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Single-Isocenter-Multiple-Lesion (SIML) Targeting Accuracy of a Radiosurgery System Equipped with In-Room Volumetric Imaging and 6-Dimesional Robotic Couch

J Han

J Han*, J Kim , A Hsia , Z Xu , S Ryu , Stony Brook University, Stony Brook, NY


WE-RAM2-GePD-T-6 (Wednesday, August 2, 2017) 10:00 AM - 10:30 AM Room: Therapy ePoster Lounge

Purpose: To evaluate the geometric accuracy of a radiosurgery system Edge for treating multiple lesions simultaneously with single iso-center setup, using cone-beam computed tomography (CBCT) imaging, 6-dimensional (6D) robotic couch, and automatic image registration algorithm.

Methods: Eight 3 mm ball bearing (BB) markers were inserted to an anthropomorphic head phantom. The markers were away up to 9 cm from isocenter. A computed tomography (CT) scan was acquired with 1.0 mm slice thickness. In order to estimate the geometric targeting accuracy; 1) the phantom was setup in the treatment position using CBCT imaging and automatic intensity-based registration algorithm (rigid-body, mutual information, down-hill simplex, and multi-resolution), 2) mega-voltage (MV) portal images were acquired at 16 different combinations of gantry and couch angles and 3) the BB offsets were measured from the planned position on the MV images.

Results: The positioning accuracy (µ ± σ) over all gantry and couch combinations was 0.5±0.2 mm. The accuracy with zero couch angle was 0.3 ± 0.1 mm, and that with non-zero couch angles was 0.6±0.2 mm. Analysis with zero gantry angle, which eliminated potential gantry sag, indicated the dependence on the lesion-to-isocenter distance; a 0.2 mm average accuracy degradation from the closest to farthest target.

Conclusion: The radiosurgery system in this study was geometrically accurate with targeting error of <1 mm for lesions up to 9 cm away from isocenter. The positioning accuracy degraded by 0.3 mm from couch rotations and up to 0.2 mm due to the 9 cm target-to-isocenter distance. The preliminary results in this study is suggestive that the radiosurgery system investigated in this study is capable of providing necessary geometrical accuracy for single-isocenter-multi-lesion treatment setup. It should be noted, however, that the results in this study was based on a phantom. Further analysis is necessary with real patient data.

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