title: Dosimetric and workflow evaluation of first commercial synthetic CT software for clinical use in pelvis.
abstract: To evaluate a commercial synthetic CT (syn-CT) software for use in prostate radiotherapy. Twenty-five prostate patients underwent CT and MR simulation scans in treatment position on a 3T MR scanner. A commercially available MR protocol was used that included a T2w turbo spin-echo sequence for soft-tissue contrast and a dual echo 3D mDIXON fast field echo (FFE) sequence for generating syn-CT. A dual-echo 3D FFE B0map was used for patient-induced susceptibility distortion analysis and a new 3D balanced-FFE sequence was evaluated for identification of implanted gold fiducial markers and subsequent image-guidance during radiotherapy delivery. Tissues were classified as air, adipose, water, trabecular/spongy bone and compact/cortical bone and assigned bulk HU values. The accuracy of syn-CT for treatment planning was analyzed by transferring the structures and plan from planning CT to syn-CT and recalculating the dose. Accuracy of localization at the treatment machine was evaluated by comparing registration of kV radiographs to either digitally reconstructed radiographs (DRRs) generated from syn-CT or traditional DRRs generated from the planning CT. Similarly, accuracy of setup using CBCT and syn-CT was compared to that using the planning CT. Finally, a MR-only simulation workflow was established and end-to-end testing was completed on five patients undergoing MR-only simulation. Dosimetric comparison between the original CT and syn-CT plans was within 0.5% on average for all structures. The de-novo optimized plans on the syn-CT met institutional clinical objectives for target and normal structures. Patient-induced susceptibility distortion based on B0maps was within 1 mm and 0.5 mm in the body and prostate respectively. DRR and CBCT localization based on MR-localized fiducials showed a standard deviation of  <1 mm. End-to-end testing and MR simulation workflow was successfully validated. MRI derived synthetic CT can be successfully used for a MR-only planning and treatment for prostate radiotherapy.
authors.affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, NY, NY 10065, United States of America.
authors.forename: Neelam
authors.initials: N
authors.lastname: Tyagi
authors.forename: Sandra
authors.initials: S
authors.lastname: Fontenla
authors.forename: Jing
authors.initials: J
authors.lastname: Zhang
authors.forename: Michelle
authors.initials: M
authors.lastname: Cloutier
authors.forename: Mo
authors.initials: M
authors.lastname: Kadbi
authors.forename: Jim
authors.initials: J
authors.lastname: Mechalakos
authors.forename: Michael
authors.initials: M
authors.lastname: Zelefsky
authors.forename: Joe
authors.initials: J
authors.lastname: Deasy
authors.forename: Margie
authors.initials: M
authors.lastname: Hunt
mesh_terms: D001842:Bone and Bones / Q000000981:diagnostic imaging; D057918:Fiducial Markers; D006801:Humans; D008297:Male; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*; D057188:Workflow