Room: AAPM ePoster Library
Purpose: To evaluate the feasibility of using IDENTIFY (Varian Medical Systems, Palo Alto, CA), a surface imaging (SI) system, for intrafraction motion monitoring during frameless stereotactic radiosurgery (SRS).
Methods: IDENTIFY was evaluated in a research vault configured for SRS. QA tests were performed to ensure that the linear accelerator met SRS performance specifications. An anthropomorphic phantom was used to assess IDENTIFY under patient-like conditions. To assess stability and drift, the phantom was monitored immediately following system startup until equilibrium. The phantom was embedded with a tungsten ball bearing (BB) to facilitate the use of IDENTIFY with concurrent MV-EPID imaging to cross-compare and validate SI reported offsets. Data analysis was done via software developed at the University of Alabama-Birmingham that utilized IDENTIFY’s log files for automated analysis and reported the SI residual error, defined as the difference between the SI reported offset and the couch walkout as determined via EPID. To evaluate the effect of isocenter location relative to the surface, the BB was placed at three depths: surface, central (~10 cm), and deep (~20 cm). A volunteer was monitored in an ENCOMPASS (Qfix, Avondale, PA) mask as the table and gantry were rotated.
Results: The IDENTIFY drift was < 0.1 mm over 15 minutes. The maximum residual error of IDENTIFY was found to be 0.4 mm at couch 337.5° when the BB was in the deep location. The residual errors were similar for other BB locations. The maximum IDENTIFY offset from reference position for the volunteer was 0.3 mm while the gantry was rotated and one camera view was obscured, and no spikes or drops in reporting were observed. The maximum magnitude difference from reference position was 0.7 mm at couch 270° for the volunteer.
Conclusion: Performance of IDENTIFY was comparable to commercially available surface imaging systems.
Funding Support, Disclosures, and Conflict of Interest: Dr. Covington and Dr. Popple received travel support from Varian Medical Systems to perform the tests detailed in this work.