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Session: Therapy General ePoster Viewing [Return to Session]

Utility of a Traditional CT Simulation in the Frameless Leksell Gamma Knife (LGK) Icon Workflow

S Herchko, S Yaddanapudi*, Mayo Clinic Florida, Jacksonville, FL


PO-GePV-T-414 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: To evaluate the utility of a traditional CT simulation scan in the frameless Leksell Gamma Knife (LGK) Icon workflow.

Methods: Two separate frameless LGK Icon workflows were evaluated to determine their effect on target coverage for 55 clinically treated stereotactic radiosurgery (SRS) plans (124 total target volumes). The standard clinical workflow utilized a traditional CT simulation scan that was co-registered to both the planning MRI and CBCT stereotactic reference (MRI-CT-CBCT), while the second workflow utilized the same treatment plan but eliminated the CT simulation and co-registered the planning MRI directly to the CBCT stereotactic reference (MRI-CBCT). All target volumes were contoured using the T1 planning MRI and shot coordinates were identical between the two plans. The percentage of each target covered by the prescription isodose line for both workflows was evaluated to determine the influence of the CT simulation co-registrations on the treatment plans, and the magnitude of the coverage difference for each target was recorded.

Results: The mean difference in coverage for all targets was 1.1%. 87/124 (70.2%) targets were within 1%, 113/124 (91.2%) were within 3%, and 123/124 (99.2%) were within 5%. 1/124 (0.8%) targets differed in coverage by > 5%.

Conclusion: Co-registering MRI images directly to CBCT images can be difficult due to the limited bone definition on MRI and limited soft tissue contrast on CBCT. Image quality and the region of interest (ROI) chosen during co-registration can impact the co-registration accuracy. A traditional CT scan can be used as an intermediate co-registration dataset, but this adds a potentially undesirable additional step in the workflow. The results reported suggest that both workflows produce similar results, and a traditional CT simulation scan is not necessary in the frameless LGK Icon workflow.


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