Leaf actuator for a multileaf collimator

Abstract

A leaf unit assembly for a multi-leaf collimator, comprising a leaf, a leaf actuator screw, and a rotatable portion. Wherein the leaf actuator screw has a first end fixedly attached to the leaf, and the rotatable portion is threadably engaged with the leaf actuator screw.

Description

Technical Field

[0001] This disclosure relates to a blade actuator for a multi-leaf collimator and a multi-leaf collimator including the blade actuator. Background Technology

[0002] Radiation therapy devices involve the generation of beams of ionizing radiation, typically X-rays or electron beams or other subatomic particles. These are directed to the patient's cancerous areas (e.g., tumors) and adversely affect the cancer cells, thereby reducing their incidence. The beams are delimited so that the radiation dose is maximized in the patient's cancer cells and minimized in healthy cells, thus improving the efficiency of treatment and reducing side effects on the patient.

[0003] In radiotherapy devices, beam-limiting devices such as multi-leaf collimators (MLCs) can be used to delimit the beam. This is a collimator consisting of a large number of long, thin blades arranged side-by-side in an array. The blades are typically made of a high atomic number material (usually tungsten), making them essentially opaque to radiation.

[0004] Each leaf is longitudinally movable, allowing its leading edge (or tip edge) to extend into or retract from the radiation beam. All leaves can be retracted to allow the radiation beam to pass through, or all leaves can be extended to completely block the radiation beam. Alternatively, within operational limits, some leaves can be retracted and some extended to define any desired shape. Thus, the array of leaf tips can be positioned to define a variable edge of the collimator. Multi-leaf collimators typically consist of two rows of this array (i.e., leaf rows), each extending into the radiation beam from opposite sides of the collimator. The variable edge provided by the two leaf rows thus collimates the radiation beam to a selected cross-sectional shape, typically the cross-sectional shape of the target tumor volume to be irradiated. In other words, the two leaf rows combine to provide a variable-shaped aperture for shaping the radiation beam.

[0005] Each leaf can move independently of the others, thereby defining the shape of the radiation beam by defining the shape of the aperture. In some cases, the leaves move uniformly to define the position of the radiation beam by defining the position of the aperture. In use, it may be necessary to rapidly change the shape and / or position of the aperture. For example, in some applications, real-time MRI imaging of the treated subject is performed to track the position of a tumor to be irradiated by a radiotherapy device. In this case, the contour of the tumor may change from the perspective of the direction of travel of the radiation beam, for example, due to the patient's movement during treatment (e.g., due to breathing). The shape and position of the multi-leaf collimator aperture can be changed such that the shape and position of the radiation beam track the changing shape and / or position of the tumor contour. Thus, even when the tumor moves, the beam always irradiates as much of the tumor as possible while irradiating as little of the surrounding healthy tissue as possible.

[0006] The movement speed of each blade is important for ensuring that changes in the shape and / or position of the aperture are consistent with changes in the shape and / or position of the tumor contour. The blade actuator (i.e., the device for moving the individual blades) plays a crucial role in achieving the appropriate blade speed. However, the form and mechanism of the blade actuator not only control the speed but also affect the positioning accuracy of each blade, as well as the stability and durability of the blade actuator itself. Typically, a trade-off exists between speed in one aspect and positioning accuracy, stability, and / or durability in another.

[0007] The goal is to provide a precision blade actuator with high speed, high durability, and high stability. Summary of the Invention

[0008] Aspects and features of the invention are set forth in the appended claims. Attached Figure Description

[0009] The following describes specific embodiments by way of example only and with reference to the accompanying drawings, wherein:

[0010] Figure 1 This illustrates a multi-leaf collimator blade unit assembly according to the prior art;

[0011] Figure 2 A multi-leaf collimator blade unit according to one embodiment is shown;

[0012] Figure 3 A multi-leaf collimator according to one embodiment is shown; and

[0013] Figure 4 It shows Figure 3 A view of a multi-leaf collimator. Detailed Implementation

[0014] Multi-leaf collimator

[0015] A multi-leaf collimator includes a row of blades comprising a plurality of blades. The blades are individually movable longitudinally within the row of blades, allowing them to extend into and out of the path of a radiation beam. The multi-leaf collimator may have two opposing rows of blades, with the radiation beam passing through an aperture between the two opposing rows of blades.

[0016] Each blade is configured to attenuate radiation. The blades of the multi-leaf collimator define the shape of the aperture. The blades are plate-like structures arranged side-by-side in a stacked manner, much like cards in a deck of cards. The blades can slide relative to each other and move independently of each other, such that when viewed from the side, the "deck of cards" (i.e., the leaf rows) has a profile at its ends, defined by the position of the "cards" (i.e., the blades) relative to each other. A portion of the radiation beam is blocked by the leaf rows, causing the beam to take on the same shape as the profile defined by the position of the blades.

[0017] The blades can be substantially rectilinear in shape within their plane. The blades are relatively thin in the direction perpendicular to the beam axis and perpendicular to the blade's plane, allowing for high-resolution aperture shapes. The blades are relatively deep in the direction of the radiation beam axis to make them sufficiently opaque at X-ray wavelengths / energies. The blades are relatively elongated (relatively long in the direction perpendicular to their thickness and depth), allowing them to be positioned over a wide range while maintaining contact with the blade guide. The blades comprise dense materials (high atomic number materials) capable of absorbing and / or scattering X-rays, such as tungsten. Blade actuators cause individual blades to move relative to other blades in the blade row.

[0018] Figure 1 The blades 152 of a multi-leaf collimator and the blade actuator driver 150 for moving the blades 152 are shown. The blades 152 and the blade actuator driver 150 are referred to herein as "blade units".

[0019] In a blade row comprising multiple blades 152, each blade will have a corresponding blade actuator driver 150. Each blade actuator 154 is arranged to drive the corresponding blade such that the blades 152 can move independently of each other in their respective blade row. That is, each blade actuator 154 is arranged to produce a relative linear motion between one blade 152 and other blades in the blade row.

[0020] The blade actuator 154 includes a blade actuator motor 158. A suitable controller (not shown) is typically provided, configured to signal the blade actuator motor 158 to move one or more appropriate blades 152 to provide the desired orifice shape or position. All blades can be driven uniformly or individually. A control system suitable for monitoring and controlling the blade position ensures that collisions between blades in opposing rows are avoided. Blade movement can define the orifice shape (and thus the radiation beam), or the shaped orifice provided by the blades can be moved relative to the axis of the radiation beam.

[0021] In known systems, each blade actuator may include a blade actuator screw 156 (e.g., a rotatable threaded rod, such as a rotatable threaded rod suitable for an ACME screw, ball screw, or lead screw assembly). The blade 152 itself is coupled as a load to the end of the blade actuator screw 156. The blade actuator motor 158 driving the blade actuator screw may be a DC motor, a DC servo motor, a DC brushless motor, a DC brushless servo motor, an AC motor, an AC servo motor, or a stepper motor. The blade actuator motor is coupled to the blade actuator screw 156 at the end of the blade actuator screw opposite to the end coupled to the blade 152.

[0022] In the known system, blade 152 is connected to blade actuator screw via nut 154. Nut 154 is threaded into blade actuator screw 156. Nut 154 is fixedly attached to blade 152 such that rotation of nut about its axis causes a corresponding rotation of blade. That is, nut is rotatably fixed relative to blade.

[0023] The blade tail (the portion of blade 152 furthest from the blade tip at the blade end) may have an inserting region to receive portions of the blade actuator 154. The nut 154 includes an elongated bore 160 extending along a considerable portion of the blade's length in the blade tail. The blade actuator screw 156 can enter the elongated bore 160 through the internally threaded portion of the nut that engages with the blade actuator screw 156.

[0024] When multiple blades are arranged in a single blade row in a multi-blade collimator, the other blades in that row rotationally restrict the movement of blade 152, but allow linear movement of blade 152 within the blade plane. In use, the blade actuator screw 156 is rotated by the blade actuator motor 158 (as shown by arrow A). The blade actuator screw 156 is threadedly engaged with a nut 154. However, the nut does not rotate with the blade actuator screw because the blade tail rotationally restricts the movement of the nut. Instead, the blade actuator screw 156 interacts with the threaded portion in the blade tail to convert the rotational motion of the blade actuator screw into linear motion of the threaded portion, and thus into linear motion of the blade. The rotation of the blade actuator screw 158 is parallel to the blade actuator screw axis and drives the threaded portion within the blade plane, thereby driving the blade (as shown by arrow B).

[0025] The stroke of the blade actuator 154 is sufficient to allow the leading edge of the blade to extend to at least half of the radiation beam path, and also allows it to retract to exit the radiation beam path. Therefore, the stroke can be between approximately half and approximately twice the radiation beam diameter of the multi-leaf collimator according to its design. The stroke can be between approximately one-quarter and approximately one blade length.

[0026] It should be noted that, Figure 1 In the illustration, the blade 152 and the blade actuator screw 156 are shown as separate. In use, the blade actuator screw 156 is threadedly engaged with the nut 154 on the blade 152.

[0027] Known systems use blade actuator screws to convert motor torque into linear motion to actuate the blades. However, these systems have certain limitations.

[0028] Trade-offs between speed and accuracy in traditional blade actuators

[0029] The linear velocity of blade 152 depends on the pitch of blade actuator screw 156 and the rotational angular velocity of blade actuator screw 156. When the multi-leaf collimator is running in real time to track the tumor contour, a blade velocity greater than 5 cm / s is expected.

[0030] High blade speeds can be achieved in two different ways: by rotating the blade actuator screw at high rpm; or by manufacturing a blade actuator screw with a large pitch. The blade actuator screw is the lead screw of the motor.

[0031] Larger pitch leads offer higher efficiency. However, large-pitch leads have several drawbacks. Leads with large pitches typically have multi-start threads and high helix angles to achieve large linear displacement of the nut with each full rotation of the lead screw. However, if the lead screw efficiency exceeds 50%, the actuator may require major overhaul or reverse drive. Furthermore, high pitch is undesirable in multi-leaf collimators because it means that in the gantry position where the blades are driven against gravity, the blades may lose position once power is removed from the blade actuator motor. Additionally, when using high-pitch blade actuator leads, it is more difficult to accurately position the components because the control system can "overshoot" the desired position.

[0032] Lead screws with lower pitch typically have a lower tendency to reverse drive, are somewhat self-locking, and facilitate more precise positioning with less control system input. However, lead screws with lower pitch are less efficient. To achieve high linear speeds, lead screws with lower pitch require higher rotational speeds. When rotating lead screws with high aspect ratios (which are often the case with blade actuator screws because they are designed to fit within the width of a single blade), there is a critical rotational speed. When the lead screw reaches its critical speed, it begins to vibrate to unacceptable levels. This increases wear (reducing component life), increases noise, and reduces efficiency.

[0033] The critical speed in known blade actuators is limited by a number of factors, the screw cannot rotate above this limit without causing damage, and the maximum possible linear speed at which the blade will not be damaged by vibration is limited.

[0034] The critical speed depends on the length and diameter of the blade actuator screw and the construction of the support bearing.

[0035] The blade width (or the spacing between blades) determines the available space for the components of the blade actuator. For example, the diameter of the blade actuator screw 156 is limited by the mechanical width of the blades 152. The length of the blade actuator screw 156 is selected based on the blade stroke required for a specific multi-leaf collimator or its application. The construction of the support bearing is also limited because, in known blade actuators, it is not possible to support the end of the blade actuator screw, which must be free to allow for relative linear movement between the blade actuator screw and the blades.

[0036] Due to the aforementioned constraints, the critical speed (in rpm) of the blade actuation screw is limited, and the screw cannot rotate above this limit without causing damage. Therefore, in blade actuator design, the maximum possible linear speed of the blade is also limited before the vibration level increases to an unacceptable degree.

[0037] New blade actuator

[0038] According to one embodiment of the present disclosure, a blade unit is provided, the blade unit including a blade actuator having a blade actuator screw that is non-rotatable relative to the blade, as described below.

[0039] The blade unit has an actuator that relies on a blade actuator screw that cannot rotate or move linearly relative to the blade. This is achieved by rigidly attaching the blade actuator screw to the rear of the blade, thus preventing its rotation. Instead of rotating the blade actuator screw to move the blade linearly, a blade actuator motor rotates another component threaded onto the blade actuator screw, pushing or pulling the blade actuator screw relative to that component, causing the blade actuator screw to move with the blade. Thus, the function of the blade actuator screw is solely to provide linear motion, i.e., pushing and pulling the blade.

[0040] In a preferred arrangement, the blade actuator screw is coupled at one end to the blade (e.g., the blade tail) such that it cannot rotate relative to the blade. A nut or other rotatable part (e.g., a worm gear) threaded onto the blade actuator screw is arranged to be rotated by the blade actuator motor, causing the lead screw (and thus the blade) to move linearly relative to the nut. Thus, when the motor rotates the nut, the blade actuator screw and the blade are driven linearly, causing the leading edge of the blade to move into and out of the path of the radiation beam. In a blade actuator design with a rotating blade actuator screw, the nut coupled to the blade tail (e.g., the blade actuator screw nut) is now mounted at the end of a rotatable tube. The tube is then coupled to the motor and gearbox assembly. The tube is long enough that the blade actuator screw can be withdrawn within the length of the tube.

[0041] Figure 2 An embodiment of the present disclosure is shown. The blade unit 200 includes a blade 252 and a blade actuator 250. The blade actuator includes a blade actuator screw 256 (e.g., a blade actuator screw adapted for a lead screw arrangement), a blade actuator motor 258, and a rotatable portion 254. The blade actuator screw 256 is connected at its first end to the tail of the blade via a connecting portion 257. The connecting portion 257 includes a small plate or shim having a first receiving portion and a second receiving portion, the first receiving portion being arranged to receive the first end of the blade actuator screw 256, and the second receiving portion being arranged to receive a protrusion on the blade 252. The blade actuator screw includes external threads.

[0042] The portion of the blade actuator screw 256 remote from the first end is inserted into a rotatable portion 262 comprising a tube or sleeve. When the blade actuator is inserted into the rotatable portion, the rotatable portion surrounds a section of the blade actuator screw 256. The rotatable portion 254 includes a threaded portion on its inner surface to engage with at least a portion of the distal portion of the blade actuator screw 256. The rotatable portion 254 is rotatable about the axis of the blade actuator screw 256 via the blade actuator motor 258. Because the blade actuator screw 256 is connected to the blade tail at its first end, it cannot rotate about its own axis.

[0043] During operation, the blade actuator motor 258 rotates the rotatable portion 254 about the axis of the blade actuator screw 256 (as shown by arrow A). A threaded portion on the inner surface of the rotatable portion 254 converts the relative rotational motion between the rotatable portion 254 and the blade actuator screw 256 into a relative linear motion between them. The blade actuator screw 256 applies a force to the blade 252, and the blade 252 moves linearly relative to the rotatable portion 254 and the blade actuator motor 258 together with the blade actuator screw 256.

[0044] exist Figure 2 In the illustration, the blade 252 and the rotatable part 254 are shown as separate. In use, the rotatable part 254 is threadedly engaged with the blade actuator screw 256 on the blade 252.

[0045] Figure 3A multi-leaf collimator according to one embodiment is shown. The multi-leaf collimator includes a first leaf row 310 and a second leaf row 320, the two leaf rows being opposite each other with respect to an aperture. The blades 252 in the second leaf row are in a fully extended position. This can be seen from the alignment between the tips of the blades (the tips of the blades 252 protrude into the aperture between the two leaf rows). The tips of the blades 252 extend further into the aperture than all other aligned and retracted blades in the second leaf row 320. The blades in the first leaf row 310 are all retracted and aligned.

[0046] As shown by blade 252, in the fully extended state, most of the length of the blade actuator screw 256 is outside the rotatable portion 254, and the threaded end of the blade actuator screw 256 furthest from the first end is still engaged with the threaded portion of the rotatable portion 254. In this state, the distance between the rotatable portion 254 and the blade 252 is at its maximum. In the fully retracted state, most of the length of the blade actuator screw 256 is inside the rotatable portion 254, and the distance between the blade 252 and the rotatable portion 254 is at its minimum.

[0047] exist Figure 3 In the middle section, blade 252 is in the fully extended position, and the lead screw 256 is visible and not surrounded by the rotatable portion 258. In the opposite blade row, blade 352 is in the fully retracted state, and the lead screw is completely surrounded by the rotatable portion, so that the lead screw... Figure 3 It is not visible in the middle.

[0048] In one specific example, the orifice of the multi-leaf collimator is located at a 5mm isocenter. The multi-leaf collimator has 160 blades with a blade width of approximately 1.7mm to 2mm. The blade travel is approximately 100mm. In this example, the diameter of the blade actuator screw does not exceed 2mm, and its length is at least 100mm.

[0049] like Figure 4 As shown, a series of six-blade actuators are mounted in a square bracket 410.

[0050] The support 410 includes a first support portion 420 having two arms 422, 424 and an elongated plate portion 426 disposed between the two arms to form a U-shape on three sides constituting the square shape of the support 410. The elongated plate portion 426 has six through holes 440 therein, each of the first series of through holes 440 being sized to receive and support a blade actuator motor 258. The first support portion 420 retains each blade actuator motor 258 by applying torque resistance to prevent rotation of the motor housing relative to the first support. The first support portion 420 also applies linear force resistance to the motor housing in the axial direction of the blade actuator motor 258 to prevent linear movement of the motor housing relative to the first support portion 420.

[0051] The support also includes a second support portion 430 disposed between the ends of the two arms 422, 424 to form a square shape of the support 410. The second support portion 430 is an elongated plate having six through-holes 442 of a second series, each through-hole containing a bearing arranged to receive and support a corresponding tube (rotatable portion 254) of the blade actuator. Advantageously, the shape of the support 270 provides light and stable support for the blade actuator mounted therein. Further advantageously, the support provides stability to the rotatable portion, particularly at high rotational speeds, which increases the maximum possible critical speed and thus the maximum possible efficiency of the rotatable portion 254. The support also helps reduce noise and vibration of the rotatable portion 254 at all speeds, especially at high speeds.

[0052] The corresponding centers of the through holes in the first series 440 are aligned with the corresponding centers of the through holes in the second series 442, so that when the blade actuators are mounted in the bracket 410, the axes of the blade actuator motor 258 and the rotatable portion 424 of each blade actuator are collinear. When coupled into the blade unit, the second bracket portion 430 is positioned closer to the blade tail than the elongated plate portion 426 of the first bracket portion 420. The first bracket portion 420 is removably connected to the second bracket portion 430 by screws that secure the feet at the ends of each arm 422, 424 to the corresponding ends of the second bracket portion 430. Advantageously, this allows for disassembly of the bracket and easy removal and replacement of the blade actuator 254 for maintenance and repair.

[0053] like Figure 4As shown, the rotatable portion 254 is formed as a tube with threaded portions on its inner surface. Attached to the motor 258, the rotatable portion 254 has a series of machined slots 262 that facilitate a flexible connection system between the blade actuator motor output shaft and the rotatable portion 254. The machined slots are patterned such that the rotatable portion 254 remains integrally formed as a single piece, as no single slot extends around the entire circumference of the rotatable portion 254. The machined slots are configured to pass through the walls of the rotatable portion 254, such that each slot extends around a portion of the circumference of the rotatable portion 254. The slots are offset from each other in the axial direction of the rotatable portion 254, and the start and end positions of any slot are offset from those start and end positions in the circumferential direction of the rotatable portion 254. This provides some flexibility in the connection between the motor output shaft and the rotatable portion 254. The slots allow the rotatable portion to bend such that its axis is no longer perfectly parallel to the axis of the motor output shaft (i.e., forming an acute angle with it). Advantageously, it can accommodate small misalignments between the blade actuator motor mounting and the blade / blade actuator screw.

[0054] The blade actuator screw can be made of any solid material. Particularly suitable materials are those with low corrosion, low wear, high strength, and / or low density. Lightweight and rigid materials are most suitable. For example, the blade actuator screw can be made of aluminum, steel, titanium, or any alloy thereof, or composite materials such as carbon fiber composites.

[0055] Actuator control

[0056] Typically, a suitable controller (not shown) will be provided, which is arranged to provide signals to the blade actuator 250 to move one or more appropriate blades 252, thereby providing the desired shape or position of the aperture. As those skilled in the art will understand, the blade actuator 254 (in particular the blade actuator motor 258) is connected to a suitable drive for converting step, speed, and / or direction inputs from the controller into actuator current and voltage.

[0057] In the above embodiment, the motor is aligned with the moving line it is driving. This design is called a "direct drive".

[0058] advantage

[0059] Advantageously, the blade unit according to the embodiment allows for high blade speeds because the blade actuator screw is rotary stationary. Therefore, vibration of the blade actuator screw caused by its rotation is eliminated. The blade actuator screw can still be manufactured to fit within the width of the blade because there is no need to increase its diameter to maintain stability. The rotatable part can have a larger diameter than the blade actuator screw because it is not constrained by the thickness of a single blade. Due to the larger diameter, the rotatable part has a higher critical speed than the blade actuator screw. Therefore, the rotatable part can operate at a higher rotational speed than the blade actuator screw without reaching its critical speed and without damage due to vibration.

[0060] The higher rotational speed of the rotatable part directly translates to a higher linear speed of the blade. Therefore, for the same blade actuator screw pitch, higher blade speeds are possible without compromising the stability and durability of the blade actuator. Thus, the advantages of low-pitch lead screws (improved positioning performance and self-locking) can be incorporated into blade actuator designs. Blade actuators can have high rotational speeds and therefore provide high blade speeds without the limiting factors discussed earlier.

[0061] The disclosed blade unit design allows for faster blade speeds without suffering from the aforementioned difficulties regarding vibration, blade position accuracy, or control system complexity. Alternative designs offer all the advantages of direct-drive blade actuator designs but avoid the issues associated with reaching critical speeds and lead screw overhauls.

[0062] Therefore, in this embodiment, the blade actuator provides rapid, accurate, and reliable changes in the shape and / or position of the aperture. Thus, during treatment, even if the patient (and consequently the tumor) is moving, the radiation dose delivered to the target tissue can be maximized while the dose applied to the healthy tissue surrounding the target tissue can be minimized.

[0063] A multi-leaf collimator or beam-limiting device for defining a radiation beam is proposed. The multi-leaf collimator includes blades, and the beam-limiting device includes any of the multi-leaf collimators described herein. A radiotherapy apparatus including said beam-limiting device is also proposed.

[0064] A method for driving the blades of the multi-leaf collimator described herein is also provided, the method comprising driving a blade actuator to generate relative linear motion between blades in at least one row of blades.

[0065] It is understandable that when the terms “parallel,” “perpendicular,” or “in a plane” are used to describe the relative arrangement of features and components, minor deviations are permissible as long as they do not affect the functionality and / or operation of the multi-leaf collimator module described herein.

[0066] The features of the above aspects can be combined in any suitable manner. It should be understood that the above description is only by way of specific embodiments of the aspects, and many modifications and changes will be made to the extent that are within the capabilities of those skilled in the art and are intended to be covered by the scope of the appended claims.

Claims

1. A blade unit assembly for a multi-leaf collimator, comprising: blade; A blade actuator screw having a first end fixedly attached to the blade; and The rotatable part is threadedly engaged with the blade actuator screw; A blade actuator motor is connected to the rotatable part; Support bracket, comprising: The first part includes a first opening configured to receive and support the blade actuator motor. and The second part includes a second opening having a bearing therein, and the second opening is arranged to receive and support the rotatable portion. The center of the first opening is aligned with the center of the second opening, such that the axis of the blade actuator motor and the axis of the rotatable part of each blade actuator are collinear.

2. The blade unit assembly according to claim 1, wherein, The first end of the blade actuator screw is connected to the blade to prevent relative rotational movement between the blade and the blade actuator screw about the axis of the blade actuator screw.

3. The blade unit assembly according to claim 1 or claim 2, wherein, The blade actuator screw has a second end opposite to the first end, wherein the rotatable portion is a tube surrounding the second end of the blade actuator screw.

4. The blade unit assembly according to claim 1, wherein, When the rotatable part rotates relative to the blade, the rotatable part is configured to produce a relative linear motion between itself and the blade.

5. The blade unit assembly according to claim 1, wherein, The blade actuator screw is configured to move between an extended position and a retracted position, in which most of the blade actuator screw is outside the rotatable portion, and in the retracted position, most of the blade actuator screw is surrounded by the rotatable portion.

6. The blade unit assembly according to claim 1, wherein, The rotatable portion includes a plurality of slots, each slot extending around a portion of the circumference of the rotatable portion, the slots being offset from each other in the direction of the axis of the rotatable portion.

7. The blade unit assembly according to claim 1, wherein, The rotatable part has a first end that is threadedly engaged with the blade actuator screw and a second end that is connected to the blade actuator motor.

8. The blade unit assembly according to claim 1, wherein, The blade actuator screw has a diameter of 2 mm or less and / or a length of 100 mm or more.

9. A multi-leaf collimator for a radiotherapy apparatus, comprising a leaf row including a plurality of blade unit assemblies according to any of the preceding claims, wherein rotational movement of the blades relative to each other is restricted such that rotation of each of the rotatable portions imparts linear movement of a corresponding blade actuator screw and a blade relative to the rotatable portion.

10. The multi-leaf collimator according to claim 9, wherein, The rotatable portion of each blade unit assembly is operable to move the corresponding blade in a linear motion, independent of the other blades in the blade row.

11. The multi-leaf collimator according to any one of claim 9 or claim 10, wherein, The first part is removably attached to the second part.

12. A radiotherapy device comprising a multi-leaf collimator according to any one of claims 9 to 11.

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