Thanks to the finite range of the protons, proton-therapy is of undeniable therapeutic interest. However, proton treatment planning suffers from uncertainties in the computation of the protons range. As a means of measuring the proton energy loss along the path of the beam, proton radiography could be used to significantly increase the accuracy of proton therapy. We developed with this aim in mind a new prototype of proton imaging system based on multi-layer ionization chambers. The first tests on patients are planned end of this year.