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Program Information

Intercomparison of Three Gamma Knife Perfexions Using the Installer Diode Tool

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J Donaghue

J Donaghue1*, S Gajdos2 , (1) The Cleveland Clinic Foundation, Cleveland, OH, (2) Akron General Medical Center, Stongsville, OH


SU-I-GPD-T-525 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: By using the Elekta Install Diode Tool (IDT), comparison of the profile data between three Elekta Gamma Knife Perfexions to ensure consistency of dosimetric data was performed.

Methods: The IDT mounts directly to the treatment table and measures profile data for three collimator settings. The offset of the center position is compared to the expected calibrated center. FWHM and penumbra data can also be extracted from the measurement data.The accuracy of the patient positioning system for the Perfexion is verified on a semi-annual basis by Elekta field service engineers. The test checks the center of the three primary collimator settings. The IDT sweeps twice along the major axes in both the positive and negative directions. The center of the profile is determined by averaging the center position of the FWHM of the profile taken in both directions.

Results: Three Perfexions were used in the data accrual. The FWHM for the 4-mm collimator for the three units was found to be: 6.176 ± 0.027 mm, 6.127 ± 0.017 mm, and 5.099 ± 0.015 mm for the lateral, longitudinal, and vertical axes respectively. For 8-mm collimator: 10.913 ± 0.044 mm, 10.916 ± 0.036 mm, and 9.853 ± 0.018 mm. For 16-mm collimator: 21.310 ± 0.064 mm, 21.256 ± 0.062 mm, and 17.341 ±0.040 mm.The penumbra for the 4-mm collimator, as averaged for each direction, was found to be 2.546 mm, 2.542 mm, and 1.263 mm. For 8-mm collimator: 3.713 mm, 3.791 mm, and 2.177 mm. For 16-mm collimator: 8.212 mm, 8.691 mm, and 2.432 mm.

Conclusion: The IDT can be used to verify that key dosimetric data is within the expected range for the Perfexion unit. Since the IDT is part of the standard Elekta test equipment, this data comparison can be applied to all existing Perfexions units.

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