A feasibility study of a deuterium-deuterium neutron generator-based boron neutron capture therapy system for treatment of brain tumors.

Abstract

Boron neutron capture therapy (BNCT) is a binary treatment modality that uses high LET particles to achieve tumor cell killing. Deuterium-deuterium (DD) compact neutron generators have advantages over nuclear reactors and large accelerators as the BNCT neutron source, such as their compact size, low cost, and relatively easy installation. The purpose of this study is to design a beam shaping assembly (BSA) for a DD neutron generator and assess the potential of a DD-based BNCT system using Monte Carlo (MC) simulations. The MC model consisted of a head phantom, a DD neutron source, and a BSA. The head phantom had tally cylinders along the centerline for computing neutron and photon fluences and calculating the dose as a function of depth. The head phantom was placed at 4cm from the BSA. The neutron source was modeled to resemble the source of our current DD neutron generator. A BSA was designed to moderate and shape the 2.45-MeV DD neutrons to the epithermal (0.5eV to 10keV) range. The BSA had multiple components, including moderator, reflector, collimator, and filter. Various materials and configurations were tested for each component. Each BSA layout was assessed in terms of the in-air and in-phantom parameters. The maximum brain dose was limited to 12.5 Gray-Equivalent (Gy-Eq) and the skin dose to 18Gy-Eq. The optimized BSA configuration included 30cm of lead for reflector, 45cm of LiF, and 10cm of MgF2 for moderator, 10cm of lead for collimator, and 0.1mm of cadmium for thermal neutron filter. Epithermal flux at the beam aperture was 1.0×105 nepi /cm2 -s; thermal-to-epithermal neutron ratio was 0.05; fast neutron dose per epithermal was 5.5×10-13 Gy-cm2 /φepi , and photon dose per epithermal was 2.4×10-13 Gy-cm2 /φepi . The AD, AR, and the advantage depth dose rate were 12.1cm, 3.7, and 3.2×10-3 cGy-Eq/min, respectively. The maximum skin dose was 0.56Gy-Eq. The DD neutron yield that is needed to irradiate in reasonable time was 4.9×1013 n/s. Results demonstrated that a DD-based BNCT system could be designed to produce neutron beams that have acceptable in-air and in-phantom characteristics. The parameter values were comparable to those of existing BNCT facilities. Continuing efforts are ongoing to improve the DD neutron yield.