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Analysis of Initial Setup Accuracy and Intrafraction Motion of Two Frameless Immobilization Systems in Cranial Stereotactic Radiosurgery

T Tseng*, R Sheu , S Green , S Sharma , K Dharmarajan , Y Lo , Mount Sinai Medical Center, New York, NY


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: To evaluate the reproducibility and immobilization effectiveness of two clinically-used frameless systems in single fraction cranial stereotactic radiosurgery.

Methods: The two different frameless immobilization systems are under study: 1) open-face mask (OFM)-Encompass SRS Fibreplast (Qfix) and 2) closed-face mask (CFM)-Brainlab frameless system (Brainlab). The study was performed involving 29 OFM patients (40 isocenters) initially setup with the optical surface management system (OSMS, Varian) and 26 CFM patients (39 isocenters) initially setup with the ExacTrac infrared array system (IR, Brainlab). Initial setup was followed by ExacTrac kV imaging to shift patients to treatment position with 6D robotic couch based on automated bony anatomy matching. Intrafraction motion was corrected with ExacTrac kV imaging at each planning couch angle. The shifts for initial setup and intrafraction motion were collected to compare the reproducibility and immobilization effectiveness of both systems. Two-tailed t-test was applied for statistical significance comparison.

Results: The correctional radial shifts (mean±STD, median) of initial setup for OFM+OSMS and CFM+IR measured by ExacTrac were 4.85±2.19mm, 4.49mm and 2.11±1.42mm, 1.72mm, respectively (p<0.001). To achieve sub-millimeter/sub-degree accuracy, OFM+OSMS more often succeed with initial setup and no shifts were required compared to CFMIR (<1mm shifts in Lat-50% vs. 25.6%, Long-60% vs. 38.5%, Vert-75% vs. 10.3%, Pitch-85% vs. 71.8%, Roll-67.5% vs.66.7% and Yaw-60% vs. 76.9%). Intrafraction motion radial shifts (mean±STD, median) for OFM+OSMS and CFM+IR were 0.79±0.30mm, 0.77mm and 0.79±0.48mm, 0.72mm, respectively (p=0.903). Intrafrational shifts (>1mm, >1degree) were required for 6.3% of the OFM+OSMS patients and 5.7% of the CFM+IR patients.

Conclusion: With the assistance of OSMS system, open face mask was able to achieve better initial setup accuracy that reproduced simulation position compare to closed mask and infrared array alignment. However, both frameless mask systems were able to achieve similar immobilization effectiveness during treatment and only few intrafractional shifts need to be applied.


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