LEAF DRIVE MOUNT FOR A MULTI-LEAF COLLIMATOR

Abstract

A mount for an array of leaf drive units corresponding to a single leaf bank of a multi-leaf collimator comprises a plurality of separable mounting plates. Each mounting plate comprises an array of mounting holes, and each mounting hole is arranged to receive a respective one of the leaf drive units.

Claims

1. A mount for an array of leaf drive units corresponding to a leaf bank of a multi-leaf collimator, the mount comprising: a plurality of separable mounting plates, each mounting plate comprising an array of mounting holes, each mounting hole arranged to receive a respective one of the leaf drive units.

2. The mount according to claim 1, wherein center points of the mounting holes in the array are aligned in columns extending in a first direction and in rows extending in a second direction oblique to the first direction.

3. The mount according to claim 1, wherein center points of the mounting holes in the array are aligned in columns extending in a first direction, and at least one edge of each of the mounting plates is parallel to the first direction.

4. The mount according to claim 1, wherein center points of the mounting holes in the array are aligned in columns extending in a first direction and in rows extending in a second direction oblique to the first direction, wherein a first edge each of the mounting plates is parallel to the first direction, and wherein a second edge of each of the mounting plates is parallel to the second direction.

5. The mount according to claim 1, wherein the plurality of mounting plates includes a first mounting plate and a second mounting plate arranged adjacent to the first mounting plate, wherein center points of each mounting hole in the first mounting plate are arranged in a first series of columns and center points of each mounting hole in the second mounting plate are arranged in a second series of columns, wherein adjacent columns in the first series of columns and the second series of columns have a first spacing therebetween, and wherein a particular column in the first series of columns closest to the second mounting plate and a particular column in the second series of columns closest to the first mounting plate have a second spacing therebetween, the second spacing being equal to the first spacing.

6. The mount according to claim 1, wherein the mount includes a plurality of retainers attached to the mounting plates, each retainer arranged to rigidly couple a particular leaf drive unit to a particular mounting plate.

7. The mount according to claim 6, wherein each retainer is positioned adjacent to a mounting hole and includes: a head including a retaining face arranged to face the mounting plate; and a shaft extending from the head and arranged to rotatably engage with the mounting plate such that rotation of the retainer about an axis of the shaft moves the retaining face closer to or further from the mounting plate.

8. A multi-leaf collimator comprising: a leaf bank including an array of individually moveable leaves; an array of leaf drive units; and a mount comprising a plurality of separable mounting plates, each mounting plate comprising an array of mounting holes, each mounting hole arranged to receive a particular leaf drive unit of the array of leaf drive units, wherein each leaf drive unit is received in a respective mounting hole and configured to drive a linear movement of a respective leaf.

9. The multi-leaf collimator according to claim 8, wherein the mount includes a plurality of retainers attached to the mounting plates, each retainer arranged to rigidly couple a particular leaf drive unit to a particular mounting plate, and wherein each leaf drive unit includes: a motor comprising a casing, the casing including an engaging member, wherein at a first rotational position of the casing the engaging member engages the retainer to couple the casing to the mounting plate, and wherein at a second rotational position of the casing the engaging member is disengaged from the retainer.

10. The multi-leaf collimator according to claim 9, wherein the engaging member is a flange having a recess.

11. The multi-leaf collimator according to claim 9, wherein the casing includes a locating member arranged to engage with the retainer when the motor casing is at the second rotational position so as to prevent further rotation of the motor casing once the motor casing has reached the second position.

12. The multi-leaf collimator according to claim 9, wherein the retainer engages the engaging member of more than one motor casing.

13. A drive arrangement for a multi-leaf collimator comprising: a mounting plate for mounting a leaf drive unit; a retainer attached to the mounting plate; and a motor configured to actuate a leaf of the multi-leaf collimator, the motor comprising a casing including an engaging member, wherein at a first rotational position of the casing the engaging member engages the retainer to couple the casing to the mounting plate and wherein at a second rotational position of the casing the engaging member is disengaged from the retainer.

14. The drive arrangement according to claim 13, wherein the retainer is positioned adjacent to a mounting hole located on the mounting plate, and wherein the retainer includes: a head including a retaining face arranged to face the mounting plate; and a shaft extending from the head and arranged to rotatably engage with the mounting plate such that rotation of the retainer about an axis of the shaft moves the retaining face closer to or further from the mounting plate.

15. The drive arrangement according to claim 13, wherein the engaging member is a flange having a recess.

16. The drive arrangement according to claim 13, wherein the casing includes a locating member arranged to engage with the retainer when the motor casing is at the second rotational position so as to prevent further rotation of the motor casing once the motor casing has reached the second position.

17. The drive arrangement according to claim 13, wherein the retainer engages the engaging member of the motor casing and an engaging member of a second motor casing.

18. The drive arrangement according to claim 13, wherein the drive arrangement is included in a multi-leaf collimator.

19. The drive arrangement according to claim 18, wherein the multi-leaf collimator comprises a leaf bank including an array of individually movable leaves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Specific embodiments are described below by way of example only and with reference to the accompanying drawings in which:

[0071] FIG. 1 shows a partially assembled multi-leaf collimator;

[0072] FIG. 2 shows an exploded view of one implementation of a leaf motor and the interface between the leaf actuator screw and the leaf motor;

[0073] FIG. 3 shows a different implementation of the leaf motor to that shown in FIG. 2;

[0074] FIGS. 4a and 4b each show an isometric view of leaf motor of FIG. 3 and the mounting thereof in one of the mounting plates;

[0075] FIG. 5 is an isometric view of a mount; and

[0076] FIG. 6 is an elevation view of the mount.

DETAILED DESCRIPTION OF THE DRAWINGS

[0077] MLC Assembly

[0078] Defining a Useful Co-Ordinates Convention

[0079] For ease of description, a cartesian co-ordinates system is defined in the Figures by a mutually perpendicular first axis (y), second axis (z) and third axis (x). The first axis defines a first direction (+y) and a second direction (−y) opposite to the first direction. The second axis defines a third direction (+z) perpendicular to the first direction and a fourth direction (−z) opposite to the third direction. The third axis defines a fifth direction (+x) perpendicular to both the first direction and the third direction and a sixth direction (−x) opposite to the fifth direction. The first and second axes define a first plane (yz), the first and third axes define a second plane (xy) perpendicular to the first plane, and the second and third axes define a third plane (xz) perpendicular to the first and second planes. This co-ordinates system and convention is used consistently throughout the Figures.

[0080] FIG. 1 shows a partially assembled multi-leaf collimator 100 comprising a leaf bank 20, a first and second leaf guide 301, 302, a leaf drive array 40 and a leaf drive mount 50.

[0081] The leaf bank 20 includes an array of leaves 200 arranged side by side so that a face of one leaf is in contact with a face of an adjacent leaf. The leaves 200 are arranged substantially parallel to each other but a gradient in thickness in the first direction from a first edge of each leaf 200 to a second edge opposite the first edge causes the leaf bank 20 to adopt a trapezoidal cross section in the third plane as shown in FIG. 6. Thus, the plane of a leaf 200 positioned in the middle of the leaf bank 20 is arranged to be substantially parallel to the first plane (yz), but the planes of the other leaves either side of that leaf 200 form a progressively greater angle with the first plane (yz) with distance in the fifth and sixth directions from the centre of the leaf bank 20. The leaves 200 are arranged to move relative to each other in the first and second directions. The leaves 200 are described in more detail below.

[0082] The leaf drive array 40 includes a plurality of leaf drive units 400. Each leaf drive unit 400 includes a leaf motor 410, a leaf actuator screw 430, a leaf nut 450 and a leaf nut holder 470. The leaf actuator screw 430 is coupled to the leaf motor 410 and is arranged so that its axis is parallel to the first direction. The leaf motor 410 is arranged to rotate the leaf actuator screw 430 about its axis (i.e. clockwise and anticlockwise around the first direction). The leaf nut 450 is held in position in a leaf actuator screw slot 250 in the leaf 200 by a leaf nut holder 470 fixed to the leaf 200. The leaf nut 450 is held by the leaf nut holder 470 to be static relative to the leaf 200, with the exception that a small amount of relative linear motion between the leaf nut 450 and the leaf 200 is allowed in the third and fourth directions. The leaf nut 450 contains features which interact with the leaf 200 to keep the leaf nut 450 rotationally static relative to the leaf 200. The leaf nut 450 is arranged to receive the leaf actuator screw 430 and to guide it into the leaf actuator screw slot 250. The rotational motion of the leaf actuator screw 430 translates into linear motion of the leaf nut 450, and hence the leaf 200, relative to the leaf actuator screw 430.

[0083] The leaf drive units 400 are staggered in the first direction so that the leaf nut holder 470 of any one leaf does not interfere with the leaf nut holders 470 of the leaves 200 immediately adjacent to it on either side. The leaves 200 also contain grooves to accommodate the portions of the leaf nut holders 470 of adjacent leaves 200 which are proud from the face of the leaf 200. The leaf motor 410, leaf nut 450, leaf nut holder 470 and the grooves in the leaves are described in more detail below.

[0084] The leaf drive mount 50 includes three separate mounting plates 510, 520, 530 arranged in a plane parallel to the third plane (xz). The leaf drive mount includes mounting holes 512 therein for receiving the leaf motors 410 and mounting screws 514 for securing the leaf motors 410 to the mounting plates 510, 520, 530. The leaf drive mount 50 and each of its components are described in more detail below.

[0085] The first and second leaf guide 301, 302 each comprise a rectangular frame for guiding and supporting the leaves 200 in their linear motion in the first and second directions respectively into and out of the path of the radiation beam.

[0086] A complete multi-leaf collimator assembly further includes a second, opposing arrangement including leaf bank, leaf guides, leaf drive array and leaf drive mount which are arranged to substantially mirror the assembly described above relative to a plane parallel to the third plane (xz) and aligned with the centre of the axis of the radiation beam.

[0087] In use, the leaf drive arrays drive the leaves 200 of their respective leaf banks 200 to move into and out of the path of a radiation beam passing in the fourth direction through an aperture formed between the leading edges of the leaves 200 of one leaf bank 20 and those of the leaves 200 of the opposing leaf bank 20. The leaves 200 of each leaf bank 20 are moveable independently of each other, which enables the shape of the aperture to be changed according to treatment requirements. The aperture acts as a beam shaper by blocking portions the radiation beam to redefine its cross-sectional shape in the second plane (yz). That is, the radiation beam having passed through the aperture takes on the cross-sectional shape of the aperture in the second plane (yz).

[0088] Multi-Leaf

[0089] Leaf Actuator Screw

[0090] FIG. 2 shows an exploded view of one implementation of a leaf motor 410 and the interface between the leaf actuator screw 430 and the leaf motor 410. The leaf actuator screw 430 includes a first coupling member 431 fixed to the end of the non-threaded section 430a. The first coupling member 431 comprises a first cylindrical section 431a for receiving and forming a rigid connection with the non-threaded section 430a of the leaf actuator screw 430. A second cylindrical section 431b having a smaller diameter than the first cylindrical section 431a extends in the second direction from an end face of the first cylindrical section 431a. The second cylindrical section 431b has a coupling groove 433 formed across an end face thereof.

[0091] Leaf Motor

[0092] In the implementation shown in FIG. 2, the leaf motor 410 includes a leaf motor casing 420. The leaf motor casing includes a first casing 420a and a second casing 420b removable from the first casing 420a. The leaf motor 410 further includes a second coupling member 426 fixed to an output shaft of the motor and having coupling protrusions 427 arranged to interlock with the coupling groove 433 in the second cylindrical section 431b of the first coupling member 431.

[0093] The first casing 420a is arranged to enclose a rotor, stator and commutator of the leaf motor 410, but not the second coupling member 426, which protrudes from an end of the first casing 420a. The first casing 420a includes a main section including two cylindrical tubes having the same diameter and arranged end to end. At a first end of the main section, the casing has a neck smaller in diameter than the main section. The neck includes a flange which forms a terminal end of the first casing 420a, the second coupling member 426 protruding in the first direction from said terminal end.

[0094] At a second end of the main section opposite the first end, there is an end cap 423 having the same diameter as the two cylindrical tubes. The end cap 423 has a wiring cutaway in one part of the circumferential region of the end cap 423 for allowing two wires connected to the internal components of the leaf motor 410 to protrude side by side from the end cap 423 in a radial direction of the end cap 423.

[0095] The second casing 420b includes a cap section 421b arranged to fit over the neck and flange of the first casing 420a. The second casing also includes a neck section 422b having a diameter smaller than that of the cap section 421b, the neck section having the leaf motor casing mounting flange 425 described earlier around the circumference thereof. The second casing 420b is arranged to house the first coupling member 431 and second coupling member 426 in the neck section 422b thereof.

[0096] Motor with Integral Casing and Integral Leadscrew

[0097] FIG. 3 shows a different implementation of the leaf motor 410 than that shown in FIG. 2. In the implementation of FIG. 3, the leaf motor 410 includes a leaf motor casing 420 having substantially the same outer appearance as the first casing 420a and second casing 420b described above. In this implementation, the leaf motor casing 420 is also arranged to enclose the rotor, stator and commutator. However, instead of being removably coupled to the motor output shaft, the leaf actuator screw 430 is integrally formed with the motor output shaft. Put another way, the leaf actuator screw 430 is the motor output shaft. That is, the motor output shaft and the leaf actuator screw may be formed from one monolithic rod.

[0098] The leaf motor casing 420 includes a main section including two cylindrical tubes having the same diameter and arranged end to end. At a first end of the main section, the casing includes a neck smaller in diameter than the main section and connected by a shoulder to the main section. The neck includes a mounting flange 425, which is substantially the same as that described with reference to FIG. 2. At a second end of the main section opposite the first end, there is an end cap 423 substantially the same as the end cap described with reference to FIG. 2.

[0099] The neck of the leaf motor casing 420, the mounting flange, the shoulder connecting the neck to the main section and the cylindrical tube adjacent the shoulder are monolithic. Alternatively, these parts of the leaf motor casing are separate but pressed/bonded together so that they are not removable without deformation. That is, these parts of the leaf motor casing are integrally formed so that they are not removable from each other.

[0100] Mounting of the Leaf Motor in the Mounting Plate

[0101] FIGS. 4a and 4b each show an isometric view of leaf motor 410 of FIG. 3 and the mounting thereof in one of the mounting plates 510. FIG. 4a shows the rotational position of the leaf motor relative to the mounting plate upon insertion or removal of the leaf motor from the mounting hole 512. FIG. 4b shows the rotational position of the leaf motor 410 relative to the mounting plate when the leaf motor is inserted into the mounting hole 512 and locked in position by two mounting screws 514.

[0102] As described earlier, the leaf motor casing 420 is mounted to a respective mounting plate 510 by two mounting screws 514 cooperating with the mounting flange 425 to hold the mounting flange 425 to the second face of the mounting plate 510. The mounting flange 425 further includes two curved recesses 425a each arranged to receive an edge of the head of a corresponding mounting screw 514 located to one side of the mounting hole 512 in the mounting plate 510. The two curved recesses 425a are at opposite positions relative the central axis of the leaf motor casing 420, so that in a particular rotation of the leaf motor 410 about the first direction, they are able to locate with corresponding mounting screws 514 positioned on opposite sides of the mounting holes 512. The curved recess 425a has a shape and dimensions which correspond to those of the part of the head of the mounting screw 514 which normally overlaps the mounting flange 425.

[0103] Thus, by turning the leaf motor casing 420 about its axis, it can adopt one of two rotational positions relative to the respective mounting plate 510. The two rotational positions include a first rotational position (see FIG. 4a) in which the mounting screws 514 each completely overlap a respective curved recess 425a in the mounting flange 425, and a second rotational position (see FIG. 4b) in which the mounting screws 514 each overlap a portion of the mounting flange 425.

[0104] In the first rotational position, the end of the leaf motor 410 can be inserted into the mounting hole 512 in the mounting plate 510 even when the corresponding mounting screws 514 are in position in the mounting plate 510. This is because each curved recess is arranged to receive the edge of the head of the mounting screw 514. Following insertion of the end of the leaf motor 410 into the mounting hole 512, the leaf motor casing 420 can be rotated to the second rotational position.

[0105] In the second rotational position, the leaf motor casing 420 can be held against the mounting plate 510 by tightening the mounting screws 514 so as to urge the mounting flange 425 against the second face of the mounting plate 510.

[0106] By loosening the mounting screws 514, the leaf motor casing 420 can be rotated back to the first rotational position. In the first rotational position, the leaf motor casing 420 can also be removed from the mounting hole 512 in the mounting plate 510 even when the corresponding mounting screws 514 are in position in the mounting plate 510, again because the two curved recesses 425a are each shaped and dimensioned to receive the edge of the head of a respective mounting screw.

[0107] Referring back to FIG. 2, a ridge 429b may be located in neck section 422b between the cap section 421b and the mounting flange 425. The top surface of the ridge 429b (i.e. the surface distal from the outer circumferential surface of the neck section 422b) is flush with the outer circumferential surface of the mounting flange 425. The sides of the ridge cross section are convex and the circumferential position of the ridge 429b around the neck section 422b is such that one side of the ridge 429b is flush with one half of the curved recess 425a. The shape and position of the ridge 429b are such that the side surface of the ridge flush with the curved recess 425a acts as a locating surface for the curved recess 425a. The purpose of the ridge 429b is to increase the cross section of the neck section 422b because the wall thickness of the neck section 422b is typically fairly thin. Thus, the ridge 429b gives the neck section 422b greater stiffness. Additionally, the ridge 429b acts as a stop (i.e. locating means) and limits the rotation of the leaf motor casing 420 once it is engaged under the head of the mounting screw 514. Visibility of the mounting screws 514 is limited due to motors and components obscuring the view. The ridge 429b assists in collocating the curved recess 425a and the mounting screws 514. If the ridge 429b was not present it would be possible to continue rotating the leaf motor casing 420 until the mounting flange would be inadvertently engaged/disengaged with the screw heads again.

[0108] That is, without the ridge 429b, sight of the mounting flange 425 is necessary to ensure that the leaf motor casing 420 can be rotated accurately to the first rotational position when the leaf motor 410 is inserted into the mounting hole 512. Otherwise the leaf motor 410 must be pulled in the second direction while rotating. However, with the ridge 429b included, the leaf motor casing 420 can be rotated until the head of the mounting screw meets the locating surface of the ridge 429b. The first rotational position is then assured and the leaf motor 410 can be removed from the mounting hole 512. A corresponding ridge is located on the opposite side of the neck section 422b to provide a locating surface for the corresponding curved recess 425a on the opposite side of the flange.

[0109] Leaf Drive Mount

[0110] FIGS. 5 and 6 show detailed views of the leaf drive mount 50 in situ with the other components of the multi-leaf collimator assembly 100. FIG. 5 is an isometric view and FIG. 6 is an elevation view in the first direction.

[0111] As shown in FIGS. 5 and 6, the leaf drive mount includes a first mounting plate 510, a second mounting plate 520 and a third mounting plate 530. The mounting plates 510, 520, 520 are separable from each other to facilitate ease of servicing and maintenance.

[0112] Each of the mounting plates 510, 520, 530 has a first face parallel to the third plane (xz) and proximal to the leaves 200, and a second face parallel to the first face and distal from the leaves 200. In use, the leaves 200 are situated between the leaf drive mount 50 and the path of the radiation beam, such that the leaf drive mount 50 lies behind a tail portion 220 of the leaves 200 and intersects the plane of each of the leaves 200.

[0113] Each of the mounting plates 510, 520, 530 contains a two-dimensional array of mounting holes 512, each of the mounting holes 512 having a central axis in the first direction and passing through the mounting plate 510 between the first face and the second face. Each of the mounting holes 512 is arranged to receive the cylindrical neck of a leaf motor casing 420 of one of the leaf motors 410 inserted into the mounting hole 512 in the first direction from the side of the mounting plate 510 having the second face. The leaf actuator screw 430 corresponding to the respective leaf motor 410 passes through the mounting hole 512 and emerges from the side of the mounting plate 510 having the first face. The mounting flange 425 of the leaf motor casing 420 is arranged to engage with the second face of the mounting plate 510 so as to prevent the whole of the neck of the casing from being insertable into the mounting hole 512. Thus, the leaf motor movement in the first direction is restricted by the mounting flange 425.

[0114] Each of the mounting plates 510, 520, 530 includes an array of threaded holes in the second face thereof for receiving respective mounting screws 514. When in situ in the threaded holes, the mounting screws 514 are arranged to overlap a face of the mounting flange 425 distal from the mounting plate 510 so as to prevent movement of the leaf motor 410 in the second direction.

[0115] The 2D array of mounting holes 512 in each mounting plate 510, 520, 530 includes three columns. Each of the columns is arranged at an acute angle to the third direction to take into account the staggered positioning of the leaf drive units 400 described earlier. The array is arranged in six rows, and the pattern of staggering of the leaf drive units 400 repeats every six leaves in the fifth direction.

[0116] As shown in FIG. 6, the sides of the mounting plates are angled to be substantially parallel to the angled columns. This allows consistent spacing of the leaf drive units 400 in the fifth direction by permitting a separation of the order of the width of a leaf 200 between a first mounting hole 512A in the final row of the final column of one mounting plate 520 and a second mounting hole 512B in the first row of the first column of an adjacent mounting plate 530.

[0117] A mounting screw 514 (i.e. the aforementioned retainer) is arranged on two opposing sides of every mounting hole 512. The mounting screws form a 2D array having rows between the rows of mounting holes 512 and columns between the columns of mounting holes. The mounting screws are positioned such that one mounting screw 514 can interact with one leaf motor in the mounting hole row above and one leaf motor in the mounting hole row below. Thus, the number of mounting screws can be reduced.

[0118] It may be understood that when the terms ‘parallel’, ‘perpendicular’ or ‘in the plane of’ are used to describe the relative arrangement of features and components, small deviations therefrom are permitted provided that they do not affect the functional and/or operational aspects of the multi-leaf collimator modules described herein.

[0119] Features of the above aspects can be combined in any suitable manner. It will be understood that the above description is of specific embodiments by way of aspect only and that many modifications and alterations will be within the skilled person's reach and are intended to be covered by the scope of the appendant claims.