Epithermal Neutron Sources Based on 9Be(d,n)10B

M.E. CAPOULAT; D.M. MINSKY; A.J. KREINER

Hsinchu, Taiwan

Congreso; 6th Young Researcher Boron Neutron Capture Meeting; 2011

National Tsing Hua University

The purpose of this work is to evaluate the 9Be(d,n)10B reaction as an epithermal neutron source for Accelerator-Based (AB)-BNCT to work in conjunction with a low-energy accelerator (1.2-1.4 MeV)[1].MethodologyTwo computational models of neutron sources were built from energy-angle distributions and neutron yields available in the literature. The first source model was based on a thick metallic Be target and a 30 mA deuteron beam of 1.2 MeV (hereafter, “thick target”). The second model (hereafter, “thin target”) consists of an optimized neutron source based on a 4.8 μm thick Be target and a 30 mA deuteron beam of 1.35 MeV [2]. This source model was assumed to be isotropic due to the lack of sufficient data about angular distributions for this energy range. The influence of this approximation on our results was also evaluated.A Snyder head phantom was considered for brain tumors and all tissue compositions were taken from ICRU-46 report.A Beam Shaping Assembly (BSA) consisting of a moderating volume of Al and AlF3/Al layers delimited by reflecting lead walls was proposed. The whole BSA was covered with a 4 cm thickness of 7.5% Lithium Polyethylene as a neutron shielding material (Fig.1).A BSA optimization study was performed by means of Monte Carlo MCNP simulations. Thicknesses from 40 to 70 cm and cross-sections from 25x25 to 48x48 cm were considered for the moderating volume. The beam-port diameter was fixed at 15 cm.The optimal configuration was determined for each computational source as the one that maximized the Maximum Dose delivered to the Tumor (MDT) within the constraints imposed by treatment time (60 min.) and healthy tissue dose limits (16.0 and 11.0 RBEGy for the Maximum Healthy Skin (MHSD) and Healthy Brain Doses (MHBD) respectively).For the optimal configurations, depth dose profiles along the ion beam direction were evaluated in order to calculate the treatable tumor depth range (TTDR). The TTDR’s were determined as the positions inside the brain where the total RBE-doses to tumor were ≥ 40.0 RBEGy.ResultsThe optimal thickness and cross-section for both computational sources are summarized in Table 1, together with the corresponding MTDT, MHBTD , MHBTD, TTDR values and treatment times.ConclusionsThe obtained results show that 9Be(d,n) should provide acceptable doses and treatment times for brain tumor irradiation, and constitutes an alternative to the traditional 7Li(p,n)-based BNCT source. In this case, protons of about 2.4 MeV are required. For a 9Be(d,n)-based source, deuterons of about half of this energy are enough. Therefore, we consider that a 9Be(d,n)-based source implies, concerning voltage requirements, a significant advantage for the design and construction of an accelerator for AB-BNCT.Experimental validation of the 9Be(d,n) reaction yield estimations should be made in order to obtain more accurate results and then reevaluate the BSA performance with a thorough dosimetry analysis.References[1] Kreiner, A.J. et al. Appl. Radiat. Isot. (In press) doi:10.1016/j.apradiso.2011.01.040[2] Capoulat, M.E., et al . Appl. Radiat. Isot. (In press) doi:10.1016/j.apradiso.2011.02.015