Abstract
Accelerator-based neutron sources have been developed and installed in recent decades for boron neutron capture therapy (BNCT) in several clinical facilities. Lithium is one of the targets that can produce epithermal neutrons from the 7Li(p,n)7Be near-threshold reaction, and accelerator-based BNCT systems employing a Li target are promising for cancer treatment. The accurate evaluation of the characteristics of an accelerator-based neutron source is a key to estimating the therapeutic effects of the accelerator-based BNCT. Particle and Heavy Ion Transport code System (PHITS) is a general-purpose Monte Carlo code, which can simulate a variety of diverse particle types and nuclear reactions. The latest PHITS code enables simulating the generation of neutrons from the 7Li(p,n)7Be reactions by using the Japanese Evaluated Nuclear Data Library 4.0 high-energy file. Thus, the PHITS code can be adopted for dose estimation during treatment planning for the accelerator-based BNCT. In this study, we evaluated the neutron fluence using the PHITS code by comparing it to reference data. The subsequent neutron transport simulations were performed to evaluate the boron trifluoride detector responses and the recoiled proton fluence detected by a CR-39 plastic detector. These comparative studies confirmed that the PHITS code can accurately simulate neutrons generated from an accelerator using a Li target. The PHITS code has a significant potential for a detailed evaluation of neutron fields and for predicting the therapeutic effects of the accelerator-based BNCT.
Highlights
Introductionboron neutron capture therapy (BNCT) is expected to become available at several clinical institutes around the world in the near future.[12]
Boron neutron capture therapy (BNCT) is a radiation therapy that can selectively eradicate solid tumors by using short-range ionizing particles with high biological effects generated by the10B(n,α)7Li nuclear reaction in tumor cells.[1,2] The clinical trials of boron neutron capture therapy (BNCT) started in 19513 and accelerated after the development of para-boronophenylalanine[4] and the accelerator-based neutron source.[5,6] Because the conventional BNCT can only be conducted scitation.org/journal/adv in limited facilities with nuclear reactors,[7–11] the accelerator-basedBNCT is expected to become available at several clinical institutes around the world in the near future.[12]
Note that to compare the shapes of energy spectra more conveniently, the relative fluence was calculated with respect to the maximum value for each angle
Summary
BNCT is expected to become available at several clinical institutes around the world in the near future.[12]. Among metal targets available for the accelerator-based BNCT, lithium (Li) is a target that enables producing low-energy neutrons (i.e., epithermal and thermal neutrons) from the 7Li(p,n)7Be near-threshold reaction. The irradiation fields for BNCT are complex due to the production of recoils and γ contamination.[13]. To quantify these complex neutron fields, several measurement approaches, including the boron trifluoride (BF3) detector,[14] scintillator using optical fiber (SOF),[15] and CR-39 plastic detector,[16,17] have been developed. To address the difficulty of evaluating the dose within tumor and normal cells for the complex neutron fields, Monte Carlo computational simulations of radiation transport have become a powerful approach.[18–20]
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