Production of target fragments from reactions of 160 MeV proton beams in aluminum and polyethylene was measured with CR-39 plastic nuclear track detectors (PNTD). Due to the detection limit of PNTD, primary protons cannot be detected; only low-energy short-range target fragments are registered. As a feasibility study, a so called ''two step etching method'' was employed to get the linear energy transfer (LET) spectra, absorbed dose, and dose equivalent. This method is discussed in this paper, together with the measured results.