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If the proton therapy modality allowing excellent dose localization to the tumor volume and negligible exit dose in the patient is to be taken advantage of, a proper dosimetry system is required. We have recently designed a prompt-gamma scanning system to measure the proton range in situ by using a Monte Carlo technique employing MCNPX, FLUKA, and SabrinaTM. The gamma scanning system was designed to measure only the right-angled prompt gammas passing through a narrow collimation hole in order to correlate the position with the dose distribution. The collimation part of the scanning system, which has been constructed to measure the gammas at a 70-MeV proton energy, is made of a set of paraffin, borated carbon, and lead layers to shield the high-energy neutrons and secondary photons. However, in this study, we tried a titanium-hydride (TiH2) layer instead of the paraffin to reduce the background radiation. Our result shows that titanium hydride gives a better result when the distance between the phantom and the gamma scanner is short.