Author: Peter Balter, Elaine Eunnae Cha, Seungtaek Choi, Yao Ding, Eun Young Han, Yusung Kim, Rajat J. Kudchadker, Belinda Lee, Surendra Prajapati, Reza Reiazi, Ergys D. Subashi, Sarath Vijayan, Jinzhong Yang, Yao Zhao 👨🔬
Affiliation: The University of Texas MD Anderson Cancer Center 🌍
Purpose: This study evaluates the feasibility of an MR-only simulation, planning, and treatment (MROSPT) workflow for pelvic cancer patients using synthetic CT generated from MRI data. By validating synthetic CT-based dose calculations, the study aims to streamline radiotherapy workflows, eliminate the need for CT simulation, and enable reliable clinical implementation of MR-based radiotherapy for MR-Linac.
Methods: Nine male pelvic cancer patients underwent CT and MRI simulations. Synthetic CTs (sCT) were generated from MRI data by the Siemens syngo.via RT Image Suite protocol. Contours and IMRT treatment plans were created on the reference simulation CT (rCT) and transferred to the sCT for dose calculations. Dosimetric accuracy was evaluated using gamma analysis (2%/2mm) to compare dose calculations between rCT and sCT. Additionally, bulk synthetic CTs (bCTs) were created by overriding organ density values with their mean (bulk) density. bCT based on sCT allows treatment planning directly on MRI for efficient MR-linac workflow. Dry run of entire workflow from sim to treatment was successfully completed.
Results: Minimal differences in HU values (except bone) between rCT and sCT (5.48±2.92 HU for prostate) demonstrated the reliability of the synthetic CTs generation process. Dosimetric comparisons between treatment plans on rCT vs. sCT and rCT vs. bCT showed high agreement, with gamma analysis confirming robust accuracy. Specifically, the mean gamma pass rates for PTV dose across all patients were 0.98±0.02 and for rCT vs. sCT, 0.95±0.08 for rCT vs. bCT, and 0.97±0.02 for sCT vs. bCT.
Conclusion: The MROSPT workflow using sCT is clinically feasible and dosimetrically accurate for pelvic cancer patients.The statistically significant agreement (p-value > 0.01) between synthetic CT and CT-based dose calculations supports the adoption of this approach for pelvic cancer radiotherapy and suggests its potential to other anatomical regions. Integration of robust QA processes and treatment delivery flexibility further enhances its clinical utility.