Beam profile analysis using GafChromic films

GafChromic film dosimetry techniques were used to evaluate the beam profiles for each collimator of the Leksell Gamma Knife at the University of Kentucky Medical Center. At the conclusion of acceptance testing, representatives from Leksell exposed conventional films for beam profile processing and analysis in Sweden. At the same time, an inhouse technique using GafChromic films was utilized in the analysis of the beam profiles. GafChromic films were irradiated to 100 Gray to provide data in each of the three planes for each collimator size. The films were analyzed using a scanning helium-neon laser densitometer with a small aperture of 5-10 microns. The digitized density profiles were curve-fitted using a PC plotting algorithm. The curve-fitted density profiles were converted to relative dose using a standard calibration curve determined with a conventional cobalt-60 teletherapy beam. The results are in excellent agreement with the conventional film analysis reported by Leksell. The GafChromic method has proven to be an accurate and rapid method of analysis and could be easily incorporated into a quality assurance program.