Accuracy of automatic couch corrections with on-line volumetric imaging

Abstract

Purpose: To characterize automatic remote couch adjustment, and to assess the accuracy of automatic couch corrections following localization with cone-beam CT (CBCT). Method and Materials: Automatic couch movement was evaluated through passive reflector markers placed on a phantom, tracked with an optical tracking system (OTS). Repeated couch movements in the lateral, cranial/caudal, and vertical directions were monitored through the OTS to assess velocity and response time. In conjunction with CBCT, remote table movement for patient displacements following initial setup was available on 4 linear accelerators (Elekta Synergy). After the initial CBCT scan assessment, patients with isocenter displacements that exceeded clinical protocol tolerances were corrected using remote automatic couch movement. A verification CBCT scan was acquired after any remote movements. These verification CBCT datasets were assessed for the following time periods: one month post clinical installation, and six months later to monitor remote couch correction stability. Residual error analysis was evaluated using the verification scans. Results: The mean + standard deviation (? + ?) of couch movement as measured with the OTS were 0.16+0.48mm, 0.32+0.30 mm, 0.11+0.12mm in the L/R, A/P, and S/I couch directions. The fastest maximum velocity was observed in the inferior direction at 10.5mm/s, and the slowest maximum velocity in the left direction at 3.6 mm/s. From 1134 verification CBCT registrations for 207 patients, the residual error for each translational direction from each month evaluated are reported. The ? was less then 3 microns for all directions, and the ? was in the order of 1 mm. Conclusions: Remote automatic couch movement is reliable and effective for adjusting the patient position with precision of ~1 mm. Residual error observed in this study demonstrates that displacement is minimal after remote couch adjustment for all patients.