Abstract : The ATF2 project aims at demonstrating the strong vertical electron beam focusing capability, down to the few tens of nanometers level, of a down scale prototype of the ﬁnal focus system of the next generation of e+ e- machines. The large beam size near the IP, before and after ﬁnal focus, induces losses of particles that may generate electromagnetic backgrounds in the IP region. This background could be even larger according to ATF2 plans to operate at lower IP betas to prove the optics design and the tuning algorithms. In order to estimate the ATF2 background, an accelerator simulation code based on Geant4, will be used and compared to dedicated measurements. A simple and ﬂexible apparatus system has been designed and built : it is made of a set of readout modules made in plastic and CsI scintillators. The background simulation and benchmark with ATF2 data will be presented.