ESTRO 2023 - Abstract Book

S348

Sunday 14 May 2023

ESTRO 2023

Conclusion The ventilation pattern under mechanical ventilation consists of a uniform increase in the function of spontaneously ventilated areas with minor recruitment of non-ventilated lung alveoli. Functional volumes are therefore barely changed and the impact on LFAR should be minimal. OC-0446 Evaluation of prostate synthetic CTs from MRI using 2D cycle-GAN with multicentric learning B. Texier 1 , C. Hémon 1 , E. Collot 2 , P. Lekieffre 3 , S. Tahri 3 , H. Chourak 3,4 , P. Greer 5 , J. Dowling 5 , A. Barateau 6 , C. Lafond 7 , R. de Crevoisier 6 , J. Castelli 6 , J. Nunes 8 1 LTSI, INSERM, UMR 1099, Univ Rennes1 , CLCC Eugène Marquis, Rennes, France; 2 LTSI, INSERM, UMR 1099, Univ Rennes1, CLCC Eugène Marquis, Rennes, France; 3 LTSI, INSERM, UMR 1099, Univ Rennes1, CLCC Eugène Marquis , Rennes, France; 4 CSIRO Australian e-Health Research Centre , Herston, Queensland, Australia; 5 CSIRO Australian e-Health Research Centre, Herston , Queensland, Australia; 6 LTSI, INSERM, UMR 1099, Univ Rennes 1, CLCC Eugène Marquis, Rennes, France; 7 LTSI, INSERM, UMR 1099, Univ Rennes 1, CLCC Eugène Marquis , Rennes, France; 8 LTSI, INSERM, UMR 1099, Univ Rennes 1, CLCC Eugène Marquis , Rennes, France Purpose or Objective In order to improve the current radiotherapy workflow, MR imaging is proposed as a reference instead of gold standard CT. Indeed, MR allows a better delineation of at-risk-organs thanks to a good soft-tissue contrast. The main drawback of MR is the lack of information about electronic density of tissues which is essential for dose calculation. To face this issue, synthetic CT (sCT) generation from MR is proposed to take advantage of MR accuracy and electronic density information. Moreover, sCT generation is so far dependent on acquisition devices and prevent from its application to all care centers. In this study, we propose a multicentric sCT generation to obtain a generalizable model. Materials and Methods In this study, sixty-nine prostate cancer patients CT and T2-MR were acquired in treatment position. They are from two different centers: 39 patients received a MR imaging with a 3T acquisition device and 30 on a 1.5T acquisition device. All MR were preprocessed to correct their non-uniformity with a N4 bias field correction, a histogram equalization and a filtering by gradient anisotropic diffusion. For the second center, bladders are injected on CTs: a density assignation of 0HU (reference value) was applied to the bladder in CT for each patient. To generate sCT, 2D cycle-GAN was used, using two ResNet 9blocks as generators and two 70*70 patch-GANs as discriminators. The perceptual loss was computed to compare sCT to CT and the Binary Cross Entropy (BCE) as adversarial loss to classify sCT as real CT or “fake”. Perceptual loss is based on a pre-trained network (VGG16) and 4 layers are used for style and one for content. Evaluation was performed on a cross validation with 20 patients in the training cohort and 10 patients in the validation cohort. For the multicentric study, a training cohort containing 10 patients from the first center and ten patients from the second center was used.