Recently, the possibility to use compact accelerators coupled to high current ion sources for the production of intense low energy proton or deuteron beams has motivated many research laboratories to develop accelerator based neutrons sources for several purposes, including Neutron Capture Therapy (NCT). The NCT needs a high flux, about 10 9 n.cm-2.s-1, of thermal neutrons (E<10 keV) at the tumour site. Up to now, the NCT required neutron flux was mainly delivered by nuclear reactors. However, the production of such neutron flux is now possible using proton or deuteron beams on specific targets able to stand a high pow er (~15- 30 kW) on a small area (~10 cm2). This specific target design, materials and supports, has to cope with extreme physical constraints . The LPSC team has conceived an original solution formed by a thin (8 μm) rotating beryllium target depos ited on a graphite wheel and coupled with a beryllium sputtering device for periodic 9Be layer restoration. By means of 9Be (d,n) 10B nuclear reaction, this target irradiated by a 10- -20 mA deuteron beam (1.45 MeV) should produce the required neutron flux. In order to validate the target design of the neutron flux production and the beryllium target thermal capabilities, we built a 30 cm diameter rotating Beryllium target prototype and a compact electron beam line able to deliver a power density of 3kW/cm2.
Background and purpose: Accelerator-Based Boron Neutron Capture Therapy is a radiotherapy based on compact accelerator neutron sources requiring an epithermal neutron field for tumour irradiations. Neutrons of 10 keV are considered as the maximum optimised energy to treat deep-seated tumours. We investigated, by means of Monte Carlo simulations, the epithermal range from 10 eV to 10 keV in order to optimise the maximum epithermal neutron energy as a function of the tumour depth.Methods: A Snyder head phantom was simulated and mono-energetic neutrons with 4 different incident energies were used: 10 eV, 100 eV, 1 keV and 10 keV. 10 B capture rates and absorbed dose composition on every tissue were calculated to describe and compare the effects of lowering the maximum epithermal energy. The Therapeutic Gain (TG) was estimated considering the whole brain volume.Results: For tumours seated at 4 cm depth, 10 eV, 100 eV and 1 keV neutrons provided respectively 54 %, 36 % and 18 % increase on the TG compared to 10 keV neutrons. Neutrons with energies between 10 eV and 1 keV provided higher TG than 10 keV neutrons for tumours seated up to 6.4 cm depth inside the head. The size of the tumour does not change these results.Conclusions: Using lower epithermal energy neutrons for AB-BNCT tumour irradiation could improve treatment efficacy, delivering more therapeutic dose while reducing the dose in healthy tissues. This could lead to new Beam Shape Assembly designs in order to optimise the BNCT irradiation.
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