Program Information
Registration Accuracy of MR-Based Images to On-Board Megavoltage Cone-Beam CT for Brain Patient Setup
D S Pinnaduwage1*, J Chen1 , M Descovich1 , Ken-Ping Hwang2,3 and J Pouliot1 , (1) Department of Radiation Oncology, University of California San Francisco, San Francisco, CA, (2) Global MR Applications and Workflow, GE Healthcare, Houston, TX, (3) Department of Imaging Physics, The University of Texas M.D. Anderson Cancer Center, Houston, TX
Presentations
SU-C-18A-5 Sunday 1:00PM - 1:55PM Room: 18APurpose: To quantify the difference in isocenter shifts when co-registering MR and MR-based pseudo CTs (pCT) with on-board megavoltage cone-beam CT (CBCT) images.
Methods: Fast Spoiled Gradient Echo MRs were used to generate pCTs (research version of Advantage Sim MDâ„¢, GE Healthcare) for ten patients who had prior brain radiotherapy. The planning CT (rCT) for each was co-registered with the MR, and the plan isocenter and two other reference points were transferred to the MR and pCT. CBCT images (with the machine isocenter) from a single treatment day were co-registered with the 3 test images (MR, pCT and rCT), by two observers and by an automated registration algorithm. The reference points were used to calculate patient shifts and rotations from the registrations. The shifts calculated from the test image registrations were compared to each other and to the shifts performed by the therapists who treated the patients on that day.
Results: The average difference in absolute value between the isocenter shifts from the MR-, pCT- and rCT-CBCT registrations, and the therapist shifts, were 2.02, 3.01 and 0.89 mm (craniocaudal), 1.14, 1.34 and 0.46 mm (lateral), and 1.37, 3.43 and 1.43 mm (vertical), respectively. The MR- and pCT-CBCT registrations differed by 1.99, and 2.53 mm (craniocaudal), 1.36, and 1.37 mm (lateral), and 0.74 and 2.34 mm (vertical), respectively, from the average rCT-CBCT shifts. On average, differences of 2.39 (craniocaudal), 1.28 (lateral) and 2.84 mm (vertical) were seen between the MR and pCT shifts. Rotations relative to the CBCT coordinate system were on average <2° for the MR and rCT, and <6° for the pCT.
Conclusion: In this study, FSPGR MR-CBCT registrations were more precise compared to the pCT-CBCT registrations. For improved accuracy, MR sequences that are optimal for bony anatomy visualization are necessary.
Funding Support, Disclosures, and Conflict of Interest: GE healthcare has provided a research version of Advantage Sim MD to UCSF. No financial support was provided.
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