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Session: Imaging for Patient Setup and Target Alignment [Return to Session]

End to End Comparison of Surface Guided Imaging Versus Orthogonal X-Ray Imaging for Single Isocenter, Multiple Target SRS Treatment Using 3D Gel Head Phantoms

V Bry1*, D Saenz1, E Pappas2, G Kalaitzakis3, N Papanikolaou1, K Rasmussen1, (1) UT Health San Antonio, San Antonio, TX, (2) Department of Biomedical Sciences, University of West Attica, Athens, Greece (3) Department of Medical Physics, University of Crete, Heraklion, Greece


TU-D1030-IePD-F1-3 (Tuesday, 7/12/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 1

Purpose: Two end-to-end tests evaluate the accuracy of the C-RAD Catalyst HD system for position verification at non-coplanar couch angles in comparison to Brainlab Exactrac for single-isocenter, multiple target Stereotactic Radiosurgery (SRS) using two 3D polymer gel inserts.

Methods: A single isocenter SRS plan was generated in Brainlab Elements to treat five targets in one fraction. A 3D printed head phantom (RTsafe, Athens, Greece) with two separate cylindrical gel inserts were used and immobilized in an open-face mask for radiation delivery. Cone Beam Computed Tomography (CBCT) and Brainlab Exactrac were used for position verification at the initial 180-degree angle as a baseline and a surface imaging reference image was captured. One gel insert was treated using positional verification at couch angles with Brainlab Exactrac and the other according to the C-RAD Catalyst HD. Shift discrepancies were recorded for each couch angle. 42 hours after irradiation, gel inserts were again placed inside the phantom and scanned in a 1.5 Tesla MRI. MR images were fused with the patient CT data/structure set for further analysis of spatial dose distribution.

Results: Shift discrepancies between the Catalyst HD and Exactrac were <1mm in the translational direction and <0.5° in the angular direction at couch angles. Discrepancies between calculated and measured dose parameters ranged from 0.11%-2.43% for Mean Dose and 2.52%–14.62% for D95%. 3D Gamma Index (GI) Passing Rates evaluated for each PTV at a variety of thresholds: 3%/2mm (Exactrac≥93.1% & C-RAD ≥87.2%), 5%/2mm (Exactrac≥95.6% & C-RAD ≥94.6%) and 5%/1mm (Exactrac≥81.8% & C-RAD ≥83.7%) demonstrate comparable accuracy for both setup modalities.

Conclusion: Dose metrics for the surface imaging setup were consistent with the x-ray imaging setup, demonstrating high accuracy for treatment delivery. Results indicate the feasibility of using surface imaging for position verification at couch angles for single-isocenter, multiple-target SRS using gel dosimetry.

Funding Support, Disclosures, and Conflict of Interest: This research was funded in part by C-RAD, the Cancer Prevention and Research Institute of Texas (CPRIT) Research Training Award Number RP170345 and the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health (NIH) under Award Number TL1TR002647.


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