Monte Carlo calculations and GafChromic film measurements for Leksell Gamma Knife unit

The Leksell Gamma Knife is a standard radiosurgical tool for treating brain lesions by directing beams of gamma radiation to a specific region. The diameter of the gamma beams is confined by collimator systems and the available collimator sizes are 4, 8, 14 and 18 mm. The reduction in dose rate for each collimator helmet is called the output factor. Experimental determination of output factors is difficult due to the extremely narrow beams by which the dose is determined. In the present work, the Monte Carlo technique and GafChromic films were employed to verify the dose distribution and the output factor of Gamma Knife (type B) radiosurgery. The output factors measured with GafChromic film and the results of our Monte Carlo trials were within uncertainty range and showed consistency with the value provided by the manufacturer of Leksell Gamma knife, Elekta. Moreover, good agreement in dose profiles along x, y, and z axes for all collimator helmets were summed up over all 201 sources. (author)