Optimization parameters for BDE in BNCT using near threshold 7Li(p,n)7Be direct neutrons

The dose contribution of 10B(n,α)7Li reaction in BNCT using near threshold 7Li(p,n)7Be direct neutrons can be increased through the use of materials referred to as boron-dose enhancers (BDE). In this paper, possible BDE optimization criteria were determined from the characteristics of candidate BDE materials namely (C2H4)n, (C2H3F)n, (C2H2F2)n, (C2HF3)n, (C2D4)n, (C2F4)n, beryllium metal, graphite, D2O and 7LiF. The treatable protocol depth (TPD) was used as the assessment index for evaluating the effect of these materials on the dose distribution in a medium undergoing BNCT using near threshold 7Li(p,n)7Be direct neutrons. The maximum TPD (TPDmax) did not exhibit an explicit dependence on material type as evidenced by its small range and arbitrary variations. The dependence of TPD on BDE thickness was influenced by the BDE material used as indicated by the sharply peaked TPD versus BDE thickness curves for materials with hydrogen compared to the broader curves obtained for those without hydrogen. The BDE thickness required to achieve TPDmax (BDE(TPDmax)) were also found to be thinner for materials with hydrogen. The TPDmax, the dependence of TPD on BDE thickness, and the BDE(TPDmax) were established as appropriate BDE optimization parameters. Based on these criteria and other practical considerations, the suitable choice as BDE among the candidate materials considered in this study for treatments involving tumors located at shallow depths would be (C2H4)n while beryllium metal was judged as more appropriate for treatment of deep-seated tumors.