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Filmless Quality Assurance Tests for the Leksell Gamma Knife Icon™

B Maraghechi*, T Kim, J Dise, S Goddu, T Mitchell, J Kavanaugh, J Zoberi, S Mutic, N Knutson, Washington University, St. Louis, MO


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

To perform the annual radiation delivery quality assurance (QA) and treatment planning system validation tests for Gamma Knife® Icon™ system without the use of films.

Annual QA tests for a Leksell Gamma Knife® (LGK) Icon™ system were performed using film-based and filmless techniques. Output calibration, relative output factors (ROF), radiation profiles, sector uniformity/sector counting, and verification of the unit center point (UCP) and radiation focal point (RFP) coincidence tests were performed for the annual QA. Gafchromic EBT3 radiochromic films, PTW model TN31010 ionization chamber, and a PTW MicroDiamond detector were used for the measurements. Profiles were measured by translating a detector in a spherical phantom across the radiation center with programmed couch motions. Results were compared and verified with the values of treatment planning system (TPS) in both the film-based and filmless methodologies.

The measured dose rate of the LGK Icon was within 0.3% of the TPS value set at the time of commissioning using a calibrated ionization chamber. ROF for the 8 mm and 4 mm collimators were found to be 0.5% and 1.8% different from TPS values using the MicroDiamond detector vs 2.6% and 1.9% for film. Excellent agreement was found between TPS and measured dose profiles using the MicroDiamond detector which was within 1%/1mm vs 2%/1mm for film. Sector uniformity was found to be within 1% for all eight sectors measured using an ion chamber. Verification of UCP and RFP coincidence (within 0.3 mm at isocenter) using the MicroDiamond detector yielded similar results compared to when the test was performed by pinprick film test.

The annual QA of a LGK Icon was successfully performed by employing filmless techniques. Comparable results were obtained using radiochromic films. Utilizing active detectors instead of films simplifies the QA process and saves time without loss of accuracy.


Gamma Knife, Quality Assurance, Small Fields


Not Applicable / None Entered.

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