An assembly for a radiotherapy device

Abstract

A mirror assembly for a radiotherapy apparatus is provided. The mirror assembly comprises a frame configured to engage with a patient positioning system of the radiotherapy apparatus, said patient positioning system comprising a couch. A mirror is connected to the frame, and the mirror assembly is configured to support a plurality of pre-determined mirror positions.

Description

[0001] An assembly for a radiotherapy device

[0002] A mirror assembly suitable for a radiotherapy apparatus.

[0003] Background

[0004] Radiotherapy can be described as the use of ionising radiation, such as X-rays, to treat a human or animal body. Radiotherapy is commonly used to treat tumours within the body of a human or animal patient, or subject. In such treatments, ionising radiation is used to irradiate, and thus destroy or damage, cells which form part of the tumour.

[0005] It can be beneficial to present visual information to the patient during treatment, for example to reduce the patient's anxiety, or to provide breathing guidance. The visual provision of breathing guidance may be particularly beneficial, as this can allow the patient to control the depth and / or timing of their breathing in such a way as to align the position of their internal organs with an expected position according to a radiotherapy treatment plan, permitting gated delivery of the radiotherapy treatment in line with the patients breathing.

[0006] However some radiotherapy apparatus, particularly MR Linac systems, require a patient to be positioned in a bore of the radiotherapy apparatus for treatment. The bore may occlude the patient's view of a treatment room, and make visual presentation of information to the patient challenging.

[0007] Summary

[0008] An invention is set out in the claims.

[0009] Figures

[0010] Specific examples will now be disclosed, by way of example only, with reference to the drawings of which:

[0011] Fig. 1 shows an exemplary radiotherapy apparatus, the mirror assembly of the present invention being suitable for use with such apparatus;

[0012] Fig. 2 shows a mirror assembly comprising a frame and a mirror pivotable connected to the frame;

[0013] Fig. 3 shows an alternative mirror assembly comprising a frame and a mirror releasably connected to the frame;

[0014] Figs. 4a - 4d each show a respective configuration of a releasably attachable mirror for use with the mirror assembly of Fig. 2.

[0015] Fig. 5 shows an exemplary system for display of information to a patient in a radiotherapy apparatus.

[0016] Overview

[0017] In overview the disclosure relates to a mirror assembly for a radiotherapy apparatus. The assembly comprises a frame configured to engage with a patient positioning system of the radiotherapy apparatus, said patient positioning system comprising a couch. A mirror is connected to the frame, and the mirror assembly is configured to support a plurality of pre-determined mirror positions.

[0018] This overcomes problems arising from the nature and use of a radiotherapy treatment apparatus, particularly an MR Linac system, which introduces challenges in providing a system for visual presentation of information to a patient during treatment. Depending on the treatment to be delivered, the patient will be set up in a particular position and / or utilizing specific patient positioning devices. The assembly is adaptable / customizable for each patient to accommodate this range of possible patient positions, and can also fit within the limited space around the patient within the bore. The solution provides for rapid and repeatable set up of the system around the patient, since a typical radiotherapy treatment plan is delivered over a plurality of treatment sessions, and is MR compatible.

[0019] Detailed Description

[0020] Fig. 1 shows an exemplary radiotherapy (RT) apparatus or device 100. The device and its constituent components will be well known to the skilled person but is described here generally for the purpose of providing useful accompanying information for the present disclosure. The radiotherapy device 100 is based on a linear accelerator (linac).

[0021] The device shown in Fig. 1 combines magnetic resonance (MR) imaging capability with a linac-based radiotherapy capability, and is known as an MR-linac device. However, the present disclosure may be implemented in any radiotherapy device, for example, a linac-based radiotherapy device without magnetic resonance imaging capability. In operation, the MR scanner produces MR images of the patient, and the RT apparatus produces and shapes a beam of radiation and directs it toward a target region within a patient's body in accordance with a radiotherapy treatment plan.

[0022] The MR-linac device 100 shown in Fig. 1 comprises an RF power source 102, an RF transmission apparatus 103, an acceleration waveguide 104, an electron source 106, a treatment head including a collimator 108 such as a multi-leaf collimator used to shape a treatment beam 110, MR imaging apparatus 112 (shown partially cut away), and a patient support surface 114. The RF transmission apparatus 103 comprises a waveguide component, which may be a copper waveguide. The depicted device does not have the usual 'housing' which would cover the MR imaging apparatus and RT apparatus in a commercial setting such as a hospital. In use, the device would also comprise the housing, part of which, together with the ring-shaped gantry, defines a bore. In particular, a part of the housing encloses the inner surface of the ring-shaped gantry, defining a bore through the device 100. The patient support surface 114 is moveable and can be used to support a patient and move them, or another subject, into the bore when an MR scan and / or when radiotherapy is to commence.

[0023] The patient support surface 114 forms part of a patient positioning system, which may also comprise a support stand and / or a treatment table. The patient support surface 114 may alternatively be called a couch.

[0024] The MR imaging apparatus 112 is configured to obtain images of a subject positioned on the patient support surface 114. The MR imaging apparatus 112 may be conventional MR imaging apparatus operating in a known manner to obtain MR data, for example MR images. The skilled person will appreciate that such MR imaging apparatus 112 may comprise a primary magnet, one or more gradient coils, one or more receive coils, and an RF pulse applicator.

[0025] The RT device has a beam generation system comprising the RF power source 102, the acceleration waveguide 104, and the electron source 106. The beam generation system is configured to produce a beam of ionising radiation, otherwise known as the treatment beam 110, that is collimated and shaped by the collimator 108 and directed towards the bore. Typically, a radiation detector is positioned diametrically opposed to the collimator. The radiation detector is suitable for, and configured to, produce radiation intensity data. In particular, the radiation detector is positioned and configured to detect the intensity of radiation which has passed through the subject. The radiation detector may form part of a portal imaging system.

[0026] The beam generation system is attached to the rotatable gantry 116 so as to rotate with the gantry 116. In this way, the beam generation system is rotatable around the patient so that the treatment beam 110 can be applied from different angles around the gantry 116. In a preferred implementation, the gantry is continuously rotatable. In other words, the gantry can be rotated by 360 degrees around the patient, and in fact may continue to be rotated past 360 degrees. The gantry is ring-shaped, i.e. a ring-gantry.

[0027] The device 100 of Fig. 1 is controlled by a controller (not shown). The controller is a computer, processor, or other processing apparatus. The controller may be formed by several discrete processors; for example, the controller may comprise an MR imaging apparatus processor, which controls the MR imaging apparatus 112; an RT apparatus processor, which controls the operation of the RT apparatus; and a subject support surface processor which controls the operation and actuation of the patient support surface 114. The controller is communicatively coupled to a memory, e.g. a computer readable medium.

[0028] As can be seen from Fig. 1 the housing defining the bore will restrict the visual field of a patient positioned in the bore. The present invention relates to a mirror assembly, which allows the presentation of visual information to the patient when they are positioned in the bore. The mirror assembly comprises an angled mirror, enabling the patient to see along the longitudinal direction of the bore and thereby view information displayed to the rear of the radiotherapy apparatus (i.e. the opposite side of the bore to the patient positioning system 114). For example, information may be displayed on a screen or projected onto a wall positioned to the rear of the radiotherapy apparatus and viewed in reflection by the patient via the mirror assembly.

[0029] Fig. 2 shows a mirror assembly 200 according to the present invention, comprising a frame 201, and a mirror 202 pivotably connected to the frame 201.

[0030] The frame 201 comprises an arch shaped portion and end parts 203a, 203b. End parts 203a, 203b are configured to releasably engage with a component of the patient positioning system, for instance the patient support surface 114. In some examples, end parts 203a, 203b each comprise a rail 204a, 204b respectively, extending from and generally perpendicular to the plane of the arch shaped portion. In some examples, the patient support surface 114 comprises one or more guide tracks. The rails 204a, 204b are configured to slidably engage with said guide tracks. Although not shown, in some embodiments one or both of the rails 204a, 204b comprises at least one flexible rail element arranged to fit into said guide track. Each flexible rail element comprises at least one protrusion arranged to releasably snap-lock the end part in said corresponding guide rail so as to allow the rail 204a, 204b to slide in the guide track and at the same time preventing the rail 204a, 204b from being removed from said guide track.

[0031] In some embodiments, a stop device comprising an adjustable spring element is arranged to fit onto the flexible rail element, wherein the adjustable spring element can be adjusted to adjust a width of the flexible rail element via an adjustment element. Said stop device may be configured to provide an adjustable friction fit between the flexible rail element and the guide track. The friction fit may be such that the likelihood of accidental displacement of the frame, for example by a patient adjusting their position, is reduced, while still allowing for movement of the frame within or from the guide track with the application of sufficient force.

[0032] In some examples, the frame 201 comprises cut-out portions 205a, 205b, each of the cut-out portions configured to act as a grab handle to improve the ease of handling of the frame 201. The cut out portions 205a, 205b are adjacent the end parts 203a, 203b, respectively.

[0033] The mirror 202 is pivotable relative to the frame 201, for example by means of a hinged connection. Preferably, the pivotal movement of the mirror 202 is limited to rotation about a single axis, or in other words the mirror 202 has only one degree of rotational freedom. When the mirror assembly 200 is attached to the patient support surface 114, the mirror 202 can be rotated relative to the frame 201. This rotation corresponds to an angular adjustment of the face of the mirror 202 with respect to a longitudinal axis defined by the direction of the bore. For example, a first angular position of the mirror may be defined where the face of the mirror is at an angle of about 30 degrees to the longitudinal axis of the bore, and a second angular position of the mirror may be defined where the face of the mirror is at an angle of 50 degrees to the longitudinal axis of the bore. Such first and second mirror positions may allow patient set up for treatment in different positions to achieve a similar field of view of information displayed to the rear of the bore. For example, depending on the patient setup, the patient's head may be elevated above the patient support surface 114 to varying extents. The mirror assembly 200 is configured to support a plurality of predetermined mirror positions to accommodate different patient setups. Said pre-determined mirror positions comprise a plurality of angular positions. Said angular positions may comprise any angular position for the face of the mirror between about 0 degrees and about 90 degrees to the longitudinal axis of the bore, for instance between about 10 degrees and about 80 degrees, or between about 20 degrees and about 70 degrees.

[0034] A typical radiotherapy treatment plan is delivered over a course of treatment sessions. To maintain patient throughput and accurately deliver the planned treatment, it is important that patient setup can be performed rapidly and with a high degree of repeatability.

[0035] The frame 201 may comprise a plurality of visual or tactile indications of a pre-determined mirror position, so as to define an index for the mirror position. In the present example, each of the plurality of pre-determined mirror positions comprises an angular mirror position.

[0036] In some examples, the attachment of the mirror 202 to the frame 201 may comprise a means for providing a resistance to movement of the mirror between or away from one of the pre-determined positions. For example, the connection may comprise a ratchet mechanism, or a cogwheel configured for bidirectional rotation. For example, the cogwheel may cooperate with a resilient protrusion. Teeth of the cogwheel may be contoured such that a resistance to movement of the mirror 202 is higher at the plurality of mirror positions than between said plurality of mirror positions. The protrusion and cogwheel may be configured such that the resistance to movement of the mirror 202 increases with a first angular displacement of the mirror 202 and decreases with a second angular displacement of the mirror 202; wherein, the first angular displacement of the mirror 202 is away from a first of the plurality of mirror positions and the second angular displacement of the mirror is towards a second of the plurality of mirror positions. Both the first and second angular displacements of the mirror 202 occur between adjacent mirror positions. Such a mechanism can aid in the speed and repeatability of patient set-up by providing a tactile indication of the mirror position and by reducing the likelihood of accidental displacement of the mirror away from the selected pre-determined mirror position.

[0037] Alternatively or additionally, the frame 201 may be provided with means to releasably lock the mirror in a pre-determined mirror position. For example, a locking element such as an insertable locking pin, a clip, or a twist lock mechanism may be provided.

[0038] Fig. 3a shows an alternative mirror assembly 300. Mirror assembly 300 comprises a frame 301, an arch shaped portion and end parts 303a, 303b and rails 304a, 304b as described in relation to Fig. 2 (alike features retain the same reference numbers increased by 100). Frame 301 also comprises cutout portions 305a, 305b as described in relation to Fig. 2.

[0039] Mirror assembly 300 is shown with a releasably attachable mirror 306 releasably connected to the frame 301. Releasably attachable mirror 306a may be interchangeable with one of a plurality of releasably attachable mirrors 306a, 306b, 306c, 306d shown in Figs. 4a-d. The releasably attachable mirrors 306a-d are each connectable to the frame 301 by means of an engagement member 310. The engagement member 310 is provided at an end of a neck 308 of the mirror 306a-d, the neck 308 extending away from rear of the mirror 309 and the engagement member 310 extending either side of, and perpendicular to the neck 308, forming a T-shape with the neck 308.. The mirrored face of releasably attachable mirror 306a-d is provided on the opposite side of an upper or rear face 309 of the mirror 306a-d.

[0040] The frame 301 comprises a plurality of receiving positions 307a, 307b, 307c, comprising slots configured to engage with the engagement member 310 of any of the releasably attachable mirrors 306a-d. In the example of Fig. 3a, the engagement member 310 is received in the receiving position 307a of the frame 301, but alternatively may be received in any of receiving positions 307a, 307b, 307c. Each of receiving positions 307a-c define a vertical mirror position. Each vertical mirror position is provided at a different height above the patient support surface 114. The vertical position of the mirror is therefore provided by the plurality of receiving positions 307a-c of the frame 301. As the mirror 306a-d is moved between the receiving positions the vertical position of the mirror 306a- d is adjusted accordingly. Providing means for adapting the height of the mirror 306a-d can allow a greater range of treatment positions to be accommodated whilst still enabling the patient to view information displayed behind the bore.

[0041] The engagement member 310 is provided at a first end of the neck 308 and is configured to engage with a receiving position 307a-c of frame 301. Engagement member 310 and receiving positions 307a-c may be configured to provide an interference fit between the engagement member and the receiving position. An angular position of the mirrored surface can be defined by the angle between the upper face 309 and the neck 308. In the present example, the angular position of the mirror 306a-d is fixed. The fixed angular position of the mirror 306a-d may be between 0 degrees and 50 degrees. In other examples, the mirror may be pivotably connected to the neck, for instance in a manner similar to that described for the attachment of mirror 202 to frame 201, to permit angular adjustment of the mirror position without the need to exchange the releasably attachable mirror for an alternative releasably attachable mirror. Preferably, the angular position of the mirror is fixed.

[0042] In the present embodiment, the mirror is integral with the neck 308 and engagement member 310. In other examples the neck may be integral with the frame 301, and the mirror may be releasably attached to the neck. According to embodiments of the present invention, mirror assembly 300 may be provided as a kit, comprising frame 301 and a set of interchangeable releasably attachable mirrors 306a-d. Any of releasably attachable mirrors 306a-d may be releasably connected to frame 301 to form mirror assembly 300.

[0043] Figs. 4a-d shows an exemplary set of releasably attachable mirrors 306a-d. Mirrors 306a, 306c comprise a first neck length and mirrors 306b, 306d comprise a second neck length; the second neck length being greater than the first neck length. Each of mirrors 306a-d differs in one or both of the length of the neck and the angular position of the mirror.

[0044] By providing a set of releasably attachable mirrors 306a-d comprising different neck lengths and angular positions for the mirrored surface, a plurality of patient positions can be accommodated in a manner which allows for rapid and repeatable patient set-up.

[0045] In the examples of Figs. 3a -4d, the mirror assembly 300 is configured to support a plurality of predetermined mirror positions, the plurality of pre-determined mirror positions comprising a plurality of vertical positions and a plurality of angular positions.

[0046] Fig. 5 shows an exemplary system 500 according to the present disclosure, comprising a projector 501 provided within housing 502, and arranged to display information on a surface 503 positioned behind the bore 504 of system 500. The system 500 may comprise an MR-Linac as described in relation to Fig. 1.

[0047] A patient may be positioned within the bore on patient support surface 114. The patient support surface 114 may comprise guide tracks 511a, 511b positioned either side of the patient support surface 114, configured to engage with the mirror frame 201, 301 by means of rails 205a, 205b, 305a, 305b respectively.

[0048] In use, the mirror assembly 200, 300 may be engaged with the patient support surface 114 by means of the guide tracks 511a, 511b, and positioned over the head of a patient on the patient support surface 114. By means of the mirrored surface of the mirror assembly 200, 300, a patient may be able to view the information displayed on the surface 503 whilst in the bore 504.

[0049] In the present example, the projector 501 may be provided with means to vertically adjust the position of the displayed information on the surface 503. Such adjustment may further increase the range of treatment positions that can be accommodated by either mirror assembly 200 or 300.

[0050] In the present example, the projector 501 is configured to mirror the projected information, such that when viewed by a patient through the mirror assembly, the information appears in the expected orientation (i.e. is not flipped in the reflection).

[0051] In the present example, a single projector 501 is provided. In other examples, two projectors may be provided and configured to produce a 3D stereoscopic display when viewed in reflection in the mirror assembly 200, 300.

[0052] In other examples, a screen, particularly an MR-compatible screen may be provided on the surface 503 as an alternative to a projector.

[0053] In some examples, the projector 501 may be configured to project the displayed image on the surface 503 in a fixed position. The projector 501 may be configured to project the image such that it is displayed at a fixed height on the surface 503 or equivalently to project the image at a fixed angle from the location of the projector 501. The projector 501 may not comprise components configured to adjust the position (e.g. the height) of the displayed image on the surface 503. In some examples, in which a screen is provided instead of the projector 503, the screen may be disposed in a fixed position (e.g. on the surface 503), such that its position (e.g. its height) cannot be adjusted. The screen may not comprise or be coupled to any components configured to adjust the height of the screen.

[0054] As described herein, the mirror assembly 200, 300 may comprise rails 204a, 204b, 304a, 304b configured to slidably engage with the guide tracks 511a, 511b on the patient support surface 114. The mirror assembly 200, 300 may be configured for movement to various different longitudinal positions along the length of the patient support surface 114 by sliding the rails 204a, 204b, 304a, 304b in the guide tracks 511a, 511b. Moreover, as described herein, the mirrors of the mirror assemblies 200, 300 may be rotatable / pivotable to various different angular positions with respect to the respective frames 201, 301. The mirrors may be configured for pivoting to a number of different discrete angular positions, or may be pivotable in a continuous manner to any angular position within the angular range of the mirror assemblies 200, 300.

[0055] The combination of the mirror assembly 200, 300 being selectively moveable to different longitudinal positions along the length of the patient support surface 114, and the mirror being angularly rotatable / pivotable, enables the projected image or the screen to be positioned in a fixed location on the surface 503 and still be visible by patients positioned according to various different treatment setups, as will be explained in more detail below.

[0056] According to some previous approaches, a fixed position of the mirror may be provided, for example at the end of the patient support surface 114. This may enable a patient lying supine on the table to look along the bore at a monitor mounted at bore height, coincident with the isocentre.

[0057] In some examples, projected images and screens which are moveable may be used so as to be able to accommodate different treatment setups while still allowing patients to see the projected images and screens in those different treatment setups. In some treatment setups, the head of the patient may be positioned flat against the patient support surface 114. In other treatment setups, the head of the patient may be elevated from the patient support surface 114, for example by positioning a patient positioning device under the head of the patient. Moving the position at which the image is displayed means that the image can be moved to where it is visible from the location of the head of the patient.

[0058] Such moveable projected images and screens may enable the patient to be set up / positioned outside the bore and subsequently moved into the bore. Setup of patients outside of the bore typically requires the image to be at the level of the isocentre. In this arrangement, the mirror allows the patient to look parallel along the bore such that the mirror / image setup is the same before and after moving the patient into the bore. When the head of the patient is elevated, the projected image / screen may be moved higher, meaning that setup in this case can only be performed in the treatment position inside the bore.

[0059] However, moving of the projected image / screen leads to the need for providing movement mechanisms in the treatment room which are MR-compatible, which can add significant engineering complexity and cost. It has been realized according to the present disclosure that a fixed projection / screen position can be implemented in combination with a mirror which is pivotable and longitudinally moveable along the patient support surface 114, and that this combination of features enables the patient to view the projection / screen whether or not the head of the patient is elevated.

[0060] In particular, according to the present disclosure, the projected image / screen may be positioned at a vertical height higher than a vertical height of the isocentre. The vertical height of the projected image may be in the range of approximately 200 mm to approximately 500 mm above the vertical height of the isocentre. For example, the vertical height of the projected image / screen may be approximately 250 mm or approximately 300 mm or in the range of approximately 250 mm to approximately 300 mm above the vertical height of the isocentre. Depending on the geometry of the radiotherapy apparatus / bore, it has been determined that this can provide an optimal height of the projected image / screen such that the bore does not intersect with the top of the image and the forehead of the patient does not intersect with the bottom of the image. The vertical height of the projected image / screen may refer to a position in a vertical centre of the projected image / screen (half way between the top and the bottom of the projected image / screen). The vertical height of the isocentre may correspond to a vertical height of the centre of the bore 504.

[0061] According to the arrangement of the present disclosure, the patient, disposed on their back on the patient support surface 114, can view the mirror positioned diagonally in front of and above them (e.g. angled approximately 20° above horizontal). The light path from the screen / projected image to the mirror can pass between the top of the bore 504 of the radiotherapy device and the forehead of the patient, be reflected by the mirror, and thereby reach the eyes of the patient.

[0062] When the patient is lying with their head on the patient support surface 114, the mirror assembly 200, 300 may be positioned relatively closer to the head of the patient than when the patient has their head elevated. When the patient is lying with their head on the patient support surface 114, the angular position of the mirror may be such that the plane of the mirror is closer to horizontal and further from vertical than the situation in which the patient has their head elevated. Moreover, by adjusting the longitudinal position and / or the angle of the mirror, patients of different sizes may be positioned at various different longitudinal positions along the length of the patient support surface 114 and still be able to view the displayed image without requiring movement of the projection or screen. This can further increase the range of treatments that are possible with the arrangement of the present disclosure.

[0063] Therefore, the combination of features of the mirror assembly and the fixed projection / screen height enable a reduction of engineering complexity and an increase in flexibility of the patient setups that can be accommodated.

Claims

Claims1. A mirror assembly for a radiotherapy apparatus, comprising a frame configured to engage with a patient positioning system of the radiotherapy apparatus, said patient positioning system comprising a couch; and a mirror connected to the frame, wherein the mirror assembly is configured to support a plurality of pre-determined mirror positions.

2. A mirror assembly according to claim 1, wherein the mirror is pivotably connected to the frame.

3. A mirror assembly according to claim 2, wherein the frame comprises an indexer.

4. A mirror assembly according to claim 2 or 3, wherein the mirror is pivotably connected to the frame by a hinge.

5. A mirror assembly according to claim 2 or 3, wherein the mirror is pivotably connected to the frame by a ratchet mechanism.

6. A mirror assembly according to any preceding claim, wherein the mirror position is lockable.

7. A mirror assembly according to any preceding claim, wherein the plurality of mirror positions comprises a plurality of discrete positions.

8. A mirror assembly according to any preceding claim, wherein the plurality of mirror positions comprise a plurality of angular positions.

9. A mirror assembly according to any one of claims 2 to 8, wherein the mirror is pivotably connected to the frame such that a resistance to movement of the mirror is higher at a plurality of mirror positions than between said plurality of mirror positions.

10. A mirror assembly according to claim 9, wherein the resistance to movement of the mirror increases with a first angular displacement of the mirror and decreases with a second angular displacement of the mirror; wherein the first angular displacement of the mirror is away from a first of the plurality of mirror positions, and the second angular displacement of the mirror is towards a second of the plurality of mirror positions.

11. A mirror assembly according to claim 10, wherein the first and second angular displacements of the mirror each occur between adjacent mirror positions.

12. A mirror assembly according to any one of claims 1 to 11, wherein the mirror is releasably connected to the frame.

13. A mirror assembly according to claim 12, wherein the mirror assembly further comprises a neck connected to the mirror, the neck comprising a means for releasably connecting the mirror to the frame.

14. A mirror assembly according to claim 13, wherein the neck is integral with the frame.

15. A mirror assembly according to claim 13, wherein the neck is integral with the mirror.

16. A mirror assembly according to any preceding claim, wherein the frame is configured to slidably engage with the patient positioning system.

17. A mirror assembly according to any preceding claim, wherein the frame comprises an archshaped portion, a first end part, and a second end part, said first and second end parts each comprising a rail being slidable in a corresponding guide track of the patient positioning system.

18. A mirror assembly according to claim 18, wherein the rail of each of said first and second end parts comprises at least one flexible rail element arranged to engage with a guide track of the patient support system.

19. A mirror assembly according to claim 18, wherein said flexible rail element comprises at least one protrusion arranged to releasably lock said end part in said guide track.

20. A mirror assembly according to claim 18 or 19, the frame further comprising a stop device configured to provide an adjustable friction fit between the flexible rail element and the guide track.

21. A mirror assembly kit comprising a mirror assembly according to any one of claims 1 to 3, and a plurality of releasably attachable mirrors.

22. A mirror assembly kit according to claim 22, wherein the plurality of pre-determined mirror positions comprise a plurality of vertical positions.

23. A mirror assembly kit according to claim 22 or 23, wherein the frame comprises a plurality of receiving positions, each receiving position configured to receive a releasably attachable mirror.

24. A mirror assembly kit according to claim 22, 23 or 24, wherein each of the plurality of releasably attachable mirrors comprises a neck, the neck comprising a means for releasably connecting the mirror to the frame.

25. A mirror assembly kit according to claim 25, wherein the means for releasably connecting the mirror comprises a protrusion configured to form an interference fit with a receiving position of the frame.

26. A mirror assembly kit according to claim 25 or 26, wherein for each of the plurality of releasably attachable mirrors: the neck comprises a length, the mirror comprises a face, and a mirror angle is defined between the length of the neck and the face of the mirror.

27. A mirror assembly kit according to claim 27, wherein each of the plurality of releasably attachable mirrors has at least one of a neck length or a mirror angle which is different from that of another of the plurality of releasably attachable mirrors.

28. A radiotherapy apparatus including a mirror assembly according to any one of claims 1 to 28, and a projector.

29. A radiotherapy apparatus according to claim 29, wherein the projector projects information onto a surface, and the mirror assembly is configured to allow a patient in a treatment position in the radiotherapy apparatus to view a reflection of said projected information on said surface.

30. A radiotherapy apparatus comprising: a patient support apparatus;a mirror assembly comprising: a frame which is slidably engageable with the patient support apparatus; and a mirror which is pivotable with respect to the frame; and a display device configured to display an image at a fixed height.

31. A radiotherapy apparatus according to claim 30, wherein the display device is a display screen fixed at the fixed height and configured to generate the image.

32. A radiotherapy apparatus according to claim 30, wherein the display device is a projector configured to project the image at the fixed height on a surface.

33. A radiotherapy apparatus according to any of claims 30-32, wherein the frame comprises at least one rail slidably moveable within a guide track of the patient support apparatus.

34. A radiotherapy device according to any of claims 30-33, wherein the frame is slidably moveable along a longitudinal length of the patient support apparatus.

35. A radiotherapy apparatus according to any of claims 30-34, wherein the fixed height is above a height of the isocentre of the radiotherapy apparatus.

36. A radiotherapy apparatus according to claim 35, wherein a vertical position of the displayed image is in the range of approximately 250 mm to approximately 300 mm above a vertical position of the isocentre.

37. A radiotherapy apparatus according to any of claims 30-36, wherein the display device does not comprise and is not coupled to any component configured to alter a height of the displayed image.

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