Recently, the Medium Energy Ion Scattering (MEIS) technique has been used as an additional tool for characterization of nanoparticles and quantum dots [1,2,3], where basically their shape, composition, size distribution and stoichiometry have been successfully obtained. Other promising MEIS application, namely the determination of depth distributions of different elements in a single nanoparticle has been recently appeared in the literature [4]. In this way, the MEIS technique can be able to give elemental and depth information hardly achieved by any other analytical technique.  Thus, we have developed a Monte Carlo simulation and fitting software [5] that considers any geometry, size distribution, density of the nanostructures and also the asymmetry of the energy loss-distribution. Here we investigate Pb nanoislands (NIs) synthesized by ion implantation with low temperature and long aging time treatments followed by a high temperature thermal annealing. This process leads to the formation of a dense 2D NIs array located at the SiO2/Si interface. The 2D MEIS spectra (energy and angle), we have studied the nanostructure geometry, number density and size distribution of such system. The present results are compared to transmission electron microscopy (TEM) measurements.