Room: Exhibit Hall
Purpose: Recently, our center began treating our brain SRS patients using a Varian Edge linear accelerator with optical-surface monitoring system (OSMS). Current practice is to use passive monitoring; however, we have undertaken a preliminary study to incorporate OSMS for interventions. We retrospectively analyzed four patients' time series OSMS position.
Methods: We analyzed time series residual drift for translations and rotations using RANDO. Additionally, we analyzed the patients' time series position data treated under our SRS protocol, which currently requires a CBCT prior to each VMAT arc. Patient immobilization is achieved using CDR's Freedom 6 Couch extension, Intuition Click, and an open face mask. Current SRS imaging tolerances are translations under 0.5 mm or rotations under 0.3Â° before applying final couch shifts. A reference OSMS surface image was acquired before each arc assuming CBCT matching as the gold standard.
Results: The largest residual OSMS motion measured with RANDO across all couch angles was 0.2 mm translationally and 0.1Â° rotationally. Our patient analysis was performed incorporating residual drift and imaging tolerances (total 0.7 mm or 0.4Â°). It was observed that this tolerance would be acceptable for couch angles Â± 45Â° but would exceed our tolerance of 0.4Â° for larger table angles due to static offsets.
Conclusion: While the time series data remains stable for the course of treatment, the use of OSMS for large table angles may pose a problem for monitoring. The ability to use OSMS with larger table angles must be investigated as well as the possibility of using OSMS as a marker for repeat CBCT imaging should we fall out of tolerance.
Not Applicable / None Entered.