Stereotactic radiosurgery is an increasingly popular method for treating pathological processes within the brain, and the Leksell Gamma Knife is one of the leading irradiators or machines that shows excellent results in this field. The device uses narrow photon beams generated by the radioactive 60Co sources, which are precisely directed at the lesion using a stereotactic frame. The photon beam axes intersect at a common point called the isocenter. During irradiation, a high dose can be delivered, resulting in an approximately spherical distribution of the absorbed dose. A computer algorithm is used to calculate the absorbed dose, and the calculation is based on precisely determined output factors, and absorbed dose profiles, which were experimentally determined in this study. Additionally, the basis for accurate dose calculation is also the absorbed dose rate determined in the reference conditions, which is not the subject of this thesis. All measurements presented in this study were conducted at the Division of Stereotaxy, Functional Neurosurgery, and Radiosurgery of the Department of Neurosurgery, University Hospital Center Zagreb. Profiles and output factors were determined using EBT3 radiochromic film and PinPoint3D and PinPoint ionization chambers for all widths of the gamma knife photon beams obtained with collimators of sizes 4 mm, 8 mm, and 16 mm. All measurements were performed in a tissue-equivalent phantom, Solid Water. The full width at half maximum (FWHM) and penumbra widths of the profiles obtained with EBT3 film are in very good agreement with the reference values obtained from Monte Carlo simulations, while the output factor values obtained with the film deviate from the reference values, especially for the smallest gamma knife field size of 4 mm. Analysis of the profiles obtained with the PinPoint3D and PinPoint ionization chambers revealed a broadening of the penumbra for the field sizes of 4 mm and 8 mm, while the FWHM values do not significantly deviate from the reference values. The output factor values obtained with the ionization chambers significantly deviate for the small field size of 4 mm, while the values for the 8 mm field size are in line with the reference values. The broadening of the penumbra and significant deviation of output factors for the small 4 mm field are due to the pronounced volume averaging effect characteristic of ionization chambers and the disruption of lateral electronic equilibrium that can occur in small fields. The reason for the significant volume averaging effect lies in the inappropriate ratio between the active measuring volume of the ionization chamber and the photon beams. Therefore, the EBT3 film is the recommended dosimeter for dose profile determination [16], but not for determining output factors, while small ionization chambers are the recommended dosimeters for determining absorbed dose under reference conditions, but not for relative dosimetry, such as determining profiles and output factors.