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Evaluation of An Optical Surface Monitoring System for Intra-Fraction Patient Position Verification in Stereotactic Radiosurgery

F Hacker*, Z Han , Y Hu , J Bredfeldt , H Lee , S Friesen , Brigham and Women's Hospital, Boston, MA


(Tuesday, 7/16/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 3

Purpose: To evaluate a surface guided system against a bench mark x-ray guided system for verifying intra-fraction positioning during radiosurgery of multiple brain lesions using a single isocenter technique.

Methods: 25 Radiosurgery treatments using non-coplanar arcs were evaluated for intra-fraction patient positioning using the Brainlab stereoscopic x-ray ExacTrac system and the Varian Optical Surface Monitoring System (OSMS). Patients were treated on a Varian Truebeam STX equipped with ExacTrac 6.0 and using the Encompass open face mask system by QFix. Initial patient position was set with CBCT and 3D/3D matching. Patient position was then fine tuned with the ExacTrac system and 2D/3D matching. A reference surface was then acquired with the OSMS system. Immediately prior to delivery of each arc ExacTrac verification images were acquired and simultaneously the OSMS shifts were recorded. An institutional tolerance of 0.7mm/0.7degrees was used. If patient position exceeded tolerance the patient was shifted with the ExacTrac system and new verification images were acquired as well as new OSMS readings. A total of 152 positioning comparisons were evaluated.

Results: A mean (standard deviation) of 0.00(0.39)/0.16(0.49)/0.05(0.46) mm difference was observed in the Vertical/Longitudinal/Lateral directions between the ExacTrac and OSMS indicated patient positions. Rotational mean (standard deviation) differences were 0.0(0.3)/0.0(0.3)/0.2(0.4) degrees along the Rotation/Roll/Pitch axes. A total of 36 translations above 0.7mm and 7 rotations above 0.7 degrees were detected by ExacTrac. Of these 11 of the translations and 3 of the rotations were also detected by OSMS.

Conclusion: OSMS can be used to detect larger shifts of >1mm but is not currently sufficiently accurate to reliably detect the sub-millimeter shifts needed to meet our institutional tolerance. This may be improved with the recently introduced Advanced Camera Calibration for OSMS which we will evaluate in future work.


Not Applicable / None Entered.


TH- RT Interfraction motion management : setup errors, immobilization, localization

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