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Achievable Image Quality Metrics From Initial Institutional Experience with Leksell Gamma Knife Icon

C Tien*, F Guo, M Petrongolo, JE Bond, Z Chen, Yale School of Medicine, New Haven, CT


(Tuesday, 7/31/2018) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 5

Purpose: Our institution recently commissioned a Leksell Gamma Knife Icon unit, which has a unique capability for imaging. To evaluate image quality performance, we established baseline values at commissioning and report our initial results from the past six months. These metrics were compared against the vendor-provided reference values.

Methods: Imaging performance was quantified using the Catphan 503 phantom mounted using factory-supplied adapters. Spatial resolution was quantified by counting line-pairs in CTP528 high-resolution module. Contrast-to-noise (CNR) ratio was measured as the ratio between mean pixel values of polystyrene and low-density polyethylene inserts in CTP404 material inserts module. Uniformity was measured as the maximum percentage difference of mean pixel values for five points in the CTP486 image uniformity module. All tests were performed with both low-dose scan (LDS) and high-dose scan (HDS) settings. Values were compared against Elekta reference values (ERV) and baseline values monthly.

Results: Over 6 months, the spatial resolution was 7.8 ± 0.4 (LDS) and 7.9 ± 0.2 (HDS) lp/cm, compared with 6 lp/cm ERV and baseline values of 7 (LDS) and 7.5 (HDS) lp/cm. The CNR was 0.9 ± 0.0 (LDS) and 1.6 ± 0.2 (HDS), compared with 0.5 ERV (LDS) and 0.8 ERV (HDS) and baselines values of 0.85 (LDS) and 1.45 (HDS). The uniformity was 12.5% ± 0.6 (LDS) and 12.7% ± 0.5 (HDS), compared with 14% ERV and baseline values of 13% (LDS) and 13.5% (HDS).

Conclusion: Of the three metrics (spatial resolution, CNR, and uniformity) measured, our results outperformed ERV and have remained stable. ERV were conservative when compared with our clinical baselines, especially for CNR. We are releasing our actual results to provide other clinics with reference values which may be more stringent but are still achievable.


Image Analysis, Quality Assurance, Cone-beam CT


IM/TH- RT X-ray Imaging: CBCT imaging/therapy implementation

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