Method for rapidly obtaining BNCT neutron energy spectrum

Abstract

The invention discloses a method for rapidly obtaining a BNCT neutron energy spectrum, and solves the technical problems of long neutron energy spectrum obtaining time and low accuracy in the prior art. Comprising the following steps: bombarding a target material by protons with specific energy and angle to generate target neutrons; the target neutrons are moderated and shaped by the beam shaping device and then target neutrons are obtained at the exit window; extracting the proportion of the protons in each energy and direction in the accelerator proton energy spectrum, multiplying the proportion with the corresponding target neutrons in the database, and adding together to obtain a target neutron energy spectrum; and the target neutrons pass through the beam shaping device, and the neutron energy spectrum of the final exit window is obtained by adopting the same method according to the target neutron energy spectrum. According to the method, the required neutron energy spectrum can be rapidly obtained through proton energy spectrum calculation, when the neutron energy spectrum is unreasonable, the next neutron energy spectrum can be rapidly obtained through calculation, and compared with a traditional method, the neutron energy spectrum can be obtained more rapidly, and the error-tolerant rate is higher.

Description

Technical Field

[0001] The present invention relates to the technical field of neutron spectrum measurement, and in particular to a method for quickly obtaining a BNCT neutron spectrum. Background Art

[0002] Boron Neutron Capture Therapy (BNCT) is a binary targeted radiotherapy precision radiotherapy technology, which is the core of the next generation of radiotherapy research. Its basic principle is to inject patients with high concentrations of 10 Boron drugs are concentrated in tumor cells through human metabolism and less distributed in other tissues. These drugs are non-toxic and harmless to the human body and have no effect on cancer cells. 10 B(n,α) 7 Li releases energy, and the range of the released α and Li in the body is about 10μm, killing tumors within the cellular scale and protecting normal tissue cells to the greatest extent.

[0003] In addition to using reactor neutron sources, BNCT neutrons are usually obtained by bombarding specific target materials with protons produced by accelerators to produce nuclear reactions. The generated target neutrons are slowed down and shaped by beam shaping devices to obtain neutron beams with specific energy spectra that can meet human body treatment needs.

[0004] The neutron energy spectrum is an important parameter in the BNCT treatment plan. For tumors at different treatment depths, the required neutron energy spectrum is also different. Deeper tumors require a harder neutron energy spectrum and higher neutron energy, while shallower tumors require a softer neutron energy spectrum and lower neutron energy. For the skin surface, thermal neutrons can meet the requirements.

[0005] The neutron energy spectrum is usually obtained by calculating with the corresponding Monte Carlo software, such as MCNP, Geant4, etc., setting a specific number of particles, building a model and filling materials according to the actual situation, simulating the particle transport process, and finally obtaining a neutron beam after passing through a beam shaping device (Beam Shape Assem, BSA). However, for neutrons at different treatment depths, it is necessary to change the proton energy to obtain a neutron energy spectrum suitable for the treatment depth. The applicant has found that the prior art has at least the following technical problems:

[0006] (1) The entire transport process needs to be recalculated, which takes a long time to calculate, delays the formulation of treatment plans, increases patient waiting time, and increases patient risks;

[0007] (2) Neutron flux rate of the exit window (order of magnitude: 10 8 ~10 9) compared to the neutron yield after proton targeting (magnitude: 10 12 ~10 13 ) decreases by 4 to 5 orders of magnitude, while the initial particle number calculated is usually much lower than the yield, which will increase the uncertainty of the final result and reduce the accuracy of dose calculation;

[0008] (3) The equipment needs to be equipped with a high-performance computer, which increases the overall weight and cost of the device. Summary of the invention

[0009] The object of the present invention is to provide a method for quickly obtaining a BNCT neutron spectrum, so as to solve the technical problems of the prior art that the neutron spectrum is obtained in a long time and with low accuracy.

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] The present invention provides a method for quickly obtaining a BNCT neutron energy spectrum, which is an energy spectrum superposition method, comprising:

[0012] According to the upper and lower limits of the proton energy generated by the accelerator, multiple groups of proton energies are obtained, the target neutron energy spectrum and direction after the proton energy is hit are determined, and a database of the target neutron energy spectrum and direction after protons of different energies and different directions are obtained;

[0013] The protons obtained with different energies and directions are bombarded on the target material to produce target neutrons;

[0014] The target neutrons are slowed down and shaped by the beam shaping device and then obtained at the exit window;

[0015] Calculate the neutron energy spectrum and direction data of the exit window of neutrons with different energies and directions on the target surface after passing through the beam shaping device;

[0016] The proportion of protons of each energy and direction in the accelerator proton energy spectrum is extracted and multiplied by the corresponding target neutrons in the database, and then added together to obtain the target neutron energy spectrum; the target neutrons pass through the beam shaping device and the same method is used according to the target neutron energy spectrum to obtain the neutron energy spectrum of the final exit window.

[0017] Furthermore, the energy spectrum and directionality of protons produced by the accelerator As shown in formula (1):

[0018]

[0019] Where: represents the proton injection rate; Energy is E pi , direction is θ pj proton fluence rate.

[0020] Furthermore, the neutron energy spectrum and directionality after monoenergetic proton targeting As shown in formula (2):

[0021]

[0022] Where: Energy is E pi , direction is θ pj The total neutron fluence rate after proton targeting; and Indicates that the energy in the neutron spectrum is nk th Directivity in nm th of neutrons; Indicates the direction Energy neutron fluence rate.

[0023] According to formula (1) and formula (2), the target neutron energy spectrum formed after accelerator proton energy spectrum target is shown in formula (3):

[0024]

[0025] Where: represents the total target neutron fluence rate; Energy is E nk Direction θ nm Neutron flux rate; δ(E pi ,θ nj ) indicates that the energy of the proton after hitting the target is E pi , direction is θ nj The proton-neutron conversion coefficient; L Target Indicates the target consumption rate during proton targeting; K Target represents other correction coefficients of possible targets; ∈ represents the residual correction of spectral analysis.

[0026] Furthermore, the energy is E nk Direction θ nm After the neutrons pass through the beam shaping device, the neutron energy spectrum at the exit window is as shown in formula (4):

[0027]

[0028] Further, according to formula (3) and formula (4), when the target material and the structure of the beam shaping device are known, the neutron energy spectrum of the exit window is obtained from the accelerator proton energy spectrum:

[0029]

[0030]

[0031] Where: is the total neutron fluence rate in the exit window;

[0032] α(E nk ,θ nm ) is the energy E nk , direction is θ nm The loss rate of neutrons due to decay, absorption, and scattering.

[0033] Based on the above technical solution, the embodiments of the present invention can at least produce the following technical effects:

[0034] (1) The method for quickly obtaining the BNCT neutron spectrum provided by the present invention, in traditional calculations, after evaluating the patient's tumor, it is necessary to find a suitable accelerator proton spectrum to calculate the required neutron spectrum, and Monte Carlo simulation is required on site, which will undoubtedly increase the patient's waiting time. In addition, if the neutron spectrum obtained by the proton spectrum is unreasonable, it needs to be recalculated, and the longer waiting time will increase the risk of tumor deterioration. Through the ESSM method, a complete database can be established in advance before the instrument leaves the factory. After each tumor evaluation, the required neutron spectrum can be quickly obtained by proton spectrum calculation. When the neutron spectrum is unreasonable, the next neutron spectrum can be quickly calculated. Compared with the traditional method, the neutron spectrum is obtained more quickly and has a higher fault tolerance rate.

[0035] (2) The method for quickly obtaining the BNCT neutron energy spectrum provided by the present invention can calculate the number of particles to reduce statistical errors and uncertainties. For the traditional method, when calculating, it is assumed that the number of input protons is N, and the neutron energy spectrum is obtained. Due to the proton-neutron conversion rate of the target and the slow absorption of neutrons, the number of emitted neutrons is small, and the statistical error is large. If the error is reduced by increasing the number of particles, the calculation time will be increased, and the tumor treatment time will be increased. For the ESSM method, it is assumed that the proton energy spectrum interval is n during calculation, and the number of particles input for each proton energy is N; the neutron energy interval is m, and the number of particles input for each neutron energy is M, then the total number of particles actually calculated is (nN+mM), which is much higher than the particle number N of the traditional method, greatly amplifying the number of particles and reducing the calculation uncertainty.

[0036] (3) The method for quickly obtaining the BNCT neutron spectrum provided by the present invention is traditionally performed on-site, and when calculating the neutron spectrum that can be used for tumor treatment, a high-performance computer needs to be configured, which increases the overall weight and cost of the equipment. However, the calculation process of the ESSM method is completed before leaving the factory, so only the calculated database and program software need to be transferred to the computer. Even an ordinary laptop can quickly obtain the desired neutron spectrum by indexing the database, making the BNCT equipment more portable and reducing the equipment cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0038] Figure 1 is a schematic diagram of an embodiment of the present invention;

[0039] Figure 2 A schematic diagram of a BSA according to an embodiment of the present invention;

[0040] Figure 3 This is a comparison of the target neutron energy spectra produced by ESSM theoretical calculation and traditional simulation of proton target shooting;

[0041] Figure 4 This is a comparison chart of the neutron energy spectra of ESSM theoretical calculation and traditional simulation of neutrons passing through the BSA exit window target;

[0042] Figure 5 Comparison of neutron energy spectra of neutrons passing through the BSA exit window in different directions calculated by ESSM theory and traditional simulation. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0044] This embodiment provides a method for quickly obtaining a BNCT neutron energy spectrum, the method being an energy spectrum superposition method ESSM (Energy Spectrum Superposition Method), comprising:

[0045] According to the upper and lower limits of the proton energy generated by the accelerator, multiple groups of proton energies are obtained, the target neutron energy spectrum and direction after the proton energy is hit are determined, and a database of the target neutron energy spectrum and direction after protons of different energies and different directions are obtained;

[0046] The protons obtained with different energies and directions are bombarded on the target material to produce target neutrons;

[0047] The target neutrons are slowed down and shaped by the beam shaping device and then obtained at the exit window;

[0048] Calculate the neutron energy spectrum and direction data of the exit window of neutrons with different energies and directions on the target surface after passing through the beam shaping device;

[0049] The proportion of protons of each energy and direction in the accelerator proton energy spectrum is extracted and multiplied by the corresponding target neutrons in the database, and then added together to obtain the target neutron energy spectrum; the target neutrons pass through the beam shaping device and the same method is used according to the target neutron energy spectrum to obtain the neutron energy spectrum of the final exit window.

[0050] Therefore, in the actual program implementation Figure 1 As shown in the figure, after the target and BSA models are determined, the ESSM method is used to establish databases of two physical processes in advance through Monte Carlo simulation, namely, the database of target neutrons formed by protons hitting the target and the database of target neutrons entering the BSA and being shaped into exit window neutrons. When the accelerator proton energy spectrum and directionality are known, the exit window neutron energy spectrum can be quickly obtained by retrieving the corresponding neutron parameter information in the database.

[0051] The mathematical principle of the ESSM method is as follows:

[0052] Energy spectrum and directionality of protons produced by accelerators As shown in formula (1):

[0053]

[0054] Where: represents the proton injection rate; Energy is E pi , direction is θ pj proton fluence rate.

[0055] Neutron energy spectrum and directionality after monoenergetic proton targeting As shown in formula (2):

[0056]

[0057] Where: Energy is E pi , direction is θ pj The total neutron fluence rate after proton targeting; and Indicates that the energy in the neutron spectrum is nk th Directivity in nm th of neutrons; Indicates the direction Energy neutron fluence rate.

[0058] Therefore, according to formula (1) and formula (2), the target neutron energy spectrum formed after accelerator proton energy spectrum target is as shown in formula (3):

[0059]

[0060] Where: represents the total target neutron fluence rate; Energy is E nk Direction θ nm Neutron flux rate; δ(E pi ,θ nj ) indicates that the energy of the proton after hitting the target is E pi , direction is θ nj The proton-neutron conversion coefficient; L Target Indicates the target consumption rate during proton targeting; K Target represents other correction coefficients of possible targets; ∈ represents the residual correction of spectral analysis.

[0061] Energy is E nk Direction θ nm After the neutrons pass through the beam shaping device, the neutron energy spectrum at the exit window is as shown in formula (4):

[0062]

[0063] Therefore, according to formula (3) and formula (4), when the target and BSA structures are known, the neutron energy spectrum of the exit window can be obtained from the accelerator proton energy spectrum:

[0064]

[0065] Where: is the total neutron flux rate in the exit window; α(E nk ,θ nm ) is the energy E nk , direction is θ nm The loss rate of neutrons due to decay, absorption, and scattering.

[0066] Figure 2 A simple model of a proton firing target to generate neutrons and passing through the BSA uses a Be target, Cu and V substrates, and a moderator composed of Pb, D2O, and polyethylene, respectively. Cd is used to absorb thermal neutrons.

[0067] (1) The first physical process: Protons hitting the target produce target neutrons

[0068] like Figure 3As shown in the figure, the calculation results of the ESSM method and the traditional method are basically the same, but the traditional method takes about 1 hour to calculate the number of 1E8 particles, but it only takes 28 seconds to extract data from the database and use the ESSM method to obtain the final result, and the energy spectrum acquisition time is increased by 128.5 times.

[0069] (2) The second physical process: target neutrons obtain target neutrons through BSA

[0070] like Figure 4 As shown in the figure, the calculation results of the ESSM method and the traditional method are basically the same, but the traditional method takes about 1.5 hours to calculate the number of 1E8 particles, but it only takes 54 seconds to extract data from the database and use the ESSM method to obtain the final result, and the calculation time is increased by 108 times.

[0071] (3) Reduce calculation uncertainty

[0072] like Figure 5 As shown in the figure, the neutron emission rate in different directions is low, so when the traditional method (green) is used for calculation, the energy spectrum fluctuates greatly and the statistical error is large; however, the neutron energy spectrum calculated by the ESSM method is smoother and the statistical error is smaller, which can better guarantee the accuracy of subsequent energy spectrum calculation and dose calculation.

[0073] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of the present invention to be protected is defined by the attached claims and their equivalents.

Claims

1. A method for quickly obtaining a BNCT neutron spectrum, characterized in that: The method is an energy spectrum superposition method, comprising: According to the upper and lower limits of the proton energy generated by the accelerator, multiple groups of proton energies are obtained, the target neutron energy spectrum and direction after the proton energy is hit are determined, and a database of the target neutron energy spectrum and direction after protons of different energies and different directions are obtained; The protons obtained with different energies and directions are bombarded on the target material to produce target neutrons; The target neutrons are slowed down and shaped by the beam shaping device and then obtained at the exit window; Calculate the neutron energy spectrum and direction data of the exit window of neutrons with different energies and directions on the target surface after passing through the beam shaping device; The proportion of protons of each energy and direction in the accelerator proton energy spectrum is extracted and multiplied by the corresponding target neutrons in the database, and then added together to obtain the target neutron energy spectrum; the target neutrons pass through the beam shaping device and the same method is used according to the target neutron energy spectrum to obtain the neutron energy spectrum of the final exit window.

2. The method for rapidly obtaining a BNCT neutron spectrum according to claim 1, characterized in that: Energy spectrum and directionality of protons produced by accelerators As shown in formula (1): Where: represents the proton injection rate; Energy is E pi , direction is θ pj proton fluence rate.

3. The method for rapidly obtaining a BNCT neutron spectrum according to claim 2, characterized in that: Neutron energy spectrum and directionality after monoenergetic proton targeting As shown in formula (2): Where: Energy is E pi , direction is θ pj The total neutron fluence rate after proton targeting; and Indicates that the energy in the neutron spectrum is nk th Directivity in nm th of neutrons; Indicates the direction Energy neutron fluence rate; According to formula (1) and formula (2), the target neutron energy spectrum formed after accelerator proton energy spectrum target is shown in formula (3): Where: represents the total target neutron fluence rate; Energy is E nk Direction θ nm Neutron flux rate; δ(E pi ,θ nj ) indicates that the energy of the proton after hitting the target is E pi , direction is θ nj The proton-neutron conversion coefficient; L Target Indicates the target consumption rate during proton targeting; K Target represents other correction coefficients of possible targets; ∈ represents the residual correction of spectral analysis.

4. The method for rapidly obtaining a BNCT neutron spectrum according to claim 3, characterized in that: Energy is E nk Direction θ nm After the neutrons pass through the beam shaping device, the neutron energy spectrum at the exit window is as shown in formula (4): According to formula (3) and formula (4), the neutron energy spectrum of the exit window is obtained from the accelerator proton energy spectrum: Where: is the total neutron fluence rate in the exit window; α(E nk ,θ nm ) is the energy E nk , direction is θ nm The loss rate of neutrons due to decay, absorption, and scattering.

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