A method for opening holes in radiotherapy fixation membranes based on finite element analysis

Abstract

The present invention discloses a radiotherapy fixed membrane opening method based on finite element analysis, the method comprising: performing CT scanning on a certain part of a patient who needs radiotherapy, obtaining CT scanning grayscale image slices of the part; converting the obtained CT image slices into STL format, providing geometric input for establishing mesh models of different opening types; cutting the obtained complete fixed membrane geometric model, separating the surface of the opening area and deleting the opening area, obtaining a fixed membrane geometric model with different opening positions; meshing the obtained fixed membrane geometric model with different opening types, and for the position where more local features are lost, decompressing the compressed geometric edges until a mesh model with better quality is obtained, and performing finite element calculation, by comparing the calculation results, selecting the opening method with the least influence on the fixing effect for opening. The method can effectively reduce the influence of the opening on the fixing effect of the fixed membrane.

Description

Technical Field

[0001] The invention relates to the technical field of radiotherapy positioning modeling methods, and in particular to a radiotherapy fixed membrane hole opening method based on finite element analysis. Background Art

[0002] In radiotherapy, head, neck and shoulder fixation membranes are widely used to keep the patient's head, neck and shoulders in a precisely positioned posture to improve the accuracy of radiotherapy. Due to different special conditions of patients, such as facial openings and openings in body surface wounds, it is necessary to make openings of different positions and sizes in the head, neck and shoulder fixation membrane. However, the size, position and shape of the openings often affect the fixation effect of the head, neck and shoulders and the comfort of the patient. Therefore, how to minimize the impact of the openings on the fixation effect of the fixation membrane is still a problem that needs to be solved. Summary of the invention

[0003] The technical problem to be solved by the present invention is how to provide a radiotherapy fixed membrane hole opening method based on finite element method, which can effectively reduce the influence of the hole opening on the fixing effect of the fixed membrane.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a radiotherapy fixed membrane opening modeling method based on finite element, comprising the following steps:

[0005] S1: Perform CT scanning on a certain part of the patient who needs radiotherapy, and obtain a CT scan grayscale image slice of the part;

[0006] S2: converting the obtained CT scan grayscale image slices into STL format to provide input for building mesh models of different opening types;

[0007] S3: cutting the obtained complete fixed membrane geometric model, separating the surface of the opening area and deleting the opening area, so as to obtain fixed membrane geometric models with different opening positions and types;

[0008] S4: meshing the obtained fixed membrane geometry model with different opening positions and types;

[0009] S5: Perform quality statistics and optimization on the divided meshes, decompress the compressed geometric edges at locations where more local features are lost, and repeat step 4 S4 until a mesh model with better quality is obtained;

[0010] S6: Import the fixed membrane mesh model with different opening positions and types obtained in step S5 into the finite element calculation unit, and combine the application to assign the fixed membrane material properties and thickness information, and set the fixed membrane boundary conditions and loads to complete the fixed membrane opening calculation. By comparing the calculation results, select the opening method with the least impact on the fixed membrane to open the fixed membrane.

[0011] The beneficial effects of adopting the above technical scheme are: the method models the fixation membrane according to the actual part structure of the patient, and proposes a method for rapid opening modeling at different positions according to different needs, and uses finite element software to simulate the application of forces in different directions on the fixed membrane grid model, and understands the maximum displacement part and the maximum force position of the head, neck and shoulder fixation membrane of various opening types during use through the deformation results, so that the fixation membrane can fit the patient better, and can effectively reduce the influence of the opening on the fixation effect of the fixation membrane, improve the fixation effect and enhance the comfort of use. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0013] Figure 1 is a flow chart of the method described in an embodiment of the present invention;

[0014] FIG. 2 is a schematic diagram of geometric modeling and mesh division of fixed membrane models with different openings in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of 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.

[0016] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0017] Overall, such as Figure 1 As shown, an embodiment of the present invention discloses a radiotherapy fixed membrane opening modeling method based on finite element, comprising the following steps:

[0018] S1: Perform a CT scan on a certain part of the patient who needs radiotherapy to obtain a CT scan grayscale image slice of the part. The CT machine in the prior art can be used for the CT scan.

[0019] S2: converting the obtained CT images into STL format to provide input for building mesh models of different opening types;

[0020] Wherein, step S2 specifically includes the following steps:

[0021] Step S2-1: Use a CT simulation positioning machine (which can be Brilliance Bigbore) to reconstruct the CT images of the head and neck patients who need radiotherapy obtained in step S1. Select Irs in the CT machine, enter the reconstruction database, select the data of the radiotherapy patient, click View Recon, enter the reconstruction state, select the appropriate layer thickness in the Thickness option, select Overlap in the Increment option, and click Recon to complete the reconstruction. Export the reconstructed data to DICOM format. Thin layer reconstruction can reduce the step effect to a certain extent.

[0022] Step S2-2: Import the DICOM format data obtained in step S2-1 into the MIM software, select the MIM bed removal tool, open the import sequence, perform bed removal operations, and preprocess the trunk outline. Switch to the "Trunk" tool, select the sagittal view, and drag the left mouse button from the first layer on the head side to the last layer on the foot side. Switch to the "2D Brush" tool, use different brush sizes to correct and adjust details, switch to the "Smooth" tool, and moderately smooth the trunk outline to ensure that the outline is smooth and accurate, and finally save the outline result. Export the trunk in Structure as an STL format file.

[0023] Step S2-3: Import the torso model (patient head, neck, and shoulder model) in STL format obtained in step S2-2 into Materialise 3-matic software for Laplacian smoothing. Smoothing can bring better quality and smoother STL fixed membrane (patient head and neck model) models, and avoid the complexity and stress concentration that may occur in geometry extraction and finite element analysis. Laplacian smoothing iteratively moves each vertex of the mesh to the position of the centroid of its surrounding neighborhood. The Laplacian coordinate representation is as follows:

[0024]

[0025] Where N(i) is the vertex v i The neighboring point set, w ij Represents vertex v i The weight of the jth neighbor of . If the weights are all 1, then the formula simplifies to taking the difference between the average of the vertex and its neighbors:

[0026]

[0027] where d i is the vertex v i The scheme of selecting all neighboring nodes with equal weights is called an umbrella weighting scheme. Another common weighting scheme is to use the cotangent weights between the angles in the graph, defined as:

[0028]

[0029] Where α ij and β ij For point v i With v j The opposite angle of the triangle to which the sides belong.

[0030] Step S2.4: The torso model (patient head, neck, and shoulder model) smoothed in step S2.3 is exported in STL format and input into the mesh processing software. Through the geometric reverse extraction function, the torso triangular mesh model in STL format is used as input to reversely extract the surface geometry model. The software used is Hypermesh.

[0031] S3: cutting the complete (patient head and neck geometric model) fixed membrane geometric model obtained in step S2, separating the surface of the opening area and deleting it, to obtain geometric models with different opening positions;

[0032] The step S3 specifically includes the following steps:

[0033] Step S3-1: Establish an XY plane parallel to the body as a cutting plane, and delete the back geometric area by cutting the complete (patient head and neck geometric model) head, neck and shoulder fixation membrane geometric model.

[0034] Step S3-2: compress the surface boundary to compress unnecessary micro-geometry edges, so that when dividing the mesh, the compressed edges are ignored, and a continuous mesh with better quality is generated.

[0035] Step S3-3: Based on the free boundary of the fixed film geometric model cut in step S3-1, a fixed length is stretched along the Z direction, and the outer boundary of the fixed area is drawn to establish the geometric surface of the fixed area.

[0036] Step S3-4: Create cutting surfaces of different opening areas in the XY plane, including eyes, nostrils, mouth, chin, shoulders and other parts, cut the fixed membrane geometric model through the cutting surface, retain the remaining area, and obtain fixed membrane geometric models with different opening positions and types.

[0037] The implementation process is:

[0038] S3-4-1) Establish an appropriate number of nodes as control points.

[0039] S3-4-2) Connect nodes through smooth curves.

[0040] S3-4-3) Stretch the smooth curve along the Z direction to generate the cutting surface.

[0041] S3-4-4) Cut the complete head, neck and shoulder fixation membrane geometric model through the cutting surface to obtain fixed membrane geometric models with different opening positions and types.

[0042] S4: meshing the obtained fixed membrane geometry model with different opening positions and types;

[0043] S5: Perform quality statistics and optimization on the divided meshes. For locations where more local features are lost, perform decompression on the geometric edges compressed in step S3-2, and repeat step S4 until a mesh model with better quality is obtained.

[0044] S6: Input the fixed membrane mesh model with different opening types obtained in step S5 into the finite element calculation unit, assign material properties and thickness in combination with the application, set boundary conditions and loads to complete the fixed membrane opening modeling, and open holes in the fixed membrane according to the results of the opening modeling.

[0045] Figure 2a-2f is a schematic diagram of geometric modeling and meshing of fixed membrane models with different openings in the present invention, wherein Figure 2a It is the smoothed STL format triangulated network. Figure 2b is the complete fixed membrane geometry model after reconstruction, Figure 2c This is the fixed membrane geometry model after edge compression and cutting of the back area. Figure 2d The fixed membrane geometry after modeling the fixed region, Figure 2e The fixed membrane geometry model after opening the forehead, nostrils and mouth. Figure 2f It is a fixed membrane quadrilateral mesh model.

[0046] In summary, the method models the fixation membrane according to the real part structure of the patient, and proposes a method for rapid opening modeling at different positions according to different needs. The finite element software is used to simulate the force applied in different directions on the fixed membrane grid model. The deformation results are used to understand the maximum displacement part and the maximum force position of the head, neck and shoulder fixation membrane with various opening types during use, so that the fixation membrane can fit the patient better, effectively reduce the influence of the opening on the fixation effect of the fixation membrane, improve the fixation effect and enhance the comfort of use.

Claims

1. A method for opening a hole in a radiotherapy fixed membrane based on finite element analysis, characterized in that The steps include: S1: Perform CT scanning on a certain part of the patient who needs radiotherapy, and obtain a CT scan grayscale image slice of the part; S2: converting the obtained CT scan grayscale image slices into STL format to provide input for building mesh models of different opening types; S3: cutting the obtained complete fixed membrane geometric model, separating the surface of the opening area and deleting the opening area, so as to obtain fixed membrane geometric models with different opening positions and types; The step S3 comprises the following steps: Step S3-1: Establish an XY plane parallel to the body as a cutting plane, cut the complete torso geometry model, and delete the back geometry area; Step S3-2: compress the surface boundary to compress unnecessary micro-geometry edges. When dividing the mesh, ignore the compressed edges to generate a continuous mesh with better quality. Step S3-3: Based on the free boundary of the trunk geometric model cut in step S3-1, stretch a fixed length along the Z direction, draw the outer boundary of the fixed area, and establish the geometric surface of the fixed area; Step S3-4: establishing cutting planes of different opening areas in the XY plane, cutting the fixed membrane geometric model through the cutting planes, retaining the remaining areas, and obtaining fixed membrane geometric models with different opening positions and types; S4: meshing the obtained fixed membrane geometric models with different opening positions and types; S5: Perform quality statistics and optimization on the divided meshes, decompress the compressed geometric edges at locations where more local features are lost, and repeat step S4 until a mesh model with better quality is obtained; S6: Import the fixed membrane mesh model with different opening positions and types obtained in step S5 into the finite element calculation unit, and combine the application to assign the fixed membrane material properties and thickness information, and set the fixed membrane boundary conditions and loads to complete the fixed membrane opening calculation. By comparing the calculation results, select the opening method with the least impact on the fixed membrane to open the fixed membrane.

2. The radiotherapy fixed membrane hole opening method based on finite element analysis as claimed in claim 1, characterized in that: The step S2 comprises the following steps: Step S2-1: reconstruct the CT image of the torso obtained in step S1 using a CT simulation positioning machine, and export the reconstructed data into a DICOM format; Step S2-2: Import the DICOM format data obtained in step S2-1 into the MIM software, select the MIM bed removal tool, open the import sequence, perform bed removal operation, and preprocess the trunk outline; switch the trunk tool, select the sagittal view, and drag the left mouse button from the first layer on the head side to the last layer on the foot side; switch the 2D brush tool, use different brush sizes to correct and adjust the details, switch the smoothing tool, and moderately smooth the trunk outline to ensure that the outline is smooth and accurate, and finally save the outline result; export the trunk in Structure as an STL format file; Step S2-3: Smoothing the torso model in STL format obtained in step S2-2; smoothing iteratively moves each vertex of the mesh to the position of the centroid of its surrounding neighborhood, and the Laplace coordinate is expressed as follows: Where N(i) is the vertex v i The neighboring point set, w ij Represents vertex v i The weight of the jth neighbor of If the weights are all 1, then the formula simplifies to taking the difference between the vertex and the average of its neighbors: where d i is the vertex v i The number of neighbors of the node; This scheme of selecting all neighboring nodes with equal weights is called an umbrella weighted scheme; Another weighted scheme is to use the cotangent weights between the angles in the graph, defined as: Where α ij and β ij For point v i With v j The opposite angle of the composed side in the triangle to which it belongs; Step S2-4: Export the fixed membrane model smoothed in step S2-3 in STL format and input it into the mesh processing software. Through the geometric reverse extraction function, the trunk triangular mesh model in STL format is used as input to reversely extract the trunk surface geometry model.

3. The radiotherapy fixation membrane opening method based on finite element analysis as claimed in claim 1, characterized in that: The step S3-4 comprises the following steps: S3-4-1: Establish an appropriate number of nodes as control points; S3-4-2: Connect nodes by smooth curves; S3-4-3: Stretch the smooth curve along the Z direction to generate the cutting surface; S3-4-4: Cut the complete head, neck and shoulder fixed membrane geometric model through the cutting surface to obtain fixed membrane geometric models with different opening positions and types.

4. The radiotherapy fixed membrane hole opening method based on finite element analysis as claimed in claim 1, characterized in that: The certain part in step S1 includes the head, neck and shoulders.

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