Cut-away view of the radiation unit of the Leksell Gamma Knife Perfexion with large tungsten ring collimator and holes drilled in it for three collimator sizes. With permission of ELEKTA INSTRUMENT AB, Stockholm, Sweden.
(A) ELEKTA INSTRUMENT AB, Stockholm, Sweden, spherical polystyrene phantom with film cassette insert for film dosimetry. The phantom is shown fixed in the phantom adapter and ready for exposure in the Leksell Gamma Knife Perfexion. (B) Different phantom components including film cassette that can hold film and be fixed between two hemispheres of the phantom. An exposed Kodak EDR2 film with 16 mm collimator is also shown.
Characteristic curves for (A) Kodak EDR 2 film, (B) Gafchromic EBT film, and (C) Gafchromic MD-V2-55 film. The solid line represents the fifth degree polynomial fit to the ten film points after background corrections were applied for all films. PV stands for pixel value. Fifth degree polynomial coefficients are given in Table II.
Monte Carlo calculated values of ROFs for different collimator sizes (4, 8, and 16 mm) and five different rows as calculated by ELEKTA INSTRUMENT AB, Stockholm, Sweden. These values are also stored as default values in the Leksell GAMMA PLAN treatment planning system. However, only effective ROF for each collimator that represents overall contribution of all five rows can be experimentally measured by a Leksell Gamma Knife Perfexion user.
The fifth degree polynomial coefficients , , , , , and of fitting functions for characteristic curves of EDR2, EBT, and MD-V2-55 films.
ROF values measured by different film dosimeters and their comparison with MC calculated values provided by ELEKTA INSTRUMENT AB, Stockholm, Sweden. Deviations between measured and calculated values are given in parenthesis. Measured values of ROFs are corrected for transition doses.
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