Space segmentation radiotherapy control method and system

Abstract

The invention discloses a space division radiotherapy method for realizing different grid apertures and grid intervals based on an orthogonal double-layer multi-leaf collimator (MLC), in one embodiment, the orthogonal double-layer MLC is used to collimate radioactive rays by optimizing the angle of a rack, the rotation angle of a treatment bed and the rotation angle of the collimator, and the radiation intensity of the radiation rays is improved. According to the invention, grid irradiation fields with different grid apertures and grid intervals and high conformity are formed, so that high-conformity space division irradiation with different grid apertures and grid intervals based on the medical linear accelerator is realized, and the accessibility of the space division irradiation technology is improved.

Description

Technical Field

[0001] This application relates to the field of radiotherapy technology, and more specifically, exemplary embodiments relate to a small-beam radiotherapy (hereinafter referred to as small-beam radiotherapy) system and control method based on an orthogonal bilayer multileaf collimator (MLC). The orthogonal bilayer MLC is used to collimate radiation to form a sub-beam array, which can be used to perform spatially fractionated radiation therapy (SFRT) on the target area. Background Technology

[0002] Unlike traditional radiotherapy techniques that aim for uniform dose distribution within the target area, spatially fractionated radiotherapy (SFRT) uses a dedicated physical grid collimator or a conventional multi-leaf collimator (MLC) to create alternating high-dose (peak) and low-dose (valley) regions within the target area. Studies have shown that this non-uniform dose distribution has multiple advantages: First, the peak dose within the target area can significantly exceed the prescribed dose of conventional radiotherapy, thus more effectively killing tumor cells in the peak region; second, normal tissues surrounding the target area receive only lower doses of irradiation, resulting in significantly reduced toxicity; and more importantly, although tumor cells in the valley region do not directly receive high-dose irradiation, they can still exhibit radiation damage effects similar to those in the peak region.

[0003] Based on the dimensional characteristics of dose distribution, SFRT can be divided into one-dimensional, two-dimensional, and three-dimensional SFRT. One-dimensional SFRT forms an alternating peak-valley distribution through a strip-shaped radiation field in a single direction (e.g., Figure 1 (As shown in the left figure), but it has the drawback of excessively high skin dose in the incident direction and insufficient dose in the exit direction; two-dimensional SFRT forms a parallel columnar high-dose zone through multi-angle irradiation (such as... Figure 1 As shown in the middle figure), it overcomes the aforementioned shortcomings of one-dimensional SFRT dose distribution; three-dimensional SFRT, through the optimized arrangement of sub-target regions in three-dimensional space, forms a spherical high-dose peak within the target region, while minimizing the radiation dose to organs at risk, achieving an alternating distribution of high and low doses in three dimensions (as shown in the middle figure). Figure 1 As shown in the right figure, it significantly improves the therapy ratio (TR).

[0004] Based on beam unit size, SFRT can be divided into fine-beam radiotherapy (i.e., single beam size 5mm~2cm), mini-beam radiotherapy (i.e., single beam size 0.1~5mm), and micro-beam radiotherapy (i.e., single beam size 50~100μm). Among them, fine-beam radiotherapy has been widely used in the clinical treatment of patients with large-volume tumors and has achieved encouraging clinical results. Compared with fine-beam radiotherapy, mini-beam radiotherapy and micro-beam radiotherapy use smaller beam sizes, theoretically achieving higher peak-valley dose ratio (PVDR) and treatment ratio (TR), and potentially expanding the indications for SFRT from large-volume tumors to conventional-volume and even small-volume tumors. Therefore, it has attracted the attention of many researchers and preclinical studies have been conducted.

[0005] In theory, the clinical application of small-beam radiotherapy and micro-beam radiotherapy should consider the following factors: the radiation used should have sufficient penetrability (energy) to deposit a sufficient dose at deep tumors in large animals or humans while reducing the dose on the skin surface in the direction of the radiation field; the radiation source used should be highly accessible, and the dose rate of the radiation should be high enough to complete the treatment within an acceptable time; the collimation system should be able to achieve continuous adjustment of beam size and spacing to facilitate clinical application and reduce application costs.

[0006] Due to the extremely small size of microbeam radiotherapy, existing preclinical experiments rely on synchrotrons to provide high-dose-rate radiation sources and dedicated collimation systems, making the technology inaccessible. Small-beam radiotherapy, on the other hand, has a relatively large beam size, making it easier to meet the dose-rate requirements of the radiation source. In particular, the beam size of small-beam radiotherapy is comparable to that of proton / heavy ion pencil beam scanning modes. Therefore, current physics and preclinical studies of proton / heavy ion-based small-beam radiotherapy have demonstrated significant tumor control effects and low toxicity. However, its clinical application is limited by its reliance on expensive particle accelerators. Small-beam radiotherapy based on kilovolt-level X-rays has also achieved promising results in animal models. Although its cost is lower, it still requires dedicated small animal irradiation experimental platforms and dedicated collimation systems, and its X-ray penetration is insufficient, making it difficult to meet the treatment needs of deep tumors in large animals or humans.

[0007] Medical electron accelerators, as the mainstream equipment for radiotherapy, are highly accessible and possess high-energy megavolt-level X-ray output capabilities, making them a good choice as a radiation source for small-beam radiotherapy. Researchers have designed a dedicated physical collimator for small-beam radiotherapy that can be fixed to the treatment head of a medical electron accelerator and studied the dosimetric characteristics of the small beam current (approximately 1 mm in size) formed by this collimator under a 6 MV beam current provided by the accelerator. Actual measurements and Monte Carlo simulations show that its PVDR is approximately 1.5-2.0 at a depth of 3 cm, meeting the requirements for small-beam radiotherapy. However, the size and spacing of the small beam current formed by this dedicated physical collimator cannot be continuously adjusted, requiring customization according to different needs, which is inconvenient and expensive. Furthermore, this external dedicated physical collimator is relatively heavy, inconvenient to install and adjust, and poses a risk of collision with patients in clinical applications.

[0008] MLC (Medium-Liquid Cavity) is a standard feature of modern medical linear accelerators, built into the accelerator's treatment head. Its position is continuously adjustable in the direction of blade movement under computer control, with a positioning accuracy of 0.1 mm. Experience in fine-beam radiotherapy shows that using MLC for beam shaping has similar treatment response rates to using dedicated physical collimators. Therefore, MLC is more advantageous than dedicated physical collimators as a beam shaping device for small beams.

[0009] However, currently, medical electron accelerators and MLCs are only used for fine-beam radiotherapy, not for small-beam radiotherapy. The main reason for this is that existing conventional MLCs, due to limitations in their blade width and arrangement (parallel alignment), struggle to form highly conformal small-beam arrays. As shown in Figure 2, the inherent width of MLC blades typically ranges from 2.5 mm to 10 mm, a characteristic that limits their ability to form highly conformal radiation fields perpendicular to the blade's direction of motion. This is especially true for three-dimensional small-beam radiotherapy, where achieving targeted radiation to individual sub-target areas (such as...) is extremely difficult. Figure 2 The highly conformal radiation field (as shown by the inner dot-shaped sphere) requires individual conformal treatment of each target point, even when combined with a lead gate perpendicular to the direction of MLC movement, which limits the treatment efficiency.

[0010] Furthermore, although existing MLCs employ a tongue and groove structure to reduce inter-blade leakage, some dose leakage still exists between blades, which increases the dose in the valley region of the irradiation field, thus limiting the improvement of peak-valley dose ratio (PVDR). Summary of the Invention

[0011] To overcome the shortcomings of existing technologies, this invention proposes a system and control method for spatial fractionation radiotherapy based on orthogonal bilayer MLC. Orthogonal bilayer MLC is used to collimate radiation, which can be used to form sub-beam arrays and perform small-beam radiotherapy on the target area, thereby improving the accessibility of spatial fractionation irradiation technology.

[0012] According to one aspect of the present invention, a method for controlling spatial fractionation radiotherapy is provided, the method comprising: collimating a beam generated by a beam module using an orthogonal double-layer multi-leaf collimator, wherein the orthogonal double-layer multi-leaf collimator includes a first multi-leaf collimator and a second multi-leaf collimator, the first multi-leaf collimator including a first leaf array movable along a first direction, and the second multi-leaf collimator including a second leaf array movable along a second direction, the second multi-leaf collimator being located below the first multi-leaf collimator, and the second direction being perpendicular to the first direction; wherein, after being collimated by the orthogonal double-layer multi-leaf collimator, the beam obtains a radiation field of a predetermined size, the aperture or minor axis of the radiation field being less than 5 mm. Preferably, the aperture or minor axis of the radiation field is less than 2.5 mm.

[0013] In some embodiments, the method further includes: dividing the spatially segmented radiotherapy target area into multiple parallel sub-target area groups; determining the gantry angle corresponding to different treatment bed rotation angles based on the sub-target area arrangement parameters, such that the projections of each sub-target area in the beam direction view remain grouped under the treatment bed rotation angle and the corresponding gantry angle, thereby establishing a radiation field parameter library; and selecting feasible radiation field parameter configurations from the radiation field parameter library, wherein the feasible radiation field parameter configurations include multiple combinations of treatment bed rotation angles and gantry angles.

[0014] In some implementations, establishing a field parameter library and screening feasible field parameter configurations includes: setting the rotation angle of the treatment bed; calculating the gantry angle at the rotation angle of the treatment bed, such that the projections of each sub-target area in the beam direction at the gantry angle remain in a grouped arrangement; repeating the above steps to obtain a field parameter library of multiple treatment bed rotation angles and gantry angles; and screening feasible combinations of treatment bed rotation angles and gantry angles from the field parameter library according to the collision avoidance range and / or field layout rules of the electron linear accelerator.

[0015] In some embodiments, the method further includes: controlling the dual-layer multi-leaf collimator to rotate to a direction parallel or perpendicular to the long axis of the sub-target region; and controlling the movement of the first blade array and the second blade array according to the projection of the sub-target region in the beam direction view, such that the beam passes through the first blade array and the second blade array to form a strip-shaped small beam field conforming to the projection, thereby obtaining a one-dimensional or two-dimensional spatially segmented irradiation field. The minor axis dimension of the strip-shaped small beam field is, for example, 0.5-2.5 mm.

[0016] In some embodiments, the method further includes: based on the determined feasible field parameter configuration and sub-target area arrangement parameters, combined with the blade width configuration of the double-layer multi-leaf collimator, further increasing the rotation angle of the double-layer multi-leaf collimator step by step according to a certain step size, and calculating the field conformity at each collimator rotation angle to establish a relationship curve between the collimator rotation angle and the field conformity; and selecting the collimator rotation angle corresponding to the field conformity closest to 1 to form a three-dimensional spatially segmented irradiation field.

[0017] In some embodiments, determining the collimator rotation angle includes: calculating the diameter and minimum spacing of the sub-target areas in the beam direction view under each combination of treatment bed rotation angle and gantry angle based on the sub-target area arrangement parameters, treatment bed rotation angle, and gantry angle; setting the collimator rotation angle; calculating the conformity index of the grouped irradiation field of each sub-target area under the collimator rotation angle, wherein the conformity index is the DSC value of the irradiation area formed by the grouped irradiation field and the projected area of ​​the grouped sub-target areas in the beam direction view; determining the field conformity corresponding to the collimator rotation angle based on the average value of the conformity index of the grouped irradiation field of each sub-target area; repeating the above steps to establish a relationship curve between the collimator rotation angle and the field conformity; and selecting the collimator rotation angle corresponding to the field conformity closest to 1 based on the relationship curve.

[0018] In some embodiments, the arrangement parameters of the sub-target regions include at least one of the following: the diameter of the sub-target regions, the spacing between the sub-target regions, the translation matrix of the sub-target regions, or the rotation matrix of the sub-target regions.

[0019] According to another aspect of the present invention, a spatial fractionation radiotherapy system is provided, comprising: a gantry; a beam module disposed on the gantry for generating a radiation beam; an orthogonal double-layer multi-leaf collimator disposed on the gantry, including a first multi-leaf collimator and a second multi-leaf collimator, the first multi-leaf collimator including a first leaf array movable along a first direction, the second multi-leaf collimator including a second leaf array movable along a second direction, the second multi-leaf collimator being located below the first multi-leaf collimator, and the second direction being perpendicular to the first direction; and a controller communicatively coupled to the gantry, an electron linear accelerator, and the orthogonal double-layer multi-leaf collimator for controlling the movement of the first leaf array and the second leaf array, such that the radiation beam, after being collimated by the double-layer multi-leaf collimator, obtains a radiation field of a predetermined size, the aperture or minor axis of the radiation field being less than 5 mm. In one embodiment, the beam module may be an electron linear accelerator.

[0020] In some implementations, the spatial fractionation radiotherapy system may also include equipment such as a treatment bed, which can be used to carry the patient and can be moved and positioned, for example, under the control of a controller.

[0021] In some embodiments, the controller includes a treatment bed and gantry angle optimization module and a collimator angle optimization module. The treatment bed and gantry angle optimization module is configured to: determine the gantry angle corresponding to different treatment bed rotation angles based on the sub-target area arrangement parameters, such that the projections of each sub-target area in the beam direction view remain grouped under the treatment bed rotation angle and the corresponding gantry angle, thereby establishing a beam field parameter library; and select feasible beam field parameter configurations from the beam field parameter library, wherein the feasible beam field parameter configurations include combinations of multiple treatment bed rotation angles and gantry angles. The collimator angle optimization module is configured to: based on the determined feasible beam field parameter configurations and the sub-target area arrangement parameters, combined with the blade width configuration of the double-layer multi-leaf collimator, gradually increase the rotation angle of the double-layer multi-leaf collimator at a certain step size, calculate the beam field conformity at each collimator rotation angle, establish a relationship curve between the collimator rotation angle and the beam field conformity; and select the collimator rotation angle corresponding to the beam field conformity closest to 1.

[0022] In some embodiments, the collimator angle optimization module is configured to determine the collimator rotation angle in the following manner: based on the sub-target area arrangement parameters, treatment bed rotation angle, and gantry angle, calculate the diameter and minimum spacing of the sub-target areas in the beam direction view under each combination of treatment bed rotation angle and gantry angle; set the initial collimator rotation angle; calculate the conformity index of the grouped irradiation fields of each sub-target area under the collimator rotation angle, wherein the conformity index is the DSC value of the irradiation area formed by the grouped irradiation fields and the projected area of ​​the sub-target area in the beam direction view; determine the field conformity corresponding to the collimator rotation angle based on the average value of the conformity index of the grouped irradiation fields of each sub-target area; repeat the above steps to establish a relationship curve between the collimator rotation angle and the field conformity; and select the collimator rotation angle corresponding to the field conformity closest to 1 based on the relationship curve.

[0023] After adopting the above technical solutions, the beneficial effects of this invention are as follows: by using orthogonal double-layer MLC to collimate the radiation beam, various grid sizes can be formed, especially small beam grid arrays smaller than the width of a leaf blade, which can then be used for small-beam radiotherapy. In some specific embodiments, through group irradiation strategies and collimator angle optimization, one-dimensional, two-dimensional, and three-dimensional small-beam spatial fractionation radiotherapy with continuously adjustable beam size and spacing based on a medical linear accelerator can be achieved, improving the accessibility of spatial fractionation irradiation technology. Attached Figure Description

[0024] To more clearly illustrate the above and other objects, features, and advantages of this application, the accompanying drawings used in the description of the embodiments are briefly introduced below. The drawings are used to provide a further understanding of the embodiments of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. The drawings are not intended to be drawn to scale; in the drawings, the same reference numerals generally represent the same elements or steps. For clarity, not every element or step is shown in every drawing.

[0025] Figure 1 This is a schematic diagram of one-dimensional, two-dimensional, and three-dimensional dose distribution using spatial fractionated radiotherapy (SFRT).

[0026] Figure 2 This is a schematic diagram of the field of view formed by a conventional MLC.

[0027] Figure 3 This is a schematic diagram of one-dimensional and two-dimensional small-beam radiotherapy irradiation fields based on the orthogonal bilayer MLC of this application embodiment;

[0028] Figure 4 This is a schematic diagram of a three-dimensional lattice irradiation field for small-beam radiotherapy based on the orthogonal bilayer MLC and group irradiation strategy of this application embodiment;

[0029] Figure 5 This is a schematic diagram illustrating the influence of subfield conformity on subtarget area diameter, spacing, and subtarget area matrix relative to the arrangement direction of the MLC blades.

[0030] Figure 6 A schematic diagram showing how the sub-target matrix remains in a grouped parallel arrangement when projected onto the BEV after the rotation of the treatment bed and gantry is compensated for by the rotation of the sub-target matrix relative to the accelerator coordinate system.

[0031] Figure 7 This is a flowchart illustrating the overall process of optimizing the firing field parameters in an embodiment of this application.

[0032] Figure 8 This is a schematic diagram of the control system composition of the sub-beam array generation method based on orthogonal double-layer MLC involved in the embodiments of this application;

[0033] Figure 9 This is a flowchart illustrating the optimization of the treatment bed rotation angle and frame angle in an embodiment of this application.

[0034] Figure 10 This is a schematic diagram of the treatment bed and gantry angle optimization method involved in the embodiments of this application;

[0035] Figure 11 This is a flowchart illustrating the collimator angle optimization implementation in an embodiment of this application.

[0036] Figure 12This is a schematic diagram showing the relationship between the rotation angle of the orthogonal double-layer MLC collimator and the conformity of the irradiation field of the three-dimensional lattice grouping of the orthogonal double-layer MLC in an embodiment of this application. Detailed Implementation

[0037] To make the technical means, creative features, achieved objectives and effects of this invention readily understandable, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and this invention is not limited to the precise forms of these exemplary embodiments.

[0038] As described above, current SFRT technology can only be applied to thin-beam radiotherapy, and there are difficulties and challenges in its application to small-beam and micro-beam radiotherapy. Therefore, addressing the shortcomings of existing small-beam radiotherapy methods, this invention provides a method for collimating radiation beams (including but not limited to proton beams, heavy ion beams, X-rays, electron beams, gamma rays, etc.) using orthogonal double-layer MLC to form a small-beam grid (sub-beam) array. Through group irradiation strategies and collimator angle optimization, spatial segmentation irradiation of the target area is implemented, enabling one-dimensional, two-dimensional, and three-dimensional small-beam spatial segmentation radiotherapy with continuously adjustable beam size and spacing based on a medical linear accelerator. This improves the accessibility, ease of use, and reduces the cost of spatial segmentation irradiation technology.

[0039] In some embodiments, the orthogonal dual-layer MLC employs a dual-layer design, comprising a first MLC and a second MLC. The first MLC includes a first blade array movable along a first direction, and the second MLC is located below the first MLC and includes a second blade array movable along a second direction, wherein the second direction is perpendicular to the first direction. That is, the blades of the two MLC layers are arranged vertically, with the movement direction of the upper MLC blades perpendicular to the movement direction of the lower MLC blades, and the projections formed by the upper and lower blades are perpendicular to each other. Under the control of a controller, the upper and lower blades can move vertically to a specific position, causing the rays emitted from the electron linear accelerator to pass through the two blade arrays to form a radiation field of a predetermined size. This orthogonal design allows the size of the formed radiation field to be continuously adjustable in both vertical directions, with a positioning accuracy higher than 0.1 mm, which is beneficial for achieving small beams with higher radiation field conformity. The aperture or minor diameter of the radiation field is, for example, 0.1~5 mm, preferably 0.1~2.5 mm. Another major advantage of orthogonal double-layer MLC is that the gap between adjacent blades is effectively blocked by another layer of blades, which greatly reduces leakage between blades.

[0040] By maintaining synchronous motion with zero relative positions for each blade in the upper (or lower) layer of an orthogonal bilayer MLC, a "tungsten gate-like" function can be achieved. Therefore, orthogonal bilayer MLCs can form all the radiation fields that existing medical electron accelerators based on conventional single-layer MLCs can create. Furthermore, since each blade constituting the "tungsten gate-like" structure can actually move relatively independently under controller control, offering greater degrees of freedom, theoretically, the radiation fields formed by orthogonal bilayer MLCs can achieve higher geometric conformity and dose conformity.

[0041] According to an exemplary embodiment of this application, one-dimensional and two-dimensional small-beam radiotherapy can be achieved using orthogonal bilayer MLC. The upper (or lower) layer MLC of the orthogonal bilayer MLC can be used to replace the lead gate in the conventional accelerator head. Similar to the fine-beam radiotherapy of existing medical electron accelerators based on conventional MLC, the bilayer multi-leaf collimator is rotated by a controller to be parallel (or perpendicular) to the long axis of the sub-target area (or grid dose) of the spatially segmented radiotherapy target area. Then, according to the projection of the sub-target area on the BEV, the movement of the blades of the orthogonal bilayer MLC is controlled so that the beam passes through the bilayer blades one by one to form strip-shaped small beams conforming to the projection for group irradiation. Figure 3 A schematic diagram of one-dimensional and two-dimensional small-beam radiotherapy irradiation fields based on orthogonal double-layer MLC is shown. As shown in the figure, the spatially segmented radiotherapy target area can include multiple parallel sub-target area groups. The MLC blades can be controlled to form the required strip-shaped small beams for grouped irradiation. Although the upper and lower MLC layers are combined to illustrate the shape of the irradiation field, it can be understood that the upper and lower MLC layers are arranged vertically in space, and each MLC layer can have similar characteristics. Figure 2 The structure comprises multiple sets of blade pairs, arranged in parallel and adjacent to each other. In a specific implementation, for example, the movement of the upper MLC blades can be controlled first, so that the ray beam passes through the upper blade array to form a strip-shaped radiation field. Then, the movement of the lower MLC blades can be controlled, so that the strip-shaped radiation field is compressed in the width direction to form a strip-shaped small beam radiation field.

[0042] According to an exemplary embodiment of this application, MLC-based three-dimensional small beam radiotherapy lattice irradiation can be achieved through a dual-layer MLC, for example, by using fixed-angle intensity-modulated radiotherapy, rotational intensity-modulated radiotherapy, and three-dimensional conformal irradiation.

[0043] Fixed-angle intensity-modulated (IMM) and rotational intensity-modulated (IMM) methods achieve highly conformal dose distribution to the sub-target matrix through the superposition of multiple subfields, without emphasizing the geometric conformal of the irradiation range of each subfield to the sub-target matrix. As mentioned earlier, orthogonal bilayer MLCs can form all the radiation fields that existing medical electron accelerators based on conventional single-layer MLCs can form, and with greater degrees of freedom. Therefore, dose distributions that are not inferior to those of conventional single-layer MLCs can be achieved using existing inverse optimization algorithms.

[0044] Three-dimensional conformal irradiation achieves a highly conformal dose distribution to the sub-target matrix (e.g., morphology) by forming a geometrically highly conformal irradiation field with the sub-target matrix. Clearly, due to the discrete distribution of the sub-target matrix and the inherent parallel arrangement of blades in the same layer of MLC, neither conventional single-layer MLC nor orthogonal double-layer MLC can achieve highly conformal dose distribution to the sub-target matrix using a single irradiation field (e.g., morphology). Figure 2 As shown in the left figure), this application proposes a grouped irradiation strategy. Its core lies in dividing the spatially segmented radiotherapy target area into multiple independent and parallel subgroups along the main axis of the sub-target matrix. At each selected gantry angle, based on the projection of each sub-target area in the beam direction view (BEV), the movement of the double-layer MLC blades is controlled, so that the radiation beam forms several conformal subfields with the projection height through the MLC blade array, and irradiates them one by one. Each small beam field irradiates only the sub-target area of ​​a specific subgroup (e.g., ...). Figure 4 As shown, the sub-target area is exemplarily divided into five groups, and five small beams of irradiation are performed accordingly, thereby minimizing the interaction between sub-target areas, especially between sub-target areas within different groups, and further improving PVDR and TR.

[0045] In contrast, due to constraints such as the parallel arrangement, blade width, and target matrix layout of conventional single-layer MLC blades, under a group irradiation strategy, although rotating the collimator may improve the conformity of the resulting sub-beams and grouped sub-target areas, it will still inevitably encircle a certain range of normal tissue (such as...). Figure 2 (As shown in the middle and right figures).

[0046] Using orthogonal double-layer MLC, conformal irradiation fields can also be formed for grouped sub-target regions using the same strategy described above. Furthermore, since the blades constituting the "tungsten gate-like" structure can actually move relatively independently, with greater degrees of freedom, the conformal irradiation field formed will have significantly better conformal performance than that formed by conventional single-layer MLC (e.g., ...). Figure 4 or Figure 5 (As shown).

[0047] To optimize the sub-target matrix arrangement and maximize the number of sub-targets, the sub-target matrix may be rotated and / or translated relative to the electron linear accelerator coordinate system. This rotation and translation affect the relative positions of the projected sub-targets on the BEV at a specific gantry angle. In this case, to achieve three-dimensional conformal lattice irradiation of small-beam radiotherapy based on orthogonal double-layer MLC and a group irradiation strategy, the rotation angles of the treatment bed and gantry can be controlled to compensate for the rotation / translation of the sub-target matrix relative to the accelerator coordinate system. This ensures that the projections of each sub-target on the BEV at that treatment bed and gantry angle remain in a grouped arrangement, serving as the basis for subsequent one-dimensional, two-dimensional, and three-dimensional small-beam radiotherapy group irradiation. Figure 6 shows a schematic diagram of how the sub-target matrix is ​​still grouped and parallel when projected onto the BEV after the rotation of the treatment bed and gantry is compensated for by the rotation of the sub-target matrix relative to the accelerator coordinate system. The left figure is a three-dimensional schematic diagram of the sub-target matrix after rotating 30 degrees around the X-axis; the right figure is a schematic diagram of the projection of the sub-target matrix onto the BEV field under the optimized treatment bed rotation angle (0 degrees) and gantry angle (90 degrees).

[0048] Due to the inherent parallel arrangement of each layer of blades, the conformity of the small beam field formed by orthogonal double-layer MLC irradiation is still influenced by a number of factors. These factors include the diameter and spacing of the sub-target areas, the width of the MLC blades, and the orientation of the sub-target matrix relative to the MLC blades (e.g., ...). Figure 2 (As shown). Based on the orthogonal double-layer MLC design of this invention, some embodiments systematically explore the influence of different sub-target matrix arrangement parameters (e.g., sub-target diameter and spacing, and the arrangement direction of the sub-target matrix relative to the MLC blades) on conformity, and establish the relationship curve between the collimator angle and the overall conformity of the small-beam radiation field with different diameters and spacings. Based on this intuitive quantitative basis, the collimator angle with the best conformity performance is selected as the preferred recommended value for the clinical application of three-dimensional small-beam radiotherapy, thereby further improving the conformity of the small-beam radiation field.

[0049] Figure 7 A general flowchart for optimizing small beam field parameters according to an embodiment of this application is shown, as follows: Figure 7 As shown, the field parameter optimization method begins in step 110, which determines the corresponding gantry angle (α) that matches the rotation angle (γ) of different treatment beds based on the sub-target area matrix arrangement parameters.

[0050] For example, subtarget matrix arrangement parameters may include subtarget size (e.g., subtarget diameter), spacing between subtargets, subtarget translation matrix, and rotation matrix. When the subtarget matrix (relative to the accelerator coordinate system) is rotated / translated, the gantry angle will affect the relative positions of the subtarget groups projected onto the BEV. Therefore, the preferred or optimal gantry angle (α) corresponding to different treatment bed rotation angles (γ) can be calculated to ensure that, at these treatment bed rotation and gantry angles, the relative positions of the subtarget projections in the beam directional view (BEV) image remain unchanged (or, the subtarget matrix maintains a precise layered arrangement), thus allowing the continued use of group irradiation strategies. Based on this, a field parameter library can be established, including multiple (γ, α) combinations.

[0051] In step 120, based on the limitations such as the anti-collision range of the medical linear accelerator, feasible field layout parameters (e.g., meeting clinical safety standards) are selected from all possible (γ, α) combinations in the field parameter library. The selected field layout parameters include combinations of multiple treatment bed rotation angles and gantry angles.

[0052] In step 130, based on the optimized treatment bed angle (γ) and gantry angle (α) and sub-target matrix arrangement parameters obtained above, the diameter d and minimum spacing D' of the sub-target area on the feasible field BEV under each combination of treatment bed angle and gantry angle (γ, α) are calculated.

[0053] In step 140, based on the determined frame angle and sub-target area matrix layout parameters, combined with the blade width configuration information of the orthogonal double-layer MLC, the rotation angle (β) of the collimator is gradually increased according to a certain step size, and the field conformity (CI) is calculated at each collimator rotation angle to establish the relationship curve between the collimator rotation angle and the field conformity.

[0054] Finally, in step 150, based on the established β-CI relationship curve, the collimator rotation angle corresponding to the field conformity that is closest to the predetermined value (e.g., 1) is selected, which can be used as the small beam irradiation field parameter for clinical use.

[0055] Through the method described in the above embodiments, the field parameters (treatment bed rotation angle γ, gantry rotation angle α, and collimator rotation angle β) for small-beam radiotherapy are all obtained through optimization. On the one hand, the sub-target areas on the BEV images of each field remain in a layered arrangement, thus continuing the layered irradiation strategy and reducing the dose contribution to adjacent sub-target areas. On the other hand, each layered irradiation field can achieve maximum field conformity. Both of these factors contribute to improving PVDR, thereby achieving a higher treatment ratio.

[0056] According to an exemplary embodiment of this application, the above-described method for optimizing small-beam radiotherapy field parameters based on orthogonal bilayer MLC can be implemented, for example, by a control device such as a controller in a spatially segmented radiotherapy system. Figure 8 The diagram illustrates a partial structural composition of the controller 100, which may include a treatment bed and gantry angle optimization module 110 and a collimator angle optimization module 120. It should be understood that the control device 100 can be integrated as a software module into the small-beam radiotherapy system. This software module can be stored in memory, and its included computer instructions can be executed by, for example, a processor to perform the aforementioned operations. Alternatively, the control device 100 (including its various modules and units) can also be implemented using specialized hardware (e.g., an ASIC) or firmware. All implementations of the control device 100, including software, hardware, and firmware, should be understood to fall within the scope of this invention.

[0057] In one embodiment, the treatment bed and gantry angle optimization module 110 can calculate the preferred / optimal gantry angle (α) corresponding to / matching different treatment bed rotation angles (γ) based on the sub-target matrix arrangement parameters, ensuring that the sub-target matrix maintains a precise layered arrangement in the beam direction view (BEV) image at that gantry angle. Simultaneously, considering the collision avoidance limitations of the medical linear accelerator, several sets (e.g., 7-9 sets) of feasible treatment bed rotation angle-gantry angle combinations that meet clinical safety standards are selected from all possible (γ, α) combinations as field arrangement parameters.

[0058] The collimator angle optimization module 120 can calculate the field conformity (CI) corresponding to different collimator rotation angles (β) based on the sub-target area matrix arrangement parameters and the treatment bed and gantry angle optimization module 110, combined with the leaf geometry characteristics (e.g., leaf width configuration) of the orthogonal double-layer multi-leaf collimator (MLC), and construct a curve relating the collimator rotation angle to the field conformity (β-CI). Based on the characteristics of this curve, the collimator rotation angle β corresponding to the optimal field conformity (e.g., closest to 1) is selected as the field parameter for clinical small-beam radiotherapy. For example, a global optimal search strategy can be used to determine the collimator angle β* that minimizes CI, and output it as the final clinical beam parameter.

[0059] The following provides a more detailed description of the functions implemented by the treatment bed and gantry angle optimization module 110 and the collimator angle optimization module 120.

[0060] Figure 9 A flowchart illustrating a specific implementation of a treatment bed and gantry angle optimization module according to an exemplary embodiment of this application is shown. As shown, in step 310, the initial rotation angle γ of the treatment bed is set in conjunction with the sub-target area matrix arrangement parameters. min(e.g., 0°, 5°, etc.) and angle increment γ step Next, in step 320, starting from the minimum value of the rotation angle of the treatment bed (i.e., k=1), in step 330, the gantry angle under the rotation angle of the treatment bed is calculated so that the relative positions of the projections of each sub-target area in the beam direction view at the gantry angle remain unchanged.

[0061] Reference Figure 10 This diagram illustrates a method for optimizing the angles of the treatment bed and gantry. It assumes the center of the sub-target matrix is ​​located at an isocenter (e.g., the intersection of the accelerator's beam and the gantry's rotation axis), and the gantry's rotation plane around this isocenter is A. The positive normal vector of the sub-target matrix is ​​assumed to be n. When the sub-target matrix has no rotation or translation, n aligns with the principal axis of the medical linear accelerator. When the optimized sub-target matrix undergoes a rotation R, the positive normal vector n changes, but the BEV at any angle on plane B perpendicular to the positive normal vector n also rotates with the matrix. Therefore, the rotation of the sub-target matrix relative to the medical linear accelerator coordinate system can be compensated by rotating the angles of the treatment bed and gantry. Specifically, the ideal combination of gantry and treatment bed angles can be obtained by solving for the intersection line (shown by the thin black dashed line) between the medical linear accelerator gantry rotation plane A and plane B perpendicular to the positive normal vector n of the sub-target matrix. With this angle combination, the gantry is both within the rotation plane A of the medical linear accelerator gantry, which can be clinically implemented, and within the plane perpendicular to the positive direction normal vector n of the sub-target matrix. This keeps the phase position between the projections of the sub-target matrix in the BEV direction unchanged, that is, it can still maintain the grouped arrangement, thus continuing the grouped irradiation strategy.

[0062] The mathematical description of the above process is as follows:

[0063] Before rotation, the normal vectors m and n of the sub-target matrix (m is the positive irradiation direction, and n is the positive matrix direction) are represented in the medical linear accelerator coordinate system as follows:

[0064]

[0065]

[0066] Assume that the rotation matrix R applied to the optimized subtarget region matrix is:

[0067]

[0068] Then m and n after rotation are:

[0069]

[0070]

[0071] Therefore, the angle between the line of intersection of the rotation plane A of the frame and the plane B perpendicular to the normal vector n and the Z-axis is:

[0072]

[0073] Therefore, after applying any rotation R to the sub-target matrix, a gantry illumination angle α can be calculated, ensuring that the relative positions of the sub-target projections in the BEV remain unchanged at this gantry angle, thus allowing the continued use of group illumination strategies (such as...). Figure 6 (As shown). Furthermore, after converting the illumination angle to the sub-target area matrix coordinate system, we obtain:

[0074]

[0075] Then, the rotation angle γ of the next treatment bed can be set. k+1 The aforementioned steps are repeated until all candidate treatment bed rotation angles have been selected, resulting in a library of field parameters for multiple treatment bed rotation angles and gantry angles. Thus, in step 340, a series of field parameters (combinations of gantry angle α and treatment bed angle γ) for a sustainable group irradiation strategy are established.

[0076] It can be understood that after applying a rotation angle γ to the treatment bed, the corresponding rotation matrix is:

[0077]

[0078] Therefore, the overall rotation matrix is ​​transformed into:

[0079]

[0080] At this point, following the aforementioned method, another one can be calculated. , making This allows for multi-field irradiation.

[0081] In step 350, based on the collision avoidance range of the medical linear accelerator and the basic principles of field placement (e.g., placing the field nearby, placing the field along the long axis of the target area, avoiding organs at risk, etc.), a certain number (7-9 groups) of feasible field placement parameters (combinations of treatment bed rotation angle and gantry angle) that meet clinical safety standards are selected from all possible (γ, α) combinations as clinically recommended field parameters.

[0082] At this point, the required field parameters (treatment bed angle and gantry angle) for small-beam radiotherapy based on orthogonal MLC can be optimized, maximizing the radiation field (TR). For one-dimensional or two-dimensional small-beam radiotherapy, simply rotate the collimator to be parallel (or perpendicular) to the long axis of the sub-target area, and use orthogonal double-layer MLC to form the required strip-shaped small beams for grouped irradiation (e.g., Figure 3 (As shown). For three-dimensional small beam radiotherapy, although orthogonal bilayer MLC design and group irradiation strategies can effectively improve the conformity of the small beam field, the conformity of the small beam field formed by group irradiation using orthogonal bilayer MLC is still affected by a number of factors. These factors include the diameter and spacing of the sub-target areas, the width of the MLC blades, and the orientation of the sub-target matrix relative to the MLC blades (e.g., ...). Figure 5 (As shown). To achieve a higher PVDR, the collimator angle needs further optimization.

[0083] Figure 11 A flowchart illustrating the specific implementation of the collimator angle optimization module according to an exemplary embodiment of this application is shown. As shown, in step 410, the diameter d and (minimum) spacing D' of the sub-target area on the BEV are calculated under each combination of the optimized sub-target area matrix arrangement parameters, the treatment bed rotation angle, and the gantry angle. This can be obtained by constructing a geometric model. The obtained sub-target area diameter d and spacing D' can be used for subsequent calculations of conformity under different collimator rotation angles.

[0084] In step 420, the initial rotation angle βmin of the collimator and the angle increment step βstep are set. Next, in step 430, the rotation angle βk of the collimator is set, starting from the minimum value to be selected (i.e., k=1). In step 440, the conformity of each group of irradiation fields under this collimator rotation angle is calculated.

[0085] In one embodiment, the conformity index CI of each group of small-beam irradiation fields under this combination of irradiation field parameters (treatment bed rotation angle, gantry angle, and collimator angle) can be calculated according to the tightest conformity method (i.e., the blade end face is as tangent as possible to the outer contour of the sub-target area). CI is defined as the irradiation area S formed by the grouped irradiation fields. field The projected area S of the grouped sub-target regions on the BEV T The ratio, i.e., the Dice Similarity Coefficient (DSC) value:

[0086]

[0087] The overall conformity index of the firing field is the arithmetic mean of the conformity indices of the small beam firing fields of each group. The field conformity index is used as the angle of rotation of the collimator.

[0088]

[0089] Then, set the next collimator rotation angle β. k+1Repeat the aforementioned steps until all collimator rotation angles have been selected. This establishes a collimator rotation angle β and a small-beam field overall conformity index in step 450. Relationship curves (such as) Figure 12 As shown, the horizontal axis represents the collimator rotation angle, and the vertical axis represents the overall conformity index of the small beam field.

[0090] In step 460, the collimator rotation angle β and the overall conformity index of the small beam field are... On the relationship curve, the one closest to 1 is preferred. The corresponding collimator rotation angle β (e.g., 36°) is used as the collimator parameter for the optimal small beam field under the current combination of treatment bed rotation angle and gantry angle.

[0091] The principles of the invention have been described above with reference to specific embodiments. Those skilled in the art will understand that the specific embodiments described above are for illustrative purposes only, and the invention is not limited to the above embodiments. Many modifications and variations in detail and form can be made without departing from the spirit and scope of the invention, such as certain variations, modifications, alterations, additions, and sub-combinations of the disclosed embodiments. The scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling spatially fractionated radiotherapy, the method comprising: The beam generated by the beam module is collimated using an orthogonal double-layer multi-leaf collimator. The orthogonal double-layer multi-leaf collimator includes a first multi-leaf collimator and a second multi-leaf collimator. The first multi-leaf collimator includes a first blade array that can move along a first direction. The second multi-leaf collimator includes a second blade array that can move along a second direction. The second multi-leaf collimator is located below the first multi-leaf collimator, and the second direction is perpendicular to the first direction. The ray beam obtains a predetermined size of radiation field after being collimated by the orthogonal double-layer multi-leaf collimator, and the aperture or minor diameter of the radiation field can be less than 5 mm.

2. The control method as described in claim 1, further comprising: The spatial segmentation radiotherapy target area is divided into multiple parallel sub-target areas. Based on the sub-target area arrangement parameters, the corresponding gantry angles for different treatment bed rotation angles are determined, ensuring that the projections of each sub-target area in the beam direction view remain grouped under the treatment bed rotation angle and the corresponding gantry angle, thereby establishing a beam field parameter library; and Feasible field parameter configurations are selected from the field parameter library, which include combinations of multiple treatment bed rotation angles and gantry angles.

3. The control method as described in claim 2, wherein, The process of establishing a shooting field parameter library and filtering feasible shooting field parameter configurations includes: Set the initial rotation angle of the treatment bed; Calculate the gantry angle under the rotation angle of the treatment bed, so that the projections of each sub-target area in the beam direction view at the gantry angle maintain the grouped arrangement; Repeat the above steps to obtain a library of field parameters for multiple treatment bed rotation angles and gantry angles; and Based on the collision avoidance range and / or field rules of the electronic linear accelerator, feasible combinations of treatment bed rotation angle and gantry angle are selected from the field parameter library.

4. The control method as described in claim 2, further comprising: Control the dual-layer multi-leaf collimator to rotate to a direction parallel or perpendicular to the long axis of the sub-target area; as well as Based on the projection of the sub-target area onto the beam direction, the movement of the first blade array and the second blade array is controlled so that the beam passes through the first blade array and the second blade array to form a strip-shaped small beam field conforming to the projection, thus forming a one-dimensional or two-dimensional spatially segmented irradiation field.

5. The control method as described in claim 2, further comprising: Based on the determined feasible field parameter configuration and sub-target area layout parameters, combined with the blade width configuration of the double-layer multi-leaf collimator, the rotation angle of the double-layer multi-leaf collimator is further increased step by step according to a certain step size, and the field conformity is calculated at each collimator rotation angle to establish the relationship curve between the collimator rotation angle and the field conformity. as well as Select the collimator rotation angle that corresponds to the field conformity closest to 1 to form a three-dimensional spatially segmented illumination field.

6. The control method as described in claim 4, wherein, The determination of the collimator rotation angle includes: Based on the sub-target area layout parameters, treatment bed rotation angle and gantry angle, calculate the diameter and minimum spacing of the sub-target area in the beam direction under each combination of treatment bed rotation angle and gantry angle; Set the initial angle of collimator rotation; Calculate the conformity index of the grouped irradiation fields of each sub-target area under the collimator rotation angle. The conformity index is the DSC value of the irradiation area formed by the grouped irradiation fields and the projected area of ​​the grouped sub-target areas in the beam direction view. Based on the average conformity index of the grouped irradiation fields of each sub-target area, the conformity of the field corresponding to the collimator rotation angle is determined. Repeat the above steps to establish the relationship curve between the collimator rotation angle and the conformity of the firing field; and Based on the relationship curve, select the collimator rotation angle that corresponds to the field conformity closest to 1.

7. The control method according to any one of claims 2 to 6, wherein, The arrangement parameters of the sub-target areas include at least one of the following: the diameter of the sub-target area, the spacing between the sub-target areas, the translation matrix of the sub-target area, or the rotation matrix of the sub-target area.

8. A spatial fractionation radiotherapy system, comprising: frame; A beam module, mounted on the frame, is used to generate a beam of radiation. An orthogonal double-layer multi-leaf collimator is mounted on the frame and includes a first multi-leaf collimator and a second multi-leaf collimator. The first multi-leaf collimator includes a first blade array that can move along a first direction, and the second multi-leaf collimator includes a second blade array that can move along a second direction. The second multi-leaf collimator is located below the first multi-leaf collimator, and the second direction is perpendicular to the first direction. as well as The controller is communicatively coupled to the frame, the beam module, and the orthogonal double-layer multi-leaf collimator, and is used to control the movement of the first blade array and the second blade array so that the beam obtains a predetermined size of radiation field after being collimated by the double-layer multi-leaf collimator, wherein the aperture or minor diameter of the radiation field can be less than 5 mm.

9. The spatial segmentation radiotherapy system as described in claim 8, wherein, The controller includes a treatment bed and gantry angle optimization module and a collimator angle optimization module. The treatment bed and gantry angle optimization module is configured to: determine the corresponding gantry angles for different treatment bed rotation angles based on the sub-target area arrangement parameters, ensuring that the projections of each sub-target area in the beam direction view remain grouped under the treatment bed rotation angle and the corresponding gantry angle, thereby establishing a field parameter library; and filter feasible field parameter configurations from the field parameter library, wherein the feasible field parameter configurations include multiple combinations of treatment bed rotation angles and gantry angles. The collimator angle optimization module is configured as follows: based on the determined feasible field parameters and sub-target layout parameters, combined with the blade width configuration of the double-layer multi-leaf collimator, the rotation angle of the double-layer multi-leaf collimator is gradually increased by a certain step size, and the field conformity is calculated at each collimator rotation angle to establish a curve relating the collimator rotation angle to the field conformity; and the collimator rotation angle corresponding to the field conformity closest to 1 is selected.

10. The spatial fractionation radiotherapy system as described in claim 9, wherein, The collimator angle optimization module is configured to determine the collimator rotation angle in the following manner: Based on the sub-target area layout parameters, treatment bed rotation angle and gantry angle, calculate the diameter and minimum spacing of the sub-target area in the beam direction under each combination of treatment bed rotation angle and gantry angle; Set the initial angle of collimator rotation; Calculate the conformity index of the grouped irradiation fields of each sub-target area under the collimator rotation angle. The conformity index is the DSC value of the irradiation area formed by the grouped irradiation fields and the projected area of ​​the grouped sub-target areas in the beam direction view. Based on the average conformity index of the grouped irradiation fields of each sub-target area, the conformity of the field corresponding to the collimator rotation angle is determined. Repeat the above steps to establish the relationship curve between the collimator rotation angle and the conformity of the firing field; and Based on the relationship curve, select the collimator rotation angle that corresponds to the field conformity closest to 1.

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