Session Item

Glioma patients undergoing stereotactic brain radiation therapy (SBRT) must do MRI localization to ensure the accurate location of the target during treatment. If using pseudo-CT generated from planning MRI, the patient only needs a quick MRI scan which can not only provide excellent soft-tissue contrast for the target and organs at risk (OAR), but also provide CT-like density information for dose calculation. Cumbersome and error-prone CT-MRI registration can also be eliminated to reduce planning delays. The study aims to evaluate the feasibility of commercial synthetic CT software in stereotactic radiotherapy for glioma by using multi-omics evaluation methods.

All glioma patients who had planning MRIs and were treated in SBRT from 2021 to 2022 in our institution were included. The Philips MRCAT Brain based on a convolutional neural network converts planning MRIs to pseudo-CTs. The pseudo-CTs use initial delineation, registration, and treatment plans (Eclipse version：15.6) of planning CTs. Dosimetric validation was performed using main dose-volume histogram (DVH) endpoints in respect to SABR 6.1 guidelines (Dmin, Dmax, Dmean, D95%, R50%, R100%) as well as local and global 3D gamma analysis with 1-3%/2mm, 1%/1mm criteria and a 10% threshold to the maximum dose. And tumor control probability (TCP) of planning target volume (PTV) and normal tissue complication probability (NTCP) of OARs were used for biological evaluation. Then the original radiomics features of PTV and OARs were extracted for radiomics comparison. Wilcox-test was used for comparison between initial planning CTs and synthetic CTs, and a significant difference level was set at 0.05.

34 patients were included, with 34 planning CTs and mDixon-T1pseudo-CTs, and 30 mDixon-T1-CE pseudo-CTs. The median PTV was 3.4 cc (range 0.5-27.3), with no differences in DVH metrics for PTVs and OARs. And there was no difference between the two pseudo-CT cohorts. The median 3D local gamma passing rates (1%/2mm, 1%/1mm) between planning CTs and mDixon-T1 pseudo-CTs were 99.4% (range 88.1%-100%), 92.6% (range 63.5%-99.6%). In biological evaluation, all differences of TCPs were <0.3%, normal brain's NTCPs were < 2%, and other OAR’s NTCPs were < 0.02%. Then we analyzed 60 original radiomics features (47 outliers were excluded). It was found that more than 85% features of PTV and OARs have differences.

The study is the first to compare pseudo-CTs generated by MRCAT Brain from planning MRIs with initial planning CTs for SBRT in glioma. These quantitative results strongly indicate pseudo-CTs are accurate enough to replace current planning CTs for dose calculation, and evaluation of NTCP/ TCP. And it demonstrates the great potential for MRI to replace CT in the process of head simulation and treatment planning. However, pseudo-CT can’t replace the analysis of radiomics, which also provides a direction for the improvement of pseudo-CT generation technology.