ESTRO 2025 - Abstract Book

S2978

Physics - Image acquisition and processing

ESTRO 2025

1655

Digital Poster Validation of Elekta IRIS CBCT reconstruction algorithm for treatment planning and IGRT in radiotherapy of locally advanced rectal cancer patients Martina Camilla Daniotti 1 , Sara Trivellato 2 , Gianluca Montanari 2 , Rita Marina Niespolo 3 , Lorenzo De Sanctis 4 , Giulia Rossano 4 , Valerio Pisoni 3,4 , Bianca Bordigoni 5 , Joseph Stancanello 6 , Jonathan Hugh Mason 6 , Roberto Pellegrini 7 , Stefano Arcangeli 3,4 , Elena De Ponti 2,4 1 Physics Department, Università degli Studi di Milano, Milan, Italy. 2 Medical Physics Department, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 3 Radiation Oncology Department, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 4 School of Medicine and Surgery, Università degli Studi di Milano-Bicocca, Milan, Italy. 5 Physics Department, Università degli Studi di Padova, Padua, Italy. 6 Clinical Application Development, Elekta AB, Stockholm, Sweden. 7 Global Medical Affairs, Elekta AB, Stockholm, Sweden Purpose/Objective: A new CBCT reconstruction algorithm based on poli-energetic quantitative (Polyquant) method empowered with a convolutional neural network scatter correction has been recently proposed. This study aimed to validate the use of the Polyquant CBCTs (pCBCTs) for image-guided radiotherapy (IGRT) and planning for locally advanced rectal cancer (LARC). Material/Methods: pCBCTs were calibrated with a population-based curve (pop-CC) elaborated coupling pCBCT gray levels to the CT relative electron density (RED) for ten pelvic patients. pop-CC was validated by comparing dose calculations on pCBCT and bulk density pseudo-CT using 1%/3mm local gamma-analysis. Five LARC patients treated in 25 fractions on an Elekta VersaHD with daily CBCT were retrospectively selected. The RED difference between CT and first session-pCBCT were assessed on a voxel-to-voxel basis and on a contour basis. The original plan was calculated on five pCBCTs per LARC patient and on the corresponding pseudo-CT. Dose distributions were compared with 3D local gamma analysis, setting the 3mm/1% criterium. The LARC patients’ pCBCTs were registered on the reference CTs with the Elekta XVI gray value T+R clipbox registration and then the translations and rotations obtained were compared with the results of the clinical version of XVI CBCT. The same procedure was repeated after the conversion into translations only, and statistically investigated with the t-test and ANOVA-test (confidence level p<0.05). Results: The pop-CC pCBCT calibration (Figure 1) resulted in dose calculations comparable with the pseudo-CT ones, with gamma(3%,1mm)>95%.