Unintended attenuation in the Leksell Gamma Knife® Perfexion™ calibration-phantom adaptor and its effect on dose calibration
Phantoms and adaptors used for LGK PFX calibration. Elekta Instrument AB polystyrene phantom with phantom adaptor (a). Elekta Instrument AB solid-water phantom with frame adaptor (b). Radiograph of the polystyrene phantom setup in the adaptor, approximate beam directions from sectors 3 and 7 are indicated (c).
Film setup for the demonstration of the absorption of 16, 8, and 4 mm beams by the phantom adaptor (a). Results for sectors 3 and 7 are shown in (b) and (c). Attenuation by Lucite gamma angle plate is shown in (d).
Sector output uniformity measurement for 16 mm collimator with standard Elekta Instrument AB polystyrene phantom and Elekta Instrument AB solid-water phantom with their individual phantom adaptors. Average readings together with 1 standard deviation are given in the table. While for solid-water phantom, individual sector output is consistent within 1.0%, the sector output for polystyrene phantom and C-clamp aluminum adaptor for sectors 3 and 7 is smaller. Percentage deviations of each sector output from the average output of all eight sectors were calculated by using Eqs. (1) and (2). Percentage deviations for sectors 3 and 7 attenuated readings from the average unattenuated sectors reading were calculated by Eqs. (3) and (4) and are given in parentheses in the case of polystyrene phantom.
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