ESTRO 2024 - Abstract Book

S3753

Physics - Image acquisition and processing

ESTRO 2024

285

Mini-Oral

Metal artifact in MR-based synthetic CT for intracranial radiotherapy: impact on dosimetry and setup

Lisa Milan 1 , Francesco Pupillo 1 , Stefano Leva 2 , Paula Sargenti 2 , Stefano Moretto 2 , Margherita Casiraghi 1 , Maria Antonietta Piliero 1 , Klaudia Krzekotowska 1 , Margherita Corsi 1 , Matteo Coppotelli 1 , Davide Giovanni Bosetti 2 , Gianfranco Angelo Pesce 2 , Francesco Mosè Castronovo 2 , Thomas Zilli 2,3,4 , Stefano Presilla 1 1 Imaging Institute of Southern Switzerland, Medical Physics Division, Bellinzona, Switzerland. 2 Oncology Institute of Southern Switzerland, Radiation Oncology Clinic, Bellinzona, Switzerland. 3 Università della Svizzera Italiana, Faculty of Biomedical Sciences, Lugano, Switzerland. 4 University of Geneva, 4 Faculty of Medicine, Geneve, Switzerland

Purpose/Objective:

Recent advances in generating synthetic CT (sCT) images from Magnetic Resonance (MR) data may enhance the precision of target and organs at risks (OARs) delineation. This improvement is due to the superior soft-tissue contrast provided by MR images and the elimination of CT-MR image registration. These benefits are particularly crucial in treating intracranial lesions. Commercial software capable of converting MR data into sCT images is readily accessible. In our center, we employed a commercial deep-learning-based algorithm (Magnetic Resonance for Calculating ATtenuation, MRCAT Brain; Philips Oy, Vantaa, Finland) to generate sCT images. The software guidelines recommend caution around metallic implants because dose estimations near metallic objects may deviate from those calculated on CT scans due to discrepancies in metal artifacts between MRCAT and CT images. Since a significant portion of our patients had metal implants causing artifacts in the sCT, this study aimed to evaluate their impact on dosimetry and patient repositioning, ensuring the suitability of the MRCAT image for accurate dose planning. To assess the accuracy of dose calculations, this retrospective study analyzed 33 patients with metal artifacts who underwent both CT and MRI simulation scans. The study included patients undergoing standard or stereotactic treatments with an 80% prescription isodose, utilizing thermoplastic head immobilization during both CT and MRI scans. The MRI data were obtained with a T1-weighted 3D mDIXON imaging sequence and the sCT images were automatically generated at the scanner during the image post-processing phase.Clinical plans optimized on CTs were recalculated using sCT images with Acuros XB (AXB, version 16.1) and a dose calculation grid size of 1.25 × 1.25 × 1.25 mm³. DVH parameters, including D 2% , D 98% , and D mean , were assessed for both the PTVs and GTVs, as well as D mean and/or D 2% of the optic chiasm, brainstem, lens, and eyes. The relative dose differences with respect to the CT plan were evaluated for PTVs and GTVs, while for the OARs, the dose differences were normalized to the prescribed dose. The impact of metal implants artifacts on patient positioning accuracy with sCT versus CT images was assessed for a subgroup of 10 patients. The sCT-CBCT co-registrations were analyzed and compared to the standard CT-CBCT matching used for treatment delivery. The co-registrations were carried out with 6 degrees-of-freedom by an experienced medical physicist using automatic registration tool and manual adjustments when necessary. The Material/Methods: