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Session: Imaging for Treatment Guidance [Return to Session]

Implementation of Intrafraction Motion Review (IMR) for Stereotactic Treatment of the Spine for Patients with Spinal Fixation Hardware

A Cetnar*, M Degnan, J Pichler, S Jain, S Morelli, The Ohio State University - James Cancer Hospital, Columbus, OH

Presentations

TU-D1000-IePD-F5-6 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 5

Purpose: The Intrafraction Motion Review (IMR) application on Varian TrueBeam with Advanced Imaging provides the capability of taking simultaneous kV images during MV beam delivery. We investigated IMR for monitoring intrafraction motion for Stereotactic Radiotherapy (SRT) spine cases with patients with hardware comparing practical implementation, clinically evaluating post-treatment CBCTs, and summarizing dosimetric results.

Methods: Ten plans were studied in this cohort with a total of 33 fractions obtaining a post-treatment CBCT for analysis. IMR was triggered at 20-degree gantry angle intervals during the arc-based treatment. The contour of the hardware was displayed at the treatment console with 1 mm expansion which was used to manually beam off if the hardware was visually detected outside of the region. If there was visual indication for motion greater than 1 mm, the treatment was paused and patient was reimaged using CBCT. The post-treatment CBCT was compared with the pre-treatment CBCT to estimate dosimetric changes to coverage of target volume and dose to spinal cord as primary organs at risk.

Results: For fractions where IMR was used with the 1 mm contour for visualization, 100% of the post-treatment CBCTs agreed that differences were less than 1 mm. Only one patient in the cohort exhibited motion greater than 1 mm during the retrospective study which was identified by the current methodology. While we observe intrafraction motion close to tolerance in some cases, the average translational motion is approximately 0.35 mm. The dosimetric comparison showed little differences in dosimetry for the PTV and cord. While there is statistical difference in PTV coverage, these differences are not considered clinically significant.

Conclusion: IMR has shown to be an effective method of assessing intrafraction patient motion for SRT spine patients with hardware with minor dosimetric differences within a 1mm observation threshold.

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