Development of an Image-Guidance System Quality Assurance Program for the Gamma Knife® Icon™ Radiosurgery Treatment System
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Purpose:The recently released Gamma Knife® Icon™ is equipped with an image-guidance system for tracking patient motion and correcting for inter‐ and intra-fractional shifts, mainly used with thermoplastic immobilization for fractionated and frameless stereotactic radiosurgery Intracranial treatments. This work aims to develop a comprehensive quality assurance (QA)program for Icon’s image-guidance system covering the need in this important area. We have developed tools and methodologies to go together with the ones mandated by the manufacturer, and prepared procedures and documentations needed for such a program. Method and Materials:The Icon comes with a cone‐beam CT (CBCT) and an intrafraction motion management (IFMM) system used for image-guidance treatments. We first evaluated the few quality control tests already in place, as required or recommended by the manufacturer. These check some aspects of the image-guidance system, namely the CBCT system precision using the manufacturer-provided User tool (QA tool Plus), and image quality (uniformity, contrast to noise ratio (CNR), and spatial resolution) using a Catphan® 503 phantom. We also performed CT dose index measurements using a 10-cm pencil ionization chamber in a standard CTDI acrylic head phantom. The results are reported and analyzed for these tests over a 2-year period starting at the installation of the Icon in the Gamma Knife Center of Roswell Park Comprehensive Cancer Institute. We then investigated the long-term stability of CBCT-based stereotactic space definition and its agreement with the Frame-based stereotactic space definition. We used a tool developed in-house and procedure for performing such a test and reported the results of a 6-weeks long measurements and annual measurements. We also used a three-dimensional translation/rotation stage tool that we have developed to investigate the accuracy of several image-guidance components, namely the IFMM system, the co-registration algorithm, and the delivery-after-shift. Based on the experience gained throughout this work, we proposed the additional quality control tests we have developed to be combined with themanufacturer tests in a comprehensive QA program for LGK Icon’s image-guidance system.Results:The CBCT precision check: 0.12 ± 0.04 mm (maximum deviations average). CBCT image quality: spatial resolution range: [6,7] lp/cm (low-dose (Low) preset), and [7,8] lp/cm (high-quality (High) preset); CNR: 1.07 ± 0.08 (Low), and 1.69 ± 0.10 (High); uniformity: 12.82 ± 0.69% (Low), and 13.01 ± 0.69% (High); CTDIw: 2.3 mGy (Low), and 5.7 mGy (High). Agreement of CBCT‐based with Frame‐based stereotactic coordinates range: [0.3, 0.7] mm. Accuracy of IFMM: 0.00 ± 0.12 mm (average) with 0.27 mm (max.); image accuracy of co-registration: 0.03 ± 0.06 mm (average) with 0.23 mm (max.); and accuracy of delivery‐after‐shift: 0.24 ± 0.09 mm (average) with 0.42 mm (max.). Finally, our proposal for a comprehensive image-guidance QA program combining the manufacturer tests with our user-defined tests, including their frequencies, tolerance levels, documentations, and instructions was presented.Conclusion:The manufacturer‐required QA checks together with additional user‐defined checks are an important combination for a robust quality assurance program. We have developed a comprehensive quality assurance program for LGK Icon’s image-guidance system, together with procedures and documentation to be used with such a program, ensuring the safe use of Gamma Knife® Icon™’s image guidance and motion management features in treatments of frameless stereotactic radiosurgery.