阅读说明：本技术 正电子核素活度分布计算方法、系统、设备和存储介质 (Positive electron nuclide activity distribution calculation method, system, device and storage medium ) 是由 陈金达 裴昌旭 颜俊伟 张秀玲 孔洁 苏弘 段利敏 胡正国 徐瑚珊 于 2021-08-16 设计创作，主要内容包括：本发明涉及一种正电子核素活度分布计算方法、系统、设备和存储介质,包括：基于放射治疗计划确定初始粒子数,并计算得到任意时刻靶区内各种正电子核素总活度的三维分布矩阵；基于任意时刻靶区内各种正电子核素总活度的三维分布矩阵,计算得到系统采集扫描时间内正电子湮灭的位置分布；对得到的系统采集扫描时间内正电子湮灭次数的位置分布进行高斯平滑滤波,得到正电子核素射程和活度的预测分布图像。本发明通过建立基于卷积的数学模型,能够快速、完整描述碳离子、质子等粒子治疗过程中、结束后的正电子核素活度分布。本发明可以广泛应用于粒子治疗技术领域。(The invention relates to a positron nuclide activity distribution calculation method, a system, equipment and a storage medium, wherein the positron nuclide activity distribution calculation method comprises the following steps: determining initial particle number based on a radiotherapy plan, and calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in a target area at any moment; calculating to obtain the position distribution of positron annihilation within the system acquisition scanning time based on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target region at any moment; and performing Gaussian smoothing filtering on the position distribution of the positron annihilation times in the acquisition scanning time of the system to obtain a prediction distribution image of the range and activity of the positron nuclide. By establishing a convolution-based mathematical model, the invention can rapidly and completely describe the activity distribution of positron nuclides in the particle treatment process of carbon ions, protons and the like and after the treatment. The invention can be widely applied to the technical field of particle therapy.)

1. A positron nuclide activity distribution calculation method is characterized by comprising the following steps:

determining initial particle number and beam targeting setting parameters based on a radiotherapy plan, and calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in a target area at any moment;

calculating to obtain the position distribution of positron annihilation within the system acquisition scanning time based on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target region at any moment;

and performing Gaussian smoothing filtering on the position distribution of the positron annihilation times in the acquisition scanning time of the system to obtain a prediction distribution image of the range and activity of the positron nuclide.

2. The method of calculating positron nuclide activity distributions as in claim 1 wherein said method of determining initial particle counts based on a radiation treatment plan and calculating a three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target at any given time comprises:

determining an initial particle number according to a radiotherapy plan, and setting beam targeting setting parameters under the condition of the determined initial particle number;

acquiring the spatial distribution of the positron nuclide products in a target body based on the set beam targeting setting parameters to obtain a three-dimensional distribution matrix of the preliminary positron nuclide products in the target area;

and calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment based on the three-dimensional distribution matrix of the preliminary positron nuclide products in the target area.

3. The method of claim 2, wherein the beam targeting setting parameters comprise beam parameters, target parameters and system acquisition scan time.

4. The method as claimed in claim 2, wherein the step of calculating the three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target at any time based on the three-dimensional distribution matrix of the preliminary positron nuclide products in the target comprises:

respectively calculating the generation speed and the attenuation speed of each positron nuclide product on a certain pixel point;

performing convolution operation on the generation speed and the attenuation speed of each positron nuclide product on the pixel point respectively to obtain the distribution of the activity of each positron nuclide along with time;

repeating the two steps to obtain a three-dimensional distribution matrix of the activity of each positron nuclide on each pixel point at any moment;

accumulating the change of the activity of each positive electron nuclide on each pixel point in the target area along with the change of time to obtain a three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target area at any moment.

5. The method of calculating a positron nuclide activity distribution as in claim 4 wherein said calculation of the rate of production of each positron nuclide product is by: and calculating the generation speed of the positron nuclide product on the pixel point according to the yield and the current intensity.

6. The method of calculating a positron nuclide activity distribution as in claim 4 wherein said decay rate for each positron nuclide product is calculated by: and substituting the decay constant of the positron nuclide product into the decay exponential function of the positron nuclide product to obtain the decay rate of the positron nuclide product.

7. The method for calculating the activity distribution of positron nuclides as in claim 1, wherein the method for calculating the position distribution of positron annihilation within the acquisition scan time of the system based on the three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target at any time comprises:

carrying out three-dimensional filtering on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment to obtain the position distribution of positron annihilation of decay of all positive electron nuclides in the target area at any moment;

and (3) performing time domain integration on the position distribution of positron annihilation of all positron nuclides decaying in the target area at any moment to obtain the position distribution of positron annihilation in the system acquisition scanning time.

8. A positron nuclide activity distribution calculation system, comprising:

the positron nuclide activity distribution calculation module determines the initial particle number based on the radiotherapy plan and calculates to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment;

the positron annihilation position distribution calculation module is used for calculating and obtaining position distribution of positron annihilation within the system acquisition scanning time based on a three-dimensional distribution matrix of total activity of various positron nuclides in the target area at any moment;

and the image prediction module is used for performing Gaussian smooth filtering on the obtained position distribution of positron annihilation times within the system acquisition scanning time to obtain a prediction distribution image of the range and activity of the positron nuclide.

9. A processing apparatus comprising at least a processor and a memory, the memory having stored thereon a computer program, characterized in that the processor, when executing the computer program, executes to carry out the steps of the method for positron nuclide activity distribution calculation as defined in any of claims 1 to 7.

10. A computer storage medium having computer readable instructions stored thereon which are executable by a processor to perform the steps of the method of calculating a positron nuclide activity distribution as defined in any one of claims 1 to 7.

Technical Field

The invention relates to the field of monitoring and simulation calculation based on positron emission computed tomography in particle therapy, in particular to a method, a system, equipment and a storage medium for calculating positron nuclide activity distribution in particle therapy, and belongs to the technical field of particle therapy.

Background

For particle therapy of heavy ions and protons, on-line image monitoring of the dose distribution of particle deposition during therapy can be achieved using in-beam PET (PET) technology to assess the efficacy of the therapy and to refine subsequent treatment plans. The principle is that gamma photon pairs generated by positron annihilation generated by coincidence detection treatment are utilized to reconstruct the distribution of positrons, and the number of detected coincidence events is influenced by the size of the activity of the gamma photon pairs; the spatial distribution reflects the range and dose distribution of the incident beam. However, the actual dose distribution of the incident beam has a certain difference from the activity of the positron species.

As shown in FIGS. 1(a) and 1(b), the currently commonly used positron nuclide calculation method is based on Monte Carlo simulation¹²C or proton bombardment of the target body, statistics¹¹C、¹⁵Spatial distribution of positive electron species such as O. After the initial activity of the end of the first beam bombardment is obtained, the remaining time in the period is exponentially attenuated. And (3) solving the activity of the positive electronic nuclide when the beam current in the first period is completely finished (namely when the beam current in the second period is coming) as an initial condition of the differential equation established in the second period, namely an initial value, re-establishing the differential equation, solving the differential equation again, repeating the steps in a circulating mode, continuously iterating the steps, and finally solving the activity of the positive electronic nuclide in the beam current bombardment process. However, the method is too computationally intensive and complex to model, usually only depicts one activity at one time point in each cycle, and cannot be describedThe treatment time and the complete time profile after the treatment is over are described.

At present, in the particle treatment processes such as carbon ion treatment and proton treatment, the existing related algorithm for positive electron nuclides needs more computing resources, and huge cluster calculation is needed to be applied to clinical calculation; the calculation time is long, more than several days are needed frequently, and the application convenience is limited by the large calculation cost and long calculation time of the existing algorithm and model. Therefore, the disadvantages are mainly expressed as:

1. it is difficult to build a mathematical model: the results of the differential equation and the attenuation equation are mutually influenced, and the established mathematical model is relatively complex;

2. the calculation amount is huge: because the differential equation needs to be solved continuously and reciprocally, the calculated amount is very large under the condition of a plurality of beam periods;

3. the description of activity is limited: only the activity size at discrete time points can be described; because the calculated amount is large, only the first differential equation can be solved generally, and the subsequent positive electron nuclide activities are accumulated and summed to obtain the activity of part of time points;

4. the application range is narrow: the solution can be only carried out under the condition of periodic beam current; in response to the point scanning in the actual treatment process, the differential equation is not a first-order linear differential equation any more, the solving difficulty is increased, the calculated amount is larger, and a mathematical expression cannot be given;

5. the dimension is single: it is difficult to describe the variation of the three-dimensional spatial distribution.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide a method, a system, an apparatus and a storage medium for calculating the activity distribution of positive electron nuclides in particle therapy, which can rapidly and quantitatively calculate the spatial distribution and size variation of the activity of positive electron nuclides.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect of the present invention, a positron nuclide activity distribution calculation method is provided, which includes the following steps:

determining initial particle number and beam targeting setting parameters based on a radiotherapy plan, and calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in a target area at any moment;

calculating to obtain the position distribution of positron annihilation within the system acquisition scanning time based on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target region at any moment;

and performing Gaussian smoothing filtering on the position distribution of the positron annihilation times in the acquisition scanning time of the system to obtain a prediction distribution image of the range and activity of the positron nuclide.

Preferably, the method for determining initial particle number based on radiation therapy planning and calculating a three-dimensional distribution matrix of total activity of various positive electron species in a target region at any time includes:

determining an initial particle number according to a radiotherapy plan, and setting beam targeting setting parameters under the condition of the determined initial particle number;

acquiring the spatial distribution of the positron nuclide products in a target body based on the set beam targeting setting parameters to obtain a three-dimensional distribution matrix of the preliminary positron nuclide products in the target area;

and calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment based on the three-dimensional distribution matrix of the preliminary positron nuclide products in the target area.

Preferably, the beam targeting setting parameters include beam parameters, target parameters and system acquisition scanning time.

Preferably, the method for obtaining a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any time by calculation based on the preliminary three-dimensional distribution matrix of the positron nuclide products in the target area includes:

respectively calculating the generation speed and the attenuation speed of each positron nuclide product on a certain pixel point;

performing convolution operation on the generation speed and the attenuation speed of each positron nuclide product on the pixel point respectively to obtain the distribution of the activity of each positron nuclide along with time;

repeating the two steps to obtain a three-dimensional distribution matrix of the activity of each positron nuclide on each pixel point at any moment;

accumulating the change of the activity of each positive electron nuclide on each pixel point in the target area along with the change of time to obtain a three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target area at any moment.

Preferably, the calculation method of the production speed of each positron nuclide product is as follows: and calculating the generation speed of the positron nuclide product on the pixel point according to the yield and the current intensity.

Preferably, the calculation method of the decay rate of each positron nuclide product is as follows: and substituting the decay constant of the positron nuclide product into the decay exponential function of the positron nuclide product to obtain the decay rate of the positron nuclide product.

Preferably, the method for calculating and obtaining the position distribution of positron annihilation within the system acquisition scan time based on the three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target region at any time includes:

carrying out three-dimensional filtering on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment to obtain the position distribution of positron annihilation of decay of all positive electron nuclides in the target area at any moment;

and (3) performing time domain integration on the position distribution of positron annihilation of all positron nuclides decaying in the target area at any moment to obtain the position distribution of positron annihilation in the system acquisition scanning time.

In a second aspect of the present invention, there is provided a positron nuclide activity distribution calculation system, including:

the positron nuclide activity distribution calculation module determines the initial particle number based on the radiotherapy plan and calculates to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment;

the positron annihilation position distribution calculation module is used for calculating and obtaining position distribution of positron annihilation within the system acquisition scanning time based on a three-dimensional distribution matrix of total activity of various positron nuclides in the target area at any moment;

and the image prediction module is used for performing Gaussian smooth filtering on the obtained position distribution of positron annihilation times within the system acquisition scanning time to obtain a prediction distribution image of the range and activity of the positron nuclide.

In a third aspect of the invention, a processing apparatus is provided, which at least comprises a processor and a memory, wherein the memory stores a computer program, and the processor executes the computer program to realize the steps of the positron nuclide activity distribution calculation method.

In a fourth aspect of the invention, a computer storage medium is provided having computer readable instructions stored thereon which are executable by a processor to implement the steps of the positron nuclide activity distribution calculation method.

Due to the adoption of the technical scheme, the invention has the following advantages:

1. according to the calculation method for positron nuclide activity distribution in particle therapy, provided by the invention, by establishing a convolution-based mathematical model, the positron nuclide activity distribution in and after particle therapy processes such as carbon ions and protons can be rapidly and completely described; and the distribution and the change of the positron activity can be obtained, and a positive electron nuclide distribution image is obtained through calculation. The incidence relation between the dose distribution of the incident beam and the activity of the positive electron species is convenient to study.

2. The calculation method for positron nuclide activity distribution in particle therapy provided by the invention does not need to set completely same and huge initial particle numbers in the modeling process, can give a reasonable calculation result by using less calculation amount, effectively reduces the calculation amount, improves the calculation efficiency and reduces the calculation cost, and is beneficial to the application of the mathematical model and the algorithm in the scenes of particle therapy online image monitoring, therapy plan making, QA and the like.

Therefore, the invention can be widely applied to the technical field of particle therapy.

Drawings

FIGS. 1(a) and 1(b) are depictions of activity obtained by solving differential equations in prior art methods;

FIG. 2 is a flow chart of a method for calculating the distribution of positive electron nuclide activities in particle therapy according to the present invention;

FIG. 3 is a result of activity magnitude calculations for various positron nuclides in an embodiment of the present invention;

FIGS. 4(a) -4 (d) are the calculation results of the spatial distribution of the sizes of the activities of the positive electron species in the embodiment of the present invention, wherein FIG. 4(a) is the two-dimensional distribution of the physical dose absorbed by the target; FIG. 4(b) is a two-dimensional distribution of positron species activity at the end of bombardment; FIGS. 4(c) and 4(d) are two-dimensional distributions of positive electron species activity at the end of bombardment for 30s and 120s, respectively.

Detailed Description

The invention is described in detail below with reference to the figures and examples.

The calculation method for positron nuclide activity distribution in particle therapy provided by the invention can be used for quickly and quantitatively calculating the space distribution and size change condition of positive electron nuclide activity by establishing a convolution-based mathematical model, and is convenient for researching the incidence relation between the dose distribution of the incident beam and the positive electron nuclide activity. The implementation method is simple, the mathematical model is easy to establish, the calculated amount is reduced, and the complete activity change condition of the whole treatment process and even after the treatment is finished can be described.

The basic principle of the invention is as follows: in particle therapy, a patient typically requires several irradiation sessions. In each irradiation process, the beam is periodically led out by a synchrotron and is injected into a patient body through a vacuum film window, an ionization chamber and the like. According to a radiotherapy plan, a certain number of particles (tens to hundreds of pulses), i.e. a suitable dose, are incident into the target volume. During the interaction between the beam and the target, positive electronic nuclide is generated through fusion elimination reaction, so that the positive electronic nuclide is only generated during the irradiation process, and is exponentially attenuated at any time. This is a weighted superposition of a decaying exponential function on the resulting function, which is a significant feature of convolution. For this process, its effect satisfies two principles: the linear principle and the superposition principle. The linear principle means that if the number of positive electron species generated at an instant is n, the positive electron species passes throughThe number of positive electron species after t time isIf the number of positron nuclides generated at an instant is 2n, the number of positron nuclides after t time has elapsed isA plurality of; the principle of superposition is that the activity of a positron species at any time is related to the generation of a previous positive electron species. Based on this, the generation of each positron nuclide during irradiation can be calculated.

For a certain target volume, the rate of positron emission species generation is relatively constant under the same irradiation conditions. Let the decay constant of a positive electronic nuclide i be λ_iIf the variation of the generation speed with time is a function f, the generation speed of the positron species i is f (τ) at time τ, and f (τ) d τ positive electron species are generated within time bin d τ. At time T, the positive electron species generated in time bin d τ undergoes an exponential decay for a duration of (T- τ), at which point the number of positive electron species should be:

then the sum of the number of all positron species generated within 0-T time at time T should be:

the time T can be obtained according to equation (2), and the activity of the positron nuclide i is:

order toFor g (T- τ), the above formula can be written as:

A_i，T＝λ_i(f*g)(τ) (5)

A_T＝∑λ_i(f*g)(τ) (6)

it can be seen that at any time T, for a positron nuclide i, its activity can be expressed as the convolution of a function f of its generation rate over time with an exponential decay function g, whose activity is a decay constant λ_iThe product of this convolution. From this we can get the activity magnitude of a certain positive electron species at any time.

For the change of the positron nuclide spatial distribution, the above calculation idea can be referred to, that is, the target area is composed of many tiny pixel points, and for each pixel point, the activity size can also be expressed as convolution of the generation rate and the decay rate.

The spatial distribution of activity of a certain positron species can be expressed as a function of its three-dimensional position (x, y, z): a. the_i，T(x, y, z) having a size of:

A_i，T(x，y，z)＝λ_i[f_i(x，y，z)*g_i(x，y，z)](τ) (7)

the spatial distribution of all positron nuclide activities is as follows:

A_T(x，y，z)＝∑λ_i[f_i(x，y，z)*g_i(x，y，z)](τ) (8)

example 1

Based on the above principle analysis, the present embodiment provides a positron nuclide activity distribution calculation method, including the following steps:

1) and determining an initial particle number according to the radiotherapy plan, and setting beam targeting setting parameters under the condition of the determined initial particle number.

Wherein, when determining the initial particle count, the radiation therapy plan is basedDetermining, for example, if the radiation treatment plan is such that 100 shots are planned, 10 shots per shot⁸The complete calculation of each particle needs 100 cycles, and the invention only needs the initial particle number less than or equal to 1 cycle as long as the positron nuclide yield can be calculated.

When beam shooting setting parameters are set, beam parameters, target parameters and system acquisition scanning time are mainly included. The beam parameters comprise beam intensity, period, energy dispersion, emittance and the like; target parameters include relative position of the target, three-dimensional geometric parameters, materials, and the like.

2) And acquiring the spatial distribution of the positron nuclide products in the target body based on the set beam targeting setting parameters to obtain a three-dimensional distribution matrix of the preliminary positron nuclide products in the target area.

3) And calculating to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment based on the three-dimensional distribution matrix of the preliminary positron nuclide products in the target area.

Specifically, the method comprises the following steps:

3.1) calculating the generation speed and the decay speed of each positron nuclide product on a certain pixel point respectively.

The method for calculating the production speed of a certain positive electron species product comprises the following steps: and calculating the generation speed of the positron nuclide product on the pixel point according to the yield and the current intensity. The yield of a certain positive electron species is defined as the number of positron species products generated per incident particle number.

The method for calculating the decay rate of a positive electron species product comprises the following steps: substituting the decay constant of the positron nuclide product into the decay exponential function of the positron nuclide product to obtain the decay quantity, namely the decay speed, of the positron nuclide product in unit time.

And 3.2) performing convolution operation on the generation speed and the attenuation speed of each positron nuclide product on the pixel point respectively to obtain the distribution of the activity of each positron nuclide along with time.

3.3) repeating the steps 3.1) and 3.2) to obtain a three-dimensional distribution matrix of the activity of each positron nuclide on each pixel point at any moment.

And 3.4) accumulating the change of the activity of each positive electron nuclide on each pixel point in the target area along with the change of time to obtain a three-dimensional distribution matrix of the total activity of each positive electron nuclide in the target area at any moment.

4) And (3) carrying out three-dimensional filtering on the three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment to obtain the position distribution of positron annihilation of decay of all the positive electron nuclides in the target area at any moment.

For a certain positron nuclide i, the positron range influences the spatial resolution of the online image monitoring system. Because positrons are emitted at an angle of 4 pi, the blurring effect can be simulated by performing convolution operation on the spatial distribution of the activity of positive electron nuclides and a three-dimensional Gaussian convolution kernel with an average positron range, and the effect of the blurring effect is equivalent to performing three-dimensional filtering on the spatial distribution of the activity of positive electron nuclides. I.e. the position distribution of positron annihilation of the decay of a certain positron-nuclear species is:

the position distribution of all positron annihilations is:

5) and (3) performing time domain integration on the position distribution of positron annihilation of all positron nuclides decaying in the target area at any moment to obtain the position distribution of positron annihilation in the system acquisition scanning time.

Specifically, when the position distribution of positron annihilation of all positive electron nuclides decays is accumulated, and the accumulated result is subjected to fixed integration in the time domain according to the system acquisition scanning time, the calculation formula is as follows:

D(x，y，z)＝∫P_T(x，y，z)dt (11)

wherein D (x, y, z) is the scanThe distribution of positions of positron annihilations within time; p_T(x, y, z) is the distribution of the positions of all positron annihilations at any time.

6) And performing Gaussian smoothing filtering on the position distribution of the positron annihilation times in the acquisition scanning time of the system to obtain a prediction distribution image of the range and activity of the positron nuclide.

Example 2

The foregoing embodiment 1 provides a positive electron nuclide activity distribution calculation method, and correspondingly, this embodiment provides a positron nuclide activity distribution calculation system. The identification system provided in this embodiment may implement the positive electron nuclide activity distribution calculation method in embodiment 1, and the calculation system may be implemented by software, hardware, or a combination of software and hardware. For example, the identification system may comprise integrated or separate functional modules or functional units to perform the corresponding steps in the methods of embodiment 1. Since the identification system of this embodiment is basically similar to the method embodiment, the description process of this embodiment is relatively simple, and reference may be made to the partial description of embodiment 1 for relevant points.

The present embodiment provides a positron nuclide activity distribution calculation system, which includes:

the positron nuclide activity distribution calculation module determines the initial particle number based on the radiotherapy plan and calculates to obtain a three-dimensional distribution matrix of the total activity of various positive electron nuclides in the target area at any moment;

the positron annihilation position distribution calculation module is used for calculating and obtaining position distribution of positron annihilation within the system acquisition scanning time based on a three-dimensional distribution matrix of total activity of various positron nuclides in the target area at any moment;

and the image prediction module is used for performing Gaussian smooth filtering on the obtained position distribution of positron annihilation times within the system acquisition scanning time to obtain a prediction distribution image of the range and activity of the positron nuclide.

Example 3

This embodiment provides a processing device corresponding to the positive electron species activity distribution calculation method provided in embodiment 1, where the processing device may be a processing device for a client, such as a mobile phone, a laptop, a tablet computer, a desktop computer, and the like, to perform the identification method of embodiment 1.

The processing equipment comprises a processor, a memory, a communication interface and a bus, wherein the processor, the memory and the communication interface are connected through the bus so as to complete mutual communication. The memory stores a computer program that can be executed on the processor, and the processor executes the positive electron species activity distribution calculation method provided in this embodiment 1 when executing the computer program.

In some implementations, the Memory may be a high-speed Random Access Memory (RAM), and may also include a non-volatile Memory, such as at least one disk Memory.

In other implementations, the processor may be various general-purpose processors such as a Central Processing Unit (CPU), a Digital Signal Processor (DSP), and the like, and is not limited herein.

Example 4

A positron nuclide activity distribution calculation method of this embodiment 1 may be embodied as a computer program product, and the computer program product may include a computer readable storage medium having computer readable program instructions for executing the positron nuclide activity distribution calculation method of this embodiment 1 loaded thereon.

The computer readable storage medium may be a tangible device that retains and stores instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but not limited to, an electronic memory device, a magnetic memory device, an optical memory device, an electromagnetic memory device, a semiconductor memory device, or any combination of the foregoing.

It should be noted that the flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present application. Each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s).

Example 5

This embodiment further illustrates the present invention by specific examples.

In this embodiment, the Monte Carlo software Geant4/GATE is used to obtain the statistical yield and three-dimensional distribution matrix, and the initial particle number is 10⁶The beam period is 8s, the total period is 43 periods, each period is divided into 2s of beam outgoing and 6s of beam stopping, and the beam outgoing flow intensity is 175000. The target body is a cuboid made of single material and uniformly distributed (PMMA) and has the size of (100X 200X 300 mm)³). And performing convolution operation on the computing software MATLAB to obtain a result.

Fig. 3 is a schematic diagram showing the calculation result of the positive electron species activity.

As shown in fig. 4(a) to 4(b), the effect map is calculated for the spatial distribution of the sizes of positron nuclides. Wherein, FIG. 4(a) is a two-dimensional distribution of physical dose absorbed by the target body; FIG. 4(b) is a two-dimensional distribution of positron species activity at the end of bombardment; FIGS. 4(c) and 4(d) are two-dimensional distributions of positive electron species activity at the end of bombardment for 30s and 120s, respectively.

The above embodiments are only used for illustrating the present invention, and the structure, connection mode, manufacturing process, etc. of the components may be changed, and all equivalent changes and modifications performed on the basis of the technical solution of the present invention should not be excluded from the protection scope of the present invention.