ESTRO 2020 Abstract book

S315 ESTRO 2020

challenge of using MRI in RT. The aim of this work was to assess large FOV MRI distortions in a number of scanners used for RT throughout the UK. Material and Methods MRI scans of a GRADE phantom (Spectronic Medical AB, Helsingborg, Sweden) were acquired using a protocol recommended by the manufacturer (3D gradient echo, FoV 50x50x50 cm, voxel size 1x1x2 mm and Bandwidth 490 Hz/pixel) on the following 11 MRI scanners that are used for RT in the UK: Siemens Aera (Leeds, Guy’s and St Thomas’, Royal Marsden and Christie); Siemens Prisma (Leeds); Siemens Sola (Leeds); Siemens Skyra (Christie); Siemens Espree (Newcastle); Elekta Unity (Christie); Philips Ingenia 1.5T (Christie); GE Signa PET/MR (Newcastle). Scanners are referred to as 1-11 in a randomised order (for anonymity). Analysis was performed using MriPlanner (Spectronic Medical AB, Helsingborg, Sweden), the mean and max distortions and variance (δ 2 ) between scanners were reported at <100, 100-150, 150- 200, 200-250 and ≥250 mm from the isocentre. Results The range of the mean and max distortions for all scanners at 100-150 mm (representing the typical size of a brain) were 0.28-0.62 mm and 0.69-2.81 mm respectively. The range of the mean and max distortions for all scanners at 200-250 mm (representing the typical size of a pelvis) were 0.67-2.52 mm and 2.0-10.75 mm respectively. The mean and maximum distortions are shown in figure 1 and at <100, 100-150, 150-200, 200-250 and ≥250 mm from the isocentre, δ 2 was 0.004, 0.009, 0.045, 0.232 and 0.779 mm 2 respectively. The greatest mean geometric distortion (5.04 mm) observed was scanner 9 at ≥250 mm from the isocentre. For uses requiring a small FOV (less than 150 mm from the isocentre) such as brain imaging, both mean and maximum distortions would be < 2 mm except for the maximum distortion of one scanner. For uses requiring a large FOV (up to 250 mm from the isocentre) such as the head and neck and the entire pelvis, the mean distortions would be < 2 mm except for those from one scanner.

Conclusion Geometric distortion was assessed on 11 scanners used for RT across the UK and for all scanners distortion increased with distance to isocentre. Variance of geometric distortions between scanners was found to be low (<0.8) and increased with distance to isocentre. The vast majority of scanners showed mean distortions of > 2 mm at a distance ≥ 250 mm from the isocentre, but these values have limited clinical relevance. This assessment demonstrates feasibility of the technique to be repeated in a UK wide audit of all MRI scanners used clinically for RT. PH-0532 Standardization of brain MRI across machines and protocols: bridging the gap for MRI-based radiomics A. Carré 1,2,3 , G. Klausner 1,3 , M. Edjlali 4,5,6 , M. Lerousseau 1,2,7 , J. Briend-Diop 1,2 , R. Sun 1,2,3,7 , S. Ammari 8 , S. Reuzé 1,2,3 , E. Alvarez-Andres 1,2,9 , T. Estienne 1,2,7 , S. Niyoteka 1,2 , E. Battistella 1,2,7 , M. Vakalopoulou 2,7 , F. Dhermain 3 , N. Paragios 9 , E. Deutsch 1,3 , C. Oppenheim 4,5,6 , J. Pallud 5,6,10 , C. Robert 1,2,3 1 Molecular Radiotherapy - Gustave Roussy - Inserm, Paris-Sud University - Paris-Saclay University, 94805 - Villejuif, France ; 2 Department of Medical Physics - Gustave Roussy, Paris-Saclay University, 94805 - Villejuif, France ; 3 Department of Radiotherapy - Gustave Roussy, Paris-Saclay University, 94805 - Villejuif, France ; 4 Department of Neuroradiology, Sainte-Anne Hospital, 75014 - Paris, France ; 5 Paris Descartes University, Sorbonne Paris Cité, Paris, France ; 6 UMR 1266 INSERM - Ima-Brain, Institute of Psychiatry and Neurosciences of Paris, Paris, France ; 7 Mathématiques et Informatique pour la Complexité et les Systèmes, CentraleSupélec - Paris-Saclay University, 91190 - Gif-sur-Yvette, France ; 8 Department of Radiology - Gustave Roussy, Paris-Saclay University, 94805 - Villejuif, France ; 9 TheraPanacea, Radiotherapy, Paris, France ; 10 Department of Neurosurgery, Sainte-Anne Hospital, 75014 - Paris, France Purpose or Objective Magnetic Resonance Images (MRI) properties are highly dependent on acquisition and reconstruction parameters. Today, there is no consensus about the optimal pre- processing of MR images which is critical to the generalizability of published radiomic models. Radiomics consists in the extraction of a wide variety of quantitative image-based features to provide decision support. This study aims at assessing the impact of three standardization methods namely Nyul (Nyul et al. 1999), WhiteStripe (Shinohara et al., 2014) and Z-Score (Zero mean and unit variance) used in combination with two methods for intensity discretization (Fixed Bin Size and Fixed Bin Number) on first and second-order radiomic features from brain MRI and at proposing a unified methodology for Two independent MRI datasets were used. The first one included 20 institutional patients with WHO grades II and III gliomas who underwent T1w-gd and T2w-flair sequences on two different MR devices (1.5T and 3.0T) with a one- month delay. The Jensen Shannon Divergence was used to compare pairs of intensity histograms before and after normalization. Stability of first-order and second-order features across the two acquisitions was analyzed using the concordance correlation coefficient and the intra-class correlation coefficient. The second dataset was extracted from the public TCIA database and included 108 patients with low-grade glioma and 135 patients with future radiomic studies. Material and Methods

Figure 1. A) The reported mean geometric distortion at different distances from the isocentre for all scanners. B) The reported maximum geometric distortion at different distances from the isocentre for all scanners