A multi-leaf collimator for a radiotherapy machine and a radiotherapy machine

Abstract

A multi-leaf collimator and a radiotherapy machine are disclosed. In one embodiment, the end face of the blade tip of the multi-leaf collimator is not a complete plane or curved surface, but is distributed with a plurality of protrusions and depressions. When the blades are relatively closed, the protrusions and depressions at the tips of the two blades just fit together, so as to completely avoid the problems of end leakage radiation, end collision and dose gradient region.

Description

Technical Field

[0001] The present invention belongs to the field of radiotherapy equipment, and particularly relates to a multileaf collimator blade with an end face design, a multileaf collimator composed of such blades, and a radiotherapy machine with a corresponding collimator. Background Art

[0002] A multileaf collimator (MLC) is an important component of contemporary radiotherapy machines. It is installed directly below the head of a radiotherapy machine and is used to limit the irradiation range of the radiation beam, form an irregular radiation field suitable for various target shapes, and achieve conformal radiotherapy; during irradiation, if the positions of the MLC blades are adjusted, the intensity distribution of the radiation in the irradiation range can be adjusted to achieve intensity-modulated radiotherapy. Compared with traditional radiotherapy, conformal radiotherapy and intensity-modulated radiotherapy can better achieve the purpose of radiotherapy, that is, kill tumors as much as possible while protecting surrounding normal tissues.

[0003] A blade is the basic unit that makes up a multileaf collimator. It is made of a heavy metal material (such as tungsten alloy) and is strip-shaped. Its length is determined by the maximum radiation field to be formed; its width ranges from a few millimeters to a few centimeters. The narrower the width, the more suitable the formed radiation field is for the target shape; the thickness is at least 5 half-value layers of the metal material used, so that the radiation in the blocked area of the blade is attenuated to less than 5%. Each blade is driven by an independent motor, and multiple blades are arranged adjacent to each other closely to form a blade group.

[0004] Regarding the improved design of multileaf collimators and multileaf collimator blades, researchers have proposed various different solutions from different perspectives, and some of these solutions have been applied in manufacturing and use. One is to design the arrangement method of the blades, from the traditional single layer to double layer or even triple layer arrangements. Another improved design is to optimize the width and end face shape of the blade in the projection on the isocenter plane, changing the original equal-width blades and flat end faces, and obtaining the optimal blade width and end face shape through optimization methods.

[0005] There are two problems that need to be considered emphatically in the design of the cross-sectional shape of the blade end in the cross-section perpendicular to the isocenter plane and parallel to the blade movement direction. When a pair of blades is in the open state, the end is in the transition area from the area blocked by the blade to the open irradiation area. The end design affects the dose in the transition area, that is, the penumbra. A focusing design should be adopted to make the penumbra as small as possible and have the smallest change with different blade positions. When the cross-sectional shape of the blade end face is a straight line segment, to achieve the focusing effect, the blade must move along a circular arc trajectory centered on the radiation source; if the blade moves along a straight line trajectory perpendicular to the central axis of the radiation beam, after the blade reaches the specified position, it needs to rotate a small angle so that the flat end face is tangent to the divergence of the radiation.

[0006] Another problem faced by the end design is that there is always a gap when the opposing leaves close. If the gap is too small, it is prone to collisions; if it is too large, too much radiation leaks through, causing side effects during irradiation. There are always problems of collisions and radiation leakage. For example, the minimum projected width of the leaf gap of the Varian company at the isocenter plane is 0.05 cm, and the minimum projected width of the leaf gap of the Elekta company at the isocenter plane is 0.5 cm. For non-focusing end faces, when the opposing leaves close, there is still a relatively wide dose gradient region below the leaf ends. The radiation leakage caused by the leaf gap and the dose gradient region below the leaf ends not only irradiate normal tissues unnecessarily, but also increase the difficulty of accelerator modeling and dose calculation, and increase the dose calculation error. Summary of the Invention

[0007] In order to overcome the deficiencies in the prior art, the present invention proposes to improve the multi-leaf collimator by changing the end design of the multi-leaf collimator blades. Specifically, aiming at the problem that the opposing blades of the existing collimator cannot actually close completely and there is a gap in the middle, the present invention proposes to design the ends of the multi-leaf collimator blades so that the opposing blades can fit together to improve the working performance of the multi-leaf collimator.

[0008] According to an exemplary embodiment, there is provided a multi-leaf collimator for a radiotherapy machine, which includes multiple pairs of opposing blades, and each pair of blades includes a first blade and a second blade that can move relative to each other. Among them, in a first plane perpendicular to the isocenter plane of the radiotherapy machine and parallel to the blade movement direction, the first blade and the second blade can be moved and adjusted to a closed position, and the end faces of the first blade and the second blade fit together at the closed position.

[0009] In one embodiment, the end face of the blade is configured with a broken line profile composed of multiple depressions and multiple protrusions.

[0010] In one embodiment, the multiple depressions and multiple protrusions on the end face of the blade are staggered.

[0011] In one embodiment, the contour lines of the multiple protrusions on the end face of the blade form an arc segment.

[0012] In one embodiment, the projections of the multiple depressions and multiple protrusions on the end face of the blade in a second plane perpendicular to the isocenter plane and the blade movement direction are longitudinally staggered along the direction of the line connecting the radiation source and the collimator center.

[0013] In one embodiment, the projections of the multiple depressions and multiple protrusions in a second plane perpendicular to the isocenter plane and the blade movement direction are arranged in a grid-like staggered pattern.

[0014] In one embodiment, the ends of the first blade and the second blade have a first thickness in the direction of the line connecting the radiation source and the center of the collimator, and the blade body portions other than the ends have a second thickness, and the first thickness is greater than the second thickness.

[0015] In one embodiment, the first thickness decreases from the end face to the blade body portion to the second thickness.

[0016] In one embodiment, the fitting depth of the end faces of the first blade and the second blade at the closed position can be calculated according to the shape of the blade end and the distance of the fitting position from the blade center line. Preferably, when the end faces of the first blade and the second blade are arc-shaped, the fitting depth at the fitting position located at the blade center line is greater than twice the contour height of the arc segment of the blade end face; the fitting depth decreases towards the upper and lower edges of the blade, and the fitting depth at the edge is greater than zero.

[0017] According to an exemplary embodiment, a radiotherapy machine is provided, including: a multi-leaf collimator including a plurality of pairs of blades arranged oppositely, each pair of blades including a first blade and a second blade capable of relative movement, wherein in a first plane perpendicular to the isocenter plane of the radiotherapy machine and parallel to the blade movement direction, the first blade and the second blade can be moved and adjusted to a closed position, and the end faces of the first blade and the second blade are fitted to each other at the closed position; and a controller that controls the fitting degree of the end faces of the first blade and the second blade at the closed position so that the first blade and the second blade do not collide at the closed position.

[0018] The beneficial effects of the present invention are as follows: At the closed position, the opposite first blade and the second blade are fitted to each other in the blade movement direction and no longer have the gap between the ends when the blades of the traditional collimator are closed. Therefore, the shielding performance for rays can be enhanced, and the leakage rays and the dose gradient region are reduced. At the same time, the fitting degree between the blades can be adjusted so that the blades do not collide when closed. Compared with the traditional collimator, the adjustment range of the blades is increased and it is easier to operate. The present invention solves the problems of collision, leakage rays and dose gradient region of the relative blades in the use of the multi-leaf collimator. Therefore, the conformal intensity modulation effect of the collimator can be improved, and the difficulty of collimator modeling and plan optimization can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The above and other objects, features, and advantages of the present invention will become more apparent. The drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings, the same reference numerals generally represent the same components. It should be understood that the sizes and dimensions of the components shown in the drawings are not necessarily drawn to scale, and they may be different from those in the embodiments shown here for implementation. In addition, some embodiments may combine any suitable combination of features from two or more drawings.

[0020] Figure 1 shows a structural and functional schematic diagram of a multi-leaf collimator;

[0021] Figure 2 shows a schematic diagram of the working states of a pair of opposing blades of a conventional design, specifically showing the axonometric views when opened (a) and closed (b), the side views when opened (c) and closed (d), and the front views of the end faces of the two blades (e);

[0022] Figure 3 shows a schematic diagram of the working states of a pair of blades with an embedded end design according to an embodiment of the present application, specifically showing the axonometric views when opened (a) and closed (b), the side views when the blades are opened (c) and closed (d), and the front views of the end faces of the two blades (e). The protrusions and depressions at the blade ends are arranged horizontally;

[0023] Figure 4 shows the embedded depth (a) when the opposing blades are closed according to an embodiment of the present application, as well as the dimensions (b) and (c) of the arcuate end faces of the blade ends;

[0024] Figure 5 Illustrates a schematic diagram of the working states of a pair of blades with an embedded end design according to another embodiment of the present application, specifically showing the axonometric views when opened (a) and closed (b), the side views when the blades are opened (c) and closed (d), and the front views of the end faces of the two blades (e). The protrusions and depressions at the blade ends are arranged in a grid pattern. Detailed implementation manners

[0025] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. It should be understood that the present application is not limited by the exemplary embodiments described here.

[0026] Figure 1 is a structural and functional schematic diagram of the multi-leaf collimator of the present invention, which is installed in the treatment head of a radiotherapy machine. As Figure 1As shown, the multi-leaf collimator is arranged below the radiation source. The collimator includes two leaf groups on side A and side B, which are symmetrically arranged above the isocenter plane of the treatment machine. Under the irradiation of the radiation source, the radiation beam passes through the gap between the leaf groups and reaches the tumor target area to be irradiated. The leaves of the collimator can be individually driven by a driving mechanism such as a motor to move each leaf separately, so as to form different radiation fields in the isocenter plane. The contour of the radiation field determines the irradiated area. If the irradiated area is inconsistent with the desired irradiation range, some parts of the target area may be missed by the radiation, or the radiation may irradiate nearby normal tissues.

[0027] Figure 2 FIG. illustrates a schematic diagram of the working state of the opposing leaves of a conventional collimator. Among them, (a) and (c) show the relative positions of the opposing leaves in the open state, and (b) and (d) show the relative positions of the opposing leaves in the closed state. For the illustrated example, the projected shape of the leaf end face in a plane perpendicular to the isocenter plane and parallel to the leaf movement direction is an arc segment. As described above, there is always a slit when the opposing leaves of a conventional collimator are closed. If the slit is too small, it is easy to collide, and if the slit is too large, radiation leakage may occur. It is difficult to overcome the problems of collision and radiation leakage simultaneously.

[0028] FIG. 3 shows a collimator adopting an embedded end design according to an embodiment of the present application. Combining Figure 1 with FIG. 3, the multi-leaf collimator of the present application includes multiple pairs of opposing leaves (only one pair of opposing leaves is shown in FIG. 3). Each pair of opposing leaves includes a first leaf 1 and a second leaf 2, which can move relative to each other to close or open so as to absorb, block or transmit radiation. As shown in FIGS. 3(a) and 3(c), the shapes of the first leaf 1 and the second leaf 2 present a point-symmetric structural configuration. As shown in FIGS. 3(b) and 3(d), in a plane perpendicular to the isocenter plane of the radiotherapy machine and parallel to the leaf movement direction (the long axis direction of the leaf in the figure) (hereinafter simply referred to as the "first plane"), the first leaf 1 and the second leaf 2 can be moved and adjusted to the closed position, and the end face 11 of the first leaf 1 and the end face 21 of the second leaf 2 are mutually embedded at this closed position. Through this embedded design, the opposing leaves can effectively shield radiation within a wide adjustment range in the closed state, improving the safety and operability of the radiotherapy system.

[0029] In one embodiment, as shown in FIG. 3, the blade may be composed of a blade body 12 and a tip 13. The end face of the blade tip 13 has a broken line profile formed by a plurality of depressions and a plurality of protrusions. For the collimator according to this embodiment, in a cross-section perpendicular to the isocenter plane and parallel to the blade movement direction, the end face profile of the blade tip 13 is different from the straight line segment or arc segment of the existing blade, but a broken line segment formed by depressions and protrusions, and the depressions and protrusions are staggered. When the blades are relatively closed, the depressions and protrusions of the two blades are mutually engaged. For example, the protrusion of blade 1 is engaged in the corresponding depression of blade 2, and at the same time, the protrusion of blade 2 is engaged in the corresponding depression of blade 1. Such a design divides the gap between the two opposing blades into several small segments, and the gaps are distributed at different positions along the ray direction (i.e., the short axis direction of the blade). Therefore, there is no longer any leakage ray directly passing through the gap, and the problems of leakage ray and dose gradient region when the opposing blades are closed can be better solved.

[0030] In the example shown in FIG. 3, as shown in FIG. 3(e), the projections of the plurality of depressions and the plurality of protrusions at the blade tip in a plane perpendicular to the isocenter plane and the blade movement direction (hereinafter referred to as the "second plane") are longitudinally staggered along the direction of the connection line between the ray source and the collimator center (for example, the short axis direction of the blade). In the figure, the blank area represents the protrusion, and the shaded area represents the depression, and the protrusions and depressions adopt a longitudinal arrangement. The lengths of the protrusions and depressions in the longitudinal projection can be designed to be the same or different, and the present application does not make specific limitations thereto. Preferably, as shown in FIG. 3(e), the lengths of the projections of each protrusion and depression in the longitudinal direction are the same, so that the processability of the blade can be improved.

[0031] The number of protrusions and depressions at the tip of each blade may be more than 2, for example, more than 4. Preferably, the number of protrusions at the tip of each blade is the same as the number of depressions. In the tip design shown in FIG. 3, each blade tip has 6 protrusions and 6 depressions. In actual manufacturing, the number of protrusions and depressions can be increased according to the processing ability, which can better retain the focusing ability of the blade.

[0032] As can be seen from FIG. 3, the tips of blade 1 and blade 2 adopt a design in which depressions and protrusions are staggered. At the same time, the contour lines of the plurality of protrusions on one side of the blade can also form a specific shape, such as a straight line segment or an arc segment. Preferably, as shown in FIG. 3, the contour lines of the plurality of protrusions together form an arc segment, or rather, the end face profile at the protrusion is from Figure 2A section of spaced arc is formed on the blade end face contour shown, which can improve the focusing performance of the blade. Correspondingly, the contour lines of multiple depressions on the other blade also form an arc segment with the same contour, so that the two blades can fit together at the closed position without collision. The radius of curvature of the arc segment can be determined according to the size of the blade, for example, it can be 8 - 30 cm. When the protrusion has an arc-shaped contour line, the extension lengths of the protrusions at the blade end are also different. For example, as shown in Figure 3, the lengths of the protrusions increase sequentially along the ray direction from the top of the blade end, and the protrusion located in the central part has the maximum length.

[0033] When the opposing blades are closed, the protrusions and depressions of blade 1 and blade 2 can fit together respectively. However, when the blades are opened, the depression positions at the blade ends make the thickness of the blade attenuating the rays thinner, and the ray penetration amount increases. For this reason, in one embodiment, the thickness h1 of the blade end 13 in the direction of the connection line between the radiation source and the center of the collimator (i.e., the short axis direction of the blade) can be set to be greater than the thickness h2 of the blade main body part 12 other than the end. For example, h1 can be approximately 2 times h2. When the end 13 and the main body part 12 are made of the same material (such as tungsten alloy), it can ensure that the thickness of the blade end attenuating the rays is basically the same as the thickness of the blade main body part (such as about 6 - 10 cm). At the same time, as shown in Figure 3, the thickness of the blade end part 13 is not a constant value. It decreases from the blade end face 13 to the thickness h2 in the direction of the blade main body part, or rather, it increases from h2 to h1 at the end protrusion along the blade movement direction. The collimator blade designed in this way is similar to the shape of a person's outstretched finger arm when viewed from the side.

[0034] The depth of the depression at the blade end in Figure 3 can be determined according to the size of the end and the fitting depth when the opposing blades are closed. Figure 4 Shows a schematic diagram of the fitting depth when the opposing blades are closed according to an embodiment of the present application. As Figure 4 (a) shows, the fitting depth when two opposing blades are closed can be defined as the distance between the vertices of the arc-shaped end faces of the two blades, which can be calculated according to the shape of the blade end and the distance from the fitting position to the blade center line. For example, for the Figure 4 (a) shown arc-shaped end face, the fitting depth has a maximum value d at the horizontal center line of the blade and decreases towards both side edges. It can be understood that for other blade end shapes, the fitting depth may have other values or distributions. Figure 4 (b) shows the blade end design according to an embodiment of the present application and the dimensions of the circular arc projection of the corresponding end face. Assuming the radius of the arc is R, the chord length corresponding to the arc is l, and the contour height of the arc is h. Let the smaller one of the distances from the depression position to the top and bottom of the blade be x, then the depth y of the depression can be expressed as

[0035]

[0036] When y obtained according to the above formula is less than 0, it indicates that the relative blade fitting depth is small, and a part of the arc end face does not contact even when the blade is closed, so there is no need to set a recess. When the two arc end faces of the relative blades are just completely fitted, the fitting depth d should be equal to 2h. At this time, the recess depth (i.e., the extension length of the protrusion at the blade center) at the blade center can be calculated to be 2h, and the recess depth at the blade edge is 0. Considering that the attenuation of the rays should be kept as uniform as possible when the blade is closed, the arc end faces of the blades should be completely fitted, and in this case, the fitting depth should be 2h or slightly greater than 2h. In one embodiment, the above-mentioned fitting depth 2h can be 1.5 cm to 4 cm to ensure the ray shielding performance of the relative blades when they are closed.

[0037] Figure 4 (c) shows the blade end design according to another embodiment of the present application and the dimensions of the corresponding circular arc projection of the end face, which corresponds to the blade end design shown in FIG. 3. Similar to Figure 4 (b), let the smaller one of the distances from the position of the recess to the top and bottom surfaces of the blade be x, then the recess depth y can also be expressed as

[0038]

[0039] When the two arc end faces of the relative blades are just completely fitted, the fitting depth d should be equal to 2h + c, where c is the length of the straight section at the top of the end face, and this straight section is connected to the arc section. At this time, the recess depth (i.e., the extension length of the protrusion at the blade center) at the blade center can be calculated to be 2h + c, and the recess depth at the blade edge is c. That is, the fitting depth at the fitting position located at the blade center line is greater than twice the contour height of the arc section of the blade end face, and decreases to c towards both side edges of the blade. In one embodiment, the length c of the above-mentioned straight section can be 0.5 - 1.5 cm, and the fitting depth 2h + c can be 1.5 cm to 4 cm to ensure the ray shielding performance of the relative blades within a large adjustment range when they are closed.

[0040] Figure 5 shows the design of the blade end according to another embodiment of the present application, as shown in Figure 5 (a)-5(d). The blades in this embodiment are similar to the blades shown in FIG. 3, and both include a blade body and an end part connected to the body. The overall outer contour of the end is also similar. The difference lies in the configuration structure of the protrusions and recesses at the blade end. As shown in Figure 5As shown in (e), the projections of the multiple depressions and multiple protrusions at the blade ends are arranged in a grid-like staggered pattern in a second plane perpendicular to the isocenter plane and the blade movement direction. In the figure, the blank areas represent the protrusions and the shaded areas represent the depressions. The protrusions and depressions adopt a grid-like arrangement with horizontal and vertical staggered distributions. As Figure 5 As shown in (a) and (e), each blade end has 24 protrusions and 24 depressions, which are staggered both horizontally and vertically. This can further improve the ray shielding performance of the collimator blades when they are closed.

[0041] Another embodiment of the present invention provides a radiotherapy machine, including the multi-leaf collimator of the above type, and a controller that can control the degree of fitting of the end faces of the opposing first blade and second blade at the closed position, so that the first blade and the second blade do not collide at the closed position. For example, the fitting depth of the opposing blades can be controlled by adjusting the sizes of the depressions and protrusions, as well as the movement range of the blades, to ensure that the blades do not collide when closed. By configuring the blade end design described above, it is not necessary for the ends of the opposing first blade and second blade to directly contact each other, and the movement of the blades can be controlled within a relatively large tolerance range to ensure that there are no problems of ray leakage and dose gradient regions.

[0042] The basic principles of the present application have been described above in conjunction with specific embodiments. However, it should be noted that the advantages, benefits, effects, etc. mentioned in the present application are only examples and not limitations. It cannot be considered that these advantages, benefits, effects, etc. are essential for each embodiment of the present application. In addition, the above-disclosed specific details are only for the purpose of illustration and facilitation of understanding, and not for limitation. The above details do not limit the present application to necessarily adopt the above specific details for implementation.

[0043] In this document, words such as "including", "comprising", "having", etc. are open-ended terms, meaning "including but not limited to", and can be used interchangeably with each other. The words "or" and "and" used here refer to the word "and / or" and can be used interchangeably with it, unless the context clearly indicates otherwise. The word "such as" used here refers to the phrase "such as but not limited to" and can be used interchangeably with it.

[0044] The above is only a preferred arrangement of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A multi-leaf collimator for a radiotherapy machine, comprising a plurality of groups of blade pairs arranged oppositely, each group of blade pairs including a first blade and a second blade capable of relative movement, wherein, In a first plane perpendicular to the isocenter plane of the radiotherapy machine and parallel to the blade movement direction, the first blade and the second blade can be moved and adjusted to a closed position, and the end faces of the first blade and the second blade are fitted to each other at the closed position. Wherein, the end face of the blade is configured with a broken line profile composed of a plurality of depressions and a plurality of protrusions, and each of the plurality of protrusions has an upper surface and a lower surface, and the upper surface and the lower surface extend along a direction parallel to the blade movement direction. Wherein, the plurality of depressions and the plurality of protrusions on the end face of the blade are staggered, and the contour lines of the plurality of protrusions on the end face of the blade form an arc segment. Wherein, the fitting depth of the end faces of the first blade and the second blade at the closed position is calculated according to the shape of the blade end and the distance from the fitting position to the blade center line, and the fitting depth at the center line of the fitting position is greater than twice the contour height of the arc segment of the blade end face.

2. The multi-leaf collimator according to claim 1, wherein, The projections of the plurality of depressions and the plurality of protrusions on the end face of the blade in a second plane perpendicular to the isocenter plane and the blade movement direction are longitudinally staggered along the direction of the connection line between the radiation source and the collimator center.

3. The multi-leaf collimator according to claim 1, wherein, The projections of the plurality of depressions and the plurality of protrusions on the end face of the blade in a second plane perpendicular to the isocenter plane and the blade movement direction are arranged in a grid-like staggered pattern.

4. The multi-leaf collimator according to any one of claims 1 to 3, wherein, The ends of the first blade and the second blade have a first thickness in the direction of the connection line between the radiation source and the collimator center, and the blade body part other than the ends has a second thickness, and the first thickness is greater than the second thickness.

5. The multi-leaf collimator according to claim 4, wherein, The first thickness of the blade decreases from the end face to the direction of the blade body part to the second thickness.

6. A radiotherapy machine, comprising: A multi-leaf collimator, including a plurality of pairs of blades arranged oppositely, each pair of blades including a first blade and a second blade capable of relative movement. Wherein, in a first plane perpendicular to the isocenter plane of the radiotherapy machine and parallel to the blade movement direction, the first blade and the second blade can be moved and adjusted to a closed position, and the end faces of the first blade and the second blade are fitted to each other at the closed position. Wherein, the end face of the blade is configured with a broken line profile composed of a plurality of depressions and a plurality of protrusions, and each of the plurality of protrusions has an upper surface and a lower surface, and the upper surface and the lower surface extend along a direction parallel to the blade movement direction. Wherein, the contour lines of the plurality of protrusions on the end face of the blade form an arc segment. Wherein, the fitting depth of the end faces of the first blade and the second blade at the closed position is calculated according to the shape of the blade end and the distance from the fitting position to the blade center line, and the fitting depth at the center line of the fitting position is greater than twice the contour height of the arc segment of the blade end face; and A controller, which controls the fitting degree of the end faces of the first blade and the second blade at the closed position, so that the first blade and the second blade do not collide at the closed position.

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