ESTRO 2025 - Abstract Book

S3301

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

ESTRO 2025

3232

Digital Poster Performance characterisation of a real-time prostate cancer 6DoF IGRT system Paul Zhi Yuan Liu 1 , Paul Keall 1 , Ricky O'Brien 1 , Indrajit Ghosh 1 , Brendan Whelan 1 , Tim Montanaro 1 , Shoa Rizvi 1 ,

Fabienne Lathuilière 2 , Sébastien Tremblay 2 , Doan Trang Nguyen 1 1 Seetreat Medical, -, Sydney, Australia. 2 Elekta, -, Stockholm, Sweden

Purpose/Objective: The clinical evidence for real-time prostate cancer image guided radiotherapy (IGRT) is compelling, with grade 2+ toxicities halved. 1,2 However, there is currently no commercially available real-time prostate cancer 6 Degree-of freedom (6DoF) IGRT system for conventional linear accelerators. To address this gap, a real-time prostate cancer 6DoF IGRT system was developed following IEC standards within a quality management system in an ISO-13485 certified environment. The aim of this work is to characterise the ability of this system to accurately track 6DoF prostate motion. Material/Methods: The real-time prostate cancer 6DoF IGRT system leverages the approach of the kilovoltage intrafraction monitoring system (KIM) that demonstrated efficacy and clinical benefit in a multi-institutional trial. 3 In this method, x-ray projection images are acquired during treatment delivery. Markers implanted into the prostate are segmented from the projection images using a multiple algorithm approach. The 2D marker positions are converted to 3D marker positions using a Kalman filter method 4 to calculate target position and rotation (Figure 1). The 6DoF IGRT system performance was tested in silico using seven static and 27 clinically recorded dynamic motion traces with known ground truth. The 6DoF IGRT system performance was characterised by (1) quantifying the mean and standard deviation of the geometric error from the ground truth position and rotation, (2) quantifying the percentage of tracking results within 2 mm of the ground truth position and (3) quantifying the end-to-end computation time of the system.

Results: The 6DoF IGRT system successfully tracked prostate motion for all static and dynamic motion traces. Across the 27 dynamic motion traces (n = 10,076 x-ray projections), the mean and standard deviation of the position error were