A double-layer multi-leaf collimator and a field shaping optimization method

Abstract

The present invention provides a method for optimizing the position of double-layer grating blades. The optimization method obtains the position of each blade on each side of the main collimation layer corresponding to the current radiation field by constructing the mapping relationship between the radiation field and the position of the blades on the main collimation layer. Then, according to the position difference between the position of each blade on each side of the auxiliary collimation layer and the position of each blade on each side of the main collimation layer deviating from the central axis, based on the actual radiation source situation and the relative blade spacing on both sides of the main collimation layer, a sequence of influencing factors for the radiation field size of each blade on each side of the auxiliary collimation layer is established. The position of the blades on the auxiliary collimation layer is optimized through the influencing factors, so as to optimize the target area dose, improve the treatment accuracy, and improve the gain of radiotherapy.

Description

Technical Field

[0001] The present invention relates to the technical field of radiotherapy, and particularly relates to a method for optimizing the positions of double-layer grating blades, a double-layer grating, and a field-forming method. Background Art

[0002] In the radiotherapy industry, in order to solve the need for radiotherapy accuracy, multi-leaf collimators are mostly used. By the interactive movement of the blades, a conformal irradiation field that matches the projected shape of the target area is formed, so that the tumor target area can be accurately irradiated, and the healthy tissue part is protected by the blade shielding area, thereby achieving the goal of killing tumors and improving the quality of life of patients. With the development of radiotherapy technology, single-layer, double-layer, and multi-layer multi-leaf collimators have emerged successively. According to different types of blade focusing, different styles of multi-leaf collimators such as single-focus and double-focus have been developed successively.

[0003] During the tumor irradiation process, an irregular radiation field is often formed, and the positions of the beam-limiting systems in the ray transmission path will have a certain impact on the dose distribution in the target area. The irregular radiation field poses a great challenge to the position adjustment of the beam-limiting systems in the ray transmission path, especially for double-layer and multi-layer gratings. For double-layer and multi-layer gratings, one or two layers are often used as the main collimator layer to be responsible for forming the conformal field, and the rest are auxiliary layers for adjusting the dose distribution in the radiation field area. Often, a tiny position difference will have a great impact on the target area dose. Therefore, how to reasonably determine the position of the auxiliary layer is a relatively big challenge. Summary of the Invention

[0004] A method for optimizing the positions of double-layer grating blades proposed by the present invention can at least solve one of the above technical problems by optimizing the positions of the blades in the auxiliary layer and adjusting the target area dose.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for optimizing the positions of double-layer grating blades, including a first grating blade group and a second grating blade group, is characterized by including the following steps.

[0007] S1. Set one of the grating blade groups as the main collimator layer for forming a conformal radiation field L i , and the other grating blade group as the auxiliary collimator layer for assisting in field formation;

[0008] S2. Construct the mapping relationship between the radiation field L i and the positions of the blades in the main collimator layer, and obtain the positions L ZAi and L ZBi of each side of the blades in the main collimator layer corresponding to the radiation field;

[0009] S3. Construct the position difference ΔX between the positions of the blades on each side of the auxiliary collimator layer and the central axis deviation of the blades in the main collimator layerAi , ΔY Bi sequence;

[0010] S4. Based on the actual size of the radiation source and the relative blade spacing E on both sides of the main collimation layer n , establish the influence factor ξ of the leaf field size on each side of the auxiliary collimation layer Ain , ξ Bin ;

[0011] S5. According to steps S2 - S4, obtain the position L' of the leaves on each side of the current auxiliary collimation layer ZAi , L' ZBi

[0012] L' ZAi = L ZAi ± (1 + ξ Ain )ΔX Ai

[0013] L' ZBi = L ZBi ± (1 + ξ Bin )ΔY Bi

[0014] S6. The leaves of the auxiliary collimation layer with optimized positions, together with the leaves of the main collimation layer, form an optimized radiation field to achieve precise irradiation.

[0015] As a preferred solution: In step S2, the radiation field L i and the position L of the leaves on each side of the main collimation layer ZAi , L ZBi have the following mapping relationship:

[0016] L i = L Ai + L Bi

[0017]

[0018]

[0019] where δ A , δ B is a variable that changes according to the distances of the leaves on sides A and B from the radiation beam axis. S represents the distance from the source to the isocenter, and F represents the distance from the center of the leaves of the main collimation layer to the source.

[0020] As a preferred solution: In step S3, based on the ideal point source and the off-axis distance D of the leaves of the main collimation layer i , establish the position difference ΔX Ai , ΔY Bi sequence between the position of the leaves of the auxiliary collimation layer and the deviation of the leaves of the main collimation layer from the central axis.

[0021] As a preferred solution: in the step S4, the influence factors ξ Ain , ξ Bin are established as follows:

[0022] a) Based on the actual radiation source, establish the influence factor sequences ξ Ai , ξ Bi of the blade position difference sequence. Therefore, based on the blade off-axis distance D i under the actual radiation source, the established position difference sequence is (1 + ξ Ai )ΔX Ai , (1 + ξ Bi )ΔX Bi ;

[0023] b) Based on the relative blade spacing E n of the main collimation layer, establish the influence factor sequence e i of the relative blade spacing. Under the superposition influence of this factor, the blade position influence factor changes to ξ Ain = e i ξ Ai , ξ Bin = e i ξ Bi

[0024] As a further preferred solution, both the first grating blade group and the second grating blade group are arranged by multiple pairs of blade spacings.

[0025] As a further preferred solution, the first grating blade group and the second grating blade group are distributed up and down on the radial two sides of the irradiation source central axis, one of which is the near-source end blade group and the other is the far-source end blade group.

[0026] As a further preferred solution, the blades of the near-source end blade group and the far-source end blade group are arranged in an interleaved manner.

[0027] As a further preferred solution, both the first grating blade group and the second grating blade group are movable; during position optimization, the first grating blade group can move along the second axis parallel to the first axis; the second grating blade group can move along the third axis parallel to the first axis.

[0028] As a further preferred solution, the outermost side of the far-source end is provided with blades for ray shielding.

[0029] As a further preferred solution, the end face structures of the blades at the near-source end and the far-source end are different.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1. The double-layer grating blade position optimization method of the present invention can optimize the position of the auxiliary collimation layer blades according to the position of the main collimation layer blades, so as to optimize the target area dose.

[0032] 2. The double-layer grating blade optimization method proposed by the present invention can optimize the position of the auxiliary collimation layer blades according to the actual situation of the radiation source and the actual field size, and further optimize the target area dose. Description of the Drawings

[0033] Figure 1 is a schematic diagram of the mapping between the radiation field and the blade position in the embodiment of the present invention;

[0034] Figure 2 is a schematic diagram of the off-axis position difference sequence of the blades in the embodiment of the present invention;

[0035] Figure 3 is a schematic diagram of the mapping relationship of the radiation field size influence factor in the embodiment of the present invention;

[0036] Figure 4 is a schematic diagram of the double-layer grating structure in the embodiment of the present invention;

[0037] Figure 5 is a schematic diagram of the blade box structure in the embodiment of the present invention;

[0038] Figure 6 is a schematic diagram of the blade arrangement in the embodiment of the present invention;

[0039] Figure 7 Schematic diagram of blade focusing in the embodiment of the present invention;

[0040] Figure 8 Schematic diagram of the shielding blade in the embodiment of the present invention;

[0041] Figure 9 Schematic diagram of the end face structure of the blade in the embodiment of the present invention;

[0042] Figure 10 is a radiation field schematic diagram based on different end faces. Detailed Embodiments

[0043] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention.

[0044] This embodiment discloses a double-layer grating blade position optimization method, which includes a first grating blade group and a second grating blade group. The specific optimization method includes the following steps:

[0045] S1. Set one of the grating blade groups as the main collimation layer for forming a conformal radiation field Li , another set of grating blades is the auxiliary collimation layer for field forming assistance;

[0046] S2. Construct the radiation field L i and the mapping relationship of the blade positions of the main collimation layer to obtain the positions L ZAi , L ZBi ;

[0047] S3. Obtain the position differences ΔX Ai , ΔY Bi ;

[0048] S4. Based on the actual radiation source size and the relative blade spacing E n on both sides of the main collimation layer, establish the influence factors ξ Ain , ξ Bin ;

[0049] S5. According to steps S2 - S4, obtain the current blade position relationship of the auxiliary collimation layer as follows:

[0050] L’ ZAi = L ZAi ±(1 + ξ Ain )ΔX Ai

[0051] L’ ZBi = L ZBi ±(1 + ξ Bin )ΔY Bi

[0052] When the main collimator is located in the lower layer, the above formula is:

[0053] L’ ZAi = L ZAi -(1 + ξ Ain )ΔX Ai

[0054] L’ ZBi = L ZBi -(1 + ξ Bin )ΔY Bi

[0055] When the main collimator is located in the upper layer, the above formula is:

[0056] L’ ZAi = L ZAi +(1 + ξ Ain )ΔX Ai

[0057] L’ ZBi = L ZBi +(1 + ξBin ) ΔY Bi

[0058] S6. The auxiliary collimator layer blades with optimized positions, together with the main collimator layer blades, form an optimized radiation field to achieve precise irradiation.

[0059] As a preferred solution: as Figure 1 shown, in the step S2, the radiation field L i and the positions of the blades on each side of the main collimator layer L ZAi , L ZBi have the following mapping relationship:

[0060] L i = L Ai + L Bi

[0061]

[0062]

[0063] In the formula, δ A , δ B are variables that vary according to the distances of the blades on the A and B sides from the radiation beam axis. S represents the distance from the source to the isocenter, and F represents the distance from the center of the main collimator layer blades to the source.

[0064] As a preferred solution: in the step S3, based on the off-axis distance D i of the ideal point source and the main collimator layer blades, a sequence of the position difference ΔX Ai , ΔY Bi between the positions of the auxiliary collimator layer blades and the main collimator layer blades deviated from the central axis is established, as Figure 2 shown.

[0065] Among them, D i refers to the distance of the main collimator layer blades from the radiation central axis. Specifically: for a certain radiation field, the blades on the A side of the main collimator layer move to a position with a distance D Ai from the radiation center, and the blades on the B side move to a position with a distance D Bi from the radiation center; ΔX Ai , ΔY Bi refer to the theoretical position gaps between the auxiliary collimator layer blades and the main auxiliary collimator layer blades under the ideal point source, where ΔX Ai refers to the theoretical position gap between the A-side auxiliary collimator blades and the main collimator layer blades, and the same applies to the B side. This position difference varies with the off-axis distance D i of the main collimator layer blades at different physical positions.

[0066] As a preferred solution: in the step S4, the influencing factors ξ Ain , ξ BinThe establishment process is as follows:

[0067] a) Based on the actual radiation source, establish the influence factor sequence ξ of the blade position difference sequence Ai and ξ Bi . Therefore, based on the off-axis distance D of the blade i , the established position difference sequence is (1 + ξ Ai )ΔX Ai , (1 + ξ Bi )ΔX Bi ;

[0068] It should be noted that since the actual radiation source is not an ideal point source but has a certain size, affected by this, there is a certain gap between the position of the auxiliary collimator layer blades and that under the ideal point source, and this gap is adjusted by the influence factor ξ i . For the blades on side A, this influence factor is ξ Ai ; for the blades on side B, this influence factor is ξ Bi .

[0069] b) Based on the relative blade spacing E n of the main collimator layer, establish the influence factor sequence e i of the relative blade spacing. Under the superposition influence of this factor, the blade position influence factor changes to ξ Ain = e i ξ Ai , ξ Bin = e i ξ Bi .

[0070] It should be noted that E n refers to the sequence composed of the relative blade spacings on sides A and B of the main collimator layer. For example, the maximum spacing between the blades on sides A and B is 100, and a relative blade spacing sequence E n is established with an interval of 1 as the unit.

[0071] Examples of the influence of the radiation source size and the relative blade spacing of the main collimator layer on the blade position on each side of the auxiliary collimator layer (for illustrative purposes only, the specific numbers have no practical significance) are as follows:

[0072] The blade on side B of the main collimator layer is located at a position 25 mm off-axis, and the field size in the physical position is 50 mm, that is, the relative blade spacing is 50 mm. Under the ideal point source, through theoretical calculation, it is obtained that the position difference between the blades of the auxiliary layer on side B and the blades of the main collimator layer is 5 mm, and the off-axis distance is 20 mm;

[0073] Since the radiation source is not an ideal point source, it is known from actual measurements that the position difference between the blades of the auxiliary layer on the B side and the blades of the main collimator layer needs to reach 5.25 mm to form a theoretical radiation field. Therefore, the influence factor of the actual radiation source on the position of the blades of the auxiliary layer on the B side is (5.25 - 5) / 5 = 0.05. By analogy, a sequence of influence factors for the position difference of the blades of the auxiliary collimator layer when the main collimator layer is at different positions is established.

[0074] When the position of the blades on the B side of the main collimator layer remains unchanged and the relative blade pitch increases to 60 mm, that is, the relative blade pitch increases. Affected by this, the measured position difference between the blades of the auxiliary layer on the B side and the blades of the main collimator layer needs to become 5.2 mm to form a theoretical radiation field. Therefore, the influence factor of this relative blade pitch on the position of the blades on the B side is (5.2 / 5 - 1) / 0.05 (the influence factor affected by the radiation source) = 0.8. When the relative blade pitch becomes 70 mm, the influence factor obtained based on the actual measurement results is 0.75... By analogy, a sequence of influence factors for the position difference of the blades of the auxiliary collimator layer when the relative blade pitch is different is established.

[0075] Based on the two influencing factors, the total influence factor ξBin = eiξBi = 0.05×0.8 = 0.04.

[0076] As Figure 4 shown, the first grating blade group and the second grating blade group are distributed up and down on the radial two sides along the central axis of the irradiation source, one of which is the near-source end blade group and the other is the far-source end blade group; the blades of the near-source end blade group and the blades of the far-source end blade group are arranged alternately.

[0077] As Figure 4 shown, in this embodiment, both the first grating blade group and the second grating blade group are composed of multiple pairs of blade pitches arranged.

[0078] Both the first grating blade group and the second grating blade group in this embodiment are movable. As shown in the figure,

[0079] During position optimization, the first grating blade group can move along the second axis parallel to the first axis; the second grating blade group can move along the third axis parallel to the first axis.

[0080] In this embodiment, the outermost side of the far-source end is provided with blades for ray shielding.

[0081] It should be noted that the above main and auxiliary collimator layers are not limited to the specified collimator layers. For example, Figure 1 in the attached example, the main collimator layer is the lower-layer blades and the auxiliary collimator layer is the upper-layer blades, and vice versa.

[0082] In summary, through the above-mentioned position optimization, the blades of the auxiliary collimation layer are optimized according to the positions and relative blade spacings of the main collimation layer blades, so that the auxiliary collimation layer reaches the optimal position, realizes the optimization of the dose within the radiation field, enables the most appropriate dose to be irradiated to the most needed target area position, while reducing the radiation dose of the patient's normal tissues and improving the patient's quality of life.

[0083] On the other hand, the present invention also discloses a double-layer grating, comprising:

[0084] Two sets of boxes arranged oppositely, namely the first box 1 and the second box 2 respectively. Each box is divided into an upper space 101 and a lower space 102, and moves relatively parallel along the first axis direction; as Figure 4 shown;

[0085] The box is provided with a blade linear motion guiding groove 103; as Figure 5 shown;

[0086] A near-source end blade group 3 arranged oppositely, including multiple pairs of blades, which are respectively located in the upper spaces of the first box and the second box;

[0087] The near-source end blade group 3 moves along a second axis direction substantially parallel to the first axis direction;

[0088] A far-source end blade group 4 arranged oppositely, including multiple pairs of blades, which are respectively located in the lower spaces of the first box and the second box;

[0089] The near-source end blade group 3 moves along a third axis direction substantially parallel to the first axis direction;

[0090] The near-source end blade group 3 and the far-source end blade group 4 are arranged in a staggered manner. As Figure 6 shown.

[0091] In detail,

[0092] The near-source end blade group 3 and the far-source end blade group 4 each focus on a point along the direction perpendicular to the blade movement direction, further reducing the leakage between the blades;

[0093] The near-source end blade group 3 focuses on point S above the source, and the far-source end blade group 4 focuses on point X below the source. As Figure 7 shown; The near-source end blade group 3 and the far-source end blade group 4 can focus on a point along the direction perpendicular to the blade movement direction, and the focus points are respectively above the source and below the source. This enables further reduction of the leakage between the blades, allows for a smaller blade thickness to be achieved, realizes a low leakage rate between the blades, and under the same conditions, reduces the equipment size and increases the patient treatment space.

[0094] The focus point of the blade group can be above the source or below the source, or can coincide with the source.

[0095] The outermost two pairs of blades at the far source end are used for auxiliary shielding; as Figure 8 shown;

[0096] The blades for shielding on each side are connected as a whole, and the opposite end faces are completely closed;

[0097] The blades for shielding can automatically adjust their positions as the box moves;

[0098] The end face of the near source end blade 3 is different from the end face of the far source end blade 4; as Figure 9 shown;

[0099] It should be explained that the end faces of the blades are optimized for different field sizes. When the field size is small, the lower collimator layer is used as the main collimator, and the end face of the lower blades is optimized for the small field to obtain a smaller penumbra. When the field size is large, the upper collimator is used as the main collimator layer, and the end face of the upper blades is optimized for the large field to also obtain a smaller penumbra, so that the penumbra of different field sizes is in a relatively small state, thereby improving the treatment accuracy.

[0100] The following is a field forming method proposed based on the different end face structures of the blades, specifically as follows:

[0101] Embodiment 2

[0102] A field forming auxiliary method includes a double-layer grating blade composed of a near source end blade group and a far source end blade group. It is characterized in that the end face of the near source end blade is a large arc surface; the end face of the far source end blade is an arc surface; the field forming auxiliary method includes the following steps:

[0103] S1. Set the near source end blades to adapt to the fields from 0 to F away from the radiation beam axis, and the far source end blades to adapt to the fields from F to Lmax;

[0104] S2. When the double-layer grating needs to form a field between ±F, use the near source end blade group as the main collimator layer to form the required conformal field, and the far source end as the auxiliary collimator layer for field forming assistance;

[0105] S3. When the double-layer grating needs to form a field between ±F and ±Lmax, use the far source end blade group as the main collimator layer to form the required conformal field, and the near source end as the auxiliary collimator layer for field forming assistance. As Figure 10 shown.

[0106] It should be noted that in the field of multi-leaf collimators, in order to maintain the consistency of the penumbra of the radiation field, the commonly adopted method is that the end face structure of the leaves is an arc surface, so that at any position where the leaves move in the direction perpendicular to the central axis of the beam, the primary ray can be tangent to the end face. However, when using an arc-shaped end face, the penumbra of the radiation field may increase, and at the same time, the size of the penumbra will change with the position of the leaf away from the central axis of the beam. Therefore, these two factors should be fully considered in the design of the end face shape.

[0107] If the radius of curvature R of the end face is properly selected, during the entire linear movement of the leaf, the chord length of the tangent of the ray to the end face will approximately remain unchanged, and the penumbra will remain within a relatively stable range without changing with the position of the leaf. However, if the radius of curvature of the end face is optimized for a relatively large radiation field, the penumbra within the entire radiation field will be relatively larger. When optimized for a small radiation field, the penumbra of a large-sized radiation field will be larger. Therefore, based on the double-layer collimator, an optimization of the above-mentioned end face design is proposed, and based on this end face structure optimization method, the above-mentioned field formation method is proposed, that is: the end faces of the leaves in the near-source collimator layer are optimized according to the radiation field between the middle F point and the maximum open field Lmax. When forming the radiation field between the F point and Lmax, the near-source collimator layer is responsible for conformal shaping, and the far-source collimator layer is responsible for assisting and adjusting the target dose; when forming the radiation field from the radiation center to the F point, the far-source collimator layer is responsible for conformal shaping, and the near-source collimator layer is responsible for assisting and adjusting the target dose. In this way, both large and small radiation fields are taken into account, so that the penumbra is always maintained within a small range, thereby improving the treatment accuracy.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for optimizing the position of a double-layer grating blade, comprising a first grating blade group and a second grating blade group, characterized in that, including the following steps, S1. Set one of the grating vane groups as the main collimation layer for forming a conformal radiation field L i , and set the other grating vane group as the auxiliary collimation layer for field formation assistance; S2. Construct the radiation field L i Obtain the mapping relationship between the positions of the main collimator blades and the positions of the blades on each side of the main collimator corresponding to the radiation field, and obtain the positions L ZAi of L ZBi ; S3. Construct the position differences ΔX Ai and ΔY Bi between the positions of the auxiliary collimation layer blades on each side and the positions of the main collimation layer blades deviating from the central axis; S4. Based on the actual size of the radiation source and the relative blade spacing E on both sides of the main collimation layer n , an influence factor ξ of the leaf field size on each side of the auxiliary collimation layer is established Ain , ξ Bin ; S5. According to steps S2 - S4, obtain the blade positions L’ on each side of the current auxiliary collimation layer ZAi 、L’ ZBi : L’ ZAi = L ZAi ±(1 + ξ Ain )ΔX Ai L’ ZBi = L ZBi ±(1 + ξ Bin )ΔY Bi S6. The auxiliary collimation layer blades with optimized positions, together with the main collimation layer blades, form an optimized radiation field to achieve precise irradiation.

2. The double-layer grating blade position optimization method according to claim 1, wherein: In the step S2, Radiation field L i The blade position L on each side of the main collimation layer ZAi 、L ZBi The mapping relationship is as follows: L i = L Ai + L Bi where δ A , δ B are variables that vary according to the distances by which the blades on sides A and B deviate from the radiation beam axis, S represents the distance from the source to the isocenter, and F represents the distance from the center of the primary collimator blades to the source.

3. The double-layer grating vane position optimization method according to claim 1, wherein: According to the off-axis distance sequence D of the main collimator blades i , establish the theoretical position difference sequence between the auxiliary collimator blades and the collimator blades under an ideal point source: ΔX Ai , ΔX Bi .

4. The double-layer grating blade position optimization method according to claim 1, characterized in that: In the step S4, Influence factor ξ Ain , ξ Bin The establishment process is as follows: a) Establish the influence factor sequence ξ of the blade position difference based on the actual radiation source Ai , ξ Bi , and obtain the position difference sequence established based on the blade off-axis distance D i under the actual radiation source as (1 + ξ Ai )ΔX Ai , (1 + ξ Bi )ΔX Bi ; b) Based on the relative blade pitch E of the main collimation layer n , establish the relative blade pitch influence factor sequence e i . Under the superposition influence of this factor, the blade position influence factor changes to ξ Ain = e i ξ Ai , ξ Bin = e i ξ Bi .

5. The double-layer grating vane position optimization method according to claim 1, characterized in that: Both the first grating blade group and the second grating blade group are arranged with multiple pairs of blade spacings.

6. The double-layer grating vane position optimization method according to claim 1, wherein: The first grating blade group and the second grating blade group are distributed vertically on both radial sides of the central axis of the irradiation source, with one being the near-source end blade group and the other being the far-source end blade group.

7. The double-layer grating blade position optimization method according to claim 6, characterized in that: The blades of the near-source end blade group and the blades of the far-source end blade group are staggered.

8. The double-layer grating blade position optimization method according to claim 1, wherein: Both the first grating blade group and the second grating blade group are movable; during position optimization, the first grating blade group can move along the second axis parallel to the first axis; the second grating blade group can move along the third axis parallel to the first axis.

9. The double-layer grating vane position optimization method according to claim 6, characterized in that: Blades for ray auxiliary shielding are provided on the outermost side of the far-source end.

10. The double-layer grating vane position optimization method according to claim 6, characterized in that: The end faces of the blades of the near-source end blade group have different structures from the end faces of the blades of the far-source end blade group.

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