Comparison of titanium hydride (TiH2) and paraffin as neutron moderator material in a prompt gamma scanning system

Abstract

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 Sabrina (TM). 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, berated 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.