阅读说明：本技术 一种放射剂量计算系统 (radiation dose calculation system ) 是由 张鹏程 张丽媛 桂志国 舒华忠 李�杰 于 2019-09-30 设计创作，主要内容包括：本发明涉及一种放射剂量计算系统,包括信息输入模块、点核能量分布模拟模块、点核模型参数提取模块、点核查找表生成模块、坐标系转换模块、TERM值计算模块、剂量计算模块和信息输出模块。通过将直角坐标系下的二维注量分布、三维密度分布转换到球壳坐标系下,在球壳坐标系下计算各体素的TERM值,利用球壳坐标系的对称特性,直接从点核查找表中读取碰撞点信息,从而进行快速剂量计算,并将球壳坐标系下的三维剂量分布转换到直角坐标系下,输出三维剂量分布,以及统计各器官的剂量-体积曲线。本发明避免了计算碰撞点位置和旋转点核所需计算量,在射线发散入射的情况下有效地降低了点核剂量计算方法的算法复杂度。(the invention relates to a radiation dose calculation system which comprises an information input module, a point nuclear energy distribution simulation module, a point nuclear model parameter extraction module, a point nuclear lookup table generation module, a coordinate system conversion module, a TERM value calculation module, a dose calculation module and an information output module. The TERM value of each voxel is calculated under a spherical shell coordinate system by converting two-dimensional fluence distribution and three-dimensional density distribution under a rectangular coordinate system into the spherical shell coordinate system, collision point information is directly read from a point kernel lookup table by utilizing the symmetry characteristic of the spherical shell coordinate system, so that rapid dose calculation is performed, the three-dimensional dose distribution under the spherical shell coordinate system is converted into the rectangular coordinate system, three-dimensional dose distribution is output, and a dose-volume curve of each organ is counted. The invention avoids the calculation amount required for calculating the position of the collision point and the rotation point kernel, and effectively reduces the algorithm complexity of the point kernel dose calculation method under the condition of divergent incidence of rays.)

1. a radiation dose calculation system, comprising:

the information input module is used for inputting data information required by dose calculation, and the required data information at least comprises three-dimensional density information of a die body, organ delineation information, treatment head information and field information;

the core-point energy distribution simulation module is used for simulating core-point energy distribution by utilizing a Monte Carlo algorithm according to the treatment head information input by the information input module;

the point kernel model parameter extraction module is used for extracting the energy distribution of point kernels in each solid angle direction and performing parameter fitting to obtain point kernel model parameters;

The point core lookup table generation module is used for storing the point core model parameters, the collision point information and the radial sampling interval to generate a point core lookup table;

The coordinate system conversion module is used for calculating the two-dimensional fluence distribution on the surface of the mold body according to the treatment head information under a rectangular coordinate system, converting the two-dimensional fluence distribution and the three-dimensional density distribution under the rectangular coordinate system into a spherical shell coordinate system, and determining the average mass attenuation coefficient and the relative density of each voxel according to the three-dimensional density distribution under the spherical shell coordinate system;

the TERM value calculation module is used for calculating the TERM value of each voxel according to the two-dimensional fluence distribution and the three-dimensional density distribution under the spherical shell coordinate system;

The dose calculation module is used for calculating the position of the spherical shell where the dose deposition point is located and reading collision point information corresponding to the spherical shell from the point core lookup table according to the position of the spherical shell; adding the relative positions of the collision points and the positions of the dose deposition points to obtain the positions of all collision points around the current dose deposition point; determining a density value, a relative density value, an average attenuation coefficient and a radial sampling length at a collision point by using the information of the collision point; reading an included angle between a line segment from the dose deposition point to the collision point corresponding to the collision point and an incident ray at the collision point from the lookup table; thereby calculating the dosage to obtain the three-dimensional dosage distribution under the spherical shell coordinate system;

and the information output module is used for converting the three-dimensional dose distribution under the spherical shell coordinate system into a rectangular coordinate system, outputting the three-dimensional dose distribution and counting the dose-volume curve of each organ.

2. a radiation dose calculation system as claimed in claim 1 wherein the collision point information includes the relative position of the collision point in the spherical shell coordinate system, the length of the sampling interval over which the collision point is located, and the angle between the line segment from the dose deposition point to the collision point and the incident ray at the collision point.

3. A radiation dose calculation system as claimed in claim 2 wherein a piece of collision point information is stored for spherical shells of the same depth in the point kernel look-up table.

4. A radiation dose calculation system as claimed in claim 1, wherein the point kernel lookup table generation module comprises a rectangular coordinate system collision point information calculation module, a mapping module, a spherical shell coordinate system collision point information calculation module and a storage module, wherein:

The rectangular coordinate system collision point information calculation module is used for calculating an intersection point of a field central axis and a current depth spherical shell under a spherical shell coordinate system, calculating the position of the intersection point under the rectangular coordinate system, calculating the positions of collision points around the intersection point under the rectangular coordinate system, and calculating included angle values of line segments from the intersection point to the collision points and incident rays passing through the collision points;

The mapping module is used for mapping the position of the collision point calculated under the rectangular coordinate system back to the spherical shell coordinate system, and the corresponding included angle value is kept unchanged;

The spherical shell coordinate system collision point information calculation module is used for calculating the relative position difference value of the collision point position and the intersection point under the spherical shell coordinate system;

the storage module is used for storing the relative position difference value, the included angle value and the radial sampling interval.

Technical Field

the invention relates to the technical field of radiation therapy systems, in particular to a radiation dose calculation system.

Background

Radiation therapy is one of the major current treatments for malignant tumors. Dose calculation is the core of a radiotherapy plan, and the speed and the precision of dose calculation have important influence on the efficiency and the quality of the radiotherapy plan. Research shows that the accuracy of the irradiation dose is improved by l%, and the cure rate can be improved by 2%. Generally, the allowable range of the irradiation dose error is ± 5% recommended in ICRU (international compliance units & measures) 24 report. In inverse planning of intensity modulated radiation therapy, the optimization process requires multiple dose calculations (about 10 to 1000), and therefore the calculation speed is also very demanding. A dose calculation model with clinical practicability can complete single-field and low-precision dose calculation within 1 minute; the calculation of multi-field, high-precision or optimized dose is completed within 1 hour.

models for calculating dose distribution can be divided into 3 major classes: empirical models, semi-analytical models and analytical models. In order to meet the quality requirements of clinical radiotherapy planning, inverse planning dose calculations are typically performed using semi-analytical models, such as convolution/superposition dose calculation methods based on kernel (pencil-beam kernel, point-kernel) models. Although the analytical model has the highest accuracy of dose calculation, the required calculation amount is very large, and the analytical model cannot be used for inverse planning dose calculation and is generally only used for calculating the dose distribution of the final treatment plan. The dose calculation method based on the semi-analytic model is relatively small in calculation amount compared with the analytic model, but the total calculation amount is also considerable when the dose distribution is calculated for multiple times in the inverse planning. Some hardware-accelerated methods are used to accelerate convolution/superposition dose calculation methods based on kernel models, such as FPGA and GPU. Therefore, under the condition of not influencing the dose calculation precision, the calculation amount of the convolution/superposition dose calculation method based on the kernel model is reduced, or the time required by calculation is shortened, so that the method has practical significance for the rapid formulation of the radiation treatment plan.

The semi-analytic model capable of meeting the accurate requirement of clinical radiotherapy is a point nuclearantan amount calculation method. The method of the point-and-core dose calculation has a large computational complexity. In the case of ray-parallel-incidence phantoms, N is directly calculated³The dose distribution of the spots needs to be calculated as N⁶To N⁷the secondary line is integrated. Despite the acceleration using the tube-string convolution method, the M.N calculation is still required³and (c) a secondary line integral, where M is the number of solid angle samples at each dose calculation point. In the clinic, the radiation source is considered to be a point source, and the radiation is emitted to irradiate the tumor by taking the point source as a center. In the case of divergent rays incident on the phantom surface, the kernel at each collision point in the dose calculation process is rotated to be parallel to the rays passing through the collision point. Each point kernel is rotated under a rectangular coordinate system, the calculation complexity of the point kernel dose calculation method is increased, and the calculation time is increased by 2-3 times. Therefore, the calculation amount of the line integral and the calculation complexity of the point kernel rotation are reduced, the overall calculation complexity of the point kernel dose calculation method can be greatly reduced, and the time required by dose calculation is shortened.

In view of the above, there is a need for improvement in the art, and a need therefore exists for an improved method and apparatus.

Disclosure of Invention

The invention aims to provide a radiation dose calculation system, which avoids the calculation amount required by calculating the position of a collision point and a rotating point kernel, effectively reduces the algorithm complexity of a point kernel dose calculation method under the condition of divergent incidence of rays and shortens the time required by dose calculation.

In order to achieve the purpose of the invention, the following technical scheme is adopted.

A radiation dose calculation system comprising:

The information input module is used for inputting data information required by dose calculation, and the required data information at least comprises three-dimensional density information of a die body, organ delineation information, treatment head information and field information;

the core-point energy distribution simulation module is used for simulating core-point energy distribution by utilizing a Monte Carlo algorithm according to the treatment head information input by the information input module;

The point kernel model parameter extraction module is used for extracting the energy distribution of point kernels in each solid angle direction and performing parameter fitting to obtain point kernel model parameters;

The point core lookup table generation module is used for storing the point core model parameters, the collision point information and the radial sampling interval to generate a point core lookup table;

The coordinate system conversion module is used for calculating the two-dimensional fluence distribution on the surface of the mold body according to the treatment head information under a rectangular coordinate system, converting the two-dimensional fluence distribution and the three-dimensional density distribution under the rectangular coordinate system into a spherical shell coordinate system, and determining the average mass attenuation coefficient and the relative density of each voxel according to the three-dimensional density distribution under the spherical shell coordinate system;

A TERM (Total Energy recovered per unit Mass) value calculating module used for calculating the TERM value of each voxel according to two-dimensional fluence distribution and three-dimensional density distribution under a spherical shell coordinate system;

The dose calculation module is used for calculating the position of the spherical shell where the dose deposition point is located and reading collision point information corresponding to the spherical shell from the point core lookup table according to the position of the spherical shell; adding the relative positions of the collision points and the positions of the dose deposition points to obtain the positions of all collision points around the current dose deposition point; determining a density value, a relative density value, an average attenuation coefficient and a radial sampling length at a collision point by using the information of the collision point; reading an included angle between a line segment from the dose deposition point to the collision point corresponding to the collision point and an incident ray at the collision point from the lookup table; thereby calculating the dosage to obtain the three-dimensional dosage distribution under the spherical shell coordinate system;

And the information output module is used for converting the three-dimensional dose distribution under the spherical shell coordinate system into a rectangular coordinate system, outputting the three-dimensional dose distribution and counting the dose-volume curve of each organ.

Further, the collision point information comprises the relative position of the collision point in the spherical shell coordinate system, the sampling interval length of the collision point, and the included angle data of the line segment from the dose deposition point to the collision point and the incident ray at the collision point.

further, a piece of collision point information is stored in the point core lookup table for spherical shells with the same depth.

further, the point kernel lookup table generation module includes a rectangular coordinate system collision point information calculation module, a mapping module, a spherical shell coordinate system collision point information calculation module and a storage module, wherein:

The rectangular coordinate system collision point information calculation module is used for calculating an intersection point of a field central axis and a current depth spherical shell under a spherical shell coordinate system, calculating the position of the intersection point under the rectangular coordinate system, calculating the positions of collision points around the intersection point under the rectangular coordinate system, and calculating included angle values of line segments from the intersection point to the collision points and incident rays passing through the collision points;

The mapping module is used for mapping the position of the collision point calculated under the rectangular coordinate system back to the spherical shell coordinate system, and the corresponding included angle value is kept unchanged;

The spherical shell coordinate system collision point information calculation module is used for calculating the relative position difference value of the collision point position and the intersection point under the spherical shell coordinate system;

the storage module is used for storing the relative position difference value, the included angle value and the radial sampling interval.

The invention has the following beneficial effects: the invention carries out fast kernel dose calculation under the spherical shell coordinate system, and can calculate the dose distribution more fast under the condition of not changing the dose calculation precision. And dose calculation is carried out under a spherical shell coordinate system, so that on one hand, a rotation point core is avoided, on the other hand, the relative position of a collision point is stored, and the complexity of calculating line integral is reduced. Due to the special structure of the algorithm, the algorithm is very suitable for hardware (FPGA and GPU) acceleration.

drawings

FIG. 1 is a block diagram of a radiation dose calculation system of the present invention.

FIG. 2 is a schematic processing flow diagram of the checking lookup table generation module in the system of the present invention.

FIG. 3 is a schematic process flow diagram of a dose calculation module in the system of the present invention.

FIG. 4 is a schematic processing flow diagram of an information output module in the system of the present invention.

Detailed Description

The invention is described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in fig. 1, the radiation dose calculation system provided by the present invention includes an information input module 10, a nugget energy distribution simulation module 20, a nugget model parameter extraction module 30, a nugget lookup table generation module 40, a coordinate system conversion module 50, a TERM value calculation module 60, a dose calculation module 70, and an information output module 80.

the information input module 10 is used for inputting data information required by dose calculation, wherein the required data information comprises three-dimensional density information, organ delineation information, treatment head information and radiation field information of a patient. Wherein the three-dimensional density information of the patient can be CT images, MR images or patient density information acquired by other means. The organ delineation information can be obtained by delineating on the three-dimensional density information by a physicist, and can also be obtained by automatically delineating through automatic delineation software. The treatment head information comprises complete treatment head shape structure and parameter information, irradiation direction, position of isocenter and the like. In this embodiment, a spiral CT device is used to acquire CT data, which may be used to represent density information of a patient. The CT data is input into organ delineation software, and the physical engineer delineates the shape of each patient, so as to obtain the organ information of the patient.

The energy distribution simulation module 20 is configured to simulate energy distribution of the core-point model by using a monte carlo algorithm according to the input therapy head information. Simulating the energy distribution of the point kernels in a spherical coordinate system, wherein the sampling interval in the polar angle direction is 3.75 degrees, and the sampling number is 48; the sampling interval of the azimuth angle is 360 degrees, and the sampling number is 1; radial sampling with unequal intervals is used, the sampling number is 24, and the maximum range is 60 cm.

The point kernel model parameter extraction module 30 is configured to extract energy distribution of point kernels in each solid angle direction, and perform parameter fitting to obtain point kernel model parameters. In this embodiment, the energy spread function of the point kernel model is represented as:

Wherein A is_θ、a_θ、B_θAnd b_θare the values of parameters relating to the cube-corner directions. And extracting energy distribution of each solid angle direction along the radial direction, and calculating the parameter value of the point kernel model (formula 1) by a fitting method.

And the point kernel lookup table generation module 40 is configured to store the point kernel model parameters, the collision point information, and the radial sampling intervals to generate a point kernel lookup table. In the present embodiment, the collision point information is calculated by the following steps. The relation between the spherical shell coordinate system and the rectangular coordinate system is as follows:

wherein x is (x)_x,x_y,x_z) Represents a point in a rectangular coordinate system, and the antipodal position of the point in the spherical coordinate system is represented by p ═ p (p_x,p_y,p_z). The point core lookup table generation module comprises a rectangular coordinate system collision point information calculation module, a mapping module, a spherical shell coordinate system collision point information calculation module and a storage module. Calculating collision point information around the dose deposition points at different spherical shell depth positions under a spherical shell coordinate system: firstly, the rectangular coordinate system collision point information calculation module calculates the intersection point of the central axis of the radiation field and the spherical shell with the current depth under a spherical shell coordinate system, calculates the position of the intersection point under the rectangular coordinate system, calculates the actual positions of collision points of the dose deposition point in different solid angle directions and different distances under the rectangular coordinate system, and calculates the included angle between the line segment from the dose deposition point to the collision point and the incident ray at the collision point; then, the mapping module converts the coordinates of the collision points in the rectangular coordinate system into a spherical shell coordinate system, and the spherical shell coordinate system collision point information calculation module calculates and calculates the relative offset positions from the collision points to the dose deposition points in the spherical shell coordinate system; and finally, the storage module stores the relative offset position, the included angle value and the radial sampling interval of the collision point, wherein the included angle value is the same as the included angle value under the rectangular coordinate.

the dose deposited at point r by the energy released at collision point s can be written as:

wherein omega_mnIs the solid angle, η, relative to point r, at which point s is located_rmnAnd ρ_rmnIs the relative density and density values at point r, T(s), σ(s) and ds are the TERM value, density value and radial infinitesimal length at point s, and the distance between point r and point s is r_lThe distance is divided into l segments, each segment having a length Δ r_iRelative density of each segment is η_imn. Knowing the location of the s point, the T(s) and σ(s) values can be calculated; knowing the position of the r point, η can be calculated_rmnAnd ρ_rmnA value of (d); knowing the positions of the s point and the r point, the included angle between the line segment from the r point to the s point and the incident ray at the s point can be calculated, so that the parameter A is determined_m、a_m、B_mAnd b_mA value of (d); and knowing the length and relative density of each sampling interval from point r to point s, the ∑ η ∑ can be calculated_imnΔr_iThe value of (c). In the implementation, the dose is calculated by taking a dose deposition point as a center, the polar angle sampling interval is 3.75 degrees, and the sampling number is 48; the sampling interval of the azimuth angle is 45 degrees, and the sampling number is 8; the radial direction uses non-equal interval sampling, the sampling number is 60, and the maximum radius is 60 cm. Thus, the value of the radial sampling interval Δ r_iFixed, the relative density, and TERM values in each sampling interval are approximately equal to the relative density, and TERM values at the center point of the sampling interval. In summary, knowing the locations of points s and r, and the center location of each sampling interval between these two points, the dose deposition at point r of the energy released at the collision point s can be calculated using equation (3). In the point-to-point nuclear dose calculation model, it is time consuming to calculate the center position of each sampling interval and calculate the angle between the line segment from the r point to the s point and the ray from the ray source to the s point. In the invention, the central position of each sampling interval, the line segment from the r point to the s point, the included angle of the incident ray at the s point and the length of each sampling interval are collectively called collision point information. For the problem of overlarge calculated amount of directly calculated collision point information, the collision point information is stored in the lookup table in advance, so that the calculation time required by direct calculation is reduced。

The collision point information around each dose calculation point is directly stored, and the required storage space is too large. Therefore, only one piece of collision point information is stored under the same spherical shell depth under the spherical shell coordinate system by utilizing the rotation invariant characteristic of the spherical shell coordinate system, and the storage space is greatly reduced. As shown in fig. 2, selecting an intersection point of a spherical shell with a certain depth and a central axis of a field in a spherical coordinate system, and determining the position of the intersection point in a rectangular coordinate system; determining the position of the collision point around the point and the included angle value of the collision point according to the position of the point under the rectangular coordinate system; mapping the positions of the surrounding collision points back to the spherical shell coordinate system, and calculating the relative position difference between the collision points and the intersection points; and storing the relative position difference, the corresponding included angle value and each sampling interval to generate a lookup table. In this embodiment, if the polar angle sampling number is 48, the azimuthal angle sampling number is 8, and the radial direction sampling number is 60, the total number of collision points around each dose deposition point is 48 × 8 × 60. When the position and the angle value of the collision point are recorded by using the float data type, the storage space required for the collision point information on each layer of spherical shell is 48 × 8 × 60 × 4 × 4 bytes, which is about 0.35 MB. In the spherical shell coordinate system, the radial sampling interval is 0.5cm, and the sampling number is 200, so that the total storage space required by the collision point information is about 70 MB.

In the point check table-finding generation process, only a nuclear model needs to be generated once for the same treatment head.

The coordinate system conversion module 50 is used for calculating the two-dimensional fluence distribution on the surface of the phantom according to the information of the treatment head in the rectangular coordinate system. And converting the two-dimensional fluence distribution and the three-dimensional density distribution under the rectangular coordinate system into a spherical shell coordinate system. And determining the average mass attenuation coefficient and the relative density of each voxel according to the three-dimensional density distribution under the spherical shell coordinate system. The conversion relation from the spherical shell coordinate system to the rectangular coordinate system is as follows:

pα(tan(p_x)p_z/Δ,tan(p_y)p_z/Δ,p_z/Δ):＝x， (4)

Wherein

The TERM value calculating module 60 is configured to calculate a TERM value according to the two-dimensional fluence distribution and the three-dimensional density distribution in the spherical shell coordinate system. The TERM value is calculated as:

Wherein r is₀Phi (r) is the intersection point of the ray from the source to the voxel r with the surface of the phantom body₀) Is r₀The amount of energy fluence at a point is,Is the average linear mass attenuation coefficient at point l within the phantom.

The dose calculation module 70 is configured to perform dose calculation. In the implementation, the dose distribution at different positions on each layer of spherical shell is calculated layer by layer along the depth direction of the spherical shell. The dose calculation process is shown in figure 3. Calculating the position of the spherical shell where the dose deposition point is located, and reading collision point information of the corresponding spherical shell from the point core lookup table according to the position of the spherical shell; adding the relative position difference in the collision point information and the position of the dose deposition point to obtain collision point information of the current dose deposition point; determining a density value, a relative density value, an average attenuation coefficient and a radial sampling length at the collision point by using the collision point information, and acquiring an included angle between a line segment from the dose deposition point to the collision point and an incident ray at the collision point from the collision point information; and (4) calculating each parameter value by knowing the dose, substituting the parameter values into a formula (3) to calculate the dose, and obtaining the three-dimensional dose distribution under the spherical shell coordinate system. According to the point nuclear dose calculation method, the total dose distribution at the dose deposition point can be calculated by knowing the density value, the relative density value, the attenuation coefficient, the radial sampling length, the density value of the dose deposition point and the included angle value between the line segment from the dose deposition point to the collision point and the incident ray at the collision point. And calculating all parameters required by the point-kernel dose calculation method by using the collision point information in the lookup table.

The information output module 80, as shown in fig. 4, is configured to convert the three-dimensional dose distribution in the spherical shell coordinate system to the rectangular coordinate system, output the three-dimensional dose distribution, and count the dose-volume curve.

According to the technical scheme, the two-dimensional fluence distribution and the three-dimensional density distribution under a rectangular coordinate system are converted into a spherical shell coordinate system, the TERM value of each voxel is calculated under the spherical shell coordinate system, the collision point information is directly read from a point kernel lookup table by utilizing the symmetry characteristic of the spherical shell coordinate system, so that rapid dose calculation is performed, the three-dimensional dose distribution under the spherical shell coordinate system is converted into the rectangular coordinate system, the three-dimensional dose distribution is output, and the dose-volume curve of each organ is counted. The invention avoids the calculation amount required for calculating the position of the collision point and the rotation point kernel, and effectively reduces the algorithm complexity of the point kernel dose calculation method under the condition of divergent incidence of rays.

The foregoing shows and describes the general principles and features of the present invention, together with the advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.