Purpose: To compare surface imaging (SI) logs with MV images and linear accelerator trajectory logs to validate SI reported offsets on an anthropomorphic phantom for commissioning and routine quality assurance of a SI system used for stereotactic radiosurgery (SRS).
Methods: An anthropomorphic Styrofoam phantom (Floracraft, Ludington, MI) with a radiopaque tungsten carbide ball bearing (BB) place midline was tracked with SI with a region-of-interest (ROI) representative of a typical SRS ROI. Couch motion was programmed in developer mode and delivered on an Edge (Varian Medical Systems, Inc., Palo Alto, CA) linac. IDENTIFY (Varian Medical Systems, Inc., Palo Alto, CA) logs were synchronized with linac trajectory logs. Ten random couch positions were selected at couch rotations of 0, 45, 90, 270, 315° with MV images taken to account for couch walkout. The IDENTIFY residual error (ε), the difference between SI reported offset and MV or trajectory log position, was calculated. For lateral and longitudinal directions, ε was calculated from MV images. For vertical, and rotational ε, linac trajectory logs were used.
Results: The median [range] of magnitude of translational ε was (0.17 [0.05, 0.27], 0.39 [0.21, 0.47], 0.43 [0.30, 0.53], 0.43 [0.33, 0.60], 0.46[0.41, 0.63]) mm. The mean ± standard deviation (std) roll ε was (-0.01±0.01, 0.28±0.01, 0.55±0.02, -0.30±0.02, -0.26±0.01) °; mean ± std pitch ε was (0.03±0.01, 0.06±0.01, 0.21±0.01, 0.44±0.02, 0.22±0.01) °; mean ± std yaw ε was (0.02±0.01, 0.08±0.02, -0.02±0.03, -0.08±0.02, -0.02±0.01) °, for couch rotations of 0, 45, 90, 270, 315°, respectively.
Conclusion: SI system and linear acceleratory trajectory log analysis can be used to assess SI system performance with automated couch motion to validate accuracy for systems used for SRS.
Funding Support, Disclosures, and Conflict of Interest: Research support from Varian