SU G JeP2 06: Dosimetric and Workflow Evaluation of First Commercial Synthetic CT Software for Clinical Use in Pelvis.
PURPOSE evaluate a commercial synthetic CT (syn CT) software for use in prostate radiotherapy METHODS: Twenty prostate patients underwent CT and MR simulation scans in treatment position on a 3T Philips scanner. The MR protocol consisted of a T2w turbo spin echo for soft tissue contrast, a 2D balanced fast field echo (b FFE) for fiducial identification, a dual echo 3D FFE B0 map for distortion analysis and a 3D mDIXON FFE sequence to generate syn CT. Two echoes are acquired during mDIXON scan, allowing water, fat, and in phase images to be derived using the frequency shift of the fat and water protons. Tissues were classified as: air, adipose, water, trabecular/spongy bone and compact/cortical bone and assigned specific bulk HU values. Bone structures are segmented based on a pelvis bone atlas. Accuracy of syn CT for patient treatment planning was analyzed by transferring the original plan and structures from the CT to syn CT via rigid registration and recalculating dose. In addition, new IMRT plans were generated on the syn CT using structures contoured on MR and transferred to the syn CT. Accuracy of fiducial based localization at the treatment machine performed using syn CT or DRRs generated from syn CT was assessed by comparing to orthogonal kV radiographs or CBCT. RESULTS Dosimetric comparison between CT and syn CT was within 0.5% for all structures. The de novo optimized plans generated on the syn CT met our institutional clinical objectives for target and normal structures. Patient induced susceptibility distortion based on B0 maps was within 1mm and 0.4 mm in the body and prostate. The rectal and bladder outlines on the syn CT were deemed sufficient for assessing rectal and bladder filling on the CBCT at the time of treatment. CBCT localization showed a median error of 1 mm in LR, AP and SI direction. CONCLUSION MRI derived syn CT can be used clinically in MR alone planning and treatment process for prostate. Drs. Deasy, Hunt and Tyagi have Master research agreement with Philips healthcare.
Medical physics