[en] Full text: Amorphous Silicon (a-Si) Flat Panel are radiographic detectors for indirect conversion that converts X ray radiation incident to light, using phosphors scintillator. This light will generate charges in Amorphous Silicon photodiodes, that will produce an electrical signal that will become the radiographic image. The most common scintillators used for this purpose are gadolinium orthosilicate (GSO) and cesium iodide (CsI). The aim of this work is to model through simulations with the Monte Carlo Code MCNPX the energy dependence of a gadolinium orthosilicate scintillator (GSO). The photon absorption rate (absorbed energy) in a gadolinium orthosilicate (GSO) material and the x-ray to light conversion efficiency or luminescence efficiency (emitted light energy flux over incident x-ray energy flux) will be discussed. (author)