Room: Exhibit Hall | Forum 5
Purpose: Quantitative assessment of a new onboard imaging system for Leksell Gamma Knife Icon.
Methods: CatphanÂ® 503 and Leksell QA tool plus phantoms were used to acquire CBCT scans over an eighteen-month period. The two available imaging protocols (CTDI 2.5 mGy and 6.3mGy) were used each month to acquire CBCT of the CatphanÂ® 503.Image quality metrics for Contrast to Noise Ratio (CNR), High Contrast Resolution and Image Uniformity were calculated for each scan and tracked for eighteen months.Next CBCT scans of the QA tool phantom were obtained daily before each treatment and monthly as part of the comprehensive QA program. The results of the CBCT precision test were compared to the baseline value established at commissioning. The vector deviation values of the CBCT precision results are recorded each month.
Results: The mean displacement of the CBCT precision from baseline value is 0.07 mm, maximum and standard deviation are 0.12 mm and 0.031 mm. The image uniformity exceeded the tolerance criteria on two occasions and required recalibration. Image uniformity mean values are 16.1 and 16.2 % with standard deviation of 2.6 and 3.1%. Contrast resolution mean and standard deviation values are 7.6 (0.68) and 8.8(0.75). CNR mean and standard deviation values are 1.09(0.1) and 1.75(0.11). Tw outlier data points were excluded from analysis for known maintenance/upgrade during the perio
Conclusion: Geometric precision of the Gamma Knife Icon imaging system remains consistent over the 18-month period; however, the image quality of the OBI system has an inherently large uniformity value. The effect of the large image uniformity on observer assessment of the automated image registration for peripheral target is unknown and warrants further investigation.