GB2592982A - Leaf assembly for a multi-leaf collimator - Google Patents

Abstract

A leaf assembly for a multi-leaf collimator comprises a leaf 200 and a leaf nut 450 removably mounted within the profile of the leaf, the leaf nut comprising a threaded hole for receiving a leaf actuator screw 430 oriented along a first (y) axis in the plane of the leaf. The leaf nut is mounted within the leaf such that relative movement between the leaf nut and the leaf is prevented both linearly along the first axis, and rotationally thereabout; however, a small amount of linear movement between the leaf and leaf nut is permitted along axes (x & z) perpendicular to the first (y) axis to allow for misalignment between drive motor, leaf actuator screw and leaf nut. The leaf nut is removably mounted via selective interlocking of at least part of the leaf nut, e.g. slots 454 & 456, with at least part of the leaf. In some embodiments, a leaf nut holder (470, Figs 4a & 4b) is provided which, when fastened to the leaf, limits longitudinal movement of the leaf nut relative to the leaf.

Description

LEAF ASSEMBLY FOR A MULTI-LEAF COLLIMATOR

FIELD

The present disclosure relates to a leaf nut for a multi-leaf collimator, a leaf nut holder for said leaf nut and a leaf assembly including a leaf, said leaf nut and said leaf nut holder. The present disclosure also relates to a multi-leaf collimator including said leaf assembly.

BACKGROUND

Radiotherapentic apparatus involves the production of a beam of ionising radiation, usually x-rays or a beam of electrons or other sub-atomic particles. This is directed towards a cancerous region of a patient, and adversely affects the tumour cells causing an alleviation of the patient's symptoms. The beam is delimited so that the radiation dose is maximised in the tumour cells and minimised in healthy cells of the patient, as this improves the efficiency of treatment and reduces the side effects suffered by a patient.

In a radiotherapy apparatus, the beam can be delimited using a beam limiting device such as a 'multi-leaf collimator' (MLC). This is a collimator which consists of a large number of elongate thin leaves arranged side to side in an array. The leaves are usually made from a high atomic numbered material, usually tungsten, so that they are substantially opaque to the radiation.

Each leaf is moveable longitudinally so that its tip, or leading edge, can be extended into or withdrawn from the radiation beam. All the leaves can be withdrawn to allow the radiation beam to pass through, or all the leaves can be extended so as to block the radiation beam completely. Alternatively, some leaves can be withdrawn and some extended so as to define any desired shape, within operational limits. The array of leaf tips can thus be positioned so as to define a variable edge to the collimator. A multi-leaf collimator usually consists of two banks of such arrays (i.e. leaf banks), each leaf bank projecting into the radiation beam from opposite sides of the collimator. The variable edges provided by the two leaf banks thus collimate the radiation beam to a chosen cross-sectional shape, usually that of a target tumour volume to be irradiated. That is, the two leaf banks combine to provide an aperture of variable shape for shaping the radiation beam.

It is important that the driving mechanisms for driving the individual leaves are robust, low friction and easy to install and maintain. Fulfilling one or more of these criteria can increase the complexity and cost of manufacture of the multi leaf collimator.

It is desirable to provide a multi-leaf collimator which addresses the abovementioned problems.

SUMMARY

Aspects and features of the present invention are set out in the accompanying claims.

There is provided a leaf assembly for a multi-leaf collimator, comprising: a leaf; a leaf nut removably mounted within the profile of the leaf, the leaf nut comprising a threaded hole for receiving a leaf actuator screw oriented along a first axis in the plane of the leaf; the leaf nut being mounted within the leaf such that relative movement between the leaf nut and the leaf is prevented both linearly along the first axis and rotationally about the first axis.

The leaf nut is positioned in the leaf tail to provide a simpler drive design and more accurate leaf positioning. The leaf nut is not permitted to rotate or move longitudinally relative to the leaf (so that rotation of the leaf actuator screw (usually a leadscrew) causes longitudinal movement of the nut and leaf), but a small amount of vertical movement between the leaf nut and leaf is permitted which allows for misalignment between the motor, leaf actuator screw and the leaf nut Removable leaf nut Instead of the leaf nut being an integral part of the leaf or the tail portion of the leaf, the leaf nut is removably mounted within the profile of the leaf. Advantageously, this allows the nut to be replaced, for example if worn or damaged, without replacement of the leaf or tail portion of the leaf In embodiments, the leaf nut is removably mounted so that no destruction of any part of the leaf or leaf nut is required in order to remove the leaf nut from the leaf In embodiments, the leaf nut is removably mounted via the selective interlocking of at least a part of the leaf nut with at least a part of the leaf. The interlocking is selective in that the leaf nut can be moved from a position in which the at least a part of the leaf nut and at least apart of the leaf are interlocked, to a position in which there is no interlocking between the leaf nut and the leaf. The interlocking limits the movement of the leaf linearly in at least one pair of two opposing directions and/or rotationally. Advantageously, fewer fixing means are required to limit movement of the leaf nut in the ways described herein. In addition, the interlocking assists reliable positioning of the leaf assembly components during repair/replacement so that the complexity and cost of repair/replacement is reduced.

Thus, it may be understood that the leaf nut is movable from a third position, in which the leaf nut is interlocked with the leaf, along an axis to a fourth position in which the leaf nut is free from the leaf In embodiments, the axis may be the first axis described herein (i.e. in the longitudinal direction of the leaf). The first axis defines a first direction and a second direction opposite the first direction and the leaf nut is movable in the second direction from the third position to the fourth position (the first direction being from the tail to the tip of the leaf). Advantageously, the leaf nut can be removed more easily from the tail portion of the leaf without interfering with the leaf assembly corresponding to any adjacent leaf In embodiments, the interlocking parts of the leaf nut and leaf include a recessed structure on one of the leaf nut and leaf and a corresponding protruding structure on the other of the leaf nut and leaf for insertion into the recessed structure. Advantageously, this provides a simple mechanism for preventing movement of the leaf nut relative to the leaf in one axis (perpendicularly from either side of the protruding or recessed structure) while allowing movement in an axis perpendicular to this (e.g. into/out of the recessed structure).

In embodiments, the recessed structure or protruding structure is elongate, thus allowing movement in a third axis perpendicular to these two axes (i.e. parallel to the lengthwise direction of the recessed structure or protruding structure). For example, the recessed structure may be a slot or groove on one of the leaf nut and leaf, and the protruding structure may be a structure on the other of the leaf nut and leaf corresponding to the slot or groove for engaging the slot or groove.

Alternatively, or in addition, the protruding structure includes a rib or spine on one of the leaf nut and leaf, and the recessed structure is a structure on the other of the leaf nut and leaf for engaging the rib or spine. In embodiments, the recessed structure is on the leaf nut and the protruding structure is the body of the leaf itself. That is, the recessed structure receives the body of the leaf itself.

Alternatively, or in addition, the leaf nut is removably mounted to the leaf via fixing means, such as a screw, bracket, frame, mount, clip, clasp, catch or holder. Advantageously, fewer machined features in the leaf nut and/or tail portion of the leaf are required in order to limit movement of the leaf nut. Fewer machined features reduces the complexity of machining in the leaf or leaf nut, which reduces manufacturing complexity and cost.

Prevention and limitation of leaf nut movement The interlocking parts and/or fixing means may prevent or limit movement of the leaf nut relative to the leaf in a number of ways. Movement may be prevented or limited linearly along an axis or rotationally around an axis. Here, prevention means substantially no movement (within engineering tolerances) and limitation means some limited movement is allowed.

Movement of the leaf nut relative to the leaf is prevented, rather than merely limited, along the axis of movement of the leaf in use (i.e. in the first and second directions described herein, that is into and out of the path of the radiation beam). If this such movement is not prevented, rotations of the leaf actuator screw may translate into linear movement of the leaf nut without translating into the expected degree of linear movement of the leaf Inaccuracies in leaf positioning may occur as a result.

For similar reasons, rotational movement about the axis of movement of the leaf (either clockwise or anticlockwise) is also prevented so that the rotational movement of the leaf actuator screw does not translate into rotation of the leaf nut instead of linear movement of the leaf. Such movement is undesirable, because leaf drive positioning mechanisms rely on a fixed relationship between the linear displacement of the leaf and rotation of the leaf actuator screw.

Unless the aforementioned linear and rotational movements are prevented, complex compensation mechanisms, sensing-motion feedback loops and/or control methods may be needed to ensure accurate driving and positioning of the leaf.

In embodiments, the leaf nut comprises an engaging portion configured to engage the leaf (e.g. a face of the leaf) to constrain rotational movement of the leaf nut relative to the leaf about the first axis. For example, the leaf nut comprises a slot for receiving a portion of the leaf and the walls of the slot engage the face of the leaf In embodiments, die leaf nut is mounted into the tail portion of the leaf and is constrained by a profile that fits over the edges of the tail to resist the torque reaction from the leaf actuator screw. The profile and the tail portion are designed so that minimal clearance therebetween is attained to stop rotation of the nut to reduce 'backlash' (rotation of the leaf actuator screw without translation into linear motion of the leaf). hi other embodiments, the leaf includes a recess configured to receive the engaging portion of die leaf For example, the leaf nut includes a spine and the leaf includes a slot in the plane of the leaf for receiving the spine.

The rotational movement of the leaf nut relative to the leaf around any axis other than the axis of the leaf actuator screw is prevented primarily by the leaf actuator screw itself However, die interacting features of the leaf nut arid leaf may also prevent such rotational movement.

Some linear movement of the leaf nut relative to the leaf in certain axes can be beneficial. In embodiments, the leaf nut is movable relative to the leaf in an axis extending out of the plane of the leaf (e.g. normal to the plane of the leaf). Alternatively, or in addition, the leaf nut is movable in the plane of the leaf in an axis lying across the axis of movement of the leaf (e.g. in the plane of the leaf perpendicular to the axis of movement of the leaf). That is, linear movement of the leaf nut relative to the leaf along a second axis is limited between a first and second position along the second axis, wherein the second axis lies across (e.g. perpendicular to) the first axis. Advantageously, by allowing such movement, misalignments between the leaf and the other leaf actuator components (the leaf actuator screw ancUor the leaf actuator motor) can be better accommodated. This increase in alignment tolerance ultimately reduces the stress and/or wear on the leaf drive components (e.g. the leaf drive motor, the leaf nut and/or the leaf actuator screw) in use.

Allowing the above described movement in either one of these axes may be achieved by providing one or more of the interlocking protrusion-recess arrangements described herein.

In embodiments, relative movement of the leaf nut out of the plane of the leaf is prevented in order to avoid leaf nut interference with adjacent leaves, and the leaf nut is movable in the plane of the leaf in the axis lying across the direction of movement of the leaf In embodiments the aforementioned movements (those in the axis lying across the axis of movement of the leaf and/or the axis extending out of the plane of the leaf) are limited along the respective axis. in embodiments, each recess has a stop (e.g. the floor of the recess or a strut, protrusion or rib in the recess). Alternatively, or in addition, each protruding part includes a stop (e.g. a flange or shoulder) or has a stop associated therewith (e.g. the base from which the protrusion protrudes). The stop limits the movement between the first mid second positions by preventing further movement of the protrusion into the recess. Advantageously, this prevents excessive movement of the leaf nut and mitigates the risk of damage to the leaf assembly and or leaf drive unit during installation, repair or operation. For example, the limited movement may prevent the leaf nut from impinging upon the space designated for a part of an adjacent leaf or the leaf nut of an adjacent leaf In embodiments, the aforementioned movements (those in the axis lying across the axis of movement of the leaf and/or the axis extending out of the plane of the leaf) are limited between a first and a second position along the respective axis. To achieve this, two recess/protrusion arrangements are provided, each arrangement including at least one of the aforementioned stops. That is, movement is limited between a first position and a second position by the physical interaction between the leaf nut and the leaf Alternatively, or in addition, movement is limited by a leaf nut holder (described below).

In embodiments, the interlocking parts also prevent rotation of the leaf nut relative to the leaf Alternatively, or in addition, fixing means, such as the leaf nut holder, may prevent rotation of the leaf nut relative to the leaf.

Leaf nut holder In embodiments, the leaf assembly includes a leaf nut holder arranged to hold the leaf nut and prevent or limit the movement of the leaf nut relative to the leaf The leaf nut holder is removably coupled to the leaf to allow ease of repair or replacement of leaf nut and/or the leaf nut holder itself. The leaf nut holder is a frame, mount, clip, clasp or any other structure which interacts with both the leaf nut and the leaf to fasten the leaf nut to the leaf.

In embodiments, the leaf nut holder, when fastened to the leaf, is arranged to limit movement of the leaf nut relative to the leaf longitudinally (i.e. along the first axis in the first and second directions), while allowing relative movement laterally in the plane of the leaf (along the second axis in the third and fourth directions) and/or perpendicular to the plane of the leaf (along the third axis in the fifth and sixth directions).

In embodiments, the leaf and the leaf nut holder cooperate to limit movement of the leaf nut relative to the leaf along the first axis. For example, the leaf or the leaf nut includes a stop for preventing movement of the leaf nut in the first direction from a third position in which the leaf nut is mounted in the leaf, while the leaf nut holder is arranged to provide a stop to prevent movement of the leaf nut from the third position in the second direction toward a fourth position in which the leaf nut is free from the leaf.

In embodiments, the leaf nut holder has means (e.g. an aperture or a recess) arranged to accommodate at least a portion of the leaf nut. The edges of the aperture (or recess) limit lateral movement of the leaf nut relative to the leaf between the first position and a second position while preventing movement of the leaf nut relative to the leaf in the longitudinal direction (i.e. from the third position towards the fourth position).

The leaf nut holder and leaf include interlocking means of any of the varieties described earlier in relation to the leaf nut and leaf (e.g. recess/protrusion pairs). The interlocking means prevent relative movement between the leaf nut holder and the leaf in one or more of the longitudinal direction (along the first axis), lateral direction (along the second axis) and the direction perpendicular to the plane of the leaf (along the third axis). The limitation in movement of the leaf nut holder and the interaction between the leaf nut holder and the leaf nut allows the leaf nut holder to limit movement of the leaf nut relative to the leaf in any of the ways described herein. Advantageously, fewer fixing means are required in order to limit movement of the leaf nut holder to, in turn, properly limit movement of the leaf nut in the ways described herein. Fewer fixing means simplifies the manufacturing process and reduces the probability of parts that may interfere with the operation of the multi leaf collimator.

Alternatively, or in addition, leaf nut holder is removably mounted to the leaf via fixing means, such as a screw, bracket, frame, mount, clip, clasp, catch or holder. Advantageously, fewer features in the leaf nut holder and/or tail portion of the leaf are required to limit the movement of the leaf nut holder to, in turn, limit movement of the leaf nut in the ways described herein. Fewer features reduces the complexity of machining in the leaf or leaf nut holder, which reduces manufacturing complexity and cost.

In embodiments, the leaf nut holder includes a slot for receiving an edge of the leaf and preventing movement of the leaf nut holder relative to the leaf along the first direction and/or out of the plane of the leaf For example, the leaf nut holder may include a blind slot arranged to receive an edge of the tail portion of the leaf The blind slot allows the leaf nut holder to straddle the edge of the tail portion so as to limit movement of the leaf nut holder relative to the leaf in the axis extending out of the plane of the leaf. The floor of the blind slot acts as a stop for limiting the movement of the leaf nut holder relative to the leaf in the first direction (i.e. longitudinally in the first direction into the path of the radiation beam). The use of a blind slot in this way aids the removability of the leaf nut holder from the leaf as movement of the leaf nut holder relative to the leaf is permitted longitudinally in the second direction opposite the first direction. Thus, the leaf nut holder can be slid backwards to disengage the edge of the leaf from the blind slot and remove it for repair or replacement.

In embodiments, the leaf nut is manufactured from plastic. Advantageously, the leaf nut material needs no lubrication and has a long service life. The leaf nut holder may be manufactured from steel or any other suitable metal alloy. Alternatively, the leaf nut holder may be manufactured from plastic. The leaf may be manufactured from tungsten Optionally, a tail portion of the leaf may be manufactured from a different material (e.g. steel) to allow for ease of machining the aforementioned interlocking parts into the leaf In embodiments, the leaf nut and leaf nut holder are manufactured as one piece as a plastic moulding so that a flexible connection is created between the leaf nut holder and leaf nut to allow for misalignment problems as part of the moulding. For example, the moulding may include a thin (flexible) section connecting the leaf nut to the leaf nut holder. The flexible section is configured to flex so as to allow relative movement between the leaf nut and the leaf nut holder in one or more directions while remaining relatively stiff in the leaf travel direction so as to prevent or minimise movement in this direction. Thus, the flexible section is configured to prevent relative movement between the leaf nut and leaf nut holder along the first axis, so that force from the leaf actuator screw can be transmitted to the leaf efficiently (without backlash). The flexible section may be configured to allow relative movement of the leaf nut between the first position and second position as described herein to accommodate misalignment between the leaf and the leaf actuator components. The flexible section may have a ribbon-like form to provide this functionality and the lengthwise direction of the ribbon may be parallel to the leaf travel direction with the leaf nut connected to the ribbon along one edge of the ribbon and the leaf nut holder connected to the ribbon along the opposing edge of the ribbon. The folding, bending or flexing of the ribbon along lines parallel to its lengthwise direction permits the relative movement of the leaf nut relative to the leaf nut holder.

Accommodatinu features in the leaf In embodiments, the tail portion of the leaf is configured to accommodate the leaf nut and/or the leaf nut holder. The tail portion of the leaf may also be configured to facilitate the movement (and/or prevention/limitation of movement) of the leaf nut and/or leaf nut holder in use. Alternatively, or in addition, the tail portion is configured to facilitate the fixture and removal of the leaf nut and/or leaf nut holder from the leaf.

In embodiments, the leaf includes a slot for receiving the leaf actuator screw. The slot lies in a lengthwise direction of the leaf (i.e, along the first axis). The slot is through the whole thickness of the leaf and has a width suitable for accommodating the leaf actuator screw while allowing unimpeded rotation thereof relative to the leaf. Advantageously, the slot allows the leaf actuator screw to extend into the profile of the leaf, which creates a more compact leaf assembly.

In embodiments, a section of the slot is for receiving at least a portion of the leaf nut. The section of the slot is wider than the remaining part of the slot. The leaf nut is arranged to move along the slot between the third and fourth positions. This facilitates ease of removal and replacement of the leaf nut because the leaf nut can slide back and forth along the slot and does not need to be otherwise held in place. For example, the leaf nut can be removed by removing the leaf nut holder holding the leaf nut in place, then sliding the leaf nut along the section of the slot from the third position (in place for use) to the fourth position (in which it is free from the leaf). When the leaf nut holder is removed, the movement of the leaf nut is restricted to being between the third and fourth positions by the slot, thereby reducing the risk the leaf nut will drop out. Thus, the slot aids safe, convenient and reliable removal and replacement of the leaf nut.

In embodiments, the leaf includes a rib spanning the slot. The rib has a curve in the plane perpendicular to the plane of the leaf and the first axis so that it follows the cylindrical surface of the leaf actuator screw. The inner radius of curvature of the rib is greater than the (outer) radius of the leaf actuator screw. The rib facilitates ease of mounting of the leaf actuator screw by providing a guiding surface during installation, removal and replacement of the leaf actuator screw.

In embodiments, the leaf includes a seat recessed from a face thereof for receiving the leaf nut holder, wherein the seat is arranged to prevent movement of the leaf nut holder in at least one of the two opposing directions in the first and/or second axis. The walls of the recess prevent movement by engaging with an edge of the leaf nut holder. Advantageously, the seat allows ease of placement of the leaf nut holder prior to and during fixing of the leaf nut holder to the leaf For example, the walls provide locating means for aligning corresponding fixing holes in the leaf nut holder and leaf nut for screws or other fixing means to pass therethrough to fix the leaf nut holder to the leaf.

In embodiments, the leaf nut and/or leaf nut holder has a first cross-sectional profile in a plane perpendicular to both the plane of the leaf and the first axis, and the leaf has a recess having a second cross-sectional profile on one face thereof matching at least a part of the first cross-sectional profile. In this way, the recess can receive a respective leaf nut and/or leaf nut holder corresponding to the leaf assembly of an adjacent leaf. That is, the recess is arranged to receive a portion of the leaf nut and/or leaf nut holder of an adjacent leaf while allowing (i) movement of the leaf nut holder and leaf nut of the adjacent leaf back and forth along the recess as the leaf and adjacent leaf move relative to each other and (ii) movement of the leaf nut between the first and second positions described herein. Advantageously, the leaf nut holder and/or leaf nut can have a profile which is thicker than the maximum thickness of the leaf without interfering with the motion of adjacent leaves. Thus, the leaf nut and/or leaf nut holder can be thicker and more robust.

Further embodiments Embodiments include a leaf assembly including the leaf nut and/or leaf nut holder having any of the structures defined herein.

Embodiments also include a multi leaf collimator having said leaf assembly.

Embodiments also include a radiotherapy device having said multi leaf collimator.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments are described below by way of example only and with reference to the accompanying drawings in which: Figure 1 shows a partially assembled multi leaf collimator.

Figures 2a and 2b show isometric views of a leaf including a leaf nut and leaf nut holder according to an embodiment.

Figure 3a shows a close up isometric view of a leaf nut according to an embodiment installed in the tail portion of a leaf Figure 3b shows a cross section of the leaf nut and leaf shown in Figure 3a.

Figures 4a and 4b show isometric views of a leaf nut and leaf nut holder according to an embodiment installed in the tail portion of a leaf

DETAILED DESCRIPTION OF THE DRAWINGS

MLC Assembly Defining a useful co-ordinates convention 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.

Figure 1 shows a partially assembled multi-leaf collimator 100 comprising a leaf bank 20, a first and second leaf guide 30E 302, a leaf drive array 40 and a leaf drive mount 50.

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 Figure 9. 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.

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 ammged so that its axis is parallel to the first direction. The leaf motor 4 10 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.

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.

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.

The first and second leaf guide 30E 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.

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.

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).

Composite leaf The leaf 200 can be formed from a monolithic plate comprising a single material. Alternatively, the leaf 200 can be a composite leaf comprising two plates of different materials joined together such that the plates are coplanar.

Introduction to leaf portion and tail portion

Figures 2a and 2b each show a different isometric view of such a composite leaf 200. The composite leaf includes a leaf portion 210 and a tail portion 220. The composite leaf 200 is forrned as a flat, substantially rectangular-shaped plate, notwithstanding the shape of some of the edges of the composite leaf 200 described below. The leaf portion 210 and the tail portion 220 form a first and second area of the plate, respectively. The average thickness of the composite leaf 200 is small relative to its width and length. The central plane of the tail portion 220 is coplanar with that of the leaf portion 210.

The leaf portion 210 is made from a high atomic numbered material, e.g. tungsten, so that it is substantially opaque to die radiation. The purpose of the leaf portion 210 is to block a portion of the radiation beam. The leaf portions 210 of all leaves 200 in the leaf bank 20 act together to form the edge of the aperture for shaping the radiation beam. In contrast, the tail portion 220 plays no part in attenuating or blocking parts of the radiation beam. The tail portion 220 operates to push and pull the leaf portion 210 into and out of the path of the radiation beam. Thus, functionally, the tail portion can be thought of as part of (e.g. an extension of) the leaf drive mechanism. As such, the tail portion does not need to be made of a high atomic number material and can be made from a thinner plate than the leaf portion. Furthermore, the tail portion can be manufactured from a material which is lighter and/or easier to machine than tungsten. Greater ease of machining allows functional features to be added to the tail portion 220 (e.g. the features described below) which would be much more difficult, time intensive or cost intensive to machine into the high atomic numbered material of the leaf portion 210.

Relative alignment of the composite leaf in the co-ordinates system The plane of the composite leaf 200 is in the first plane (yz) when in situ in the multi leaf collimator, with the long edges and short edges of the rectangular shape of the composite leaf 200 being aligned in the first and third directions, respectively. The composite leaf 200, and therefore the tail portion 220 and the leaf portion 210, each have a first face and a second face on the opposite side to the first face, and both faces lie substantially parallel to the first plane (yz). Figure 2a shows an isometric view from one side of the leaf 200 including the first face and Figure 2b shows an isometric view from the other side of the leaf 200 including the second face.

Shapes of the leaf portion and tail portion The first area comprises a first substantially rectangular area having a U-shaped recess 215 recessed from one side thereof, the recess 215 extending in the first direction into the first substantially rectangular area. The second area comprises a second substantially rectangular area defining a main body of the tail portion 220 and a tongue 225 protruding in the first direction from one edge of the main body. The tongue 225 has a shape and dimensions which correspond to those of the recess 215 of the first area. The tongue 225 is received in the recess 215 when the leaf portion 210 and the tail portion 220 are joined. The substantially rectangular shape of the composite leaf 200 is formed by the outline of the composite shape defined by the first area and second area.

The leaf portion 210 has a first edge 211 aligned with the first direction, a second edge 212 opposite the first edge 211 and aligned with the first direction, and a third edge 213 opposite the recess 215 and aligned with the third direction. The first edge 211 is part of the top edge of the composite leaf 200 when the leaf 200 is in Stilt in the multi-leaf collimator 100 and the radiation beam is directed vertically downward (i.e. in the fourth direction). The third edge 213 opposite the recess 215 is the leading edge of the leaf portion 210 and is the part of the leaf portion 210 which is closest to the axis of the radiation beam in use. The leading edge is slightly convex in the third direction (i.e. curved outwardly from the main part of the leaf portion 210 in the first plane) and has a radius of curvature which is greater than the length of the leaf 200 in the first direction.

The tail portion 220 has a first edge 221 aligned with the first direction, a second edge 222 opposite the first edge and oblique to the first direction and a third edge 223 opposite the tongue 225 and aligned with the third direction. The third edge 223 is the trailing edge of the composite leaf 200, meaning it is the furthest edge from the axis of the radiation beam in use. The first edge is part of the top edge of the composite leaf 200 when the leaf 200 is in situ in the multi-leaf collimator 100 in use when the radiation beam is directed vertically downward Leaf actuator screw slot 250 The tail portion 220 has a through slot therein extending in the first direction, the through slot may be described as a leaf actuator screw slot 250. The leaf actuator screw slot 250 extends from the third edge 223 of the tail portion 220 towards a terminal end of the tongue 225. The leaf actuator screw slot 250 extends in both the main body of the tail portion 220 and the tongue 225 and terminates before the end of the tongue 225.

As shown in Figure 3a, which is described in more detail below, the leaf actuator screw slot 250 includes a first slot section 250a proximal to the third edge 223 and a second slot section 250b distal from the third edge 223. The second slot section 250b is immediately adjacent and contiguous with the first slot section 250a. The first slot section 250a has a width in the third direction fractionally larger than that of the second slot section 250b. The second slot section 250b is several times longer in the first direction than the first slot section 250a.

First groove A first groove 240 extends from the third edge 223 of the tail portion 220 toward a terminal end of the tongue 225. The first groove 240 is located along the first face of the tail portion 220 parallel to the leaf actuator screw slot 250. The first groove 240 is offset from the leaf actuator screw slot 250 in the fourth direction. The first groove 240 and the leaf actuator screw slot 250 are substantially the same length The first groove 240 has a cross-sectional shape the third plane (xz) of a minor segment of a circle to accommodate convex parts of the leaf nut 450 and leaf nut holder 470 which are proud from the face of an adjacent leaf 200. The composite groove 260 is shown in closer detail in Figure 4b. Seat

Figure 2b shows an isometric view of the second face of the composite leaf 200. Figure 3a shows a close up isometric view of the second face of the tail portion 220 in the region of the first slot section 250a.

The leaf actuator screw slot 250 is a through slot in that it passes through the whole thickness of the tail portion 220 from the first face to the second face. The first slot section 250a lies in the centre of a scat 255 recessed into the second face of the tail portion 220. The seat 255 has a cross section in the shape of a highaspect-ratio (third direction length: fifth direction width) rectangle in both the second plane (xy) and the third plane (xz). The length of the scat 255 in the first direction is equal to the length of the first slot section 250a. The width of the seat 255 in the third direction is approximately equal to its length.

Through holes_ blind holes and curved rib Two blind holes 256 are formed in the second face of the tail portion 220, the blind holes 256 being centred on comers of the seat 255 distal from the third edge 223 of the tail portion 220. The blind holes 256 have the same depth as the seat 255 so that the void defined by the seat 255 is contiguous with the blind holes 256.

Two through holes are formed through the tail portion 220, the through holes emerging in different quadrants of the seat 255 in the distal half of the seat 255 from the third edge 223 of the tail portion 220.

The tail portion 220 also includes a curved rib (shown in Figure 4b described below) convex to the first face of the tail portion 220, the curved rib straddling the first slot section 250a between the two through holes.

Composite groove The second face of the tail portion 220 includes a composite groove 260 for receiving the parts of the leaf nut 450 and leaf nut holder 470 which are proud from the face of an adjacent leaf. The composite leaf 260 includes a second groove 260a and a third groove 260b of narrower width than the second groove 260a. The third groove 260b is seated inside (i.e. formed in the bottom surface of) the second groove 260a. Both the second groove 260a and the third groove 260b extend from the third edge 223 of the tail portion 220 towards a terminal end of the tongue 225. Both the second groove 260a and third groove 260b lie parallel to the leaf actuator screw slot 250 along the second face of the tail portion 220. The central axis of both the second groove 260a and third groove 260b are collinear and offset from the leaf actuator screw slot 250 in the fourth direction. The second groove 260a and third groove 260b are substantially the same length as the leaf actuator screw slot 250. The second groove 260a has the cross-sectional shape in the third plane (xz) of a high-aspect-ratio rectangle (third direction length: fifth direction width). The third groove 260b has the cross-sectional shape in the third plane (xz) of a minor segment of a circle. The cross-sectional shape of the composite groove 260 is shown in closer detail in Figure 4a.

The edge of the seat 255 closest to the first edge of the tail portion 220 is aligned with the edge of the second groove 260a so that the void defined by the seat 255 is contiguous with the void defined by the second groove 260a.

Lap joints between tail portion and leaf portion As shown in Figure 2b, lap joints are formed between the leaf portion 210 and tail portion 220.

The edge of the recess 215 of the leaf portion 210 on the second face is the same as that on the first face except that it further includes a first indent 215a, a second indent 215b and a third indent 215c. The first indent 215a is concave from the central part of the bottom of the U shape of the recess 215. The second indent 215b and third indent 215c are concave from either side of the top of the U shape of the recess 215. The first, second and third indents 215a,b,c are formed through only half of the thickness of the leaf portion 210 and are recessed back from the second face of the leaf portion 210.

The tongue 225 of the tail portion 220 comprises first, second and third protrusions 225a, 225b, 225c corresponding in shape and dimension to first, second and third indents, respectively. The first, second and third protrusions 225a, 225b, 225c are a half thickness of the tail portion 220 and have surfaces which are flush with the second face of the tail portion 220.

The lap joints joining the tail portion 220 and the leaf portion 210 are formed by faces of the leaf portion 210 formed by the first, second and third indents interfacing with faces of the first, second and third protrusions, respectively.

Leaf nut and leaf nut holder Figure 3a shows a leaf nut 450 located in situ in the first slot section 250a and a leaf actuator screw 430 passing through the leaf nut 450 and located in situ in the first and second slot sections 250a, 250b of the leaf actuator screw slot 250. Figure 3b is a cross section in a plane parallel to the third plane (xz) and passing through the leaf nut 450, the leaf actuator screw 430 the tail portion 220 in the vicinity of the seat 255.

Leaf nut The leaf nut 450 is shown in Figure 3a, and in cross-section in Figure 3b. The leaf nut 450 provides a threaded part for the leaf actuator screw 430 to engage therewith in order to convert the rotational motion of the leaf actuator screw about its axis to linear motion in the first and second directions. The leaf nut 450 includes parts 45 I, 452 which engage with the tail portion 220 in order to resist the rotational force applied to the leaf nut 450 by the rotation of the leaf actuator screw 430. These parts 451, 452 (described in more detail below) allow limited movement of the leaf nut 450 to accommodate misalignment of the leaf drive units 400.

The leaf nut 450 comprises a cylindrical part 457 having a through hole coaxial with the cylindrical part 457. The through hole is dimensioned and threaded to receive the leaf actuator screw 430. The length (i.e. dimension in the first direction when the leaf nut 450 is in situ in the first slot section 250a) of the cylindrical part 457 is approximately equal to two thirds the length (in the first direction) of the first slot section 250a.

The leaf nut 450 also comprises a first block 451 and second block 452 extending outward from opposing portions of the outer cylindrical face of the cylindrical part 457. The first block 451 extends outward from the outer cylindrical face of the cylindrical part 457 in the first direction (when the leaf nut 450 is in situ in the first slot section 250a). The second block 452 extends in the opposite direction to the first block 451 (i.e. in the second direction when the leaf nut 450 is in situ). The length of the first block 451 in the direction of the central axis of the cylindrical part 457 (i.e. the first direction in situ) is equal to the length of the cylindrical part 457 so that the end faces of the cylindrical part 457 are flush with the end faces of the first block 451. The width (i.e. dimension in the fifth direction in situ) of the first block 451 is greater than the internal diameter of the threaded through hole of the leaf nut 450 and less than the outer diameter of the cylindrical part 457.

The first block 451 has a first blind slot 454 formed therein, the first blind slot 454 extending in the second direction from the face of the first block 451 lying parallel to the second plane (xy). The first blind slot 454 runs along the full length of the first block 451 in the first direction. The first blind slot 454 is positioned so that one inner face thereof lies in a plane which lies parallel to the first plane (yz) and passes through the central axis of the cylindrical part 457. In this way, the centre of the first blind slot 454 aligns to one side of the centre of the cylindrical part 457 when viewed in the third plane (xz). This aligns the leaf actuator screw 430 to be more central in relation to the tail portion of the leaf The dimensions of the second block 452 and a second blind slot 456 in the second block 452 are the same as those of the first block 451 and first blind slot 454, respectively. The second block 452 and second blind slot 456, respectively, mirror the first block 451 and first blind slot 454 about a plane parallel to the second plane (xy) passing through the central axis of the cylindrical part 457. That is, both the blocks and the blind slots are symmetrical about the plane parallel to the second plane (xy) passing through the central axis of the cylindrical part 457.

The widths first blind slot 454 and second blind slot 456 are dimensioned to receive parts of the tail portion 220 in the seat 255 either side of the first slot section 250a. The parts of the blocks either side of the blind slots straddle the tail portion 220 in the footprint of the seat. This part of the tail portion 220 cooperates with the first block 451 and second block 452 to prevent rotational motion of the leaf nut 450 about the central axis of the cylindrical part 457 when the leaf nut 450 is in situ. Thus, the torque of the leaf actuator screw 430 applied to the leaf nut 450 when the leaf actuator screw 430 is rotated about its axis does not translate into rotation of the leaf nut 450 The depths (i.e. dimensions in the first direction) of the first blind slot 454 and second blind slot 456 are such that leaf nut 450 can travel a limited (but non-zero) distance in the first and second directions in the first slot section 250a. The movement of the leaf nut 450 in these directions accommodates small misalignments of the leaf actuator screw 430, for example due to misalignments of the leaf actuator motors in the mounting plate 510, or misalignment of the mounting plate 510 relative to the leaf bank 20.

Leaf nut holder Figures 4a and 4b show a leaf nut holder 470 arranged to hold the leaf nut 450 in position in the tail portion 220 of the leaf 200. Figure 4a shows an isometric view of the second face of the tail portion 220 in the vicinity of the seat 255. Figure 4b shows an isometric view of the first face of the tail portion 220 in the vicinity of the seat 255.

The leaf nut holder 470 is structure for housing the leaf nut 450. The leaf nut holder can be coupled to the leaf 200. The leaf nut holder 470 prevents linear movement of the leaf nut 450 in the direction of the axis of the leaf actuator screw 430. The leaf nut holder 470 allows limited (non-zero) movement of the leaf nut 450 in the plane of the leaf 200.

Notwithstanding the features described below, the leaf nut holder 470 is a substantially oblong block having a length (i.e. dimension in the first direction when in situ in the tail portion 220) approximately 50% larger than the length of the seat 255 and a width (i.e. dimension in the third direction when in situ) substantially equal to the width of the seat 255. When in situ on the tail portion 220 of the leaf 200, the leaf nut holder 470 has a first face 470a and a second face 470b each substantially parallel to the first plane (yz), a third face 470c and fourth face 470d each parallel to the second plane (xy) and a fifth face 470e and sixth face 470f each parallel to the third plane (xz). The cross-sectional profile of the leaf nut holder 470 in the third plane (xz) is such that the first face 470a of the leaf nut holder 470 has a surface topography which is the inverse of that of the composite groove 260 in the second face of the tail portion 220. Notwithstanding the features described below, the second face 470b of the leaf nut holder 470 has a surface topography which is the mirror image of the first face 470a about a plane parallel to the first plane (yz) passing through the centre of the leaf nut holder 470.

A nut guide 475 arranged to receive the leaf nut 450 is formed through the leaf nut holder 470. The nut guide 475 is an aperture passing approximately centrally through the leaf nut holder 470 in the fifth direction. The length of the nut guide 475 On the first direction) is substantially the same as the length of the leaf nut 450. Thus, movement of the leaf nut 450 is restricted by the leaf nut holder 470 in the first and second directions. The width of the nut guide 475 On the third direction) is marginally greater than the width of the leaf nut 450 so that movement of the leaf nut 450 is permitted inside the nut guide 475 in the third and fourth directions. The range of movement of the leaf nut 450 allowed by the cooperation of the first blind slot 454 and second blind slot 456 in the leaf nut 450 with the first slot section 250a in the tail portion 220 is substantially equal to the range of movement of the leaf nut 450 allowed by the width of the nut guide 475.

The leaf nut holder 470 has a cutaway portion 472 to receive the second face of the tail portion 220 of the composite leaf 200. The cutaway portion 472 is recessed back into the leaf nut holder 470 in the sixth direction from the second face 470b of the leaf nut holder 470. A void formed by the cutaway portion 472 extends over the full width and over more than half of the length of the leaf nut holder 470 so that the cutaway portion 472 defines a single shoulder 473 running in the first direction and having a face parallel to the third plane (xz). A locating slot 474 is formed in the face of the shoulder to receive the third edge 223 of the tail portion 220 The leaf nut holder 470 has two threaded through holes extending in the third direction. The axes of the threaded through holes are collinear with the respective axes of the two through holes in the seat 255 when the leaf nut holder 470 is in situ on the tail portion 220. The leaf nut holder 470 is fixed to the tail portion 220 by screws inserted through the respective through holes in the seat 255 and into the threaded through holes in the leaf nut holder 470. A ridge formed by the shoulder 473 and locating slot 474 formed therein provides further rigidity by applying a resistive force to third edge 223 of the tail portion 220 to prevent the end of the leaf nut holder 470 farthest from the leaf portion 210 from moving in the sixth direction. The locating slot provides a resistive force which prevents the leaf nut holder 470 from moving in the first direction. Thus, the third edge 223 of the tail portion 220 forming an edge of the scat 255 is received in the slot so that the leaf nut holder 470 straddles this part of the tail portion 220.

The fifth face 470e of the leaf nut holder 470 is that parallel to the third plane and distal from the leaf portion 210 when in situ. A screw guide hole 478 is formed in the leaf nut holder 470 which extends from the centre of the fifth face 470e and in the first direction through the volume of the leaf nut holder 470. The screw guide hole 478 receives the leaf actuator screw 430 and provides clearances in the third, fourth, fifth and sixth directions which allow movement of the leaf actuator screw 430 inside the leaf nut holder 470 in these directions. Thus, the leaf nut holder 470 is arranged to allow movement of the leaf nut 450 and the leaf actuator screw 430 relative to the leaf nut holder 470 (and thus relative to the tail portion 220 of the composite leaf) in the third and fourth directions.

The leaf nut holder 470 includes 45-degree chamfers between the third face 470c and the fifth face 470e, and between the fourth face 470d and the fifth face 470e so that the dimension of the fifth face 470e in the third direction is around a half that of the leaf nut holder 470.

Chamfers are also formed between the third face 470c and each of the first and second face 470b and between the fourth face 470d and each of the first face 470a and second face 470b of the leaf nut holder 470. These chamfers enable smoother movement of the leaf nut holder 270 of one leaf in the composite or first groove of an adjacent leaf Leaf actuator screw The leaf actuator screw 430 is a threaded rod having a length approximately equal to the full length of the leaf actuator screw slot 250 in the tail portion 220 of the leaf 200. The pitch and diameter of the thread match those of the leaf nut 450. The thread of the leaf actuator screw 430 extends along its full length except in the vicinity of the leaf motor 410, where it includes a non-threaded section 430a.

Figure 5 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 43 lb has a coupling groove 433 fondled across an end face thereof 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.

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.

Claims (17)

1. CLAIMSA leaf assembly for a multi-leaf collimator, the leaf assembly comprising: a leaf; a leaf nut removably mounted within the profile of the leaf, the leaf nut comprising a threaded hole for receiving a leaf actuator screw oriented along a first axis in the plane of the leaf, the leaf nut being mounted within the leaf such that relative movement between the leaf nut and the leaf is prevented both linearly along the first axis and rotationally about the first axis.
2. 2. The leaf assembly according to claim I, wherein the leaf nut and leaf have interlocking parts so that the leaf nut is movable from a third position, in which the leaf nut is interlocked with the leaf, along an axis to a fourth position in which the leaf nut is free from the leaf.
3. 3. The leaf assembly according to claim 2, wherein the leaf includes a slot for receiving at least a portion of the leaf nut and the leaf nut is arranged to move between the third and fourth positions along the slot.
4. 4. The leaf assembly according to claim 2 or 3, wherein the first axis defines a first direction and a second direction opposite the first direction and wherein the leaf nut is movable along the second direction from the third position to the fourth position.
5. 5. The leaf assembly according to claim 2, 3 or 4, wherein the leaf or the leaf nut includes a stop for preventing movement of the leaf nut along the axis from the third position away from the fourth position.
6. 6. The leaf assembly according to any of claims 2-5, further comprising a leaf nut holder removably coupled to the leaf and including a stop for preventing movement of the leaf nut from the third position toward the fourth position
7. 7. The leaf assembly according to claim 6, wherein when the leaf nut holder is coupled to the leaf, movement of the leaf nut holder relative to the leaf is prevented.
8. 8. The leaf assembly according to claims 6 or 7, wherein the leaf nut holder includes a blind slot for receiving an edge of the leaf and preventing movement of the leaf nut holder relative to the leaf along the first direction and/or out of the plane of the leaf.
9. 9. The leaf assembly according to claims 6, 7 or 8, wherein the leaf includes a seat recessed from a face thereof for receiving the leaf nut holder, wherein the seat is arranged to prevent movement of the leaf nut holder at least one axis
10. 10. The leaf assembly according to any of claims 6-9 wherein the leaf nut and/or leaf nut holder has a first cross-sectional profile in a plane perpendicular to both the plane of the leaf and the first axis, and the leaf has a recess having a second cross-sectional profile on one face thereof matching at least a part of the first cross-sectional profile so that it can receive a respective leaf nut and/or leaf nut holder corresponding to the leaf assembly of an adjacent leaf.
11. 11. The leaf assembly according to any preceding claim, wherein movement of the leaf nut relative to the leaf along a second axis is limited between a first and second position along the second axis, wherein the second axis lies across the first axis.
12. 12. The leaf assembly according to claim 11, wherein the second axis lies perpendicular to the first axis.
13. 13. The leaf assembly according to claim 11 or 12 wherein the second axis is in the plane of the leaf 14.
14. The leaf assembly according to claim 12 or 13, or claim II when dependent on any of claims 6-10, wherein the leaf nut holder is arranged to allow movement of the leaf nut relative to the leaf along the second axis from the first position to the second position.ls.
15. The leaf assembly according to any preceding claim, wherein the leaf nut comprises an engaging portion configured to engage the leaf to constrain rotational movement of the leaf nut relative to the leaf about the first axis.
16. 16. A multi leaf collimator including the leaf assembly according to any preceding claim.
17. 17. A radiotherapy device including the multi leaf collimator according to claim 16.