ESTRO 2025 - Abstract Book

S3086

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Conclusion: Image guided radiotherapy enabled compliance with rectal dose constraints in over 80% of treatment courses, meeting our clinical acceptance criteria. However, the V57 Gy constraint was not met in 93% of cases, despite moderate inter-fractional rectal volume variations. A toxicity evaluation is needed to assess the clinical significance of this constraint.

Keywords: Inter-fraction motion, IGRT, Hypofractionated RT

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Digital Poster HyperSight-ARCHER Head and Neck clinical trial: Image Quality Analysis

Abby Yashayaeva 1 , Lee R MacDonald 1,2,3 , Kenny Zhan 3 , Jennifer DeGiobbi 3 , Natasha McMaster 3 , Dave McAloney 3 , Lucy Ward 3 , Cheryl Anderson 3 , Marc LeBlanc 3 , Lara Best 2,3 , Murali Rajaraman 2,3 , Derek Wilke 2,3 , Amanda Cherpak 1,2,3 1 Department of Physics and Atmospheric Sciences, Dalhousie University, Halifax, Canada. 2 Department of Radiation Oncology, Dalhousie University, Halifax, Canada. 3 Nova Scotia Health, Queen Elizabeth II Health Sciences Centre, Halifax, Canada Purpose/Objective: Accurate Hounsfield units (HU) in patient images are essential for radiation dose calculation and anatomical visualization. This information can be skewed due to artifacts from dental work, a common occurrence for head and neck (H&N) cancer patients. This works assesses image quality of the HyperSight cone-beam computed tomography (CBCT) platform 1 and compares it with the TrueBeam CBCT 1 and fan-beam CT from a CT simulator (CTsim FBCT) 2 using images captured throughout treatment for H&N cancer patients. Material/Methods: Images for 26 H&N cancer patients were acquired as part of the HyperSight-ARCHER clinical trial 3 . Images were captured on a HyperSight CBCT, TrueBeam CBCT and FBCT. The HyperSight images were reconstructed using the metal artifact reduction (iCBCT MAR) and iCBCT Acuros algorithms. For this analysis, the four image sets were registered and compared using the artifact index 4 (AI) measured in the oral cavity and the HU uniformity in the brain was compared relative to FBCT (baseline). For various OARs, the HU accuracy and the contrast between pairs of structures in close proximity to each other were evaluated relative to FBCT (baseline). Results: A visible reduction of metal artifact in the oral cavity for the HS iCBCT MAR image is observed in Figure 1A, and the AI values are displayed in Figure 1B. The HyperSight iCBCT MAR images exhibited a significant reduction in AI values compared to the other images (p < 0.0004), but worse HU uniformity compared to HyperSight iCBCT Acuros and FBCT (p < 2x10 -10 and p < 2x10 -5 , respectively). The HU and contrast deviations from baseline are shown in Figure 2. The mean absolute deviations (MAD) from baseline for both HU and contrast, averaged across patients, were significantly closer to baseline across the OARs for the HyperSight iCBCT MAR and iCBCT Acuros images compared to TrueBeam (p < 0.016).