ESTRO 2025 - Abstract Book

S2988

Physics - Image acquisition and processing

ESTRO 2025

dose. Paired statistical analyses (paired Wilcoxon signed-rank test) were performed to assess significant differences in dose calculation accuracy between the two reconstruction algorithms for each anatomical site and threshold. Results: The average (±SD) 2%/2mm 3D GPR for brain, breast, and pelvis patients, calculated with both reconstruction algorithms, are summarized in Table 1.

Table 1. Average (±SD) 2%/2mm 3D GPR for brain, breast, and pelvis patients using FDK and Acuros algorithms. Statistical analyses confirmed significant differences (p < 0.05) between FDK and Acuros for all thresholds only for pelvis. Conclusion: The results support the hypothesis that HyperSight CBCTp reconstructed with the Acuros algorithm offers acceptable dosimetric accuracy for all evaluated anatomical regions. For pelvic cases, the lower dose comparison accuracy of FDK algorithm compared to Acuros, as confirmed by statistical analyses, can be attributed to the reduced accuracy of HU values for high-density structures, such as the femoral heads and pelvis bones. For brain cancer patients, the observed GPR values at the 10% threshold were unexpectedly lower than at the 50% threshold, likely due to dose calculation inaccuracies in the mask fixation area. The respiratory motion of breast cancer patients and the anatomical changes of pelvic cancer patients, resulted in image registration error, limited accurate dose comparison, and resulted in lower GPR than brain cases. These findings highlight the potential of the HyperSight CBCT system combined with the Acuros reconstruction algorithm to enable faster and more reliable adaptive workflows, ultimately supporting the clinical feasibility of CBCT-only treatment planning.

Keywords: IGRT, planningCBCT, reconstruction algorithm

1891

Poster Discussion Simulation free MR-guided prostate radiotherapy: using diagnostic MR for reference planning Francis Casey 1 , Joan Chick 1 , Norina Predescu 2 , Szabolcs-Botond Lőrincz-Molnár 3 , Sian Cooper 4 , Sophie Alexander 5 , Simeon Nill 1 , Uwe Oelfke 1 , Alison Tree 4 , Alex Dunlop 1 1 The Joint Department of Physics, The Royal Marsden Hospital and the Institute of Cancer Research, London, United Kingdom. 2 Product Clinical Quality, MVision AI, Helsinki, Finland. 3 Machine Learning, MVision AI, Helsinki, Finland. 4 Clinical Oncology, The Royal Marsden Hospital and the Institute of Cancer Research, London, United Kingdom. 5 Radiotherapy, The Royal Marsden Hospital and the Institute of Cancer Research, London, United Kingdom Purpose/Objective: Traditionally, radiotherapy requires a dedicated simulation scan for treatment planning, which can add weeks to the pre-treatment pathway. In this study we carried out a planning study using non RT-dedicated MR scans for reference treatment planning for MR-only prostate online adaptive radiotherapy on the Elekta Unity MR-linac (MRL) to assess their suitability instead of simulation scans.