On the upper limit for the energy of epithermal neutrons for Boron Neutron Capture Therapy

Study of accelerator-based epithermal neutron flux depending on Li and Be targets

The Li(p,n) and Be(p,n) reactions are widely used as accelerator-based neutron sources for boron neutron capture therapy (BNCT). Because the energy of the neutrons produced by these reactions is high for BNCT, a moderator is required to reduce the energy to the epithermal energy region. The neutron yields and energy spectra derived from the Li(p,n) and Be(p,n) reactions vary with the incident proton energy; a high proton energy results in a high neutron yield. However, a high proton energy can also increase the neutron energy, and in this case, a high neutron energy requires a thick moderator, which decreases the epithermal neutron flux. Notably, these tradeoffs are not completely clear. Furthermore, the upper limit of the epithermal neutron energy used in different BCNT facilities is not the same. Therefore, epithermal neutron flux estimation with applying an appropriate moderator is necessary for comparing epithernal neutron flux depending on the proton energy, target type, and epithermal neutron range definition. In this study, GEANT4 simulations were performed to determine effective moderator materials and thicknesses. After applying a moderator, we examined the epithermal neutron flux by changing the conditions that can influence the epithermal neutron flux, such as the proton energy, target species (Li and Be), and different definitions of the epithermal neutron region. The results showed that the epithermal neutron flux increases with the increasing proton energy until a certain level for both Li and Be targets. For proton energies above 3 MeV for the Li target and above 7 MeV for the Be target, the epithermal neutron flux decreases or its increase rate gradually decreases. And, when the upper energy limit of the epithermal neutron range is changed from 10 keV to 20 keV or 40 keV, the epithermal neutron flux is more than 109 cm-2 s-1 at a proton energy of 3 MeV for Li target and 8 MeV for Be target.

Beam port filters in a TRIGA MARK III nuclear reactor to produce epithermal neutrons for BNCT

Glioblastoma multiforme is the most common and aggressive brain tumor and it is difficult to treat with conventional surgery, chemotherapy, or radiation therapy. An alternative treatment is boron neutron capture therapy which requires an energy modulated beam of neutrons and a¹⁰B drug capable of adhering to the tumor. In this work, MCNP6 Monte Carlo code was used to evaluate the effect on the neutron spectrum by placing two filters along the radial beam tube of the TRIGA Mark III nuclear reactor of ININ in Mexico. Every filter was made with the same amount and type of materials: Steel and Graphite for filter 1 and Cadmium, Aluminum, and Cadmium (Cd + Al + Cd) for filter 2. Two cases were analyzed for each filter as follows: Case A for filter 1 was considering 30 cm of steel and 30 cm of graphite, while for case B, the dimensions of filter 1 were 15 cm of steel, 15 cm of graphite, 15 cm of steel and 15 cm of graphite. Cases A and B for filter 2 were analyzed considering the same dimensions and amount of materials. The work was in the aim to produce epithermal neutrons for boron neutron capture therapy. Neutron spectra were calculated at three sites along the beam tube and two sites outside the beam tube; here, the ambient dose equivalent, the personal dose equivalent, and the effective doses were also estimated. At a distance of 517 cm of core, in case B, results in an epithermal-to-thermal neutron fluence ratio of 30.39 was obtained being larger than the one recommended by the IAEA of 20.

Optimized beam shaping assembly for a 2.1-MeV proton-accelerator-based neutron source for boron neutron capture therapy

Boron Neutron Capture Therapy (BNCT) is facing a new era where different projects based on accelerators instead of reactors are under development. The new facilities can be placed at hospitals and will increase the number of clinical trials. The therapeutic effect of BNCT can be improved if a optimized epithermal neutron spectrum is obtained, for which the beam shape assembly is a key ingredient. In this paper we propose an optimal beam shaping assembly suited for an affordable low energy accelerator. The beam obtained with the device proposed accomplishes all the IAEA recommendations for proton energies between 2.0 and 2.1 MeV. In addition, there is an overall improvement of the figures of merit with respect to BNCT facilities and previous proposals of new accelerator-based facilities.

Exploring neutron capture therapy with 33S and 10B

The ³³S(n,α)³⁰Si reaction was proposed as cooperative neutron capturer to ¹⁰B(n,α)⁷Li in Neutron Capture Therapy (NCT). At that moment, the available ³³S(n,α)³⁰Si cross-section data were scarce and discrepant in key energy ranges for its use in NCT. Since then, three experiments have been carried out at n_TOF facility at CERN and at Institut Laue-Langevin. These new data are used for the calculation of the dose rate on ICRU-4 tissue by using kerma factors, a simplified model of tissue and a 13.45 keV neutron beam, energy of the most important ³³S(n,α)³⁰Si resonance. A significant enhancement of the dose rate due to the presence of ³³S is shown. In spite of the limitations, the cooperative action of ³³S and ¹⁰B is an interesting possibility to be studied for accelerator-based neutron sources with non-moderated neutrons.

Measurements of the 33S (n, α)30Si cross-section at n_TOF and ILL: Implications in neutron capture therapy

Up to a couple of years ago, the 33S(n, α)30Si cross-section data had been limited and scarce. The origin in the solar system of 36S had been the only motivation to study that cross-section. However, a few years ago, the 33S(n, α)30Si reaction was proposed as a possible target in neutron capture therapy (NCT) due to the excellent bio-properties of 33S and the significant resonance at 13.45 keV of the cross-section for which a high-energy α is emitted. Prior to the experiments carried out at n_TOF-CERN and at the Institut Laue-Langevin (ILL) facilities, the data situation was: no data from the thermal point up to 10 keV; from 10 keV to 300 keV, there was only one (n, α) measurement able to resolve the resonances with a questionable value of the 13.45-keV resonance; and the thermal point did not have a consistent value. Here we summarize three experiments that have been performed covering the whole energy range of interest in NCT and astrophysics. These experiments have solved the most important issues. The data of the present work and the evaluated data are used to calculate the dose rate in the tissue.