Abstract
The purpose of this study was to characterize automatic remote couch adjustment and to assess the accuracy of automatic couch corrections following localization with cone‐beam CT (CBCT). 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 four 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. The mean ± standard deviations (μ±σ) of couch movement based on phantom measurements with the OTS were 0.16±0.48mm,0.32±0.30mm,0.11±0.12mm in the L/R, A/P, and S/I couch directions, respectively. The fastest maximum velocity was observed in the inferior direction at 10.5 mm/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 μ was less than 0.3 mm in all directions, and σ was in the order of 1 mm. At a 3 mm threshold, 21 of the 1134 fractions (2%) exceeded tolerance, attributed to patient intrafraction movement. Remote automatic couch movement is reliable and effective for adjusting patient position with a precision of approximately 1 mm. Patient residual error observed in this study demonstrates that displacement is minimal after remote couch adjustment.PACS number: 87.55.Qr, 87.56.bd, 87.57.Q
Highlights
The goal of radiation therapy is to eradicate tumor cells while minimizing dose to surrounding normal tissue
To assess patient positioning and monitor potential changes throughout treatment, three-dimensional (3D) kilovoltage imaging provides enhanced patient setup information over traditional two-dimensional (2D) orthogonal megavoltage (MV) portals.[1,2,3,4,5,6] Volumetric imaging has a positive impact on patient positioning as front-end users are able to visualize anatomy on a 3D scale, with the ability to monitor patient displacements and soft tissue changes.[5]
Through an on-line volumetric imaging process, setup errors are detected by registration of the cone-beam computed tomography (CBCT) to the reference planning CT data set.[4]. With its application on a variety of anatomical sites, volumetric imaging through the X-ray Volumetric Imaging (XVI) software (v3.5, Elekta, Stockholm, Sweden) became rapidly adopted in the clinical environment,(2,3,7) increasing the geometric precision and accuracy of therapy by reducing systematic and random setup errors.[6,8] Radiotherapy treatments are image-guided using the 3D images and set action thresholds
Summary
The goal of radiation therapy is to eradicate tumor cells while minimizing dose to surrounding normal tissue. Recent advances in image-guided radiation therapy (IGRT) processes have increased the precision and reproducibility of radiotherapy treatments. Through an on-line volumetric imaging process, setup errors are detected by registration of the cone-beam computed tomography (CBCT) to the reference planning CT data set.[4] With its application on a variety of anatomical sites, volumetric imaging through the X-ray Volumetric Imaging (XVI) software (v3.5, Elekta, Stockholm, Sweden) became rapidly adopted in the clinical environment,(2,3,7) increasing the geometric precision and accuracy of therapy by reducing systematic and random setup errors.[6,8] Radiotherapy treatments are image-guided using the 3D images and set action thresholds. If the scan displacement exceeds threshold, an intervention in the form of a manual couch adjustment from inside the treatment room was performed, and a second (verification) CBCT followed to assess residual error. The reported accuracy of residual error after couch corrections with an unambiguous rigid phantom is within a few hundreds of a millimeter.[8]
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