We present here a numerical study of a photothermal therapy conducted on a digital phantom of a mouse's head bearing a tumor. The temperature evolution and thermal damages caused to the phantom and the tumor were calculated using heat diffusion simulations. Nanoparticles were simulated in the study as a local increase of the tumor's absorption and their effect on the therapy is studied. Finally, photoacoustic simulations were performed in order to monitor the temperature evolution in the tumor during the therapy.