The homogeneity of 25MeV/u 40 Ar 14 ion beam （40mm） was measured with 50μm polycarbonate films by means of nuclear track detection. It was 32.7% for the case of defocus and 52.4% for “defocus+sample rotation”. A simulation test of beam shaping for heavy-ion cancer therapy was carried out with an assembly of multilayer polycarbonate films as the tumour equivalent material. The Bragg-peak was moved at nine locations through energy degradation of the heavy ions. The beam cross sections at each Bragg-peak location were defined by different apertures. Thus

an ellipsoid like tumour was formed from the cross-sections of different layers. A light-ball similar to the ellipsoid tumour was obtained by means of transmission and diffraction of a light column passing through ion track pores in the irradiated polycarbonate films after chemical etching. The sphere of the light-ball corresponded to the space effected by Bragg-peaks where the energy loss of heavy ions was concentrated.