ESTRO 2025 - Abstract Book

S2868

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

3265

Digital Poster Dose calculations on HyperSight cone beam CT

Anja Einebærholm Aarberg, Ellen Marie Høye, Sara Pilskog, Turid Husevåg Sulen, Tordis Johnsen Dahle Department of Oncology and Medical Physics, Haukeland University Hospital, Bergen, Norway

Purpose/Objective: HyperSight cone beam CT (CBCT) has close to CT image quality, and can potentially be used directly for dose planning when a replan is needed in radiotherapy, instead of acquiring a new CT. Before clinical introduction, dose calculations on HyperSight-CBCT must be quality assured. The main purpose of this project was to calculate CT calibration curves for the HyperSight image protocols, and test dose calculation accuracy. Material/Methods: Calibration curves for HyperSight-CBCT were measured by scanning a Multi-Energy CT Phantom (SunNuclear) with insterts with known electron density. Dose calculations were performed using the chosen calibration curves and were tested by creating dose plans to CT and CBCT images of anthropomorphic phantoms. Lastly, CT and CBCT images for 10 protocol patients (two of each: abdomen, thorax, head/neck, pelvic and with hip prosthesis) were acquired for more clinical realistic scenarios. If the anthropomorphic phantoms showed accurate dose calculations on CBCT for a specific anatomic area, dose calculations were tested on the CBCT images of the respective protocol patients. For the patients, the CT and CBCT images were not taken on the same day, so some anatomical variations must be expected. Results: The calibration curves for protocols Pelvis, Thorax and Head reconstructed with iCBCT, Acuros and metal artefact reduction (MAR) are shown in Figure 1, together with the calibration curve used at our clinic. The Thorax and Pelvic protocols reconstructed with Acuros/MAR resulted in calibration curves similar to our clinical curve, while the Head protocol gave higher CT numbers for higher electron densities than the clinical curve for all algorithms. Dose calculations on anthropomorphic phantoms with images reconstructed with Acuros showed that dose calculation on CT/CBCT images for pelvis, abdomen and head/neck gave nearly identical dose plans, while for thorax larger differences were seen, as exemplified in Figure 2. For the protocol patients with clinical plans recalculated on CBCT, the dose calculations for pelvis and abdomen were almost identical when the CT and CBCT images were anatomical identical.