Increase in Irradiation Beam Intensity by Using a Hybrid Target System in Cyclotron-Based Neutron Capture Therapy

摘要

A cyclotron-based epithermal neutron generator has been expected to achieve the early realization of hospital-based boron neutron capture therapy. The system using a hybrid target composed of a thin tungsten (W) layer and a thick beryllium (Be) one with 30 MeV protons and a beam-shaping assembly was previously proposed as a better generator candidate than the system using only a thick W or Be layer. In this study, to clearly show that the hybrid target system is more clinically useful than the other two, all three target systems were compared using epithermal neutron intensity as a figure of merit under an equal condition of the harmful effect of fast neutron dose. We found that the hybrid system using a W layer of appropriate thickness increased the epithermal neutron intensity by 107 and 32% compared with systems using only W or Be, respectively, with the same harmful fast neutron component. It is concluded that the hybrid target system is more useful in terms of epithermal neutron intensity than systems with either W or Be as a generator using the 30 MeV proton accelerator and beam-shaping assembly.