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Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system
Tom Depuydt1, Dirk Verellen, Olivier Haas
1Radiotherapy Department, UZ Brussel, Vrije Universiteit Brussel, Laarbeeklaan 101, Brussels, Belgium. tom.depuydt@uzbrussel.be
Purpose:
VERO 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 Methods:
To 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.
Results:
The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E(90%)<0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E(90%) of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt.
Conclusions:
In 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.
