A numerical model was developed and a system of the nonlinear equations of deuterium-tritium burn-up in inertial confinement fusion have been solved to find the minimum conditions which are required for the formation of hot spot and starting the thermonuclear reactions in a self-sustaining mode. The effect of all the dominant phenomena in the nonequilibrium plasma, including the alpha particle energy deposition in the hot spot and transferring to ions and electrons, ions-electron coupling energy, and the main photons-matter interactions, which includes the bremsstrahlung radiation and the Compton scattering, were investigated. By using the Klein-Nishina equation for scattering cross-section of high energy photons, the effects of the photon-matter interactions from a relativistic point of view have also been studied. It was shown that the change of photon distribution shape can have a significant effect on the photon temperature, the photon-electron coupling energy and as a result on the electrons and the ions’ temperature in a diluted plasma.