Room: AAPM ePoster Library
Purpose: Conventional reference dosimetry conditions in terms of e.g. field size, SDD, phantom material, etc, are not achievable with the Leksell Gamma Knife (LGK) Icon due to its unique geometry and beam field. Therefore, Monte Carlo calculated correction factors intended to account for the differences between reference conditions and the machine-specific conditions of the LGK have recently been published. The purpose of this study was to experimentally verify published correction factors experimentally.
Methods: Dose-rates from an LGK Icon and an LGK Perfexion were determined using PTW 31010 and PTW 31016 detectors along with acrylonitrile butadiene styrene (ABS) and Certified Medical Grade Solid Water (SW) phantoms. Four different published sets of correction factors were investigated. A fifth set of correction factors was calculated by modifying existing factors to account for the beam attenuation caused by the ABS phantom adapter.
Results: Determined dose-rates were significantly lower (2.2 % and 1.3 % for the 31010 and 31016 detector respectively) when using the ABS phantom as compared to the SW phantom. No difference in performance between the two detectors could be seen when using the SW phantom. These results were predicted by most correction factors. Accounting for the 0.8 % beam attenuation caused by the ABS phantom adapter yielded values closer to the corrected SW measurements.
Conclusion: Correction factors should be applied if the ABS phantom is used. Correction factors may not be necessary when using the SW phantom. Out of the two phantoms, the ABS phantom is not recommended for reference dosimetry on the LGK Icon due to ambiguity of detector orientation in the phantom, and the adapter beam attenuation. The SW phantom is recommended for reference dosimetry on the LGK Icon.