Quality assurance tests for the Gamma Knife^® Icon™ image guidance system

Abstract

IntroductionThe Gamma Knife® Icon™ comes with an image guidance system for tracking patient motion and correcting for inter‐ and intrafractional shifts, mainly used with frameless thermoplastic immobilization. The system consists of a cone‐beam CT (CBCT) and a couch‐mounted infrared camera (IFMM). We report our quality assurance program for Icon's image guidance system.MethodsThe manufacturer‐provided tool is used for daily checks of CBCT positional precision. Catphan® phantom is used for monthly checks of CBCT image qualities (uniformity, contrast to noise ratio (CNR), and spatial resolution) for the two acquisition presets (low‐dose and high‐quality presets). On a semi‐annual schedule, we use a frame tool to check the agreement of CBCT‐based and Frame‐based stereotactic space coordinates by comparing the locations of five attached ball bearings in CT‐sim scans (Frame‐based coordinates determination) and in Icon's CBCT scans. On an annual basis, the accuracy of IFMM, image registration, and delivery‐after‐shift are tested using a translational stage. A weighted CT dose index is measured annually with a pencil chamber in CTDI head phantom.ResultsThe CBCT precision check: 0.12 ± 0.04 mm (maximum deviations average). CBCT image quality: spatial resolution range: [6,7] lp/cm (low), and [7,8] lp/cm (high); uniformity: 12.82 ± 0.69% (low), and 13.01 ± 0.69% (high); CNR: 1.07 ± 0.08 (low), and 1.69 ± 0.10 (high). Agreement of CBCT‐based with Frame‐based stereotactic coordinates range: [0.33, 0.66] mm. Accuracy of IFMM: 0.00 ± 0.12 mm (average) with 0.27 mm (max.); image registration: 0.03 ± 0.06 mm (average) with 0.23 mm (max.); and delivery‐after‐shift: 0.24 ± 0.09 mm (average) with 0.42 mm (max.). CTDI w: 2.3 mGy (low), and 5.7 mGy (high).ConclusionsThe manufacturer‐required QA checks together with additional user‐defined checks are an important combination for a robust quality assurance program ensuring the safe use of Gamma Knife® Icon™'s image guidance and motion management features.

Performance of the cone beam computed tomography‐based patient positioning system on the Gamma Knife Icon™

“…The maximum deviations observed for the four BBs are 0.13, 0.12, 0.15, and 0.12 mm, respectively. These numbers are consistent with a previous study in which the maximum deviations from daily CBCT precision tests for two 2‐yr period were reported …”

“…These numbers are consistent with a previous study in which the maximum deviations from daily CBCT precision tests for two 2-yr period were reported. 5 Table I gives the X, Y, Z coordinates (referred to the axes of the Gamma Knife patient positioning system) 23 and the pitch, yaw, roll angles from the image registrations for manual shifts of the STEEV head phantom in the Z direction up to 10 mm. The result for 0 mm shift was obtained when the phantom was in the same position as the reference scan.…”

“…The physics commissioning procedure of an Icon™ system was first presented by Zeverino et al Several preliminary studies on the effect of the setup uncertainties in fractionated GKRS and the correlation between the nose tip motion and the intracranial displacements in mask‐based GKRS were also reported . A summary of the quality assurance test results for the image guidance system on a Gamma Knife Icon™ was reported by AlDahlawi et al…”

“…The physics commissioning procedure of an Icon TM system was first presented by Zeverino et al 1 Several preliminary studies on the effect of the setup uncertainties in fractionated GKRS and the correlation between the nose tip motion and the intracranial displacements in mask-based GKRS were also reported. [2][3][4] A summary of the quality assurance test results for the image guidance system on a Gamma Knife Icon TM was reported by AlDahlawi et al 5 The CBCT imaging technique introduced by Jaffrey et al has become one of the standard medical imaging modalities for patient setup in Linac-based external beam radiation therapy. 6,7 The onboard CBCT imaging module provides a treatment machine-based measurement tool that allows for a 3D visualization of the patient position on the treatment table.…”

“…Several studies have been reported on the quality assurance and the positioning accuracy tests for the CBCT imaging module on the Gamma Knife Icon TM using different test phantoms. 5,[14][15][16][17] The accuracy and the stability of the frameless GKRS were evaluated using film dosimetry in combination with an anthropomorphic phantom. 14 The CBCT-based patient positioning system was also used for the validation of the frame-based GKRS.…”