220, U1294, Lyon, France. 2 Département de physique médicale, Centre Léon Bérard, Lyon, France. 3 Département de radiologie, Centre Léon Bérard, Lyon, France. 4 Département de radiothérapie, Centre Léon Bérard, Lyon, France Digital Poster Highlight 3758
Figure 1: Example of structures used in collision detection. a) patient external (green) + cylinder surrogate arm (maroon) b) Patient surface scan (pink) c) Overlap between surface and surrogate arm at detected collision with machine (yellow).
Purpose/Objective:
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