Gantry arm adjustment

Abstract

Disclosed herein is a radiotherapy support system comprising a rotatable gantry 204, an arm 234 for supporting a source of radiation, the arm being attached to the gantry via a fixed pivot point; and

Description

FIELD The present disclosure relates to radiotherapy, in particular to the gantry and arm of a radiotherapy device. BACKGROUND Radiotherapy systems, devices, or apparatus are capable of performing imaging of a patient using a source of radiation, such as a kV source. A typical radiotherapy system comprises a rotatable gantry, to which a source arm is mounted. The source arm is an arm that comprises the kV source and is attached to the gantry and configured to support the source in a position away from the gantry. Rotation of the gantry causes corresponding rotation of the arm and the source around a patient. The source emits a beam of radiation directed inwards towards the axis of rotation. The beam of radiation is located on the target region to be treated. Precise location of the target is important to ensure enough radiation is delivered to the target and that radiation delivered to healthy tissue surrounding the target is minimized. It is important to mount the arm to a known position on the gantry so that the source is in the desired or expected position. Additionally it is desirable to be able to adjust the position of the arm relative to the gantry once it has been mounted, such that the arm (and source) can be moved to a desired position once the arm is in place, to account for tolerance in the mounting process. Further, over time the position of the arm, and therefore source, might change due to movement or bending of the cantilevered support arm under gravity or due to the forces to which it is subjected during use. The support arm, because it is generally constructed with an asymmetrical cross section, experiences different amounts of deflection at different positions of gantry rotation. SUMMARY Aspects and features of the present invention are described in the accompanying claims. 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 illustrates a radiotherapy device according to the present disclosure; Figure 2a illustrates a radiotherapy device according to the present disclosure, from a side perspective; Figure 2b illustrates a radiotherapy device according to the present disclosure, from a rear perspective; Figure 3a illustrates a gantry according to the present disclosure from a front perspective; Figure 3b illustrates a gantry according to the present disclosure from a rear perspective; Figure 4 illustrates an opening and adjustment means of a gantry according to the present disclosure; Figure 5 illustrates a hinged support according to the present disclosure. OVERVIEW There is provided a radiotherapy support system comprising a rotatable gantry, an arm for supporting a source of radiation, a fixed pivot point and adjustment means for adjusting the position of the arm relative to the gantry. The arm is attached to the gantry via a fixed pivot point. Enabling adjustment of the position of the arm relative to the gantry means that the position of the source of radiation, and therefore the isocentre, can be precisely known, controlled, corrected or otherwise adjusted. Beam accuracy is improved, hysteresis can be reduced and undesirable changes in isocentre and arm position overtime, due to e.g. movement or bending of the arm under gravity or due to the forces to which it is subjected during use, can be minimised and / or compensated for. Adjustment means may comprise a hinged support, and / or one or more bushings. The adjustment means facilitate adjustment of the arm position about an arm rotation axis, and / or lateral adjustment. SPECIFIC DESCRIPTION OF CERTAIN EXAMPLE EMBODIMENTS Figure 1 depicts a radiotherapy apparatus 120 according to the present disclosure. The arrangement should be considered as providing merely an example of a radiotherapy apparatus 120 and it will be understood that other arrangements are possible. Figure 1 depicts a crosssection through the radiotherapy apparatus 120. The apparatus 120 comprises a radiation source 100 and a detector 102 attached to a rotatable gantry 104. The gantry 104 may take the form of a substantially cylindrical drum. The gantry 104 is supported by a base 130 and is rotatable with respect to the base. The base comprises a plurality of drive wheels (not shown) which are configured to drive rotation of the gantry 104. The radiation source 100 and the detector 102 are fixed to the gantry drum 104 so as to rotate with the gantry drum 104. The radiation source 100 and the detector 102 are arranged diametrically opposite one another. The radiation source 100 is attached to an arm (not shown) which is affixed to the gantry 104. Figure 1 also depicts a subject 108 on a support surface 110. The support surface 110 may be moved longitudinally relative to the gantry drum 104 (i.e. away from the plane of the gantry drum 104), for example to aid positioning of the subject 108. As radiation is applied to the subject 108, for example according to a treatment plan, the radiation source 100 and the detector 102 rotate together with the gantry 104 such that they are always arranged 180° from one another. The radiation source 100 directs radiation towards the subject 108 from various angles around the subject 108 in order to spread out the radiation dose received by healthy tissue to a larger region of healthy tissue while building up a prescribed dose of radiation at a target region. As shown in Figure 1, radiation may be emitted in a plane which is perpendicular to the axis of rotation of the radiation source 100 and gantry 104. Thus, radiation may be applied to a radiation isocentre 112 at the centre of the gantry drum 104 regardless of the angle to which the radiation source 100 is rotated around the gantry drum 104. The radiation can be shaped or limited using a collimator, for example a multi-leaf collimator, arranged in the path of a radiation beam. Precise location of the target by the beam is important to ensure enough radiation is delivered to the target and that radiation delivered to healthy tissue surrounding the target is minimized. Therefore it is important that the source of radiation is accurately positioned and remains so throughout the life of the radiotherapy device. Figures 2a-b depict a radiotherapy apparatus 200 which is similar in form, shape and structure as the apparatus 120 depicted in Figure 1. Figure 2a depicts the radiotherapy apparatus 200 from the side, and Figure 2b depicts the radiotherapy apparatus 200 from a rear perspective. The apparatus 200 comprises a gantry 204 in the form of a drum. Embodiments of the gantry 204 may be referred to herein as a gantry, gantry drum or drum. The gantry 204 comprises an axis of rotation 216. The apparatus 500 comprises a source of radiation 230 which is coupled to the gantry 204 via an arm 234. Figure 2a schematically depicts a beam of radiation 232 being emitted from the source of radiation 230. The source of radiation 230 is part of a beam generation system which comprises an electron gun, a waveguide to accelerate electrons emitted by the electron gun toward a target, and a target which, when struck by high energy electrons, produces high energy X-rays. The gantry rotation axis 216 lies along a T-G axis, where the G refers to the (electron) gun end of the waveguide and the T refers to the target end of the waveguide in an implementation in which the waveguide is comprised within the arm 234. The use of this terminology for the T-G axis is merely used to describe the geometry of the radiotherapy apparatus 200, and does not imply that the waveguide need be oriented in this way in implementations of the present invention, or that the apparatus need comprise an electron gun or target arranged in this way. The T-G axis passes through the isocenter and is horizontal when the apparatus is viewed from the view depicted in Figure 2a. The ‘front’ of the device 200, i.e. the side on which the source of radiation 230 is positioned, can be described as the T end of the device 200. Similarly, the rear of the device 200 can be described as the G end of the device 200. The geometry of the device 200 can be further described with respect to an A-B axis, which is depicted in Figure 2b. The A-B axis passes through the isocenter, is orthogonal with the T-G axis, and is horizontal when the apparatus is viewed from the view depicted in Figure 2b. Additionally, the apparatus can be described with respect to a U-D (up-down) axis. The U-D axis also passes through the isocenter and is orthogonal with the T-G and A-B axes. Where appropriate for improving clarity of description, certain components herein may be referred to using these axes, and certain reference numerals herein are appended with letters G, T, A, B, II, D, particularly where the component is part of a plurality of similar components and it is useful to distinguish between the components by reference to the apparatus geometry. Directions may also be described herein with reference to the T-G, A-B and / or U-D axes. In particular a reference to the T-G direction may refer to a direction from the T side of the device to the G side of the device, a reference to the A-B direction may refer to a direction from the A side of the device to the B side of the device; and a reference to the ll-D direction may refer to a direction from the II side of the device to the D side of the device. In the same way, directions may be described as G-T, B-A and D-U directions. As illustrated in Figures 2a and 2b, the arm 234 is arranged with respect to the gantry such that the arm 234 passes through the gantry, extending in the T-G direction. As shown in Figure 2a, the arm 234 may not be parallel to the T-G axis, and may instead be arranged pitched in an U-D direction from the T-G axis, i.e. pitched with respect to the T-G axis in a vertical direction when the apparatus is viewed from the views depicted in Figures 2a or 2b. Figure 3a illustrates a perspective view of the front face 302 of the gantry 204. The front face 302 of the gantry drum 204 includes an opening 306 for receiving the arm (not shown in Figure 3). In the present embodiment the arm passes through the drum and is positioned piercing the drum. The arm lies between the opening 306 in the front side 302 of the drum and an opening 308 in the back side 304 of the drum. The arm being positioned through the drum provides stability, since both the front face and the back face support the arm in its position. Figure 3b illustrates a perspective view of the back or rear face 304 of the gantry drum 204. The rear face includes an opening 308, connected to opening 306 for receiving the arm (not shown). The front 302 and rear 304 faces of the gantry 204 may also be referred to herein as front 302 and rear 304 sides of the gantry 204. The arm is attached to the gantry 204 using attachment means. The gantry 204 comprises one or more fixed pivot points located on the front face 302 of the gantry. The attachment means are also positioned at the one or more pivot points, and the arm is attached to the gantry via the pivot points using the attachment means. In other embodiments the one or more attachment means may be positioned elsewhere on the gantry, separate from the pivot points. Figure 4 illustrates an exemplar embodiment of attachment means, and the opening 306 of the gantry 204. The arm can be attached to the gantry 204 at two pivot points on opposing edges of the opening 306. The opposing edges on either side of the opening 306 may be described as A and B edges or sides of the opening 306 respectively. Attachment means 400, configured to attach the arm to the gantry 204, are located at each of the pivot points. The arm is rotatable, at the pivot points, about an axis parallel to the front face 302 of the gantry drum. 5 Exemplar attachment means 400 at the pivot points are illustrated in Figure 4. The attachment means comprise a bracket 402 having a circular aperture 404. The bracket is configured to receive, in the circular aperture, a corresponding attachment member located on, or comprised in, the arm. Accordingly, the arm may comprise one or more attachment members (not shown in Figure 4). The bracket 402 is substantially C-shaped. This allows axles to be translated into and through the aperture 404 in a direction perpendicular to the front face of the drum, i.e. in a T-G direction. Attachment means are located at each pivot point, such that attachment means are located on the gantry drum on either side of the opening 306. It will be appreciated that other forms and / or locations of attachment means could be provided. In some embodiments, the components shown in Figure 4 as positioned on the gantry drum (e.g., the bracket 402 and / or aperture 404) could be positioned on the arm, and corresponding attachment members on the arm could be positioned on the gantry drum. The attachment members of the arm, along with the attachment means at the pivot points, enable mounting of the arm to the gantry. In some embodiments, the one or more attachment members on the arm comprises an axle. An axle may be positioned on either opposing side of the arm, such that the corresponding attachment member received by a bracket 402 at each pivot point on either side of the opening 306 comprises an axle on the arm. When the arm is in situ and attached to the drum, an axle sits in an aperture 404 of a bracket 402 on either side of the opening 306, i.e. on either side of the arm, and the arm is pivotable around an axis parallel to the axle. The arm is therefore pivotable around an axis running parallel to the axle on the arm. This axis may be described as an arm rotation axis. The arm rotation axis is parallel to the face of the gantry drum and may be parallel to the A-B axis or in the A-B direction, enabling rotation of the arm or motion of the arm in an U-D direction. The skilled person will appreciated that there are a number of different mechanisms which could be used to attach the arm to the gantry at a pivot point. For example, a cone shaped recess in the gantry with a cone shaped protraction from the arm configured to mate with the cone-shaped recess on the gantry could be provided. The present pivot points facilitate easy and accurate mounting of the arm during assembly of the arm and gantry drum. In addition, attaching the arm to the drum at fixed pivot points means that the arm and attachment means are in known and well-defined positions, enabling precise placement of the arm and improved beam accuracy. One or more adjustment means may be provided for adjusting the position of the arm relative to the gantry. The adjustment means may be configured to adjust the position of the arm, around a pivot point and / or in one or more of the T-G, A-B or ll-D directions. The adjustment means may secure the position of the arm when in situ, or be used to adjust or change the position of the arm during assembly or when in situ. The adjustment means may comprise one or more bushings 411, 412, which are depicted according to an exemplar embodiment in Figure 4. The bushings 411, 412 may be positioned on the same face or an opposing face of the gantry with respect to the pivot points and / or attachment means 400. The bushings may be provided on either side of the front opening 306, and / or on either side of the rear opening 308. In the embodiment shown in Figure 4, two bushings are provided on each side of the opening 306; one 411 positioned above the fastening 400 and one 412 positioned below the fastening 400 on each of an A side and a B side of the opening 306. Here, above and below may be used to describe the position of the bushings with respect to the fastenings in an U-D direction, i.e. in a vertical direction when viewed according to the perspectives shown in any of Figures 2a-b or 3a-b. The bushings 411, 412 may be adjusted towards or away from the arm when the arm is in situ in a desired position, such that the bushings secure the arm in place and / or move the arm into a desired position. In particular, the position of the bushings may be adjustable in an A-B or B-A direction parallel to the arm rotation axis, so that they can be moved into contact with opposing sides of the arm in order to hold the arm in place. The bushings can also be adjusted to be closer to or further from the arm respectively, or to provide more or less force respectively when in contact with the arm. The bushings 411,412 may be threaded such that their position in an A-B direction can be adjusted via a rotation. A lever 420 may be provided at each bushing 411,412 to actuate rotation and adjustment of the bushing 411,412. The bushings 411, 412 can also be used to adjust the position of the arm in the A-B direction. The A-B direction may be referred to with reference to adjustment means comprising the bushings 411, 412 as a lateral direction, such that the adjustment means are configured to adjust the position of the arm in a lateral direction. When the arm is in situ, the bushings 411 and 412 on one side of the opening 306 can be moved towards the arm, i.e. moved further into the opening 306, which 7 provides a contact force between the bushings 411, 412 and a side of the arm. This force acts to move the arm parallel to the A-B axis. For example, moving clearance brushes in contact with the arm on an A side of the opening 306 into the opening in an A-B direction provides a contact force which acts to move the arm in the A-B direction. Similarly, moving clearance brushes in contact with the arm on a B side of the opening 306 into the opening in a B-A direction provides a contact force which acts to move the arm in the B-A direction. The bushings 411, 412 may provide adjustment of the arm in an A-B direction in the range -3mm to +3mm. In other words, as measured from a central position, the bushings can adjust the position of the arm by up to 3mm in the A-B direction, and up to 3mm in the B-A direction. The adjustment means may additionally or alternatively comprise a hinged support. Figure 5 shows a hinged support 500 according to the present disclosure. The hinged support comprises a plate or block 502, a hinge attachment 504 and an actuator 506. The hinged support 500 shown in Figure 5 is positioned on an opposing side of the gantry to the pivot points, however in alternative embodiments the hinged support may be positioned on the same side of the gantry as the pivot points. Figure 5 shows a view of the rear 304 of the drum, i.e. the opposing side to that on which the pivot points are located, with opening 308 visible. The hinged support 500 is attached to the rear side of the drum adjacent the opening 308, such that the hinged support 500 is positioned towards an upper edge of opening 308. Figure 5 also shows the arm 234 in situ, with the plate 502 of the hinged support configured to contact an upper face of the arm. Again, as used herein, ‘upper’ refers to the up direction of the U-D axis, i.e. upwards in a vertical direction when the apparatus is viewed according to a perspective of any of Figures 2a-b or 3a-b. The plate 502 may be hingeably joined to the actuator 506 at the hinged attachment 504. The plate may hinge about the attachment 504; in other words the plate may pivot about a support plate axis which is parallel to the rear face of the drum and parallel to the A-B axis, and passes through the hinged attachment 504. When the plate 502 is in contact with the arm 234, the plate 502 can rotate or pivot or hinge about the support plate axis in order to stay flush with the upper face of the arm, no matter what position or angle the arm is about the arm rotation axis. Accordingly, the plate 502 of the hinged support 500 ensures constant contact with the arm, allowing force to be applied to the arm at any arm position. The actuator 506 is used to move the plate and hinged attachment 504 in an U-D direction. The actuator 506 may also be used to rotate the plate about the support plate axis at the hinged 8 attachment 504. The actuator 506 comprises a threaded nut 508 which, when turned about the actuator 506, causes a change in length of the actuator such that the plate 502 can be moved in the U-D direction. In other words, the position of the plate 502 is adjustable using an actuator comprising a threaded nut. Turning the nut about the actuator may be described as turning the nut about a vertical axis, or about an axis parallel to the U-D axis. The nut may be moveable about the actuator in both a clockwise and anticlockwise direction, to allow extension or contraction of the actuator, i.e. movement of the plate, in both the U direction and the D direction. In some embodiments, the thread pitch of the actuator, i.e. of the nut 508, is in the region 0.1 to 3mm. Preferably, the thread pitch is in the region 1-2mm. More preferably, the thread pitch is 1.5mm. The thread pitch corresponds to a length change, in the U-D direction, of the actuator when the nut is turned about the actuator by 180 degrees, or one half turn. As explained above, a change in actuator length causes a change in plate position, which in turn exerts a force on the arm causing the arm to rotate about the arm rotation axis. In other words, a change in actuator length causes rotation of the arm about the arm rotation axis. Therefore, turning the nut about the actuator allows adjustment of the arm position by rotation of the arm about the arm rotation axis. A half turn of the nut may correspond to a rotation of the arm about the arm rotation axis in the region 0.05-0.15 degrees, preferably 0.1 degrees. A full turn, i.e. 360 degrees, of the nut may correspond to a rotation of the arm about the arm rotation axis in the region 0.15-0.25 degrees, preferably 0.2 degrees. This may scale up for any number of turns of the nut to cause rotation of the arm through a range of angles, and as such turning the nut about the actuator can finely adjust the position of the arm. Since the arm comprises a source of radiation, rotating or adjusting the position of the arm enables adjustments to the position of the source of radiation, and therefore the position of the isocentre. This enables accurate and precise positioning and adjustment of the isocentre, and improved accuracy of radiation beam delivery. Turning the nut about the actuator a half turn corresponds to a linear change in position of the source of radiation, in the region 1 to 3mm. Preferably, the change in position of the source is in the region 2-3mm, most preferably 2.5mm. Angular changes to the position of the arm upon turning the nut as described above may also be described as angular changes to the position of the source. Therefore, a half turn of the nut may be described as corresponding to rotation of the source through an angle in the region 0.05-0.15 degrees, preferably 0.1 degrees, etc. Rotation of the arm about the arm rotation axis comprises movement of the source of radiation in an U-D direction, as well as movement in a T-G direction. Therefore, rotation of the arm about the rotation axis causes movement of the isocentre in both an U-D and T-G direction. A half turn of the nut about the actuator may correspond to a displacement of the isocentre in the U-D direction, for example in the region 1.50-3.00mm, preferably 2.00-2.50mm, more preferably 2.10-2.20mm, most preferably 2.15mm. A half turn of the nut about the actuator may also correspond to a displacement of the isocentre in the T-G direction, for example in the region 0.50-2.00mm, preferably 1.00-1.50mm, more preferably 1.30-1.35mm, most preferably 1.31mm. Adjustment means according to any aspect of the present disclosure may be used to secure and / or adjust the position of the arm when in situ. The adjustment means may comprise the hinged support and / or at least one bushing. The arm may be adjustable in an U-D direction, a T-G direction and / or an A-B direction, as well as rotated about the arm rotation axis at the fixed pivot points. The ability to adjust the position of the arm means that the position of the source, and hence the isocentre, can be finely known, controlled, corrected or otherwise adjusted and hence beam accuracy is improved and precise control of the isocentre position is provided. Adjustment in U-D, T-G and A-B directions provides spherical adjustment of the isocentre. Enabling adjustment of the arm position, both during assembly and once in situ, improves the rigidity and reliability in the system in that the arm, and hence the source and isocentre, can be maintained in a correct and precisely known position throughout the lifetime of a radiotherapy device. Hysteresis is reduced, and undesirable changes in isocentre and arm position overtime, due to e.g. movement or bending of the arm under gravity or due to the forces to which it is subjected during use, can be minimised and / or compensated for. In other words, the fatigue performance of the gantry is improved. 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

1. A radiotherapy support system comprising:a rotatable gantry;an arm for supporting a source of radiation, the arm being attached to the gantry via a fixed pivot point;adjustment means for adjusting the position of the arm relative to the gantry.

2. The system of claim 1, wherein the arm is rotatable, at the pivot point, about an axis parallel to a face of the gantry.

3. The system of claim 1, wherein the adjustment means is configured to adjust the position of the arm around the pivot point.

4. The system of claim 1 or claim 2, wherein the adjustment means comprises a hinged support.

5. The system of claim 3, wherein the hinged support comprises a plate, a hinge attachment and an actuator.

6. The system of claim 4 or 5, wherein the pivot points are positioned on one side of the gantry and the hinged support member is positioned on an opposing side of the gantry.

7. The system of any preceding claim, wherein the adjustment means further comprises one or more bushings.

8. The system of claim 7, wherein the one or more bushings are configured to adjust the position of the arm in a lateral direction.

9. The system of claim 7 or 8, wherein the pivot points and bushings are positioned on one side of the gantry.

10. The system of claim 9, wherein a hinged support member is positioned on an opposing side of the gantry.

11. The system of any preceding claim, wherein the arm extends through the gantry.1112. The system of any preceding claim, further comprising attachment means at the pivot point.

13. The system of any preceding claim, wherein the arm comprises one or more attachment 5 members.

14. The system of claim 12 or 13, wherein the attachment means comprises a bracket for receiving a corresponding attachment member of the arm.10 15. The system of claim 13 or 14, wherein the one or more attachment members comprises anaxle.

16. A radiotherapy apparatus comprising:a radiotherapy support system according to any preceding claim; and15 a source of radiation attached to the arm of the radiotherapy support system.Application No: GB2319706.4Examiner: Mike WoodhamClaims searched: 1-16Date of search: 12 April 2024Patents Act 1977: Search Report under Section 17Documents considered to be relevant:Category Relevant to claims Identity of document and passage or figure of particular relevance X 1-6& 11- 16 CA 2310533 Al (IS2 RES INC) See whole description, especially paragraphs 0007 &0009 and figures 1-5 X 1-4, 12-16 US 2015 / 0190656 Al (KUDUVALLI et al.) See whole description, especially paragraphs 0032, 0034, 0038 and figures 2a-4 &6 X 1-3,12 &16 US 2022 / 0347494 Al (DEBATTY et al.) See whole description, especially paragraphs 0058-0059, 0063, 0068 and figures 1-2 &5 X 1-3, 12 &16 DE 102014203363 B4 (SIEMENS HEALTHCARE GMBH) See whole description and figures 1-3Categories:v Ak Document indicating lack of novelty or inventive step A Document indicating technological background and or state of the art. Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of same category. before the filing date of this invention. & Member of the same patent family E Patent document published on or after, but with priority date earlier than, the filing date of this application.Field of Search:International Classification:Subclass Subgroup Valid From A61N 0005 / 10 01 / 01 / 2006 A61B 0006 / 42 01 / 01 / 2024 A61N 0005 / 00 01 / 01 / 2006 A61N 0005 / 01 01 / 01 / 2006

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