E Quan, S Krafft, M Vaccarelli, T Briere, E Han*, UT MD Anderson Cancer Ctr., Houston, TX

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  E Han

PO-GePV-T-79 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Spine SBRT uses highly conformal dose distributions and sharp dose gradients to cover targets in proximity to spinal cord or cauda, which requires precise patient positioning and immobilization to deliver safe treatments. This work evaluates the accuracy and efficiency of our newly adopted Klarity SBRT patient immobilization system in comparison with the Elekta BlueBAG BodyFIX system.

Methods: 16 patients with 18 metastatic spinal lesions (54 fractions) were prospectively enrolled in this study, who were simulated and treated using one of two systems – BlueBAG (n=7) or Klarity (n=11). All patients were initially setup to skin marks, positioned to match bony anatomy on ExacTrac images (tolerance 0.7mm translational and 0.8° rotational), and verified with CBCT and kV/MV orthogonal imaging; image-guided corrections were repeated if patient motion was observed. Table corrections/deviations given by ExacTrac during setup and intra-fractional monitoring, and deviations from pre- and post-CBCT images were analyzed to evaluate setup accuracy and efficiency of the two immobilization systems.

Results: For initial setup accuracy, the Klarity system generally showed larger differences between initial skin mark alignment and the first bony alignment on ExacTrac than BlueBAG, especially in the vertical (mean [SD] of 6.0mm [4.1mm] versus 1.9mm [1.7mm]) and lateral (mean [SD] of 5.6mm [5.3mm] versus 2.9mm [3.4mm]) directions. For setup efficiency, Klarity system achieved desired bony alignment with similar number of online imaging and shorter average setup time (14.6 minutes versus 16.9 minutes). For intra-fractional motion, translational and rotational motion during treatment were found to be less with Klarity than with BlueBAG, corresponding to a geometric uncertainty of 1.3mm versus 1.5mm laterally, and 1.7mm versus 2.4mm both longitudinally and vertically.

Conclusion: With careful image-guided positioning, the Klarity system can provide accurate and efficient patient immobilization and can be a better alternative to the BlueBAG system for Spine SBRT.

Keywords

Immobilization, Stereotactic Radiosurgery, Image Guidance

Taxonomy

TH- External Beam- Photons: General (most aspects)

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