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Session: Therapy General ePoster Viewing [Return to Session]

A Multi-Detector Comparison of the Measured Relative Output Factors for Elekta Gamma Knife ICON

D Shrestha1*, M Lowe2, S Herchko3, S Yaddanapudi4, S Stojadinovic5, (1) Mayo Clinic, Jacksonville, FL, (2) Mayo Clinic, Jacksonville, FL, (3) Mayo Clinic Florida, Jacksonville, FL, (4) Mayo Clinic, Jacksonville, FL, (5) UT Southwestern Medical Center, Dallas, TX


PO-GePV-T-369 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Small size therapeutic fields employed in stereotactic radiosurgery (SRS) necessitate multidetector use to perform high fidelity dosimetric characterizations. Small field dosimetry challenges including steep dose gradients, detector volume averaging effects and lack of lateral electronic equilibrium are evident for the relative output factors (ROF) validation of Leksell Gamma Knife system (LGK; Elekta, Stockholm, Sweden).

Methods: Four solid state and ionization chamber detectors and water equivalent dosimetry phantom were used for small field ROFs measurements for 4 mm, 8 mm and 16 mm collimator settings on the LGK ICON. The measurements obtained using PTW T60019 microDiamond, PTW 60023 microSilicon diode, Exradin A16 ionization chamber, and PTW 31016 PinPoint 3D ionization chamber were corrected according to the TRS-483 formalism for small static field dosimetry.

Results: The results of the ROF measurements for the 4 mm and 8 mm collimator settings were as follows: PTW T60019 microDiamond: 0.821, 0.891; PTW 60023 microSilicon diode: 0.816, 0.908; Exradin A16: 0.815, 0.903; PTW 31016 PinPoint 3D: 0.695, 0.879, respectively. All measured data agree within 1% of the nominal ROF values used for treatment planning in Leksell GammaPlan (LGP; Elekta, Stockholm, Sweden). An exception, however, were the results of PinPoint detector, which indicated the chamber had somewhat larger 2.4% difference for the 8 mm collimator but also that it was unsuitable for the smallest 4 mm collimator output assessment.

Conclusion: An excellent agreement within 1% was achieved between measured and standard ROF provided by Elekta. Additional detector measurements combined with the comprehensive uncertainty budget analysis would be valuable regarding detector selection for a successful SRS program.


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