Effects of neutron sources and moderator materials on therapeutic dose delivery to deep-seated lesions in proton accelerator-based boron neutron capture therapy.

This study aimed to identify the optimal conditions for delivering sufficient doses to deep-seated lesions within short irradiation times for two boron carriers of different T/N ratios. The therapeutic depth and irradiation time of a neutron beam for beam shaping assemblies (BSAs) with a Li or Be target and a MgF2 or CaF2 moderator were examined with the fast-neutron dose per epithermal neutron (FNR) as a parameter. When T/N = 3.61, the therapeutic depth was almost saturated at an FNR of about 10 × 10-13 Gy cm2; when the FNR value was about 10 × 10-13 Gy cm2, the therapeutic depth of the neutron beam for the BSA with a Be target and a MgF2 moderator was almost identical to that for the neutron beam for the BSA with a Be target and a CaF2 moderator, and slightly greater than those for the neutron beams for the BSAs with a Li target and a MgF2 or CaF2 moderator; moreover, the irradiation time of the neutron beam for the BSA with a Be target and a MgF2 moderator was shorter than that for the neutron beam for the BSA with a Be target and a CaF2 moderator. When T/N = 100, the therapeutic depths of the neutron beams for the BSAs varied greatly depending on the FNR, and were greater than the corresponding values for T/N = 3.61. We therefore concluded that the BSA with a Be target and a MgF2 moderator that produced a neutron beam with an FNR of about 10 × 10-13 Gy cm2 is optimal for delivering sufficient doses to deep-seated lesions in short irradiation times when T/N = 3.61, and stricter control over FNR is required when T/N = 100.

Monte Carlo simulation-based design of an electron-linear accelerator-based neutron source for boron neutron capture therapy.

Characteristics of a beam-shaping assembly that utilizes photo-neutrons from irradiation of a tungsten target by electrons from an accelerator were examined to produce a beam of neutrons suitable for boron neutron capture therapy. The epithermal neutron flux per kilowatt of electron-beam power almost increased to a maximum as the energy of the initial electrons was increased to 42.5 MeV, but the fast-neutron dose and the photon dose per epithermal neutron hardly changed on varying the energy of the initial electrons.

Synergistic effects of fast-neutron dose per epithermal neutron and 10B concentration on relative-biological-effectiveness dose for accelerator-based boron neutron capture therapy.

The efficacy of accelerator-based boron neutron capture therapy was examined through relative-biological-effectiveness dose calculations with the fast-neutron dose per epithermal neutron (FNR) and the 10B concentration as parameters. In the case of a tumor 10B concentration of 65 ppm, the treatment efficacy depended more strongly on the FNR when the normal-tissue 10B concentration was 0.65 ppm, which would be brought about by the administration of an advanced chemical compound, than when the 10B concentration was 18 ppm, which is attainable by the use of boronophenylalanine.

Monte Carlo simulation-based design for an electron-linear-accelerator-driven subcritical neutron multiplier for boron neutron capture therapy.

Fuel configurations for a subcritical neutron multiplier, which was embedded in a beam-shaping assembly and irradiated by electrons from a linear accelerator, were examined to maximize the production of the epithermal neutron flux for boron neutron capture therapy. The epithermal neutron flux at the treatment position increased as the area per uranium fuel plate increased and was estimated to be 2 × 109 cm-2 s-1 when the subcritical neutron multiplier was irradiated by a 4.4 kW (0.22 mA) beam of 20 MeV electrons.

Optimal moderator materials at various proton energies considering photon dose rate after irradiation for an accelerator-driven 9Be(p, n) boron neutron capture therapy neutron source.

We evaluated the accelerator beam power and the neutron-induced radioactivity of (9)Be(p, n) boron neutron capture therapy (BNCT) neutron sources having a MgF2, CaF2, or AlF3 moderator and driven by protons with energy from 8 MeV to 30 MeV. The optimal moderator materials were found to be MgF2 for proton energies less than 10 MeV because of lower required accelerator beam power and CaF2 for higher proton energies because of lower photon dose rate at the treatment position after neutron irradiation.

Optimum design and criticality safety of a beam-shaping assembly with an accelerator-driven subcritical neutron multiplier for boron neutron capture therapies.

The beam-shaping assembly for boron neutron capture therapies with a compact accelerator-driven subcritical neutron multiplier was designed so that an epithermal neutron flux of 1.9×10(9) cm(-2) s(-1) at the treatment position was generated by 5 MeV protons in a beam current of 2 mA. Changes in the atomic density of (135)Xe in the nuclear fuel due to the operation of the beam-shaping assembly were estimated. The criticality safety of the beam-shaping assembly in terms of Xe poisoning is discussed.

Optimum design of a moderator system based on dose calculation for an accelerator driven Boron Neutron Capture Therapy.

An accelerator based BNCT has been desired because of its therapeutic convenience. However, optimal design of a neutron moderator system is still one of the issues. Therefore, detailed studies on materials consisting of the moderator system are necessary to obtain the optimal condition. In this study, the epithermal neutron flux and the RBE dose have been calculated as the indicators to look for optimal materials for the filter and the moderator. As a result, it was found that a combination of MgF2 moderator with Fe filter gave best performance, and the moderator system gave a dose ratio greater than 3 and an epithermal neutron flux over 1.0×10(9)cm(-2)s(-1).