Abstract⎯The thermal physics processes of solid target cooling at proton beam irradiation in С18 cyclotron were calculated. The calculations were made with the help of finite-elements method using ANSYS program for beams with nonuniform density of particle distribution in the beam profile. It was shown that the radiation efficiency and conditions of target cooling essentially depend on distributions of particles in the beam and on efficient size of beam. A principal possibility of the cryocooling of target is shown that would essentially increase the radiation efficiency and the yield of final product -the medical isotope 99m Tc. The developed calculation method may be of use also for other processes of target irradiation with charged particle beams.