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  4. Optimization of Image Guidance Clinical Workflow for Frameless Linac-Based Stereotactic Radiosurgery (SRS) Using Three Dimensional Surface Imaging Monitoring System

Optimization of Image Guidance Clinical Workflow for Frameless Linac-Based Stereotactic Radiosurgery (SRS) Using Three Dimensional Surface Imaging Monitoring System

S Chen1*, B Agyepong2 , Y Poirier1 , N Lamichhane1 , S Becker1 , B Zhang1 , A Gopal1 , E Nichols1 , P Mohindra1 , B Yi1 , J Molitoris1 , M Mishra1 , (1) University of Maryland School of Medicine, Baltimore, MD, (2)University of Maryland Medical Center ,Baltimore,

Presentations

(Sunday, 7/14/2019) 1:00 PM - 2:00 PM

Room: Stars at Night Ballroom 1

Purpose: To investigate the optimal image guidance workflow for frameless-SRS patients treated with a dedicated Linac equipped with OBI, CBCT and optical surface monitoring system (OSMS).

Methods: This retrospective study included 60 brain metastases patients who underwent 97 frameless-SRS treatments delivered using 3-5 non-coplanar arcs and 6MV FFF beams. Each patient was immobilized with a SRS thermoplastic mask with a partial open view exposing the eyes, nose and medial portion of the cheek. During treatment, each patient was positioned and monitored following this workflow: 1) initially align patient using OSMS with the reference surface image from the planning CT; 2) fine tune patient position with CBCT using 6D couch; 3) perform second CBCT to confirm position after correction in step 2; 4) capture the OSMS surface image as a reference and monitor patient motion; 5) perform CBCT after delivery of two arcs. All couch shift data were recorded and analyzed.

Results: The magnitude of couch shifts based on first CBCT after initial setup of OSMS was 2.7±1.4mm; translational shifts were -1.0±1.2mm in RL, -0.4±1.9mm in AP, 0.0±0.9mm in SI, while the rotational corrections were -0.3±0.9° in yaw, 0.0±0.7° in roll, and 0.0±0.8° in pitch. The magnitude of shifts based on the second CBCT (compared to first) was 0.4±0.3mm; translational shifts were -0.1±0.2mm in RL, 0.0±0.3mm in AP, 0.0±0.3mm in SI, while the rotational corrections were 0.1±0.3° in yaw, 0.0±0.2° in roll, and -0.1±0.3° in pitch. The intra-fractional motion as measured from CBCT after delivery of two arcs was 0.4±0.3mm translationally and < 1° rotationally.

Conclusion: OSMS can be used for initial patient alignment within 2.7±1.4mm accuracy. Based on this analysis, a repeat CBCT after initial shifts is necessary to correct residual errors (0.4±0.3mm). However, the intra-fraction CBCT showed minimal motion and is unnecessary unless the OSMS also indicates patient motion.

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