A method and system for forming optimization of a flexible radiotherapy tissue compensator

Abstract

This invention relates to the field of tissue compensator forming technology, and discloses a method and system for optimizing the forming of flexible radiotherapy tissue compensators. The method includes: acquiring a three-dimensional model, designing thickness and material parameters at each location, and generating candidate printing postures; extracting and analyzing the overhang angle, free span, local wall thickness, radius of curvature, and boundary distance of the analysis unit, calculating the allowable forming deformation, maximum droop displacement, and cumulative deviation value, and determining the target printing posture; performing edge smoothing, thickness correction, printing parameter adjustment, and generating a water-soluble PVA support path, and generating slice path data to control printing. This invention, through quantitative optimization of printing posture and multi-dimensional hierarchical correction, can reduce the printing thickness deviation of flexible TPU compensators from >0.3mm to <0.1mm using traditional methods, with a surface roughness Ra <6.3μm, meeting the accuracy requirements for clinical dose distribution in radiotherapy.

Description

Technical Field

[0001] This invention relates to the field of tissue compensator forming technology, and more specifically, to a method and system for optimizing the forming of flexible radiotherapy tissue compensators. Background Technology

[0002] In radiotherapy for malignant tumors, when the target area is close to the body surface and the patient's body contour is irregular, tissue compensators are usually required in the irradiation area to improve dose distribution in superficial regions. Currently, most commonly used tissue compensators in clinical practice are generic structures, often requiring manual cutting. For areas with significant surface undulations or unique shapes, such as the head, neck, maxillofacial region, breast, vulva, and penis / scrotum, traditional compensators often fail to adhere adequately to the skin surface, easily creating air gaps and affecting the compensation effect. Constructing individualized 3D models based on CT images and fabricating tissue compensators using 3D printing has become a promising direction for improving the fit of tissue compensators.

[0003] Existing research and practice have shown that using flexible thermoplastic materials to prepare radiotherapy tissue compensators can, to some extent, improve the problems of traditional silicone compensators, such as excessive softness, easy collapse, and difficulty in preservation. Furthermore, it allows for personalized molding by combining medical image processing and 3D modeling techniques. The relevant technical approach typically includes: processing CT images to create a 3D model of the compensator, and then using fused deposition modeling equipment for printing.

[0004] However, when applying flexible thermoplastic materials to the printing of radiotherapy tissue compensators, especially when the compensators have structural features such as large curved surfaces, local thin walls, and overhanging edges, existing forming processes still have significant shortcomings. The report shows that scaled-down models experience deformation during printing due to their small wall thickness and complex curved surfaces, leading to localized inability to bear their own weight. Furthermore, the printed products suffer from poor surface smoothness, irregular edges, interlayer separation, and difficulty in removing supports. While these issues can be improved through secondary model correction, surface smoothing, increasing wall thickness, adjusting the printing direction, and adding segmented supports during flat printing, current technology still lacks a systematic and optimized forming method for flexible radiotherapy tissue compensators.

[0005] The thickness deviation of existing flexible compensators is generally >0.3mm, which cannot meet the accuracy requirement of ±0.1mm in clinical radiotherapy. This will lead to a superficial dose deviation of >10%, affecting the treatment effect. Summary of the Invention

[0006] In view of this, the present invention proposes a forming optimization method and system for flexible radiotherapy tissue compensators, aiming to solve the problems of insufficient forming accuracy and stability of existing flexible radiotherapy tissue compensators in the 3D printing process, which are prone to local sagging deformation, irregular edge forming and poor support adaptability due to the geometric features of the compensator such as curved surface, thin wall and overhang.

[0007] In one aspect, the present invention proposes a method for optimizing the shaping of flexible radiotherapy tissue compensators, comprising: The three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material are obtained, and several candidate printing postures are generated based on the three-dimensional model. Under each candidate printing posture, the 3D model is discretized into several analysis units. The overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit are calculated. The shortest distance from the corresponding analysis unit to the boundary of the 3D model is determined as the boundary distance. The allowable forming deformation of each analysis unit is determined according to the design thickness and allowable thickness deviation of each analysis unit. Based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, the maximum droop displacement of each analysis unit under each candidate printing posture is calculated, and the cumulative deviation value corresponding to each candidate printing posture is determined according to the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation. The candidate printing posture with the smallest cumulative deviation value is determined as the target printing posture. Under the target printing posture, the analysis unit to be corrected is determined based on the maximum droop displacement and the allowable forming deformation. For the analysis unit to be corrected whose boundary distance is less than the local wall thickness, the edge smoothing amount and thickness correction amount are determined, and the maximum droop displacement is recalculated based on the local wall thickness after thickness correction. The layer height, trace width and printing speed are determined based on the difference between the final maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected. For the analysis unit to be corrected where the final maximum sag displacement is still greater than the allowable forming deformation, a water-soluble PVA support path is generated. Based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, the slicing path data is generated, and the 3D printing equipment is controlled to print according to the slicing path data.

[0008] Furthermore, when generating several candidate printing poses based on the 3D model, including: Extract the outer contour range of the 3D model and establish a bounding box; take the normal direction of each outer surface of the bounding box as the forming direction and construct the initial printing posture corresponding to each normal direction; take the forming direction in each initial printing posture as the axis and rotate the 3D model circumferentially at a preset angle interval of 15°-45°; preferably 30°, to obtain multiple candidate printing postures.

[0009] Furthermore, when determining the allowable forming deformation amount for each analysis unit based on its design thickness and allowable thickness deviation, the following steps are included: Map the design thickness of each position of the three-dimensional model to the corresponding analysis unit; read the thickness allowable deviation of the corresponding analysis unit; subtract the thickness allowable deviation from the design thickness to obtain the minimum allowable thickness of the corresponding analysis unit; convert the thickness difference between the design thickness and the minimum allowable thickness into the allowable displacement of the corresponding analysis unit in the surface normal direction; calculate the angle θ between the surface normal direction and the forming direction, and multiply the allowable displacement by COSθ to obtain the allowable forming deformation of the corresponding analysis unit in the forming direction.

[0010] Furthermore, when calculating the maximum droop displacement of each analysis unit under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus, and density, the following are included: Extract the path segments to be deposited corresponding to each analysis unit under the corresponding candidate printing posture; equate the path segments to be deposited to a viscoelastic beam segment under gravity; under the conditions of printing speed ≤50mm / s and layer thickness ≤0.2mm, the elastic beam model can be used for approximate calculation with an error ≤10%; take the free span as the effective span of the elastic beam segment, correct the cross-sectional parameters of the elastic beam segment with local wall thickness and radius of curvature, determine the component of gravity in the downward direction with the overhang angle, and determine the self-weight load per unit length based on density; then correct the boundary constraint degree of the elastic beam segment based on the boundary distance, obtain the displacement values ​​of the midpoint and end positions of the elastic beam segment, and determine the maximum value as the maximum downward displacement of the corresponding analysis unit.

[0011] Furthermore, when determining the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement and allowable forming deformation of each analysis unit under each candidate printing posture, the following is included: The maximum droop displacement of each analysis unit under the same candidate printing posture is compared with the corresponding allowable forming deformation. The analysis unit with the maximum droop displacement less than or equal to the allowable forming deformation is recorded as zero deviation. For the analysis unit with the maximum droop displacement greater than the allowable forming deformation, the difference between the maximum droop displacement and the allowable forming deformation is recorded as the unit deviation. The unit deviations of all analysis units under the same candidate printing posture are accumulated to obtain the cumulative deviation value of the corresponding candidate printing posture.

[0012] Furthermore, under the target printing posture, when determining the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation, and when determining the layer height, trace width, and printing speed based on the difference between the maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected, the following steps are included: Analytical units with maximum sag displacement greater than the allowable forming deformation are selected as the units to be corrected; the differences between each unit to be corrected are statistically analyzed and normalized to obtain the correction level of each unit; the layer height, the trace width, and the printing speed are reduced step by step according to the correction level to obtain the printing parameter combination corresponding to each unit to be corrected.

[0013] Furthermore, when determining the edge smoothing amount and thickness correction amount for the analysis unit to be corrected where the boundary distance is less than the local wall thickness, and recalculating the maximum sagging displacement based on the local wall thickness after thickness correction, the following steps are taken: Extract edge analysis units whose boundary distance is less than the local wall thickness from the analysis units to be corrected; extract edge polylines along the contour boundary of the region where the edge analysis units are located; perform a smooth transition process on the edge polylines according to the ratio of boundary distance to local wall thickness to obtain the smoothed contour; then offset the smoothed contour outward along the surface normal of the corresponding region to obtain the thickness-corrected local contour; update the local wall thickness with the corrected local contour, and re-execute the calculation process of the maximum droop displacement.

[0014] Furthermore, when generating water-soluble PVA support paths for the analysis unit to be corrected, where the final maximum sag displacement still exceeds the allowable forming deformation, the following steps are taken: Extract the analysis units that still exceed the allowable forming deformation requirement and require correction; merge the spatially adjacent analysis units with the same downward direction into a support requirement area; project each support requirement area onto the printing platform or the lower printed area along the forming direction opposite to the target printing posture, and determine the intersection of the projection with the printing platform or the lower printed area as the support start point, and the bottom of the support requirement area as the support end point; then insert a connection trajectory between the support start point and the support end point according to the preset path spacing to obtain the corresponding water-soluble PVA support path; leave a 0.1mm separation gap between the water-soluble PVA support path and the compensator body.

[0015] Furthermore, based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, slice path data is generated. When controlling the 3D printing equipment to print according to the slice path data, this includes: First, the 3D model after thickness correction and edge smoothing, as well as the water-soluble PVA support path, are layered according to the target printing posture. The outer contour path and the internal filling path are extracted in each layer. The spacing between adjacent paths is determined according to the trace width, the layer height between layers is determined according to the layer height, and the corresponding motion commands are written into each layer path according to the printing speed. The paths of each layer are spliced ​​together in the printing order to generate slice path data. Then, the 3D printing equipment is controlled to complete the printing layer by layer according to the slice path data.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: By first generating several candidate printing postures, and extracting geometric features such as overhang angle, free span, local wall thickness, radius of curvature, and boundary distance of the analysis unit under each candidate printing posture, and combining the elastic modulus and density of the flexible thermoplastic printing material to calculate the maximum droop displacement of each analysis unit, and then determining the cumulative deviation value and selecting the target printing posture based on the relationship between the maximum droop displacement and the allowable forming deformation, the forming risk under different printing postures can be quantitatively compared before printing, thereby improving the targeting of the target printing posture selection; and after determining the target printing posture, the analysis unit to be corrected is subjected to edge smoothing, thickness correction, printing parameter adjustment, and necessary water-soluble PVA support path generation, so that the forming process of the flexible radiotherapy tissue compensator in curved, thin-walled, and edge regions is specifically optimized, which helps to reduce local droop deformation and edge forming irregularity problems, and improves the forming accuracy, edge integrity, and overall forming stability of the compensator.

[0017] On the other hand, this application also provides a shaping optimization system for flexible radiotherapy tissue compensators, used to implement the above-mentioned shaping optimization method for flexible radiotherapy tissue compensators, including: The candidate printing posture generation module is configured to acquire the three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material, and generate several candidate printing postures based on the three-dimensional model. The feature extraction module of the analysis unit is configured to discretize the three-dimensional model into several analysis units under each candidate printing posture, calculate the overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit, determine the shortest distance from the corresponding analysis unit to the boundary of the three-dimensional model as the boundary distance, and determine the allowable forming deformation of each analysis unit according to the design thickness and allowable thickness deviation of each analysis unit. The target printing posture determination module is configured to calculate the maximum droop displacement of each analysis unit under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, and determine the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation amount, and determine the candidate printing posture with the smallest cumulative deviation value as the target printing posture. The printing parameter determination module is configured to determine the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation under the target printing posture; determine the edge smoothing amount and thickness correction amount for the analysis unit to be corrected whose boundary distance is less than the local wall thickness, and recalculate the maximum droop displacement based on the local wall thickness after thickness correction; and determine the layer height, trace width and printing speed based on the difference between the final maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected. The water-soluble PVA support path generation module is configured to generate water-soluble PVA support paths for the analysis unit to be corrected, where the final maximum sag displacement is still greater than the allowable forming deformation. The printing control module is configured to generate slice path data based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, and control the 3D printing equipment to print according to the slice path data.

[0018] It is understandable that the above-mentioned system and method for optimizing the shaping of flexible radiotherapy tissue compensators have the same beneficial effects, and will not be elaborated further here. Attached Figure Description

[0019] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 A flowchart illustrating a method for optimizing the forming of a flexible radiotherapy tissue compensator, as provided in an embodiment of the present invention; Figure 2 This is a functional block diagram of a forming optimization system for flexible radiotherapy tissue compensators provided in an embodiment of the present invention. Detailed Implementation

[0020] Exemplary embodiments of the present invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the disclosure to those skilled in the art. It should be noted that, unless otherwise specified, embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] See Figure 1 As shown, this application proposes a method for optimizing the shaping of flexible radiotherapy tissue compensators, comprising: S1: Obtain the three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material, and generate several candidate printing postures based on the three-dimensional model; S2: Under each candidate printing posture, the 3D model is discretized into several analysis units. The overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit are calculated. The shortest distance from the corresponding analysis unit to the boundary of the 3D model is determined as the boundary distance. The allowable forming deformation of each analysis unit is determined according to the design thickness and allowable thickness deviation of each analysis unit. S3: Based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, calculate the maximum droop displacement of each analysis unit under each candidate printing posture, and determine the cumulative deviation value corresponding to each candidate printing posture according to the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation. The candidate printing posture with the smallest cumulative deviation value is determined as the target printing posture. S4: Under the target printing posture, determine the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation; determine the edge smoothing amount and thickness correction amount for the analysis unit to be corrected whose boundary distance is less than the local wall thickness, and recalculate the maximum droop displacement based on the local wall thickness after thickness correction; determine the layer height, trace width and printing speed based on the difference between the final maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected. S5: Generate water-soluble PVA support paths for the analysis units to be corrected, where the final maximum sag displacement is still greater than the allowable forming deformation. S6: Generate slice path data based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, and control the 3D printing equipment to print according to the slice path data.

[0022] Specifically, patient CT images are imported into Mimics software for threshold segmentation and contour extraction. A 3D model of the flexible radiotherapy tissue compensator is then created using NX software. The design thickness for each location on the model is extracted; for example, the design thickness for chest compensators is typically between 2mm and 8mm. For the flexible thermoplastic printing material, 95A hardness TPU filament is preferred, with an elastic modulus of approximately 200MPa and a density of approximately 1.2g / cm³. These parameters can be obtained through material tensile testing. When generating candidate printing postures based on the 3D model, the outer contour of the model is first extracted to establish an axially aligned bounding box. The normal directions of the six outer surfaces of the bounding box are used as initial forming directions to obtain six initial printing postures. Then, the model is rotated circumferentially at preset 30° intervals around the forming direction of each initial printing posture, ultimately generating 72 candidate printing postures. For each candidate printing posture, the 3D model is discretized into cubic analysis elements with a side length of 0.5 mm. The overhang angle, free span, local wall thickness, radius of curvature, and boundary distance of each element are calculated. The overhang angle is the angle between the surface normal of the analysis element and the forming direction; the free span is the maximum horizontal distance of the analysis element without any printed support below; the local wall thickness is the thickness of the analysis element in the forming direction; the radius of curvature is the minimum principal radius of curvature of the surface containing the analysis element; and the boundary distance is the shortest Euclidean distance from the center of the analysis element to the outer boundary of the 3D model. Based on clinical requirements for radiotherapy, the allowable thickness deviation for each analysis element is determined to be ±0.1 mm, thus the allowable forming deformation of each element is calculated to be 0.1 mm. Based on the elastic beam theory of mechanics of materials, the deposition path corresponding to each analysis unit is equivalent to a cantilever beam or simply supported beam under gravity. The free span is taken as the effective span of the beam. The moment of inertia of the beam section is corrected by the local wall thickness and radius of curvature. The component of gravity acting in the direction perpendicular to the beam axis is calculated by the sag angle. The self-weight load per unit length of the beam is calculated by the density. The boundary constraint stiffness of the beam is corrected by the boundary distance. The smaller the boundary distance, the lower the constraint stiffness. Finally, the maximum displacement value of the beam midpoint and end is obtained as the maximum sag displacement of the analysis unit. When calculating the cumulative deviation value of each candidate printing posture, the analysis unit with a maximum sag displacement less than or equal to 0.1 mm is recorded as zero deviation. The deviation value of the analysis unit with a maximum sag displacement greater than 0.1 mm is recorded as the difference between its maximum sag displacement and 0.1 mm. The deviation values ​​of all analysis units under this posture are accumulated to obtain the cumulative deviation value. The posture with the smallest cumulative deviation value is selected as the target printing posture.Under the target printing posture, all analysis cells with a maximum droop displacement greater than 0.1 mm are selected as analysis cells to be corrected. First, edge analysis cells with boundary distances less than their own local wall thickness are corrected. The edge smoothing amount and thickness correction amount are determined based on their deviation values. Edge smoothing uses cubic spline curves to smoothly transition the edge polygonal lines, with a smoothing radius ranging from 0.2 mm to 0.5 mm. The thickness correction amount is equal to the deviation value of the cell, and the maximum droop displacement is recalculated using the corrected local wall thickness. Then, based on the difference between the final maximum droop displacement of all analysis cells to be corrected and 0.1 mm, they are divided into three correction levels. Printing parameters are adjusted progressively according to the correction level. For example, level one correction corresponds to a layer height of 0.2 mm, a trace width of 0.35 mm, and a printing speed of 45 mm / s; level two correction corresponds to a layer height of 0.18 mm, a trace width of 0.32 mm, and a printing speed of 35 mm / s; and level three correction corresponds to a layer height of 0.15 mm, a trace width of 0.3 mm, and a printing speed of 25 mm / s. Finally, for the analysis units that still have a maximum droop displacement greater than 0.1 mm after thickness correction and parameter adjustment, adjacent units with a droop angle of less than 15° are merged into a support requirement area. This area is then projected onto the printing platform or the lower printed area in the opposite direction of forming. The intersection of the projections is taken as the support start point, and the bottom of the support requirement area is taken as the support end point. A linear water-soluble PVA support path is generated with a preset path spacing of 1 mm. The 3D model after thickness correction and edge smoothing is merged with the water-soluble PVA support path and imported into slicing software for layer-by-layer slicing according to the target printing posture. Combined with the layer height, trace width, and printing speed determined for each region, G-code format slicing path data is generated and sent to the fused filament manufacturing 3D printing equipment. The equipment is then controlled to complete the printing and preparation of the flexible radiotherapy tissue compensator layer by layer.

[0023] In some embodiments of this application, when generating several candidate printing poses based on a 3D model, the process includes: Extract the outer contour range of the 3D model and establish a bounding box; take the normal direction of each outer surface of the bounding box as the forming direction and construct the initial printing posture corresponding to each normal direction; take the forming direction in each initial printing posture as the axis and rotate the 3D model circumferentially at preset angle intervals of 15°-45°; preferably 30° to obtain multiple candidate printing postures.

[0024] Specifically, the extreme values ​​of the coordinates of all vertices of the 3D model along the X, Y, and Z axes are extracted, and an axially aligned bounding box that can completely enclose the 3D model is constructed based on these extreme values. Each side of the axially aligned bounding box is parallel to the X, Y, and Z axes of the 3D coordinate system, respectively. Compared to other bounding methods, the axially aligned bounding box has the advantages of fast computation speed and well-defined boundaries, facilitating the rapid determination of the overall spatial extent of the 3D model. The normal directions of the six outer surfaces of the bounding box are used as initial forming directions, corresponding to six initial printing postures. These six initial printing postures correspond to the six basic printing directions in 3D space: up, down, left, right, front, and back, thus providing initial coverage of commonly used printing directions. Based on this, the 3D model is rotated circumferentially around the forming direction in each initial printing posture at preset angular intervals to obtain multiple candidate printing postures. The preset angle interval is used to balance the comprehensiveness of posture coverage with computational load. For models with complex curved surface structures, such as flexible radiotherapy tissue compensators, the preset angle interval can be set to 15°-45°, preferably 30°. When the preset angle interval is 30°, each initial printing posture corresponds to 12 rotational postures, and combined with six initial printing postures, 72 candidate printing postures can be obtained. For models with relatively simple structures, the preset angle interval can be 45° to reduce computational load. For models with large surface variations and complex local structures, the preset angle interval can be 15° to increase the coverage density of candidate printing postures. In this way, the coverage of the candidate printing posture set for different printing directions can be improved, providing a basis for subsequent selection of the target printing posture with the smallest cumulative deviation value.

[0025] In some embodiments of this application, when determining the allowable forming deformation amount corresponding to each analysis unit based on the design thickness and allowable thickness deviation of each analysis unit, the following steps are included: Map the design thickness of each position in the 3D model to the corresponding analysis unit; read the thickness allowable deviation of the corresponding analysis unit; subtract the thickness allowable deviation from the design thickness to obtain the minimum allowable thickness of the corresponding analysis unit; convert the thickness difference between the design thickness and the minimum allowable thickness into the allowable displacement of the corresponding analysis unit in the surface normal direction; calculate the angle θ between the surface normal direction and the forming direction, and multiply the allowable displacement by COSθ to obtain the allowable forming deformation of the corresponding analysis unit in the forming direction.

[0026] Specifically, the design thickness corresponding to each location in the continuous 3D model is mapped to discrete analysis units. During mapping, the design thickness of the model corresponding to the geometric center of each analysis unit can be selected as the design thickness of that analysis unit, thus giving each analysis unit a corresponding thickness reference value. Then, the allowable thickness deviation of the corresponding analysis unit is read. The allowable thickness deviation can be pre-defined according to the requirements of compensation accuracy in radiotherapy clinical practice, preferably set in combination with the dose sensitivity and fit accuracy requirements of different anatomical sites. For example, the allowable thickness deviation for conventional sites can be 0.1 mm, for sites with high fit accuracy requirements such as the head and neck, it can be 0.08 mm, and for sites with relatively low fit accuracy requirements such as the limbs, it can be 0.12 mm. The design thickness of each analysis unit is subtracted from the corresponding allowable thickness deviation value to obtain the minimum allowable thickness of the corresponding analysis unit. The thickness difference between the design thickness and the minimum allowable thickness is then determined as the allowable displacement of the analysis unit along the body surface normal direction. Here, the body surface normal direction can be understood as the direction of local thickness change of the compensator relative to the patient's body surface at the corresponding analysis unit location. Since the actual sagging deformation during the printing process mainly occurs along the forming direction, and the surface normal direction and the forming direction are usually not completely coincident, it is also necessary to calculate the angle θ between the surface normal direction and the forming direction. When θ > 60°, the forming risk in this area increases significantly under this printing posture, and this candidate posture should be excluded first. The allowable displacement along the surface normal direction is projected onto the forming direction to obtain the allowable forming deformation of the analysis unit along the forming direction. Taking a certain analysis unit of the chest compensator as an example, when its design thickness is 5mm and the allowable thickness deviation is 0.1mm, the minimum allowable thickness is 4.9mm, and the thickness difference between the design thickness and the minimum allowable thickness is 0.1mm. This 0.1mm represents the maximum allowable displacement along the surface normal direction. If the angle between the surface normal direction and the forming direction of the analysis unit is 60°, the allowable forming deformation along the forming direction is 0.05mm. By converting the allowable thickness deviation from the surface normal direction to the forming direction, the comparison between the subsequent maximum sag displacement and the allowable forming deformation can be established on the same direction, thereby improving the accuracy of forming risk assessment.

[0027] In some embodiments of this application, when calculating the maximum droop displacement of each analysis unit under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus, and density, the calculation includes: Extract the path segments to be deposited corresponding to each analysis unit under the corresponding candidate printing posture; equate the path segments to be deposited to viscoelastic beam segments under gravity; under the conditions of printing speed ≤50mm / s and layer thickness ≤0.2mm, the elastic beam model can be used for approximate calculation with an error ≤10%; take the free span as the effective span of the elastic beam segment, correct the cross-sectional parameters of the elastic beam segment with local wall thickness and radius of curvature, determine the component of gravity in the downward direction with the overhang angle, and determine the self-weight load per unit length based on density; then correct the boundary constraint degree of the elastic beam segment based on the boundary distance, obtain the displacement values ​​of the midpoint and end positions of the elastic beam segment, and determine the maximum value as the maximum downward displacement of the corresponding analysis unit.

[0028] Specifically, under the corresponding candidate printing posture, the 3D model is segmented layer by layer along the forming direction, and the path segment to be deposited corresponding to each analysis unit is extracted within each printing layer. The path segment to be deposited refers to the continuous thermoplastic material path that will be extruded from the nozzle and deposited into the current layer within the corresponding analysis unit. Since the flexible thermoplastic material is in a transitional state with a certain degree of fluidity and recoverability after extrusion and before complete curing, the path segment to be deposited can be equivalent to a viscoelastic beam segment under gravity. Under the conditions that the printing speed is not greater than 50 mm / s and the layer thickness is not greater than 0.2 mm, the cooling and curing time after material extrusion is relatively short, and the influence of viscous flow on the overall sagging deformation is relatively weakened. At this time, an elastic beam model can be used to approximate the calculation of the viscoelastic beam segment, and the calculation error can be controlled within 10%. The free span is used as the effective span of the elastic beam segment. The effective span can be understood as the distance between the effective support positions at both ends of the path segment to be deposited when there is no lower support within the current layer. The local wall thickness and radius of curvature are used together to correct the cross-sectional parameters of the elastic beam segment. The main cross-sectional parameter is the moment of inertia of the cross-section. The basic moment of inertia of the rectangular cross-section can be calculated first based on the local wall thickness and the width of the trace, and then corrected by the radius of curvature. The overhang angle is used to characterize the degree of inclination of the path segment to be deposited relative to the forming direction, and the component of gravity in the downward direction is determined accordingly. At the same time, the self-weight load per unit length is determined based on the material density and the volume of the path segment. For the boundary region, since it is close to the outer contour of the model and the surrounding geometric constraints are relatively weak, it is also necessary to correct the degree of boundary constraint of the elastic beam segment in combination with the boundary distance. The correction factors were determined through finite element simulation and experimental calibration: Curvature radius correction factor = 1 + 0.2 × (20 / curvature radius) (curvature radius ≤ 20 mm), 1.0 for curvature radius > 20 mm; Boundary constraint stiffness factor = 0.2 + 0.6 × (boundary distance / (2 × local wall thickness)) (boundary distance ≤ 2 × local wall thickness), 0.8 for boundary distance > 2 × local wall thickness. Verification through 20 sets of standard specimen experiments showed that this correction factor can reduce the sag displacement calculation error to ≤ 8%. After determining the effective span, cross-sectional parameters, gravitational component, self-weight load per unit length, and boundary constraint correction coefficients, the appropriate beam model can be selected for displacement calculation based on the support status at both ends of the path segment to be deposited. When both ends of the path segment have effective support, a simply supported beam model can be used to calculate the displacement value at its midpoint. When only one end of the path segment is supported and the other end is suspended, a cantilever beam model can be used to calculate the displacement value at the free end. The larger of the obtained midpoint displacement value and end displacement value is determined as the maximum sagging displacement of the analysis unit under the current candidate printing posture. In this way, the sagging risk of flexible radiotherapy tissue compensators under different printing postures and different local geometric conditions can be uniformly quantified, providing a basis for subsequent cumulative deviation calculation and target printing posture selection.

[0029] In some embodiments of this application, when determining the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement and allowable forming deformation of each analysis unit under each candidate printing posture, the following steps are included: The maximum droop displacement of each analysis unit under the same candidate printing posture is compared with the corresponding allowable forming deformation. The analysis unit with the maximum droop displacement less than or equal to the allowable forming deformation is recorded as zero deviation. For the analysis unit with the maximum droop displacement greater than the allowable forming deformation, the difference between the maximum droop displacement and the allowable forming deformation is recorded as the unit deviation. The unit deviations of all analysis units under the same candidate printing posture are accumulated to obtain the cumulative deviation value of the corresponding candidate printing posture.

[0030] Specifically, the maximum droop displacement of all discrete analysis units under the same candidate printing posture is compared one by one with the allowable forming deformation amount corresponding to that analysis unit. The allowable forming deformation amount of different analysis units can be set individually according to the clinical accuracy requirements of their respective locations. Analysis units with a maximum droop displacement less than or equal to the allowable forming deformation amount are recorded as having zero deviation. Zero deviation indicates that the deformation amount of the analysis unit after printing under the current printing posture fully meets the thickness accuracy requirements of radiotherapy clinical practice, and no additional forming correction is required. For analysis units with a maximum droop displacement greater than the allowable forming deformation amount, the difference between the maximum droop displacement and the corresponding allowable forming deformation amount is recorded as the unit deviation of the analysis unit. The unit deviation directly reflects the degree of deformation deviation of the analysis unit. The larger the value, the more serious the deformation problem and the greater the impact on the accuracy of the compensator dose distribution. For example, if the allowable forming deformation amount of a head and neck compensator analysis unit is 0.08 mm and the calculated maximum droop displacement is 0.12 mm, then the unit deviation of the analysis unit is 0.04 mm. Finally, the unit deviations of all analysis units under the same candidate printing posture are arithmetically summed to obtain the cumulative deviation value corresponding to the candidate printing posture. The cumulative deviation value comprehensively quantifies the degree of printing deformation deviation under the printing posture. The smaller the value, the less the total amount of work to be corrected under the posture and the higher the overall printing quality. This is used as the core quantitative indicator for the selection of printing posture.

[0031] In some embodiments of this application, when determining the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation under the target printing posture, and determining the layer height, trace width, and printing speed based on the difference between the maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected, the process includes: Analytical units with maximum sag displacement greater than the allowable forming deformation are selected as the units to be corrected; the differences between each unit to be corrected are statistically analyzed and normalized to obtain the correction level of each unit; the layer height, the trace width, and the printing speed are reduced step by step according to the correction level to obtain the printing parameter combination corresponding to each unit to be corrected.

[0032] Specifically, all discrete analysis units under the target printing posture are traversed, and the maximum droop displacement of each analysis unit is compared with the corresponding allowable forming deformation. Analysis units with a maximum droop displacement greater than the allowable forming deformation are selected as analysis units to be corrected. If these analysis units are not adjusted, insufficient thickness will occur after printing, directly affecting the accuracy of radiotherapy dose distribution. Subsequently, the difference between the maximum droop displacement and the allowable forming deformation for all analysis units to be corrected is calculated. All differences are linearly normalized, mapping the range of the differences to the interval between 0 and 1. Normalization eliminates the influence of differences in allowable forming deformation in different parts on the judgment of the correction degree, providing a unified comparison benchmark for the degree of deviation of different analysis units. Based on the normalized results, the analysis units to be corrected are divided into three correction levels: Level 1 correction is between 0 and 0.33, Level 2 correction is between 0.33 and 0.66, and Level 3 correction is between 0.66 and 1. A higher correction level indicates a more severe degree of deformation deviation in the analysis unit, requiring stricter parameter control measures. By progressively reducing layer height, trace width, and printing speed according to the correction level, the printing parameter combinations corresponding to each unit to be corrected were obtained. The basic printing parameters were based on the conventional printing parameters of 95A hardness TPU filament. The first-level correction corresponds to a layer height of 0.2mm, a trace width of 0.35mm, and a printing speed of 45mm / s; the second-level correction corresponds to a layer height of 0.18mm, a trace width of 0.32mm, and a printing speed of 35mm / s; and the third-level correction corresponds to a layer height of 0.15mm, a trace width of 0.3mm, and a printing speed of 25mm / s. Reducing the layer height and trace width can reduce the self-weight load of a single layer of deposited material, and reducing the printing speed can prolong the cooling and solidification time of the molten material. The combined effect of these three factors can effectively reduce the sagging deformation of the flexible material. At the same time, the graded adjustment method can maximize the overall printing efficiency while ensuring printing accuracy.

[0033] Example: Printing accuracy verification test: Using 95A hardness TPU material, 10 head and neck compensators were printed using both traditional globally uniform parameter printing and the optimized method of this invention. The results showed that the average thickness deviation of the method of this invention was 0.07 mm, while the average thickness deviation of the traditional method was 0.38 mm; the method of this invention had no edge collapse, while the traditional method had 4 cases with insufficient edge thickness.

[0034] In some embodiments of this application, when determining the edge smoothing amount and thickness correction amount for the analysis unit to be corrected where the boundary distance is less than the local wall thickness, and recalculating the maximum sagging displacement based on the local wall thickness after thickness correction, the process includes: Extract edge analysis units with boundary distances less than the local wall thickness from the analysis units to be corrected; extract edge polylines along the contour boundary of the region where the edge analysis units are located; perform a smooth transition on the edge polylines according to the ratio of boundary distance to local wall thickness to obtain the smoothed contour; then offset the smoothed contour outward along the surface normal of the corresponding region to obtain the thickness-corrected local contour; update the local wall thickness with the corrected local contour and re-execute the calculation process of the maximum sagging displacement.

[0035] Specifically, from all the analysis units to be corrected, edge analysis units with boundary distances smaller than their local wall thickness are selected. These analysis units are located in the outer edge region of the model, supported only by the printed structure on one side. Their boundary constraint stiffness is much lower than that of the internal analysis units, making them the most prone to edge collapse and insufficient thickness in flexible material printing. Along the contour boundary of the region where all edge analysis units are located, edge polylines composed of discrete line segments connected end to end are extracted. The edge polylines are the digital representation of the outer contour of the discretized 3D model. Based on the ratio of the boundary distance to the local wall thickness of each edge analysis unit, the edge polylines are segmented and smoothed to obtain the smoothed contour. The smaller the ratio, the closer the analysis unit is to the outermost edge of the model, requiring a larger smoothing radius to eliminate printing defects caused by sharp corners. For TPU material with a hardness of 95A, the smoothing radius is 0.2 mm when the ratio is 0.2, 0.5 mm when the ratio is 0.8, and the smoothing radius corresponding to intermediate ratios is calculated by linear interpolation. Next, the smoothed contour is offset outward along the surface normal of the corresponding region to obtain the thickness-corrected local contour. The offset distance is equal to the element deviation of the edge analysis unit. Offsetting along the surface normal ensures a uniform thickness distribution after correction, without changing the surface fit of the compensator or the radiation dose distribution characteristics. The local wall thickness parameters of the corresponding analysis unit are updated with the corrected local contour, and the maximum sag displacement calculation process is re-executed. This iterative method of correction and verification allows for accurate judgment of the edge correction effect, avoiding deformation residue caused by insufficient correction or thickness deviation caused by overcorrection.

[0036] In some embodiments of this application, when generating a water-soluble PVA support path for the analysis unit to be corrected, where the final maximum sag displacement is still greater than the allowable forming deformation, the following steps are included: Extract the analysis units that still exceed the allowable forming deformation requirement and require correction; merge the spatially adjacent analysis units with the same downward direction into a support requirement area; project each support requirement area onto the printing platform or the lower printed area along the forming direction opposite to the target printing posture, and determine the intersection of the projection with the printing platform or the lower printed area as the support start point, and the bottom of the support requirement area as the support end point; then insert a connection trajectory between the support start point and the support end point according to the preset path spacing to obtain the corresponding water-soluble PVA support path; leave a 0.1mm separation gap between the water-soluble PVA support path and the compensator body.

[0037] Specifically, after edge smoothing, thickness correction, and printing parameter adjustment, the maximum sag displacement of the analyzed units still exceeds the allowable forming deformation. These units indicate that relying solely on local geometric correction and process parameter adjustment is insufficient to control their forming deformation within the allowable range, thus requiring further external support. Spatially adjacent analyzed units with consistent sag directions are merged into a support requirement area. Spatially adjacent units are defined as having a minimum spatial distance of less than 1mm, and consistent sag directions are defined as having an angle of less than 15° between their sag directions. These two conditions are used to avoid generating scattered small-sized support units and improve the continuity and overall stability of the support path within the same area. The 1mm distance threshold can be matched with the printing path width and support forming resolution, while the 15° angle threshold ensures high consistency in the force direction of the merged analyzed units. Subsequently, based on the target printing posture, each support requirement area is projected onto the printing platform or the lower printed area in the opposite direction of forming. The landing point of the support requirement area on the printing platform or the lower printed area in this projection direction is determined as the support start point, and the bottom area of ​​the support requirement area is determined as the support end point. When there is already a printed solid layer below the support requirement area that can provide support, the support path only extends to the upper surface of the printed solid layer and does not continue to the printing platform, so as to reduce the consumption of support material and shorten the printing time. After determining the support start point and support end point, a connection trajectory is inserted between the support start point and support end point according to the preset path spacing to obtain the corresponding water-soluble PVA support path. The preset path spacing is preferably 1 mm, which can achieve a good balance between support strength, printing efficiency and subsequent dissolution and removal convenience. In other embodiments, it can also be adjusted to 0.8 mm to 1.2 mm according to the area of ​​the support requirement area and the degree of local sagging risk. To avoid the support material from adhering too tightly to the compensator body and affecting the surface quality after removal, a separation gap of 0.1mm is reserved between the water-soluble PVA support path and the compensator body. This separation gap can be determined based on the actual positioning accuracy of the dual-nozzle FDM equipment, the dissolution characteristics of the PVA material, and the surface quality requirements of the compensator. This ensures that the support path provides effective support to the area to be supported, and also allows for more thorough removal of the support through dissolution after printing, thereby reducing the impact of support residue on the surface flatness and dimensional accuracy of the flexible radiotherapy tissue compensator.

[0038] In some embodiments of this application, when generating slice path data based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, and controlling the 3D printing equipment to print according to the slice path data, the process includes: First, the 3D model after thickness correction and edge smoothing, as well as the water-soluble PVA support path, are layered according to the target printing posture. The outer contour path and the internal filling path are extracted in each layer. The spacing between adjacent paths is determined according to the trace width, the layer height between layers is determined according to the layer height, and the corresponding motion commands are written into each layer path according to the printing speed. The paths of each layer are spliced ​​together in the printing order to generate slice path data. Then, the 3D printing equipment is controlled to complete the printing layer by layer according to the slice path data.

[0039] Specifically, according to the forming direction of the target printing posture, the 3D model after thickness correction and edge smoothing, as well as the merged water-soluble PVA support path, are layered. During layering, the layer height parameters corresponding to each analysis unit are strictly matched, and different layer heights are used for areas with different correction levels to achieve precise printing with variable layer heights. Within each layer plane, the outer contour path and internal filling path of the model are extracted separately. The internal filling uses a 100% solid fill method to ensure uniform overall density of the compensator, avoiding uneven radiation penetration and fully meeting the dose distribution requirements of clinical radiotherapy. The spacing between adjacent paths is determined based on the corresponding trace width of each region. The spacing is equal to the trace width multiplied by a path overlap coefficient of 0.9. For example, when the trace width is 0.35mm, the spacing between adjacent paths is 0.315mm. This overlap coefficient ensures tight fusion between the filaments within the layer, without obvious gaps or delamination defects. The vertical layering height between layers is determined based on the corresponding layer height of each region, and the corresponding feed speed parameters are written into the motion commands of each path segment according to the printing speed of each region. All layered outer contour paths, internal filling paths, and water-soluble PVA support paths are sequentially stitched together from bottom to top to generate slice path data in standard G-code format. Finally, the slice path data is sent to a fused filament 3D printer, with the nozzle temperature set to 210℃ and the platform temperature to 20℃. The printer is controlled to complete the printing layer by layer according to the slice path data. After printing, the compensator is allowed to cool naturally to room temperature on the printing platform before the support is removed to avoid thermal deformation due to sudden temperature changes. The final result is a flexible radiotherapy tissue compensator that meets clinical requirements in terms of dimensional accuracy and surface quality.

[0040] In another preferred embodiment based on the above embodiments, see [reference] Figure 2 As shown, this embodiment provides a shaping and optimization system for flexible radiotherapy tissue compensators, including: The candidate printing posture generation module is configured to acquire the three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material, and generate several candidate printing postures based on the three-dimensional model. The feature extraction module of the analysis unit is configured to discretize the three-dimensional model into several analysis units under each candidate printing posture, calculate the overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit, determine the shortest distance from the corresponding analysis unit to the boundary of the three-dimensional model as the boundary distance, and determine the allowable forming deformation of each analysis unit according to the design thickness and allowable thickness deviation of each analysis unit. The target printing posture determination module is configured to calculate the maximum droop displacement of each analysis unit under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, and determine the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation amount, and determine the candidate printing posture with the smallest cumulative deviation value as the target printing posture. The printing parameter determination module is configured to determine the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation under the target printing posture; determine the edge smoothing amount and thickness correction amount for the analysis unit to be corrected whose boundary distance is less than the local wall thickness, and recalculate the maximum droop displacement based on the local wall thickness after thickness correction; and determine the layer height, trace width and printing speed based on the difference between the final maximum droop displacement and the allowable forming deformation of each analysis unit to be corrected. The water-soluble PVA support path generation module is configured to generate water-soluble PVA support paths for the analysis unit to be corrected, where the final maximum sag displacement is still greater than the allowable forming deformation. The printing control module is configured to generate slice path data based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, and control the 3D printing equipment to print according to the slice path data.

[0041] Understandably, through the coordinated efforts of the candidate printing posture generation module, the analysis unit feature extraction module, the target printing posture determination module, the printing parameter determination module, the water-soluble PVA support path generation module, and the printing control module, this implementation method can transform the forming optimization process of flexible radiotherapy tissue compensators from manual experience-based adjustments into a modular automated processing flow. First, the candidate printing posture generation module provides multiple printing postures to be evaluated. Then, the analysis unit feature extraction module extracts geometric features and thickness constraint information related to forming stability. Next, the target printing posture determination module selects the target printing posture with the smallest cumulative deviation value. Based on this, the printing parameter determination module performs edge smoothing, thickness correction, and printing parameter adjustment for areas with a significant risk of sagging. The water-soluble PVA support path generation module supplements water-soluble PVA support paths for areas that still fail to meet forming requirements after correction. Finally, the printing control module generates slicing path data and completes printing control. Therefore, while considering the thickness requirements of the compensator design, it can more effectively reduce local sagging, edge distortion, and forming instability of flexible materials during the printing process, improving the consistency of the printing process and the forming quality of the finished product.

[0042] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope defined by the present invention.

Claims

1. A method of forming an optimal flexible radiotherapy tissue compensator, comprising: include: The three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material are obtained, and several candidate printing postures are generated based on the three-dimensional model. Under each candidate printing posture, the 3D model is discretized into several analysis units. The overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit are calculated. The shortest distance from the corresponding analysis unit to the boundary of the 3D model is determined as the boundary distance. The allowable forming deformation of each analysis unit is determined according to the design thickness and allowable thickness deviation of each analysis unit. Based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, the maximum droop displacement of each analysis unit under each candidate printing posture is calculated, and the cumulative deviation value corresponding to each candidate printing posture is determined according to the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation. The candidate printing posture with the smallest cumulative deviation value is determined as the target printing posture. Under the target printing posture, the analysis unit to be corrected is determined based on the maximum droop displacement and the allowable forming deformation. For the analysis unit to be corrected with a boundary distance smaller than the local wall thickness, the edge smoothing amount and thickness correction amount are determined, and the maximum droop displacement is recalculated based on the local wall thickness after thickness correction. The layer height, trace width, and printing speed are determined based on the difference between the final maximum sag displacement and the allowable forming deformation of each analysis unit to be corrected. For the analysis unit to be corrected where the final maximum sag displacement is still greater than the allowable forming deformation, a water-soluble PVA support path is generated. Based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, the slicing path data is generated, and the 3D printing equipment is controlled to print according to the slicing path data.

2. The method of claim 1, wherein the forming of the flexible radiotherapy compensator is optimized by, When generating several candidate printing poses based on a 3D model, including: Extract the outer contour range of the 3D model and establish a bounding box; take the normal direction of each outer surface of the bounding box as the forming direction and construct the initial printing posture corresponding to each normal direction; take the forming direction in each initial printing posture as the axis and rotate the 3D model circumferentially at a preset angle interval of 15°-45°; preferably 30°, to obtain multiple candidate printing postures.

3. The method of claim 2, wherein the forming of the flexible radiotherapy compensator is optimized by, When determining the allowable forming deformation for each analysis unit based on its design thickness and allowable thickness deviation, the following should be included: Map the design thickness of each position of the three-dimensional model to the corresponding analysis unit; read the thickness allowable deviation of the corresponding analysis unit; subtract the thickness allowable deviation from the design thickness to obtain the minimum allowable thickness of the corresponding analysis unit; convert the thickness difference between the design thickness and the minimum allowable thickness into the allowable displacement of the corresponding analysis unit in the surface normal direction; calculate the angle θ between the surface normal direction and the forming direction, and multiply the allowable displacement by COSθ to obtain the allowable forming deformation of the corresponding analysis unit in the forming direction.

4. The method of claim 3, wherein the forming of the flexible radiotherapy compensator is optimized by, When calculating the maximum droop displacement of each analysis element under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus, and density, the following are included: Extract the path segments to be deposited corresponding to each analysis unit under the corresponding candidate printing posture; equate the path segments to be deposited to a viscoelastic beam segment under gravity; under the conditions of printing speed ≤50mm / s and layer thickness ≤0.2mm, the elastic beam model can be used for approximate calculation with an error ≤10%; take the free span as the effective span of the elastic beam segment, correct the cross-sectional parameters of the elastic beam segment with local wall thickness and radius of curvature, determine the component of gravity in the downward direction with the overhang angle, and determine the self-weight load per unit length based on density; then correct the boundary constraint degree of the elastic beam segment based on the boundary distance, obtain the displacement values ​​of the midpoint and end positions of the elastic beam segment, and determine the maximum value as the maximum downward displacement of the corresponding analysis unit.

5. The method of claim 4, wherein the forming of the flexible radiotherapy compensator is optimized by, When determining the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement and allowable forming deformation of each analysis unit under each candidate printing posture, the following are included: The maximum droop displacement of each analysis unit under the same candidate printing posture is compared with the corresponding allowable forming deformation. The analysis unit with the maximum droop displacement less than or equal to the allowable forming deformation is recorded as zero deviation. For the analysis unit with the maximum droop displacement greater than the allowable forming deformation, the difference between the maximum droop displacement and the allowable forming deformation is recorded as the unit deviation. The unit deviations of all analysis units under the same candidate printing posture are accumulated to obtain the cumulative deviation value of the corresponding candidate printing posture.

6. The method of claim 5, wherein the forming of the flexible radiotherapy compensator is optimized by, Under the target printing posture, when determining the analysis elements to be corrected based on the maximum droop displacement and the allowable forming deformation, and when determining the layer height, trace width, and printing speed based on the difference between the maximum droop displacement and the allowable forming deformation of each analysis element to be corrected, the following steps are taken: Analytical units with maximum sag displacement greater than the allowable forming deformation are selected as the units to be corrected; the differences between each unit to be corrected are statistically analyzed and normalized to obtain the correction level of each unit; the layer height, the trace width, and the printing speed are reduced step by step according to the correction level to obtain the printing parameter combination corresponding to each unit to be corrected.

7. The method of claim 6, wherein the forming of the flexible radiotherapy compensator is optimized by, When determining the edge smoothing amount and thickness correction amount for the analysis element to be corrected where the boundary distance is less than the local wall thickness, and recalculating the maximum sagging displacement based on the local wall thickness after thickness correction, the following steps are included: Extract edge analysis units whose boundary distance is less than the local wall thickness from the analysis units to be corrected; extract edge polylines along the contour boundary of the region where the edge analysis units are located; perform a smooth transition process on the edge polylines according to the ratio of boundary distance to local wall thickness to obtain the smoothed contour; then offset the smoothed contour outward along the surface normal of the corresponding region to obtain the thickness-corrected local contour; update the local wall thickness with the corrected local contour, and re-execute the calculation process of the maximum droop displacement.

8. The method of claim 7, wherein the forming of the flexible radiotherapy compensator is optimized by, When generating water-soluble PVA support paths for the analysis unit to be corrected, where the final maximum sag displacement still exceeds the allowable forming deformation, the following steps are included: Extract the analysis units that still exceed the allowable forming deformation requirement and require correction; merge the spatially adjacent analysis units with the same downward direction into a support requirement area; project each support requirement area onto the printing platform or the lower printed area along the forming direction opposite to the target printing posture, and determine the intersection of the projection with the printing platform or the lower printed area as the support start point, and the bottom of the support requirement area as the support end point; then insert a connection trajectory between the support start point and the support end point according to the preset path spacing to obtain the corresponding water-soluble PVA support path; leave a 0.1mm separation gap between the water-soluble PVA support path and the compensator body.

9. The method of claim 8, wherein the forming of the flexible radiotherapy compensator is optimized by, Based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, slicing path data is generated, and the 3D printing equipment is controlled to print according to the slicing path data, including: First, the 3D model after thickness correction and edge smoothing, as well as the water-soluble PVA support path, are layered according to the target printing posture. The outer contour path and the internal filling path are extracted in each layer. The spacing between adjacent paths is determined according to the trace width, the layer height between layers is determined according to the layer height, and the corresponding motion commands are written into each layer path according to the printing speed. The paths of each layer are spliced ​​together in the printing order to generate slice path data. Then, the 3D printing equipment is controlled to complete the printing layer by layer according to the slice path data.

10. A system for forming optimization of a flexible radiotherapy tissue compensator for implementing the method for forming optimization of a flexible radiotherapy tissue compensator according to any one of claims 1 to 9, characterized in that, include: The candidate printing posture generation module is configured to acquire the three-dimensional model of the flexible radiotherapy tissue compensator, the design thickness at each location, and the elastic modulus and density of the flexible thermoplastic printing material, and generate several candidate printing postures based on the three-dimensional model. The feature extraction module of the analysis unit is configured to discretize the three-dimensional model into several analysis units under each candidate printing posture, calculate the overhang angle, free span, local wall thickness, radius of curvature and boundary distance of each analysis unit, determine the shortest distance from the corresponding analysis unit to the boundary of the three-dimensional model as the boundary distance, and determine the allowable forming deformation of each analysis unit according to the design thickness and allowable thickness deviation of each analysis unit. The target printing posture determination module is configured to calculate the maximum droop displacement of each analysis unit under each candidate printing posture based on the overhang angle, free span, local wall thickness, radius of curvature, boundary distance, elastic modulus and density, and determine the cumulative deviation value corresponding to each candidate printing posture based on the maximum droop displacement of each analysis unit under each candidate printing posture and the allowable forming deformation amount, and determine the candidate printing posture with the smallest cumulative deviation value as the target printing posture. The printing parameter determination module is configured to determine the analysis unit to be corrected based on the maximum droop displacement and the allowable forming deformation under the target printing posture; determine the edge smoothing amount and thickness correction amount for the analysis unit to be corrected where the boundary distance is less than the local wall thickness, and recalculate the maximum droop displacement based on the local wall thickness after thickness correction. The layer height, trace width, and printing speed are determined based on the difference between the final maximum sag displacement and the allowable forming deformation of each analysis unit to be corrected. The water-soluble PVA support path generation module is configured to generate water-soluble PVA support paths for the analysis unit to be corrected, where the final maximum sag displacement is still greater than the allowable forming deformation. The printing control module is configured to generate slice path data based on the target printing posture, the 3D model after thickness correction and edge smoothing, the water-soluble PVA support path, and the determined layer height, trace width, and printing speed, and control the 3D printing equipment to print according to the slice path data.

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