Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system

Abstract

PurposeVERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking. Materials and methodsTo determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/tilt performance were measured. ResultsThe system lag was 47.7ms for panning and 47.6ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E90%<0.82mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14mm. The 2D tumor trajectories were tracked with an average E90% of 0.54mm, and tracking error standard deviations of 0.20mm for pan and 0.22mm for tilt. ConclusionsIn terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.