WO2021248837A1 - 一种基于分象限的正交双层光栅动态调强分割方法 - Google Patents

一种基于分象限的正交双层光栅动态调强分割方法 Download PDF

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WO2021248837A1
WO2021248837A1 PCT/CN2020/130429 CN2020130429W WO2021248837A1 WO 2021248837 A1 WO2021248837 A1 WO 2021248837A1 CN 2020130429 W CN2020130429 W CN 2020130429W WO 2021248837 A1 WO2021248837 A1 WO 2021248837A1
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blade
quadrant
flux
area
segmentation
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PCT/CN2020/130429
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English (en)
French (fr)
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项云飞
文虎儿
姚毅
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苏州雷泰医疗科技有限公司
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Priority to US17/915,385 priority Critical patent/US20230132237A1/en
Publication of WO2021248837A1 publication Critical patent/WO2021248837A1/zh

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    • G—PHYSICS
    • G16—INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS
    • G16H—HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA
    • G16H20/00—ICT specially adapted for therapies or health-improving plans, e.g. for handling prescriptions, for steering therapy or for monitoring patient compliance
    • G16H20/40—ICT specially adapted for therapies or health-improving plans, e.g. for handling prescriptions, for steering therapy or for monitoring patient compliance relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/103—Treatment planning systems
    • A61N5/1036—Leaf sequencing algorithms
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/103—Treatment planning systems
    • A61N5/1031—Treatment planning systems using a specific method of dose optimization
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy
    • A61N5/1042—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head
    • A61N5/1045—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy with spatial modulation of the radiation beam within the treatment head using a multi-leaf collimator, e.g. for intensity modulated radiation therapy or IMRT

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  • the invention relates to a dynamic intensity modulation and segmentation method of a multi-leaf collimator, in particular to a quadrant-based orthogonal double-layer grating dynamic intensity modulation and segmentation method.
  • a multi-leaf collimator is generally used to adjust the beam irradiation range and intensity to achieve the field beam current Intensity adjustable radiotherapy, namely intensity modulated radiotherapy (IMRT).
  • IMRT intensity modulated radiotherapy
  • MLC was originally used in classical conformal radiotherapy to replace the block in conventional radiotherapy to form the desired shape of the irradiation field.
  • MLC consists of two closely arranged leaves. Each blade is made of tungsten alloy, in a long strip shape, and is driven by a small motor.
  • MLC conformal has significant advantages: shortens the treatment time, also shortens the time interval between simulated positioning and treatment, and greatly improves the efficiency of radiotherapy; the attenuation ability of radiation is stronger than that of the stop ;
  • the operation is simple and safe, no need to move bulky stoppers; it can be reused; it will not produce harmful gas or dust; it can flexibly respond to changes in the target area and correct errors.
  • Orthogonal double-layer grating contains two mutually perpendicular MLC layers.
  • the upper and lower layers of the corresponding blades can cooperate with each other at the edge of the target area to achieve the consistency of the MLC shape and the boundary of the target area, and improve the conformability of the field and the target area.
  • the current algorithm for MLC dynamic segmentation is mainly Sliding Window's dynamic sliding window scanning segmentation technology, but because there is always a gap between a pair of opposed blades during the scanning process, it is impossible to complete the low dose of the concave target area and the inner ring target area. Segmentation, G.
  • the existing MLC dynamic segmentation algorithms mainly have the following problems:
  • the projection width of the single-layer MLC blade on the isocenter plane is usually between 0.5cm and 1.0cm.
  • the irradiation field formed by the single-layer MLC has a stepped boundary, which cannot be completely consistent with the desired smooth boundary of the target area. .
  • the blade width of the MLC can be made thinner and thinner to improve the conformity of the shooting field, the blade width cannot be made theoretically infinitely thin due to the mechanical processing of the blade width, so the jagged shooting field edge cannot be completely eliminate.
  • a single-layer MLC cannot move from two directions to complete the tracking treatment of the dynamic target area of the lung.
  • the present invention proposes a quadrant-based orthogonal double-layer grating dynamic intensity modulation segmentation method.
  • a quadrant-based orthogonal double-layer grating dynamic intensity-modulation segmentation method specifically includes the following steps:
  • S3 Divide the quadrants, divide the field area surrounded by four groups of blades up, down, left, and right into at least two quadrants, and obtain the flux distribution and corresponding blade sequence of each quadrant;
  • S4 Carry out regional planning on the flux surface of each quadrant, obtain multiple different regions, and determine the division method of different regions;
  • step S2 includes the following content: the rays are projected under the isocenter plane coordinate system S-XY through the upper and lower layers of gratings, and the upper and lower layers of blades are respectively located in four directions of the isocenter plane.
  • the quadrant division may use the maximum point or minimum point in the target area as the division center.
  • step S3 if there is a concave flux distribution or an annular target area flux distribution, the quadrant division takes the minimum point as the division center;
  • the center of the concave target area is located on the intersection of the two quadrants.
  • each quadrant corresponds to the ray flux of a region within the range of the radiation field, and corresponds to at least a pair of mutually orthogonal blade groups.
  • step S4 specifically includes the following content: around any wave crest or trough in the flux surface, it can be divided into four regions A1, A2, A3, and A4 according to the magnitude of the partial derivative;
  • the area is area A1;
  • the area is area A2;
  • the area is area A3;
  • step S5 specifically includes the following steps:
  • step S5.1 specifically includes the following: two orthogonal blade groups, one of which is defined as an active blade and the other as a passive blade.
  • the active blade moves from the edge of the shooting field to the center of the shooting field.
  • the moving blade retreats from the center of the shooting field to the edge of the shooting field;
  • Its initial position can be determined as: the active blade is at the edge of the field, and the driven blade is at the junction of the quadrants.
  • step S5.2 specifically includes the following content: on the premise of a given accelerator dose rate and blade movement in one direction, the blade trajectory is described by the corresponding relationship between the blade position and the flux size;
  • step S5.3 specifically includes the following content: the starting position of each blade position is known, and the flux function of the next instant is solved by the flux function of the previous position.
  • the invention completes the dynamic segmentation of arbitrary shape target areas (concave target areas, annular target areas, etc.) and multiple target areas through the coordinated movement of the upper and lower orthogonal blades, and realizes the upper and lower layers of the orthogonal double-layer grating from two directions.
  • the dynamic segmentation avoids the end face perspective between the blade pairs and improves the segmentation efficiency.
  • Fig. 1 is a three-dimensional view of a strong ray flux in a concave target area provided by an embodiment of the invention.
  • FIG. 2 is the position distribution of the orthogonal double-layer grating provided by the embodiment of the invention in the field coordinate system;
  • Figure 2 (a) is a schematic diagram of the structure of the projection of the ray and the upper and lower gratings
  • Figure 2(b) shows the positional relationship between the upper blade, the lower blade and the isocenter plane.
  • Fig. 3 is a schematic diagram of quadrant division and leaf sequence allocation for flux surface provided by an embodiment of the invention.
  • Figure 4 is a diagram of three typical quadrant division modes provided by an embodiment of the invention.
  • Fig. 5 is a schematic diagram of determining the initial position of the master (slave) moving blade in the first quadrant provided by an embodiment of the invention.
  • Fig. 6 is a graph of the function relationship between the position of the right blade in the first quadrant and its flux value provided by an embodiment of the invention.
  • Fig. 7 is a graph of the function relationship between the position of the front blade in the first quadrant as the driven blade and the magnitude of the flux value provided by an embodiment of the invention.
  • Fig. 8 is a schematic diagram of solving the blade trajectory function provided by an embodiment of the invention.
  • FIG. 9 is a schematic diagram of area division around a wave crest or wave trough provided by an embodiment of the invention.
  • FIG. 10 is a schematic diagram of area division in the first quadrant provided by an embodiment of the invention.
  • Figure 11 is a three-dimensional view of the flux distribution in the first quadrant provided by an embodiment of the invention.
  • Fig. 12 is a schematic diagram of the initial position of the blade in the first quadrant after area division according to an embodiment of the invention.
  • FIG. 13 is a curve diagram of the movement trajectory of the driving blade or the driven blade in the overlapping area of the blades in the first quadrant according to an embodiment of the invention
  • Figure 13(a) is a diagram of the movement trajectory of the right blade
  • Figure 13(b) is a diagram of the movement trajectory of the front blade.
  • Fig. 14 is a three-dimensional view of flux segmented by blade trajectories provided by an embodiment of the invention.
  • a quadrant-based orthogonal double-layer grating dynamic intensity-modulated segmentation method specifically includes the following step:
  • S4 Carry out regional planning on the flux surface of each quadrant, obtain multiple different regions, and determine the division method of different regions;
  • each quadrant corresponds to two different sets of blade sequences.
  • the combination of adjacent quadrants can also form a single quadrant, which may correspond to three different sets of blades; the division of quadrants should ensure that each The total time for flux segmentation in all quadrants is the same.
  • step S2 includes the following content: the ray is projected under the isocenter plane coordinate system S-XY through the upper and lower gratings , The upper and lower layers of blades are respectively located in four directions of the isocenter plane.
  • the quadrant division can be the maximum point or minimum point in the target area as the segmentation center .
  • the remaining characteristic technologies are the same, except that, as shown in FIG. 4, for step S3, if there is a concave flux distribution or an annular target area flux In the case of distribution, the quadrant division takes the minimum point as the division center;
  • the center of the concave target area is located on the intersection of the two quadrants.
  • the " ⁇ " in Figure 4 represents the valley center 2.
  • each quadrant corresponds to the ray flux of a region within the range of the radiation field.
  • each quadrant corresponds to the ray flux of a region within the range of the radiation field.
  • step S4 specifically includes the following content: As shown in FIG. 9, for any wave crest or trough in the flux surface 1.
  • the surrounding area can be divided into four areas A1, A2, A3 and A4 according to the size of the partial derivative;
  • the area is area A1;
  • the area is area A2;
  • the area is area A3;
  • the area is area A4.
  • both regions A1 and A3 can be independently divided by right blades. Both areas A1 and A2 can be divided independently using front blades, while for area A4, two sets of blades are required to be divided orthogonally.
  • step S5 specifically includes the following steps:
  • step S5.1 specifically includes the following content: two orthogonal blade groups, one of which is defined as the active blade and the other as the passive blade.
  • the active blade moves from the edge of the shooting field to the center of the shooting field, and the driven blade is defined as the active blade.
  • the center of the shooting field retreats to the edge of the shooting field;
  • Its initial position can be determined as: the active blade is at the edge of the field, and the driven blade is at the junction of the quadrants.
  • Figure 5 shows an initial position of the blades in the first quadrant.
  • the right blade is used as a group of driving blades, and the left blade is used as a group of driven blades.
  • step S5.2 specifically includes the following content: on the premise of a given accelerator dose rate and the blade moving in one direction, the corresponding relationship between the blade position and the flux size is used to describe the blade trajectory;
  • the blade trajectory can be described by the corresponding relationship between the position of the blade and the amount of flux. ; Taking the position of the blade end surface as the blade position, it can be found that the blade position and its corresponding flux are always a monotonous function relationship without the other blades being blocked by the maximum speed of the blade.
  • step S5.3 specifically includes the following content: the starting position of each blade position is known, and the flux function of the next instant is solved by the flux function of the previous position.
  • ⁇ x, ⁇ y are the changes in the position of the blades at two adjacent moments in the coordinate system S
  • k min is the minimum flux increment efficiency corresponding to the maximum speed limit of the blade
  • g 21 (x, y) g 22 (x, y)
  • g 23 ( x, y) are the flux function values obtained by searching along the x-axis direction, the derivative along the flux surface direction, and the y-axis direction respectively.
  • the invention completes the dynamic segmentation of arbitrary shape target areas (concave target areas, annular target areas, etc.) and multiple target areas through the coordinated movement of the upper and lower orthogonal blades, and realizes the upper and lower layers of the orthogonal double-layer grating from two directions
  • the dynamic segmentation avoids the end face perspective between the blade pairs and improves the segmentation efficiency.
  • annular target area with multiple connected regions is described.
  • S4 Carry out regional planning on the flux surface of each quadrant to obtain all A1, A2, A3, A4 regions, and determine the division of different regions at the same time, as shown in Figure 10, taking the first quadrant as an example, where it is located in the first quadrant Use the right blade for independent segmentation in the A1 area, and use the right blade for the independent segmentation in the A3 area of the first quadrant; use the front blade for the A2 area in the first quadrant for independent segmentation, and the A4 area in the first quadrant needs to enter the area All right blades and front blades are divided orthogonally;
  • S5.1 Determine the initial position of the active and driven blade after the area is divided. As shown in Figure 12, it is the initial position of all the blades in the first quadrant. In the overlap area A4 in the figure, set the front blade as the driven blade. In the A4 area, the initial position of all the driven blades is located in the junction diagram of the quadrants, and the retreat movement is carried out.
  • segNum 50 100 250 500 1000 10000 ⁇
  • segNum refers to the equal fraction of the flux surface segmentation, which is inversely proportional to the segmentation step. The larger the segNum, the finer the flux surface segmentation.

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Abstract

一种基于分象限的正交双层光栅动态调强分割方法，具体包括以下步骤：S1：通过放疗计划系统计算出每个射野下的射线通量分布；S2：采用正交双层光栅进行通量分割；S3：进行划分象限，将上下左右四组叶片围成的射野区域划分成至少两个象限，得到每个象限的通量分布和对应叶片序列；S4：对各个象限的通量曲面进行区域规划，得到多个不同区域，确定不同区域的分割方式；S5：对于任一象限，采用两个互相正交的叶片组进行分割。通过上下层正交叶片的相互配合运动完成任意形状靶区以及多个靶区的动态分割，实现正交双层光栅上下两层从两个方向的动态分割，避免叶片对间的端面透视，提高分割效率。

Description

一种基于分象限的正交双层光栅动态调强分割方法 技术领域
本发明涉及一种多叶准直器动态调强分割方法，具体涉及一种基于分象限的正交双层光栅动态调强分割方法。
背景技术
对肿瘤(靶区)进行放射治疗时，为保护健康组织免受损害，一般使用多叶准直器(multi-leaf collimator，MLC)来调整射束照射范围和强度的调整，实现射野束流强度可调的放射治疗，即调强放射治疗(intensity modulated radiotherapy，IMRT)。
MLC最初应用于经典适形放射治疗，替代常规放射治疗中的挡块，形成期望的照射野形状。MLC由两组紧密排列的叶片组成。每个叶片都由钨合金制成，呈长条状，由一个小型电机驱动。与射野挡块相比，MLC适形具有显著优势：缩短了治疗时间，也缩短了模拟定位和治疗之间的时间间隔，大幅提高了放射治疗的效率；对放射线的衰减能力比挡块强；操作简便安全，不用搬动笨重的挡块；可重复使用；不会产生有害气体或粉尘；能灵活应对靶区的变化和纠正错误。
正交双层光栅包含两层互相垂直的MLC，可以在靶区边缘位置由上下两层对应的叶片互相配合来实现MLC形状与靶区边界的一致性，提高射野与靶区的适形性；由于至少有两层叶片准直装置的叶片相互垂直，都可按照要求调整出一样形状的窗口，彼此遮挡叶片间的漏射射线，射线的透漏射大大减少，也有效的减小了半影区，从而可以准确定位治疗，为少分次、大剂量治疗提供了条件，并且叠加的叶片，使得穿透叶片准直器射线衰减到安全的范围，提高了设备的使用效率，降低了医疗成本和患者的负担；同时，由于上下两层叶片相互垂直，可在互相垂直的两个方向运动。
目前关于MLC动态分割的算法主要是Sliding window的动态滑窗扫描分割技术，但是由于在扫描过程中一对相互对立的叶片间始终存在间隙，无法完成内凹型靶区和内环形靶区的低剂量分割，G.Grigorow在文献《SU-GG-T-93：Dosimetry Evaluation and Correction of DMLC Control Points for Sliding Window IMRT》提出了一种改变医用电子直线加速器剂量率和调整叶片最大速度的方法来减小叶片间的漏射，但是无法从根本上来消除一对叶片间的间隙产生的漏射问题；关于正交双层光栅动态上下两层同时进行动态分割的方法目前没有被提及，如何应用双层光栅解决内凹型靶区和环形靶区的动态分割问题，以及如何使用正交双层光栅从两个方向运动完成对肺部动态靶区跟踪治疗等等这些世界难题仍需要注入新的解决方案。
现有的MLC动态分割的算法主要存在以下问题：
第一，单层MLC的叶片在等中心平面的投影宽度通常在0.5cm～1.0cm之间，单层MLC形成的照射野具有台阶状边界，不能与期望形成的边界光滑的靶区边界完全一致。虽然可以通过将MLC的叶片宽度做的越来越薄，从而提高射野的适形度，但是因为叶片宽度机械加工的原因不能做到理论上的无限薄，所以锯齿状的射野边缘无法完全消除。
第二，由于在调强射野范围内，存在较多成对闭合的叶片，但因为机械及运动防撞的考虑，成对闭合叶片间留有间隙，存在大约20％-30％的叶片端面透射；
第三，单层MLC无法从两个方向运动完成对肺部动态靶区跟踪治疗。
发明内容
为了解决上述技术问题，本发明提出了一种基于分象限的正交双层光栅动态调强分割方法。
为了达到上述目的，本发明的技术方案如下：
一种基于分象限的正交双层光栅动态调强分割方法，具体包括以下步骤：
S1：通过放疗计划系统计算出每个射野下的射线通量分布，在等中心平面内的射野范围内，可表示为一个通量曲面F(x，y)；
S2：采用正交双层光栅进行通量分割；
S3：进行划分象限，将上下左右四组叶片围成的射野区域划分成至少两个象限，得到每个象限的通量分布和对应叶片序列；
S4：对各个象限的通量曲面进行区域规划，得到多个不同区域，确定不同区域的分割方式；
S5：对于任一象限，采用两个互相正交的叶片组进行分割。
在上述技术方案的基础上，还可做如下改进：
作为优选的方案，步骤S2包括以下内容：射线通过上下两层光栅投影在等中心平面坐标系S-XY下，上下两层叶片分别位于等中心平面的四个方位。
作为优选的方案，对于步骤S3，象限划分可以靶区内的极大值点或极小值点为分割中心。
作为优选的方案，对于步骤S3，若存在内凹型通量分布或环形靶区通量分布时，则象限划分以极小值点为分割中心；
若存在多个内凹型区域时，则使凹型靶区的中心位于其中两象限的交线上。
作为优选的方案，对于步骤S3，完成象限分割后每个象限对应射野范围内一个区域的射线通量，对应至少一对相互正交的叶片组。
作为优选的方案，步骤S4具体包括以下内容：对于通量曲面内任意一个波峰或波谷周围，按照偏导数大小可以划分为四个区域A1、A2、A3和A4；
当
Figure PCTCN2020130429-appb-000001
且
Figure PCTCN2020130429-appb-000002
时，该区域为区域A1；
当
Figure PCTCN2020130429-appb-000003
且
Figure PCTCN2020130429-appb-000004
时，该区域为区域A2；
当
Figure PCTCN2020130429-appb-000005
且
Figure PCTCN2020130429-appb-000006
时，该区域为区域A3；
当
Figure PCTCN2020130429-appb-000007
且
Figure PCTCN2020130429-appb-000008
时，该区域为区域A4。
作为优选的方案，步骤S5具体包括以下步骤：
S5.1：确定叶片初始位置；
S5.2：建立叶片运动轨迹函数；
S5.3：应用时滞微分方程求解叶片运动轨迹函数。
作为优选的方案，步骤S5.1具体包括以下内容：两个正交的叶片组，定义其中一组为主动叶片，另一组为被动叶片，主动叶片由射野边缘向射野中心运动，从动叶片由射野中心往射野边缘进行回退；
其初始位置可以确定为：主动叶片在射野边缘，从动叶片位于象限交界位置。
作为优选的方案，步骤S5.2具体包括以下内容：在给定加速器剂量率以及叶片沿一个方向运动的前提下，采用叶片位置和通量大小之间对应关系描述叶片轨迹；
以叶片端面位置作为叶片位置，在没有其余叶片遮挡的情况下，叶片位置与其对应通量大小为单调函数关系。
作为优选的方案，步骤S5.3具体包括以下内容：已知每个叶片位置的起始位置，通过前一位置的通量函数对下一瞬时的通量函数进行求解。
本发明通过上下层正交叶片的相互配合运动完成任意形状靶区(内凹型靶区、环形靶区等)以及多个靶区的动态分割，实现正交双层光栅上下两层从两个方向的动态分割，避免叶片对间的端面透视，提高分割效率。
附图说明
图1为发明实施例提供的一个内凹型靶区强射线通量三维视图。
图2为发明实施例提供的正交双层光栅在射野坐标系下的位置分布；
图2(a)为射线以及上下两层光栅的投影时结构示意图；
图2(b)为上层叶片、下层叶片与等中心平面之间的位置关系。
图3为发明实施例提供的对通量曲面进行象限划分与叶片序列分配示意图。
图4为发明实施例提供的三种典型的象限分割模式图；
图4(a)象限分割模式图之一；
图4(b)象限分割模式图之二；
图4(c)象限分割模式图之三；
图5为发明实施例提供的第一象限的主(从)动叶片初始位置确定示意图。
图6为发明实施例提供的第一象限内右叶片位置与其通量值大小之间的函数关系曲线图。
图7为发明实施例提供的第一象限内前叶片作为从动叶片时其位置与通量值大小之间的函数关系曲线图。
图8为发明实施例提供的叶片轨迹函数求解示意图。
图9为发明实施例提供的波峰或波谷周围的区域划分示意图。
图10为发明实施例提供的第一象限内的区域划分示意图。
图11为发明实施例提供的第一象限内的通量分布三维视图。
图12为发明实施例提供的区域划分后第一象限内的叶片初始位置示意图。
图13为发明实施例提供的第一象限内叶片交叠区域内主动叶片或从动叶片的运动轨迹曲线图；
图13(a)为右叶片的运动轨迹图；
图13(b)为前叶片的运动轨迹图。
图14为发明实施例提供的通过叶片轨迹分割出的通量三维视图。
其中：1-波峰或波谷；2-凹谷中心。
具体实施方式
下面结合附图详细说明本发明的优选实施方式。
为了达到本发明的目的，一种基于分象限的正交双层光栅动态调强分割方法的其中一些实施例中，一种基于分象限的正交双层光栅动态调强分割方法，具体包括以下步骤：
S1：通过放疗计划系统计算出每个射野下的射线通量分布，在等中心平面内的射野范围内，可表示为一个通量曲面F(x，y)；
S2：采用正交双层光栅进行通量分割；
S3：进行划分象限，将上下左右四组叶片围成的射野区域划分成最多四个象限，得到每个象限的通量分布和对应叶片序列；
S4：对各个象限的通量曲面进行区域规划，得到多个不同区域，确定不同区域的分割方式；
S5：对于任一象限，采用两个互相正交的叶片组进行分割。
在步骤S3中，如图3所示，每个象限对应两组不同的叶片序列，相邻象限组合也可以形成一个单独的象限，其可能对应三组不同的叶片；象限的划分应尽量保证每个象限进行通量分割的总时间一致。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，步骤S2包括以下内容：射线通过上下两层光栅投影在等中心平面坐标系S-XY下，上下两层叶片分别位于等中心平面的四个方位。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，对于步骤S3，象限划分可以靶区内的极大值点或极小值点为分割中心。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，如图4所示，对于步骤S3，若存 在内凹型通量分布或环形靶区通量分布时，则象限划分以极小值点为分割中心；
若存在多个内凹型区域时，则使凹型靶区的中心位于其中两象限的交线上。
其中，图4中的“○”代表凹谷中心2。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，对于步骤S3，完成象限分割后每个象限对应射野范围内一个区域的射线通量，对应至少一对相互正交的叶片组。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，步骤S4具体包括以下内容：如图9所示，对于通量曲面内任意一个波峰或波谷1周围，按照偏导数大小可以划分为四个区域A1、A2、A3和A4；
当
Figure PCTCN2020130429-appb-000009
且
Figure PCTCN2020130429-appb-000010
时，该区域为区域A1；
当
Figure PCTCN2020130429-appb-000011
且
Figure PCTCN2020130429-appb-000012
时，该区域为区域A2；
当
Figure PCTCN2020130429-appb-000013
且
Figure PCTCN2020130429-appb-000014
时，该区域为区域A3；
当
Figure PCTCN2020130429-appb-000015
且
Figure PCTCN2020130429-appb-000016
时，该区域为区域A4。
采用该实施方式，为了提高分割效率，进行区域划分，对一个象限中不同区域采用不同分割方式，如图10所示，在第一象限中，区域A1和A3均可采用右叶片进行独立分割，区域A1和A2均可采用前叶片进行独立分割，对于区域A4则需要两组叶片进行正交配合分割。
为了进一步地优化本发明的实施效果，在另外一些实施方式中，其余特征技术相同，不同之处在于，步骤S5具体包括以下步骤：
S5.1：确定叶片初始位置；
S5.2：建立叶片运动轨迹函数；
S5.3：应用时滞微分方程求解叶片运动轨迹函数。
进一步，步骤S5.1具体包括以下内容：两个正交的叶片组，定义其中一组为主动叶片，另一组为被动叶片，主动叶片由射野边缘向射野中心运动，从动叶片由射野中心往射野边缘进行回退；
其初始位置可以确定为：主动叶片在射野边缘，从动叶片位于象限交界位置。
值得注意的是，在定义从动叶片的时候要避免一对相对的叶片均为从动叶片。如图5所示为第一象限叶片的一种初始位置情况，右叶片作为一组主动叶片，左叶片作为一组从动叶片。
进一步，步骤S5.2具体包括以下内容：在给定加速器剂量率以及叶片沿一个方向运动的前提下，采用叶片位置和通量大小之间对应关系描述叶片轨迹；
以叶片端面位置作为叶片位置，在没有其余叶片遮挡的情况下，叶片位置与其对应通量大小为单调函数关系。
采用该实施方式，在给定加速器剂量率以及叶片沿一个方向运动的前提下，由于射线通量值大小与时间成正比，可以用叶片的位置和通量大小之间对应的关系来描述叶片轨迹；以叶片端面位置作为叶片位置，可以发现在没有其余叶片遮挡的情况下，由于叶片最大运动速度限制，叶片位置与其对应通量大小始终是一个单调的函数关系。
如图6所示，以第一象限任一右叶片为例，其位置与其对应通量之间的关系如图，记为g2(x，yi)，其中x为该右叶片某时刻对应的端面位置，yi为该右叶片在坐标系S下对应的纵坐标。同理，从动叶片位置与其对应的通量大小也为一个单调函数。如图7所示，以第一象限前叶片为例，作为从动叶片时，前叶片在坐标系S下由初始位置0往Y轴正方向回退，前叶片在每个位置独立的遮挡量为h1(xi，y)＝T-g1(xi，y)，其中T为总照射量，g1(xi，y)为前叶片位置对应的通量，y为该前叶片某时刻对应的端面位置，xi为该前叶片在坐标系S下对应的横坐标。
进一步，步骤S5.3具体包括以下内容：已知每个叶片位置的起始位置，通过前一位置的通量函数对下一瞬时的通量函数进行求解。
如图8所示，以第一象限任一点的右叶片(主动叶片)为例，建立时滞微分方程进行通量函数g2(x，y)求解，如下：
Figure PCTCN2020130429-appb-000017
其中，Δx，Δy为坐标系S下，两个相邻时刻叶片位置的变化量，
Figure PCTCN2020130429-appb-000018
为射线通量曲面沿x，y两个方向的偏导数，k min为叶片最大速度限制对应最小通量增量效率，g 21(x，y)，g 22(x，y)，g 23(x，y)分别为沿x轴方向、沿通量曲面方向导数、沿y轴方向搜索得到的通量函数值。
以上多种实施方式可交叉并行实现。
本发明通过上下层正交叶片的相互配合运动完成任意形状靶区(内凹型靶区、环形靶区等)以及多个靶区的动态分割，实现正交双层光栅上下两层从两个方向的动态分割，避免叶片对间的端面透视，提高分割效率。
为了说明本发明的具体实施过程，针对一个多连通区域的环形靶区进行说明。
具体过程如下：
S1：从放疗计划系统中导入一个多连通区域的环形靶区的射线通量，在等中心平面内的射野范围内，可以表示为一个通量曲面F(x，y)，如图1所示；
S2：采用正交双层光栅进行通量分割，如图2(a)所示，射线通过上下两层光栅投影在等中心平面坐标系S-XY下，上下两层叶片分别位于等中心平面四个方位，如图2(b)所示，其中上层叶片位于等 中心平面前后端，下层叶片位于等中心平面左右端；
S3：进行象限划分，得到四个象限的通量分布和对应叶片序列，如图11为第一象限的通量分布；
S4：对各个象限的通量曲面进行区域规划，得到所有的A1、A2、A3、A4区域，同时确定不同区域的分割当时，如图10所示，以第一象限为例，所在第一象限的A1区域选用右叶片进行独立分割，所在第一象限的A3区域选用右叶片进行独立分割；第一象限的A2区域选用前叶片进行独立分割，第一象限的A4区域则需要进过该区域的所有右叶片和前叶片进行正交配合分割；
S5.1：进行区域划分后确定主动从动叶片的初始位置，如图12所示，为第一象限内所有叶片的初始位置，图中在交叠区域A4，设置前叶片为从动叶片，在A4区域的所有从动叶片初始位置位于象限的交界图，进行回退运动。
S5.2：建立叶片运动轨迹函数，如图13所示，其为第一象限交叠区域两组正交叶片的运动轨迹，图13(a)为右叶片的运动轨迹，图13(b)为前叶片的运动轨迹。
S5.3：在不考虑半影影响的情况下通过叶片轨迹计算分割后的通量F’(x，y)，其三维分布如图14所示。采用向量二范数与初始通量图进行相对误差比较如下：
segNum 50 100 250 500 1000 10000
∑||F’-F|| 2/∑F 0.0416 0.0206 0.0084 0.0042 0.0021 2.05E-04
其中：segNum是指通量曲面分割的等分数，与分割步长成反比，segNum越大，说明对通量曲面分割的越细。
本发明相比于现有技术的有益成果为：
1.提高了适形度：能够实现对各种复杂靶区，如内凹型靶区和环形靶区的动态分割；
2.提高了分割精度：采用正交的叶片对进行配合运动，通过空间 上的交错，避免了叶片闭合位置发生碰撞，解决了叶片对间的端面透视的问题；
3.实现多靶区的强度分割：采用四组不同方位的叶片组合，可以划分至少两个，最多四个象限，对四个以内的多靶区问题进行同时分割；
4.分割效率高：通过强度分布曲面的方向导数特征，把一个波峰或波谷区域分成4个部分，采用不同的叶片分割方式，提高了分割效率；
5.能够从两个方向运动完成对动态靶区跟踪治疗：采用一对正交叶片对靶区进行分割，能够实现两个方向运动完成对动态靶区跟踪治疗。
对于本发明的优选实施方式，应当指出，对于本领域的普通技术人员来说，在不脱离本发明创造构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。

Claims (10)

  1. 一种基于分象限的正交双层光栅动态调强分割方法，其特征在于，具体包括以下步骤：
    S1：通过放疗计划系统计算出每个射野下的射线通量分布，在等中心平面内的射野范围内，可表示为一个通量曲面F(x，y)；
    S2：采用正交双层光栅进行通量分割；
    S3：进行划分象限，将上下左右四组叶片围成的射野区域划分成至少两个象限，得到每个象限的通量分布和对应叶片序列；
    S4：对各个象限的通量曲面进行区域规划，得到多个不同区域，确定不同区域的分割方式；
    S5：对于任一象限，采用两个互相正交的叶片组进行分割。
  2. 根据权利要求1所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，所述步骤S2包括以下内容：射线通过上下两层光栅投影在等中心平面坐标系S-XY下，上下两层叶片分别位于等中心平面的四个方位。
  3. 根据权利要求2所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，对于所述步骤S3，象限划分可以靶区内的极大值点或极小值点为分割中心。
  4. 根据权利要求2所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，对于所述步骤S3，若存在内凹型通量分布或环形靶区通量分布时，则象限划分以极小值点为分割中心；
    若存在多个内凹型区域时，则使凹型靶区的中心位于其中两象限的交线上。
  5. 根据权利要求2所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，对于所述步骤S3，完成象限分割后每个象限对应射野范围内一个区域的射线通量，对应至少一对相互正交的叶片组。
  6. 根据权利要求1-5任一项所述的基于分象限的正交双层光栅动态调 强分割方法，其特征在于，所述步骤S4具体包括以下内容：对于通量曲面内任意一个波峰或波谷周围，按照偏导数大小可以划分为四个区域A1、A2、A3和A4；
    当
    Figure PCTCN2020130429-appb-100001
    且
    Figure PCTCN2020130429-appb-100002
    时，该区域为区域A1；
    当
    Figure PCTCN2020130429-appb-100003
    且
    Figure PCTCN2020130429-appb-100004
    时，该区域为区域A2；
    当
    Figure PCTCN2020130429-appb-100005
    且
    Figure PCTCN2020130429-appb-100006
    时，该区域为区域A3；
    当
    Figure PCTCN2020130429-appb-100007
    且
    Figure PCTCN2020130429-appb-100008
    时，该区域为区域A4。
  7. 根据权利要求1-5任一项所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，所述步骤S5具体包括以下步骤：
    S5.1：确定叶片初始位置；
    S5.2：建立叶片运动轨迹函数；
    S5.3：应用时滞微分方程求解叶片运动轨迹函数。
  8. 根据权利要求7所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，所述步骤S5.1具体包括以下内容：两个正交的叶片组，定义其中一组为主动叶片，另一组为被动叶片，主动叶片由射野边缘向射野中心运动，从动叶片由射野中心往射野边缘进行回退；
    其初始位置可以确定为：主动叶片在射野边缘，从动叶片位于象限交界位置。
  9. 根据权利要求8所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，所述步骤S5.2具体包括以下内容：在给定加速器剂量率以及叶片沿一个方向运动的前提下，采用叶片位置和通量大小之间对应关系描述叶片轨迹；
    以叶片端面位置作为叶片位置，在没有其余叶片遮挡的情况下，叶片位置与其对应通量大小为单调函数关系。
  10. 根据权利要求9所述的基于分象限的正交双层光栅动态调强分割方法，其特征在于，所述步骤S5.3具体包括以下内容：已知每个叶片位置的起始位置，通过前一位置的通量函数对下一瞬时的通量函数进行求 解。
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