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Validation of a Commercially Available, ASi QA Device for the Verification of Aperture Size in the CyberKnife Iris Collimation System

D Alvarez

D Alvarez*, A Acha , V Mishra , A Gutierrez , Miami Cancer Institute, Miami, FL 33176


SU-I-GPD-T-558 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The QA of the CyberKnife Iris aperture is currently a time-consuming task requiring irradiating and analyzing film for each of the eleven aperture sizes. The purpose of this study is to validate and benchmark the detection resolution of the QA StereoChecker, a novel high resolution (aSi) dosimeter, relative to radiochromic film. Additionally, a secondary objective is to quantify any time savings with the QASC.

Methods: The procedure for measuring the aperture sizes of Iris was followed per recommendations of the vendor. The QASC (Standard Imaging, Middleton, WI) was aligned to a reference location and irradiated using five of the available eleven Iris aperture sizes. Images were recorded and analyzed by Standard Imaging proprietary software. After each aperture size was measured, a piece of EBT2 Gafchromic film was set on top within a Baby Blue phantom’s film tray with 1.5 cm of buildup and then irradiated. After curing for at least 24 hours, the film was then analyzed using the proprietary Accuray software, Iris QA.

Results: Overall, both dosimeters yielded acceptable results with the exception of the smallest aperture size with film. The percent differences from the expected aperture widths were within 1.0% except for the 7.5 mm and 10 mm field sizes. By contrast,the QASC had percent differences < 0.3% for all evaluated field sizes.

Conclusion: The QASC was shown to be a stable platform on which Iris aperture size verification can be performed in a significantly more efficient manner—approximately 2 hours for film versus 20 minutes for the QASC.

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