[en] The techniques of simulating the transport of electrons and photons in a substance are applied to a complex geometry system. A study is made of the beam of Bremsstrahlung photons created in the targed of a linear accelerator of electrons for medical uses. The electron beam of 5.7 MeV falls on a tungsten target 0.1 cm thick and the creation of bremsstrahlung photons is simulated. These photons undergo a non-negligible autoabsorption inside the target and are then filtered by an 0.2 cm copper foil. The preferential emission of the most energetic photons frontwards has the drawback of delivering too great an energy fluence along the centre line of the beam. This leads radiotherapists to fit a lead 'compensating cone', the shape and dimension of which are determinated empirically. This cone acts as a filter and diffuser at one and the same time. This is made evident by simulating the transport of photons in the cone. The transport of the photons issuing from this cone is simulated in laminar media. The H.V.T. are deduced from this and compared with the experimental results published in the literature. The slowing down of the secondary electrons brought into movement by these photons is simulated in a last programme that, inter alia, calculates the energy deposited and the L.E.T. spectra in terms of the depth and distance to the centre line of the beam. These last distributions then enable the distribution of quality factors and dose equivalents to be evaluated