CN116236708A - Multi-leaf collimator - Google Patents

Abstract

The application discloses a multi-leaf collimator, which comprises a plurality of leaves and a driving mechanism for driving any leaf to move; all the blades are distributed side by side along the vertical direction of the radiation beam; the dimension of all the blades along the direction of the radiation beam axis is gradually reduced from the middle part of the side-by-side distribution direction of all the blades to the two ends, and the projection width of all the blades at the isocenter plane is gradually increased from the middle part of the side-by-side distribution direction to the two ends. In the multi-leaf collimator, the thinner the leaves are, the larger the size of the leaves along the radial beam axis direction is, the closer the leaves are to the two ends of the side-by-side distribution direction, the wider the leaves are, the smaller the size of the leaves along the radial beam axis direction is, the large overall size of the radiation field can be ensured, the resolution ratio of the local radiation field is high, and the multi-leaf collimator can be well suitable for the conformal requirements of small-size tumors and can also meet the conformal requirements of large-size tumors.

Description

Multi-leaf collimator

Technical Field

The application relates to the technical field of medical instruments, in particular to a multi-leaf collimator.

Background

A multi-leaf collimator (MLC), commonly called multi-leaf collimator, multi-leaf diaphragm, etc.), is a portal forming device for tumor radiotherapy.

The multi-leaf collimator can be composed of a plurality of leaf arrays made of heavy metals such as tungsten alloy, each leaf can be controlled by a corresponding motor to realize independent movement, and the multi-leaf collimator can generate radiation fields with various specifications by controlling the positions reached by the leaves.

The thickness of the leaves is one of the important parameters of a multi-leaf collimator. The thickness of the blade may determine how fine the boundary of the radiation field is, e.g., the thinner the blade, the higher the resolution. However, thinner leaves also lead to a reduced radiation field size resulting from the same number of leaves, which limits the range of use of multi-leaf collimators, e.g. for tumors of relatively large size. In addition, thinner blades also lead to an increase in the sum of blade gaps in the same range, which in turn leads to an increase in missed shots, which increases radiation damage to normal tissue. When the leaves are thin, although the radiation field size of the multi-leaf collimator can be increased by increasing the number of leaves, this can significantly increase the system complexity of the multi-leaf collimator, leading to a significant increase in the failure rate and cost of the multi-leaf collimator, and thus is not practical.

Disclosure of Invention

The purpose of the present application is to provide a multi-leaf collimator that has a large overall radiation field size, high local radiation field resolution, and small leakage, and that can accurately and safely perform a conformal operation.

To achieve the above object, the present application provides a multi-leaf collimator comprising a plurality of leaves and a driving mechanism for driving any leaf to move; all the blades are distributed side by side along the vertical direction of the radiation beam; the dimension of all the blades along the direction of the radiation beam axis is gradually reduced from the middle part of the side-by-side distribution direction of all the blades to the two ends, and the projection width of all the blades at the isocenter plane is gradually increased from the middle part of the side-by-side distribution direction to the two ends.

In some embodiments, all of the blades include a first set of blades in the middle of the side-by-side distribution direction and a second set of blades on either side of the first set of blades.

In some embodiments, all of the blades further comprise a third set of blades; a third group of blades are arranged between the first group of blades and any one of the second group of blades; the dimension of the third group of blades along the direction of the radiation beam is equal to that of the first group of blades along the direction of the radiation beam, and the projection widths of the first group of blades, the third group of blades and the second group of blades at the isocenter sequentially increase.

In some embodiments, the projection widths of the first set of blades, the third set of blades, and the second set of blades at the isocenter plane are all integer multiples of 2.5 mm.

In some embodiments, the projected widths of the first set of blades, the third set of blades, and the second set of blades at the isocenter plane are 2.5mm, 5mm, 10mm in sequence; the number of blades of the first group of blades is larger than the number of blades of either one of the third group of blades and the second group of blades.

In some embodiments, all of the blades are provided separately in two blade cases; the two blade boxes are symmetrically distributed with the central line of the radiation beam generated by the radiation source as an axis.

In some embodiments, all of the blades converge from the isocenter plane toward the radiation source, and the intersection of the extension lines of all of the blades along the direction of the beam axis coincides with the focal point; the focal spot is located on the centre line of the radiation beam generated by the radiation source and the focal spot coincides with or is in close proximity to the radiation source.

In some embodiments, the focal spot is immediately adjacent to the radiation source and the separation is no greater than 30mm.

In some embodiments, the drive mechanism includes a plurality of linear drives, all of which are connected to all of the blades in a one-to-one correspondence.

In some embodiments, any linear drive comprises a lead screw assembly; the lead screw of the lead screw assembly is connected with the blade.

In contrast to the background art described above, the multi-leaf collimator provided by the present application includes a plurality of leaves and a drive mechanism; the driving mechanism can be used for driving any blade to move along the axial direction of the radiation beam; the plurality of blades are distributed side by side along the vertical direction of the radiation beam, and at the same time, the dimension of all the blades along the axial direction of the radiation beam is gradually reduced from the middle part of the side by side distribution direction of all the blades to two ends, and the projection width of all the blades at the isocenter plane is gradually increased from the middle part of the side by side distribution direction to two ends.

The multi-leaf collimator designs new arrangement for different leaves, the thinner the leaves are, the larger the size of the leaves along the radial beam axis direction is, so that the high resolution of local radiation fields can be ensured, rays can be effectively shielded, the increase of leakage caused by the too thin leaves in the same range is avoided, meanwhile, the smaller the size of the leaves along the radial beam axis direction is gradually widened, the smaller the size of the leaves is, the lower the resolution is, the requirements of the large-size tumors are met, and the larger radiation fields can be formed, so that the conformal effect of the multi-leaf collimator on targets with different sizes such as tumors can be ensured.

In summary, the multi-leaf collimator provided by the application has the characteristics of high resolution and large field, can improve the resolution of the multi-leaf collimator and reduce the leakage rate, and has the characteristics of low cost, large field, high resolution and the like.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present application, and that other drawings may be obtained according to the provided drawings without inventive effort to a person skilled in the art.

Fig. 1 is a schematic structural diagram of a multi-leaf collimator provided in an embodiment of the present application;

FIG. 2 is a schematic illustration of the positions of leaves and a radiation beam of a multi-leaf collimator provided in an embodiment of the present application;

FIG. 3 is a partial enlarged view of FIG. 2 at B;

FIG. 4 is a cross-sectional view at A-A of FIG. 2;

fig. 5 is a schematic view of the position of leaves of a multi-leaf collimator provided in an embodiment of the present application when producing a radiation field around a tumor.

Wherein, 100-isocenter plane, 200-radiation source, 300-focus point, 1-first group blade, 2-second group blade, 3-third group blade, 4-lead screw, 5-blade case.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

In order to better understand the aspects of the present application, a further detailed description of the present application will be provided below with reference to the accompanying drawings and detailed description.

Referring to fig. 1 to 5, fig. 1 is a schematic structural diagram of a multi-leaf collimator according to an embodiment of the present application; FIG. 2 is a schematic illustration of the positions of leaves and a radiation beam of a multi-leaf collimator provided in an embodiment of the present application; FIG. 3 is a partial enlarged view of FIG. 2 at B; FIG. 4 is a cross-sectional view at A-A of FIG. 2; fig. 5 is a schematic view of the position of leaves of a multi-leaf collimator provided in an embodiment of the present application when producing a radiation field around a tumor. Wherein fig. 1 shows only part of the components of a multi-leaf collimator.

Referring to fig. 1 and 2, the present application provides a multi-leaf collimator comprising a plurality of leaves and a driving mechanism capable of driving any one of the leaves to move along a radiation beam axis; wherein, all blades are distributed side by side along the vertical direction of the radiation beam, the dimension of all blades along the axial direction of the radiation beam is gradually reduced from the middle part of the side by side distribution direction of all blades to two ends, and the projection width of all blades at the isocenter plane 100 is gradually increased from the middle part of the side by side distribution direction to two ends.

In the multi-leaf collimator, the radiation beam axis direction can be understood as the central symmetry axis of the radiation beam; the side-by-side distribution direction is perpendicular to the beam axis direction. As regards the definition of the radiation beam and the isocenter plane 100 in this embodiment, reference is made to fig. 2, and also to the related art. In addition, in the multi-leaf collimator, the moving direction, the side-by-side distribution direction and the ray beam direction of the leaves are always perpendicular to each other, so that the driving mechanism drives any one leaf to do linear motion. Of course, the driving mechanism can also drive the blades to move in other directions, so long as the multi-blade collimator can generate a proper radiation field around the target object.

In this embodiment, there are special designs for all of the blades in three different directions/positions of the beam axis direction, the vertical direction of the beam and the isocenter plane 100, respectively.

All the leaves are arranged side by side in the vertical direction of the radiation beam and are moved by a drive mechanism, which is an essential element of a multi-leaf collimator for producing a radiation field under the radiation beam.

The dimension of all blades in the side-by-side distribution direction correlates to the projected width of all blades at the isocenter plane 100. If the dimension of the blades in the direction of the beam axis is defined as the length of the blades, the length of the blades is larger as seen in the side-by-side direction of the side-by-side distribution of all the blades, whereas the length of the blades is smaller as seen in the side-by-side direction of the side-by-side distribution of all the blades, that is, the length of all the blades decreases from the middle to the two ends in the side-by-side direction of the side-by-side distribution of all the blades. The projection width of all the blades at the isocenter plane 100 increases from the middle to the two ends in the side-by-side distribution direction, and it can be seen that the closer to the middle in the side-by-side distribution direction, the smaller the projection width of the blades at the isocenter plane 100, and the closer to the two ends in the side-by-side distribution direction, the larger the projection width of the blades at the isocenter plane 100. Since the projection width of the blade near the middle of the side-by-side distribution direction at the isocenter plane 100 is relatively small, although resolution can be improved, it is also easy to cause increase of the leakage emission, and for this reason, the length of the blade near the middle of the side-by-side distribution direction is increased, so that the leakage emission can be effectively reduced; conversely, the blades near the middle of the side-by-side distribution may have a relatively large projected width at the isocenter 100 and a relatively small leakage, and the length of the blades may be relatively small.

In this embodiment, the driving mechanism drives any one of the blades to perform linear motion, and in general, the driving mechanism drives all the blades to perform independent motion, in other words, the driving mechanism drives each blade individually. Of course, the driving mechanism can also drive a plurality of blades to synchronously move so as to meet the special requirements of the multi-blade collimator on the working performance of the multi-blade collimator.

In summary, the multi-leaf collimator provided by the application adjusts the shapes and the sizes of the leaves along the side-by-side distribution direction of the leaves, so that the high resolution of the middle area of the radiation field can be ensured, the missed emission is reduced, the field size of the radiation field can be considered, and the conformal effect on targets with different sizes such as tumors can be ensured.

It should be noted that the conformal refers to that a radiation field adapted to the shape of the tumor is generated for an observed object to be irradiated, such as the tumor, and the area where the radiation field is located can cover the area where the tumor is located, and can not cover too much area for other areas except the area where the tumor is located, so that the normal human tissues except the radiation field are prevented from being damaged by rays.

The multi-leaf collimator provided in the present application will be further described with reference to the accompanying drawings and embodiments.

In some embodiments, all of the leaves of the multi-leaf collimator comprise a first set of leaves 1 and a second set of leaves 2, the first set of leaves 1 being located in the middle of the side-by-side distribution of all of the leaves, the second set of leaves 2 being located at both ends of the side-by-side distribution of all of the leaves, it being apparent that the second set of leaves 2 are also located at both sides of the first set of leaves 1. As can be seen from the foregoing, the dimension of the first set of blades 1 in the direction of the beam axis is greater than the dimension of the second set of blades 2 in the direction of the beam axis, and the projected width of the first set of blades 1 at the isocenter plane 100 is smaller than the projected width of the second set of blades 2 at the isocenter plane 100.

In the above embodiment, all the leaves of the multi-leaf collimator are divided into at least two groups of the first group of leaves 1 and the second group of leaves 2, and since the second group of leaves 2 are located at both sides of the first group of leaves 1, it can be understood that the number of groups of the first group of leaves 1 and the number of groups of the second group of leaves 2 are 1, and the two groups of the second group of leaves 2 are located at both sides of the first group of leaves 1.

In the above embodiment, the number of blades of the first group of blades 1 may be equal to the number of blades of the second group of blades 2, or may be larger or smaller than the number of blades of the second group of blades 2.

All blades may be divided not only into the first set of blades 1 and the second set of blades 2, but also into more sets, for example, all blades comprise the first set of blades 1, the second set of blades 2 and the third set of blades 3. The third group of blades 3 is disposed between any adjacent first group of blades 1 and any second group of blades 2, in other words, the third group of blades 3 is disposed on both sides of the first group of blades 1, and the second group of blades 2 is disposed on both sides of the third group of blades 3, so that the fifth group of blades 2, the third group of blades 3, the first group of blades 1, the third group of blades 3 and the second group of blades 2 are sequentially arranged as viewed in the side-by-side distribution direction of all the blades.

It is known that the dimensions of all the blades in the direction of the radiation beam axis decrease from the middle to the two ends in the side-by-side distribution direction of all the blades, and the projection width of all the blades at the isocenter 100 increases from the middle to the two ends in the side-by-side distribution direction, when all the blades are divided into the first group of blades 1, the second group of blades 2, and the third group of blades 3, the dimensions of the first group of blades 1, the second group of blades 2, and the third group of blades 3 in the direction of the radiation beam axis may decrease in order, and in addition, the dimensions of the second group of blades 2 in the direction of the radiation beam axis may be smaller than the dimensions of the first group of blades 1 in the direction of the radiation beam axis, and as for the dimensions of the third group of blades 3 in the direction of the radiation beam axis may be equal to the dimensions of the first group of blades 1 in the direction of the radiation beam axis or may be equal to the dimensions of the second group of blades 2 in the direction of the radiation beam axis. Similarly, the projection widths of the first set of blades 1, the second set of blades 2 and the third set of blades 3 at the isocenter plane 100 may be sequentially increased, or the projection width of the second set of blades 2 at the isocenter plane 100 may be made larger than the projection width of the first set of blades 1 at the isocenter plane 100, and the projection width of the third set of blades 3 at the isocenter plane 100 may be equal to the projection width of the first set of blades 1 at the isocenter plane 100, or may be equal to the projection width of the second set of blades 2 at the isocenter plane 100.

Taking the example that the projection widths of the first group of blades 1, the second group of blades 2 and the third group of blades 3 at the isocenter plane 100 can be sequentially increased, the projection widths of the first group of blades 1, the third group of blades 3 and the second group of blades 2 at the isocenter plane 100 can be sequentially 2.5mm, 5mm and 10mm. Taking the example that the dimension of the second group of blades 2 along the direction of the radiation beam is smaller than the dimension of the first group of blades 1 along the direction of the radiation beam, and the dimension of the third group of blades 3 along the direction of the radiation beam is equal to the dimension of the first group of blades 1 along the direction of the radiation beam, the dimensions of the first group of blades 1, the third group of blades 3 and the second group of blades 2 along the direction of the radiation beam are 95mm, 95mm and 75mm in sequence.

As noted in the above examples, the projection widths of the three leaves of the first group 1, the third group 3 and the second group 2 at the isocenter plane 100 are all integer multiples of 2.5mm, and the above examples only give a numerical relationship of 2.5mm, 5mm and 10mm, and obviously the leaves of the multi-leaf collimator can be set to other dimension parameters meeting technical requirements, in consideration of the actual state of the art and industry standard.

The multi-leaf collimator that this application provided has the characteristics that the field scope is big and local field resolution is high, for example, the projection width of first group blade 1, third group blade 3 and second group blade 2 three in the isocenter plane 100 department can be 2.5mm, 5mm, 10mm in proper order, and simultaneously, the blade quantity of first group blade 1, third group blade 3 and second group blade 2 three is 32 pairs, 12 pairs, 16 pairs in proper order, then the field region that first group blade 1, third group blade 3 and second group blade 2 three formed is respectively:

2.5mm×32＝80mm；

5mm×12＝60mm；

10mm×16＝160mm；

for the radiation field described above, the radiation field formed by the first set of blades 1 is small in range but high in resolution, the radiation field formed by the second set of blades 2 is low in resolution but large in range, and the third set of blades 3 is centered in both the radiation field range and the resolution. When the radiation field formed by the first group of blades 1 is positioned at the center of the radiation field of the multi-leaf collimator and is suitable for small-size tumors, an operator can make the small-size tumors positioned at the center of the radiation field of the multi-leaf collimator, and at the moment, the operator can clearly, accurately and efficiently adapt to the small-size tumors. When the radiation field formed by the second group of blades 2 is positioned at the edge of the radiation field of the multi-blade collimator and conforms to the large-size tumor, an operator can enable the radiation field of the multi-blade collimator to cover the whole outline of the large-size tumor, and the requirement on the conforming accuracy of the large-size tumor is lower than that of the small-size tumor, so that the target conforming effect of the large-size tumor can be achieved without high resolution.

Referring to fig. 5, fig. 5 is a schematic view of the position of the leaves of the multi-leaf collimator provided in the embodiments of the present application when the radiation field is generated around the tumor. In fig. 5, the rectangular bars represent the leaves, the ellipses represent the actual shape of the malignant tumor to be irradiated, and the blank area of fig. 5 represents the target radiation field, so that fig. 5 shows the effect of the radiation field formed by the multi-leaf collimator on the shape adaptation of the malignant tumor, so that fig. 5 can also be said to be a schematic diagram of the positions of all the leaves when the multi-leaf collimator conforms to the tumor. As to how the leaf collimator adjusts to conform to the malignancy, reference is made to the prior art for specific ways of operation, which are not described herein.

In some embodiments, the multi-leaf collimator provided herein further comprises a leaf box 5; all the leaves of the multi-leaf collimator are arranged in two leaf boxes 5, and the two leaf boxes 5 are symmetrically distributed by taking the central line of the radiation beam generated by the radiation source 200 as an axis. Referring to fig. 2 and 4, the blade case 5 is omitted from the figures.

Furthermore, in some embodiments, all of the leaves of the multi-leaf collimator are concentrated from the isocenter plane 100 toward the radiation source 200, and therefore, all of the leaves are distributed obliquely along the respective ray, resulting in the intersection of the extension lines of all of the leaves along the beam axis direction coinciding with the focal point 300; wherein the focal spot 300 is located on the centre line of the radiation beam generated by the radiation source 200 and the focal spot 300 coincides with or is in close proximity to the radiation source 200.

On the basis of the above embodiment, the focal spot 300 and the radiation source 200 are immediately adjacent to each other with a distance of not more than 30mm, for example, the focal spot 300 is 18mm from the radiation source 200.

In the above embodiments, the radiation source 200 refers to the source point of the radiation generated by the electron targeting; when the radiotherapy is carried out on the patient, the malignant tumor of the patient is positioned at the isocenter of each rotating shaft of the treatment equipment, and the plane perpendicular to the rays irradiated to the isocenter is the isocenter plane; the dose of radiation passing through the multi-leaf collimator is called leakage radiation.

Referring to fig. 2 and 3, in the above embodiment, the blades are arranged at a specific inclination angle, and the extension lines of all the inclination angles of the blades are compared with the focal point 300 of the multi-leaf collimator, so that the focal point 300 is close to but not coincident with the radiation source 200, for example, as shown in fig. 2, the focal point 300 may be located 18mm above the radiation source 200, so that the rays emitted from the radiation source 200 are not directed at the gaps between the blades, and thus the leakage between the blades may be reduced.

In other embodiments provided herein, the drive mechanism may include a plurality of linear drives that connect all of the blades in a one-to-one correspondence, that is, each blade is independently driven by a corresponding linear drive.

Typically, the linear drive may be provided as a screw assembly, the blade being connected to a screw 4 of the screw assembly, e.g. the screw 4 of the screw assembly is connected to the blade. It can be seen that the driving mechanism controls the movement of all the blades by using a plurality of screw assemblies, and the required shape of the field can be formed by adjusting the positions of the blades and the blade box 5.

In the multi-leaf collimator provided by the application, the closer to the middle part of the side-by-side distribution direction, the thinner the leaf is, but the larger the dimension along the radial beam axis direction is, so that the high resolution of the local radiation field can be ensured, rays can be effectively shielded, and the increase of missed radiation caused by the over-thin leaf is avoided. With respect to the prior art, as the thickness of the blades becomes thinner, the number of gaps of several blades arranged with the same gaps in the same range increases, in other words, if the blades are arranged with the same gaps in the same range, the thinner the blades are, the more the number of blades are, resulting in an increase in the number of gaps of the blades, and further, an increase in the sum of the gaps of the blades, which eventually results in an increase in the leakage. In contrast, the present application does not limit the leakage from the angle of the gap number and the gap sum, but limits the leakage by increasing the size of the blades in the direction of the beam axis, which can achieve the effects of not only reducing the leakage amount but also avoiding increasing the number of blades and also guaranteeing high resolution.

In the multi-leaf collimator provided by the application, as the leaves near the middle part of the side-by-side distribution direction are thinner, the high local resolution of the radiation field means that the resolution of the middle region of the radiation field is high, which can just meet the conformal requirement of small-size tumor, and compared with the small-size tumor, the resolution of the edge of the radiation field is low, but is enough to meet the conformal requirement of large-size tumor.

In addition, in the multi-leaf collimator provided by the application, the focusing point 300 and the radiation source 200 are not overlapped, so that a certain included angle exists between the rays and the leaf slits, and leakage emission can be reduced.

In summary, the multi-leaf collimator provided by the application designs a new arrangement for different leaves, and combines high resolution and large field, so that the focusing point 300 and the radiation source 200 are not overlapped, the resolution of the multi-leaf collimator is improved, and meanwhile, the leakage rate of the multi-leaf collimator is reduced, so that the multi-leaf collimator has the characteristics of low cost, large field, high resolution and the like.

The multi-leaf collimator provided in this application is described in detail above. Specific examples are set forth herein to illustrate the principles and embodiments of the present application, and the description of the examples above is only intended to assist in understanding the methods of the present application and their core ideas. It should be noted that it would be obvious to those skilled in the art that various improvements and modifications can be made to the present application without departing from the principles of the present application, and such improvements and modifications fall within the scope of the claims of the present application.

Claims (10)

1. A multi-leaf collimator comprising a plurality of leaves and a drive mechanism for driving movement of any of the leaves; all of the blades are distributed side by side in the vertical direction of the radiation beam; the dimension of all the blades along the direction of the radiation beam axis is gradually reduced from the middle part to the two ends of the side-by-side distribution direction of all the blades, and the projection width of all the blades at the isocenter plane (100) is gradually increased from the middle part to the two ends of the side-by-side distribution direction.

2. A multi-leaf collimator according to claim 1, characterized in that all the leaves comprise a first set of leaves (1) in the middle of the side-by-side distribution direction and a second set of leaves (2) on both sides of the first set of leaves (1).

3. A multi-leaf collimator according to claim 2, characterized in that all the leaves (1) further comprise a third set of leaves (3); the third group of blades (3) are arranged between the first group of blades (1) and any one of the second group of blades (2); the size of the third group of blades (3) along the direction of the radiation beam is equal to the size of the first group of blades (1) along the direction of the radiation beam, and the projection widths of the first group of blades (1), the third group of blades (3) and the second group of blades (2) at the isocenter plane (100) are sequentially increased.

4. A multi-leaf collimator according to claim 3 characterised in that the projection widths of the first set of leaves (1), the third set of leaves (3) and the second set of leaves (2) at the isocenter plane (100) are all integer multiples of 2.5 mm.

5. The multi-leaf collimator of claim 4, wherein the projection widths of the first set of leaves (1), the third set of leaves (3) and the second set of leaves (2) at the isocenter plane (100) are 2.5mm, 5mm, 10mm in order; the number of blades of the first group of blades (1) is larger than the number of blades of either one of the third group of blades (3) and the second group of blades (2).

6. A multi-leaf collimator according to claim 1, characterized in that all the leaves are provided separately in two leaf boxes (5); the two blade boxes (5) are symmetrically distributed by taking radiation beams generated by the radiation source (200) as axes.

7. The multi-leaf collimator of any one of claims 1 to 6 wherein all of the leaves converge from the isocenter plane (100) toward a radiation source (200), and an intersection of extension lines of all of the leaves along the radiation beam axis direction coincides with a focal point (300); the focal spot (300) is located on the centre line of the radiation beam generated by the radiation source (200) and the focal spot (300) coincides with or is in close proximity to the radiation source (200).

8. The multi-leaf collimator of claim 7, wherein the focal spot (300) is immediately adjacent to the radiation source (200) and at a spacing of no more than 30mm.

9. A multi-leaf collimator according to any one of claims 1 to 6 in which the drive mechanism includes a plurality of linear drives, all of which are connected in one-to-one correspondence with all of the leaves.

10. The multi-leaf collimator of claim 9 wherein any of the linear drives comprises a lead screw assembly; and a screw rod (4) of the screw rod assembly is connected with the blade.

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