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Intrafraction Patient Movement During Frameless Intracranial Stereotactic Radiotherapy

E Covington

E. L. Covington*, J Kraus , X Wu , D. H. Boggs , C. D. Willey , M Bredel , J. B. Fiveash , R. A. Popple , Univ Alabama Birmingham, Birmingham, AL


WE-RAM2-GePD-JT-2 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Joint Imaging-Therapy ePoster Theater

Purpose: To compare patient movement during frameless volumetric arc therapy (VMAT) of intracranial stereotactic radiotherapy using an Optical Surface Monitoring System (OSMS) versus movement determined by CBCT.

Methods: OSMS was used to determine translational (longitudinal (LNG), lateral (LAT), vertical (VRT)) and rotational deviations, called Real Time Deltas (RTDs), from a reference position. After CBCT, an OSMS reference surface was captured and used to track patient movement throughout treatment.

Results: We observed 106 fractions of 63 treatment plans delivered by flattening filter free (FFF) beams on an Edge linear accelerator (Varian, Palo Alto, CA) with an average treatment time of 4.76 minutes and compared the results to 102 fractions on a Truebeam (Varian, Palo Alto, CA) that were evaluated with sequential CBCT separated by an average of 3.2 minutes. The average RTDs from OSMS reference capture to end of treatment was LAT = 0.01 ± 0.19 mm, LNG = -0.05 ± 0.34 mm, and VRT = 0.04 ± 0.14 mm with a mean magnitude of 0.34 mm versus LAT = -0.03 ± 0.27 mm, LNG = 0.14 ± 0.46 mm, and VRT = 0.04 ± .27 with a mean magnitude of 0.16 mm with CBCT. For non-zero couch angles, average RTDs before beam on were LAT = -0.02 ± 0.4 mm, LNG = -0.66 ± 0.52 mm, and VRT = -0.11 ± 0.15 mm. Couch walkout was investigated as a potential source of the increased longitudinal offset but was not found to be correlated during phantom studies.

Conclusion: Overall, intrafraction patient motion assessed by OSMS is consistent with previous kV image guided studies. Larger deviations reported by OSMS in the longitudinal direction suggest a systematic error in tracking patient position along this direction.

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