Optimal X-ray imaging angle analysis method for lung cancer radiotherapy image guidance

Abstract

The invention relates to the technical field of medical imaging, and discloses an optimal X-ray imaging angle analysis method for lung cancer radiotherapy image guidance, and the method comprises the steps: generating a plurality of groups of orthogonal X-ray guidance images of different projection angle combinations based on positioning CT images of tissues and organs such as lung tumor and heart of a marked patient; aiming at each group of orthogonal X-ray guide images, respectively calculating two evaluation indexes of a tumor-heart overlap ratio and a tumor boundary pixel ratio; calculating a comprehensive evaluation value based on the weighted sum of the two evaluation indexes, and selecting a projection angle combination corresponding to the X-ray guide image with the minimum comprehensive evaluation value as an optimal imaging angle; and controlling an x-ray imaging system to execute orthogonal X-ray guide image acquisition according to the optimal imaging angle for subsequent lung tumor tracking SBRT. According to the method, the optimal X-ray guide image imaging angle personalized selection suitable for implementation of tumor respiratory movement tracking SBRT can be realized for different lung cancer patients, and the SBRT tracking treatment precision is improved.

Description

Technical Field

[0001] This invention relates to the field of medical imaging technology, and in particular to an optimal X-ray imaging angle analysis method for image guidance in lung cancer radiotherapy. Background Technology

[0002] Stereotactic body radiation therapy (SBRT) is increasingly favored by clinicians due to its high precision, high fractionated dose, high therapeutic gain ratio, and low dose to surrounding normal tissues. The "Chinese Expert Consensus on Stereotactic Radiotherapy for Early-Stage Non-Small Cell Lung Cancer (2019)" states that compared with conventional radiotherapy, SBRT significantly improves local control and survival rates in early-stage non-small cell lung cancer; for inoperable early-stage non-small cell lung cancer, the local control rate exceeds 90%, with treatment efficacy comparable to surgery. However, while SBRT uses higher single-fraction doses to treat tumors, it also carries greater risks than conventional intensity-modulated radiotherapy (IMRT). Numerous studies have shown that lung tumors can shift with respiratory movements, causing CT imaging errors, affecting the accuracy of SBRT dose delivery, and reducing the safety and efficacy of clinical treatment.

[0003] Currently, a combination of surface optical tracking and X-ray stereotactic imaging is commonly used in clinical practice to achieve respiratory motion tracking (SBRT) of lung tumors. However, the techniques currently used in clinical applications typically employ orthogonal X-ray imaging at 45° to the left and right. This method utilizes geometric relationships and coordinate transformations to reconstruct three-dimensional information of the patient's body and surface to identify and track lung tumor regions. This angled imaging is easily affected by overlap with tissues such as the patient's heart, limiting tumor visibility, reducing the accuracy of tumor region identification, and even making it difficult to directly locate and track the tumor for treatment.

[0004] Therefore, there is an urgent need for an optimal X-ray imaging angle analysis method for image guidance in lung cancer radiotherapy, which can enable personalized selection of the best X-ray guided image imaging angle suitable for the implementation of SBRT for different lung cancer patients' tumor respiratory motion tracking, thereby improving the accuracy of SBRT tracking treatment. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides an optimal X-ray imaging angle analysis method for image-guided radiotherapy in lung cancer. This method enables personalized selection of the optimal X-ray guided image imaging angle suitable for tumor respiratory motion tracking SBRT implementation for different lung cancer patients, thereby improving the accuracy of SBRT tracking treatment.

[0006] This invention provides a method for analyzing optimal X-ray imaging angles for image-guided radiotherapy in lung cancer, comprising the following steps: S1. Based on the localized CT images of the patient's lung tumor and heart and other tissues and organs, generate multiple sets of orthogonal X-ray guided images with different projection angle combinations. S2. For each group of orthogonal X-ray guided images, calculate two evaluation indicators: tumor-heart overlap ratio and tumor boundary pixel ratio. S3. Calculate the comprehensive evaluation value based on the weighted sum of the two evaluation indicators, and select the projection angle combination corresponding to the orthogonal X-ray guided image with the smallest comprehensive evaluation value as the optimal imaging angle. S4. The treatment system performs orthogonal X-ray projection according to the optimal imaging angle for subsequent tumor-tracking radiotherapy.

[0007] Furthermore, in S1, based on the labeled localization CT images of the patient's lung tumor and heart and other tissues and organs, multiple sets of orthogonal X-ray guided images with different projection angle combinations are generated, including: S11. Define the projection angle combination, which includes the left orthogonal angle and the right orthogonal angle. Perform S12-S15 on the left orthogonal angle and the right orthogonal angle respectively. S12. Based on any point P in the three-dimensional space of the labeled localization CT image of the patient's lung tumor and heart and other tissues and organs, calculate the vector of the orthogonal X-ray imaging projection direction of any point P under the orthogonal angle. S13. Based on the vector of the orthogonal X-ray imaging projection direction of any point P, calculate the coordinates of the projection point P' of any point P on the orthogonal X-ray imaging plane. S14. Based on the distance from any point P to the projection point P', the intensity of the simulated X-ray source, and the linear attenuation coefficient of each voxel in the localized CT image of the patient's lung tumor and heart and other organs marked with the X-ray, calculate the pixel gray value corresponding to each voxel in the localized CT image of the patient's lung tumor and heart and other organs marked with the X-ray source at the current simulated X-ray source position. S15. Adjust the position of the simulated X-ray source and repeat S14 until the pixel gray values ​​of all voxels in the localized CT image of the patient's lung tumor and heart and other tissues and organs are obtained. Construct an orthogonal X-ray guided image under the projection angle combination based on the pixel gray values ​​of all voxels.

[0008] Furthermore, in S1, the combination of projection angles satisfies that the sum of the left orthogonal angle and the right orthogonal angle is 90°.

[0009] Furthermore, in S14, based on the distance from any point P to the projection point P', the intensity of the simulated X-ray source, and the linear attenuation coefficient of each voxel in the localized CT image of the patient's lung tumor and heart, etc., at the current simulated X-ray source location, the pixel grayscale value corresponding to each voxel in the localized CT image of the patient's lung tumor and heart, etc., is calculated. The calculation formula is as follows: ; Where H represents the pixel grayscale value, I0 represents the intensity of the simulated X-ray source, μ represents the linear attenuation coefficient of each voxel for the ray, and l represents the distance from any point P to the projection point P'.

[0010] Furthermore, in S2, the formula for calculating the tumor-cardiac overlap ratio is as follows: ; Among them, f 1i H represents the tumor-to-heart overlap ratio in the i-th group of orthogonal X-ray guided images, where i represents the i-th group of orthogonal X-ray guided images. i G represents the area of ​​the cardiac region in the i-th group of orthogonal X-ray guided images. i This represents the area of ​​the tumor region in the i-th group of orthogonal X-ray guided images.

[0011] Furthermore, in S2, the formula for calculating the tumor boundary pixel ratio is as follows: ; Among them, f 2i avg(N) represents the pixel ratio of the tumor boundary in the i-th group of orthogonal X-ray guided images. outi ) represents the average grayscale value of all pixels within a preset pixel range outside the tumor region in the i-th group of orthogonal X-ray guided images, avg(N) canceri ) represents the average gray value of all pixels within the tumor region in the i-th group of orthogonal X-ray guided images.

[0012] Furthermore, in S3, the comprehensive evaluation value is calculated based on the weighted sum of the two evaluation indicators, using the following formula: ; Where g represents the comprehensive evaluation value, and w1 and w2 represent the weighting coefficients of the tumor-heart overlap ratio and the tumor boundary pixel ratio, respectively.

[0013] The present invention also provides a treatment system for stereotactic radiotherapy of lung cancer, based on the above-mentioned optimal imaging angle, the system comprising: Treatment bed, orthogonal imaging panel, step angle adjustment device, linked X-ray tube and slide; The step-adjustment device drives the orthogonal imaging plate to tilt at the optimal imaging angle, which in turn moves the X-ray tube along the slide to make the X-rays perpendicularly incident on the orthogonal imaging plate.

[0014] The embodiments of the present invention have the following technical effects: This invention generates multiple sets of orthogonal X-ray guided images with different projection angle combinations based on the patient's localized CT images. Then, for each set of images, two evaluation indicators are calculated: the tumor-to-heart overlap ratio and the tumor boundary pixel ratio. The optimal imaging angle is determined by combining the weighted values ​​of these two indicators, thereby ensuring that the impact on the heart is minimized during treatment and that the tumor boundary is clearly defined, improving treatment precision. By utilizing simulated X-ray source position adjustment and the calculation of the linear attenuation coefficient of each voxel, the pixel grayscale value corresponding to each voxel is accurately predicted, thus constructing high-quality orthogonal X-ray guided images. This invention enables more personalized and targeted radiotherapy, improves the accuracy of tumor localization, and reduces treatment risks. Attached Figure Description

[0015] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0016] Figure 1 This is a flowchart of the optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer provided in an embodiment of the present invention; Figure 2 This is a schematic diagram illustrating the principle of generating orthogonal X-ray guided images provided in an embodiment of the present invention; Figure 3 These are seven sets of orthogonal X-ray guided images with different projection angle combinations provided in the embodiments of the present invention; Figure 4 This is a schematic diagram of the structure of a treatment system for stereotactic radiotherapy of lung cancer provided in an embodiment of the present invention. Attached image description: 1-Treatment bed; 2-Orthogonal imaging plate; 3-Stepping angle adjustment device; 4-Linked X-ray tube; 5-Slide track. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0019] This invention proposes an optimal X-ray imaging angle analysis method for image-guided radiotherapy in lung cancer. Figure 1 This is a flowchart of the optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer provided in this embodiment of the invention. See also... Figure 1 Specifically, it includes: S1. Based on the localized CT images of the patient's lung tumor and heart and other tissues and organs, generate multiple sets of orthogonal X-ray guided images with different projection angle combinations.

[0020] Based on the localized CT images of patients' lung tumors and organs such as the heart, which have been labeled by clinicians, the medical image processing software package ITK (Insight Segmentation and Registration Toolkit) is used to simulate the physical process of X-rays passing through human tissues and generate orthogonal X-ray guided images from multiple angles.

[0021] In some embodiments, Figure 2 This is a schematic diagram illustrating the principle of generating orthogonal X-ray guided images according to an embodiment of the present invention. See also... Figure 2 S1 includes the following sub-steps: S11. Define the projection angle combination, which includes the left orthogonal angle and the right orthogonal angle. Perform S12-S15 on the left orthogonal angle and the right orthogonal angle respectively.

[0022] The projection angle combination satisfies that the sum of the left orthogonal angle and the right orthogonal angle is 90°, and the angle can be set according to the actual situation.

[0023] For example, Table 1 shows the angle selection for orthogonal X-ray imaging in this embodiment. Figure 3 These are seven sets of orthogonal X-ray guided images with different projection angle combinations provided in this embodiment of the invention. The green curve in the image represents the tumor outline. See Table 1 and... Figure 3 .

[0024] Table 1. Angle Selection for Orthogonal X-ray Imaging In this embodiment, a step unit of 10° is chosen. This covers the main angle variation from 0° to 80° while avoiding data redundancy and computational burden caused by overly dense angle settings. 10° is one of the commonly used step units in clinical image acquisition and radiotherapy robotic arms, offering good operational feasibility and engineering adaptability. Compared to 10° or smaller step units, it effectively controls the number of samples and computational resource consumption while ensuring uniform angle coverage. Furthermore, the design from 0° on the left and 80° on the right to 80° on the left and 0° on the right is symmetrically distributed, covering various viewpoints from lateral to anterior, reflecting the diversity and balance of angles in image acquisition and treatment radiation. This symmetry effectively avoids incomplete information or feature extraction bias caused by angle deviation, ensuring the universality and stability of network training and angle optimization results. Since 45° is currently the most effective angle in clinical practice, it is used instead of the orthogonal angle group of 40° and 50°.

[0025] S12. Based on any point P in the three-dimensional space of the labeled localization CT image of the patient's lung tumor and heart and other tissues and organs, calculate the vector of the orthogonal X-ray imaging projection direction of any point P at the orthogonal angle.

[0026] S13. Based on the vector of the orthogonal X-ray imaging projection direction of any point P, calculate the coordinates of the projection point P' of any point P on the orthogonal X-ray imaging plane.

[0027] Suppose that the vector representation of the orthogonal X-ray imaging projection direction of any point P(x,y,z) in three-dimensional space on a patient's chest CT image is v=(cosθsinφ,sinθsinφ,cosφ), where θ is the angle between the projection of the projection direction on the XZ plane and the X-axis (i.e., the set left or right orthogonal angle), and φ is the angle between the projection direction and the Y-axis. Draw a straight line from point P along the projection direction vector v to obtain the coordinates of the orthogonal X-ray imaging plane P': x' = xcosθ + zsinθ; y'=xsinθsinφ+ycosφ-zcosθsinφ; Where (x',y') represents the coordinates of P'.

[0028] S14. Based on the distance from any point P to the projection point P', the intensity of the simulated X-ray source, and the linear attenuation coefficient of each voxel in the localized CT image of the patient's lung tumor and heart, etc., at the current simulated X-ray source position, calculate the pixel gray value corresponding to each voxel in the localized CT image of the patient's lung tumor and heart, etc., at the current simulated X-ray source position.

[0029] By integrating the product of the linear attenuation coefficient μ of all voxels in the patient's lung CT image along each simulated X-ray source and the path length l, the pixel gray value H corresponding to the X-ray intensity on the orthogonal projection image can be obtained.

[0030] Specifically, the formula for calculating pixel grayscale values ​​is as follows: ; Where H represents the pixel grayscale value, I0 represents the intensity of the simulated X-ray source, μ represents the linear attenuation coefficient of each voxel for the ray, and l represents the ray projection path length, that is, the distance from any point P to the projection point P'.

[0031] S15. Adjust the position of the simulated X-ray source and repeat S14 until the pixel gray values ​​of all voxels in the localized CT image of the patient's lung tumor and heart and other tissues and organs are obtained. Construct an orthogonal X-ray guided image under the projection angle combination based on the pixel gray values ​​of all voxels.

[0032] S2. For each group of orthogonal X-ray guided images, calculate two evaluation indicators: tumor-heart overlap ratio and tumor boundary pixel ratio.

[0033] In some embodiments, the heart, as a critical organ, directly impacts the optimization of radiation dose distribution due to its spatial overlap with the tumor region. Higher overlap may increase the risk of cardiac exposure to radiation and even lead to serious complications; therefore, the overlap area between the tumor and the heart should be minimized when selecting the angle. The overlap is calculated as the ratio of the intersection area of ​​the heart and tumor regions to the tumor area. The formula for calculating the tumor-heart overlap ratio is as follows: ; Among them, f 1i H represents the tumor-to-heart overlap ratio in the i-th group of orthogonal X-ray guided images, where i represents the i-th group of orthogonal X-ray guided images. i G represents the area of ​​the cardiac region in the i-th group of orthogonal X-ray guided images. i Let f represent the area of ​​the tumor region in the i-th group of orthogonal X-ray guided images. If f 1i If the result is close to 0, the overlap between the heart and the tumor is low, and this angle is more suitable for radiotherapy; otherwise, this angle is not suitable.

[0034] In some embodiments, the clarity of the tumor region's boundary is a crucial prerequisite for accurate treatment planning. This parameter measures the distinction between the tumor region and the background region; a larger pixel difference indicates a clearer tumor boundary, which is beneficial for precise target localization. If the pixel difference is small, the boundary may be blurred, thus reducing the accuracy of the treatment plan. Therefore, a projection angle with high discrimination should be preferred. The formula for calculating the tumor boundary pixel ratio is as follows: ; Among them, f 2i avg(N) represents the pixel ratio of the tumor boundary in the i-th group of orthogonal X-ray guided images. outi ) represents the average grayscale value of all pixels within a preset pixel range outside the tumor region in the i-th group of orthogonal X-ray guided images. For example, the preset pixel range can be a preset range of 5 pixels. avg(N) canceri Let f represent the average grayscale value of all pixels within the tumor region in the i-th group of orthogonal X-ray guided images. If f 2i If the result is close to 0, the difference between the inner and outer pixels is large, which facilitates observation during subsequent treatment; if f 2i If the value is close to 1, the pixel difference is small and the boundary is not obvious enough. This angle should be avoided for treatment.

[0035] S3. Calculate the comprehensive evaluation value based on the weighted sum of the two evaluation indicators, and select the projection angle combination corresponding to the orthogonal X-ray guided image with the smallest comprehensive evaluation value as the optimal imaging angle.

[0036] In some embodiments, the formula for calculating the comprehensive evaluation value is as follows: ; Where g represents the comprehensive evaluation value, and w1 and w2 represent the weighting coefficients of the tumor-heart overlap ratio and the tumor boundary pixel ratio, respectively. For example, in this embodiment, w1=0.55 and w2=0.45.

[0037] S4. The treatment system performs orthogonal X-ray projection according to the optimal imaging angle for subsequent tumor-tracking radiotherapy.

[0038] This invention generates multiple sets of orthogonal X-ray guided images with different projection angle combinations based on the patient's localized CT images. Then, for each set of images, two evaluation indicators are calculated: the tumor-to-heart overlap ratio and the tumor boundary pixel ratio. The optimal imaging angle is determined by combining the weighted values ​​of these two indicators, thereby ensuring that the impact on the heart is minimized during treatment and that the tumor boundary is clearly defined, improving treatment precision. By utilizing simulated X-ray source position adjustment and the calculation of the linear attenuation coefficient of each voxel, the pixel grayscale value corresponding to each voxel is accurately predicted, thus constructing high-quality orthogonal X-ray guided images. This invention enables more personalized and targeted radiotherapy, improves the accuracy of tumor localization, and reduces treatment risks.

[0039] This invention also provides a treatment system for stereotactic radiotherapy of lung cancer, which is based on the optimal imaging angle obtained in the above embodiments. Figure 4 This is a schematic diagram of the structure of a stereotactic radiotherapy system for lung cancer provided in an embodiment of the present invention. See also... Figure 4 The system includes: Treatment bed 1, orthogonal imaging plate 2 (including left orthogonal imaging plate 2(a) and right orthogonal imaging plate 2(b)), step-type angle adjustment device 3 (including left step-type angle adjustment device 3(a) and right step-type angle adjustment device 3(b)), linkage X-ray tube 4 (including left linkage X-ray tube 4(a) and right linkage X-ray tube 4(b)) and slide rail 5; The slide 5 is fixed to the roof of the treatment room, and the stepping angle adjustment device 3 and the slide 5 are linked motion devices; The stepping angle adjustment device 3 is based on the axial motor driving the orthogonal imaging plate 2 to tilt at the optimal imaging angle, and the X-ray tube 4 moves along the slide 5 to make the X-rays perpendicularly incident on the orthogonal imaging plate 2.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for analyzing optimal X-ray imaging angles for image-guided radiotherapy in lung cancer, characterized in that, Includes the following steps: S1. Based on the localized CT images of the patient's lung tumor and heart and other tissues and organs, generate multiple sets of orthogonal X-ray guided images with different projection angle combinations. S2. For each group of orthogonal X-ray guided images, calculate two evaluation indicators: tumor-heart overlap ratio and tumor boundary pixel ratio. S3. Calculate the comprehensive evaluation value based on the weighted sum of the two evaluation indicators, and select the projection angle combination corresponding to the orthogonal X-ray guided image with the smallest comprehensive evaluation value as the optimal imaging angle. S4. Control the X-ray imaging system to perform orthogonal X-ray guided image acquisition according to the optimal imaging angle, for subsequent lung tumor tracking and stereotactic radiotherapy.

2. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 1, characterized in that, In step S1, based on the localized CT images of the patient's lung tumor and heart and other tissues and organs, multiple sets of orthogonal X-ray guided images with different projection angle combinations are generated, including: S11. Define a projection angle combination, which includes a left orthogonal angle and a right orthogonal angle. Perform S12-S15 on the left orthogonal angle and the right orthogonal angle respectively. S12. Based on any point P in the three-dimensional space of the labeled localization CT image of the patient's lung tumor and heart and other tissues and organs, calculate the vector of the orthogonal X-ray imaging projection direction of the arbitrary point P under the orthogonal angle. S13. Calculate the coordinates of the projection point P' of the arbitrary point P on the orthogonal X-ray imaging plane based on the vector of the orthogonal X-ray imaging projection direction of the arbitrary point P. S14. Based on the distance from the arbitrary point P to the projection point P', the intensity of the simulated X-ray source, and the linear attenuation coefficient of each voxel in the localized CT image of the labeled patient's lung tumor and heart and other organs, calculate the pixel gray value corresponding to each voxel in the localized CT image of the labeled patient's lung tumor and heart and other organs at the current simulated X-ray source position. S15. Adjust the position of the simulated X-ray source and repeat S14 until the pixel gray values ​​corresponding to all voxels in the localized CT image of the patient's lung tumor and heart and other tissues and organs are obtained. Construct the orthogonal X-ray guided image under the projection angle combination based on the pixel gray values ​​corresponding to all voxels.

3. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 2, characterized in that, In S1, the combination of projection angles satisfies that the sum of the left orthogonal angle and the right orthogonal angle is 90°.

4. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 2, characterized in that, In step S14, based on the distance from the arbitrary point P to the projection point P', the intensity of the simulated X-ray source, and the linear attenuation coefficient of each voxel in the localized CT image of the labeled lung tumor and heart, the pixel grayscale value corresponding to each voxel in the localized CT image of the labeled lung tumor and heart is calculated at the current simulated X-ray source position. The calculation formula is as follows: ； Where H represents the pixel grayscale value, I0 represents the intensity of the simulated X-ray source, μ represents the linear attenuation coefficient of each voxel for the ray, and l represents the distance from any point P to the projection point P'.

5. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 1, characterized in that, In S2, the formula for calculating the tumor-heart overlap ratio is as follows: ； Among them, f 1i H represents the tumor-to-heart overlap ratio in the i-th group of orthogonal X-ray guided images, where i represents the i-th group of orthogonal X-ray guided images. i G represents the area of ​​the cardiac region in the i-th group of orthogonal X-ray guided images. i This represents the area of ​​the tumor region in the i-th group of orthogonal X-ray guided images.

6. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 5, characterized in that, In step S2, the formula for calculating the tumor boundary pixel ratio is as follows: ； Among them, f 2i avg(N) represents the pixel ratio of the tumor boundary in the i-th group of orthogonal X-ray guided images. outi ) represents the average grayscale value of all pixels within a preset pixel range outside the tumor region in the i-th group of orthogonal X-ray guided images, avg(N) canceri ) represents the average gray value of all pixels within the tumor region in the i-th group of orthogonal X-ray guided images.

7. The optimal X-ray imaging angle analysis method for image-guided radiotherapy of lung cancer according to claim 6, characterized in that, In S3, the comprehensive evaluation value is calculated based on the weighted sum of the two evaluation indicators, using the following formula: ； Where g represents the comprehensive evaluation value, and w1 and w2 represent the weighting coefficients of the tumor-heart overlap ratio and the tumor boundary pixel ratio, respectively.

Images