In this paper, we propose a deterministic simulation of X-ray transmission imaging on graphics hardware. Only the directly transmitted photons are simulated, using the Beer-Lambert law. Our previous attempt to simulate Xray attenuation from polygon meshes utilising the GPU showed significant increase of performance, with respect to a validated software implementation, without loss of accuracy. However, the simulations were restricted to monochromatic X-rays and finite point sources. We present here an extension to our method to perform physically more realistic simulations by taking into account polychromatic X-rays and focal spots causing blur.