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SU‐G‐JeP2‐06: Dosimetric and Workflow Evaluation of First Commercial Synthetic CT Software for Clinical Use in Pelvis
Author(s) -
Tyagi N,
Zhang J,
Happersett L,
Kadbi M,
Mechalakos J,
Deasy J,
Hunt M
Publication year - 2016
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4957026
Subject(s) - fiducial marker , nuclear medicine , medicine , scanner , radiology , computer science , artificial intelligence
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.