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Intra-Fraction Motion Monitoring for Spine SBRT Patients Using KV Cone-Beam Projections

D Markel*, D Letourneau , H Keller , N Becker , D Shultz , Princess Margaret Hospital, Toronto, ON


(Sunday, 7/29/2018) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 5

Purpose: To implement and validate a system to monitor intra-fraction motion of paraspinal patients receiving SBRT treatment using kV projections on the Elekta XVI platform acquired during treatment.

Methods: Simulated projections from a planning CT were generated using Simple RTK and registered to acquired kV cone-beam projections using Simple ITK. A custom-built anthropomorphic phantom with a human skeleton was used to quantify the uncertainty of our monitoring pipeline as a function of gantry angle and applied displacement. Known shifts of up to 1 cm in the plane of the kV panel were applied. To date, intra-fraction projections of 3 patients receiving VMAT spine SBRT treatment were acquired with a gantry angle spacing of 1°. Intra-fraction motion, as assessed by our pipeline, was quantified and compared to the shifts determined by registering the reconstructed intra-fraction CBCT to the planning CT.

Results: Phantom results demonstrated that the pipeline was able to register images with a mean accuracy of 0.82 ± 0.29 mm and 0.51 ± 0.21 mm for displacements up to 3.2 mm and 1 cm in the X and Y axes of the panel respectively. This excluded a gantry angle range of 36° where a metal bar on the couch appeared in the scan. Results from the 3 patients showed average superior-inferior shifts of up to 1.2 mm with maximum displacement reaching 2.5 mm observed in the anterior-posterior direction. Larger registration errors were observed for lateral projections and were excluded from the analysis. Up to 1.9 mm of positional error in the superior-inferior direction was determined using the intra-fraction CBCT.

Conclusion: Phantom results have demonstrated that the pipeline provides sub-millimeter monitoring accuracy of vertebrae. Patient results show that displacement during treatment determined by our monitoring method were higher than that observed with the intra-fraction CBCT.


Cone-beam CT, Registration, Patient Movement


IM/TH- Image registration : X-ray

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