A phantom evaluation of Sentinel(™), a commercial laser/camera surface imaging system for patient setup verification in radiotherapy.

Purpose: The aim of this study is to investigate the performance of Sentinel(™), a patient setup verification device based on a laser/camera system, when used on rigid-body phantoms.

Methods: The Sentinel system consists of a scanner unit, containing the laser and the camera, and surface-matching registration software. For the registration procedure, both a computed tomography (CT) and a Sentinel image can be used as a reference. Tests were performed on phantoms using an Elekta Synergy(®) beam modulator Linac equipped with a cone beam CT (CBCT), a HexaPOD RT couch top, and an iViewGT portal imaging system. Experiments conducted in this study tested reproducibility of the Sentinel surface acquisition and of set-up procedure, accuracy in quantifying known phantom mispositioning, and compared Sentinel, CBCT, and portal imaging system performance.

Results: Reproducibility of surface acquisition and setup procedure was better than 0.5 mm and 0.5° and 1 mm and 0.4°, respectively. The system accuracy was better than 1 mm and 1° when a Sentinel image was used as reference. A global worsening of Sentinel performance was observed using as reference an external surface extracted from CT study. This effect is probably due to small differences in considered surfaces, caused by different imaging modalities. The results obtained by testing the system on rigid phantoms were comparable to those obtained using CBCT and better than those obtained with conventional portal imaging systems.

Conclusions: The Sentinel setup verification device is a reproducible and consistent system able to detect misalignments with accuracy better than 1 mm and 1°. When tested on rigid body phantoms, Sentinel and CBCT performed similarly. When compared to portal imaging, both Sentinel and CBCT were more accurate.