ESTRO 2023 - Abstract Book

S1559

Digital Posters

ESTRO 2023

Conclusion This study has shown that there is moderate correlation between coverage and PTV rED in a magnetic field and that coverage can be improved when no magnetic field is present. As such, it is unlikely to be possible to produce acceptable plans for patients with a PTV rED ≲ 0.6 due to either not meeting tolerances or there being a >2% drop in coverage. PO-1828 Evaluation of a new AI-based sCT generator for MR-only radiotherapy workflows 1 Institut de Cancérologie de l'Ouest, Medical Physics, Angers, France; 2 Therapanacea, Clinical and Partnerships Affairs, Paris, France; 3 Centrale Supelec, University of Paris-Saclay, Gif-sur-Yvette, France Purpose or Objective MR-only radiotherapy workflows require specific MRI sequences to generate a synthetic CT (sCT) on which dose calculation can be performed. To add this sequences, the MR exam time is thus increased up to 15 min and registration is needed between the sCT and the MR sequence on which contours are delineated. The objective of this study is to evaluate a new deep-learning based sCT generator based on MR sequence used for contouring. Materials and Methods 90 patients were enrolled in the study for two locations (40 brain and 50 pelvis, including some hip prostheses). MR sequences used for contouring and sCT generation were T2 Space 3D (pelvis) and T1 Gd 3D (brain). The synthetic-CT AI model was trained using end-to-end ensembled self-supervised GANs endowed with cycle consistency with planning CTs and T2w-MRIs (pelvis) and T1w-MRIs (brain). For the analysis, sCTs and CTs were rigidly registered and compared. HU mean errors (ME) and mean absolute errors (MAE) between sCTs and CTs were estimated for various structures: body/PTV/brain/skull for brain patients and body/PTV/rectum wall/femoral heads/bladder for pelvis patients. A dosimetric analysis was also performed by reporting DVH metrics Dmean and D98% for PTV and OARs as well as a 2D 1%/1mm gamma analysis with a 2% threshold. Results MAE for the body was 36.3 HU for the brain and 16.5 HU for the pelvis. Largest HU ME errors were observed for the bones (skull and femoral heads respectively) (Figure 1). A. Roussel 1 , S. Dufreneix 1 , A. Cannard 2 , T. Roque 2 , K. Shreshtha 2 , N. Paragios 2,3 , C. Guillerminet 1 , D. Autret 1