GB2638651A - A radiotherapy device - Google Patents

Abstract

A radiotherapy device 200 comprising a rotatable gantry and a source of radiation coupled to the gantry. The source of radiation is configured to deliver a non-coplanar beam of therapeutic radiation towards an isocentre 214. The device comprises a bore for receiving at least part of a patient, wherein the bore comprises a tapered section which tapers from a first wider end toward a second narrower end and wherein the isocentre is located within the tapered section.

Description

A Radiotherapy Device This disclosure relates to a radiotherapy device, and in particular to a radiotherapy device configured to provide non-coplanar radiotherapy treatment.

Background

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 patient or subject. In such treatments, ionising radiation is used to irradiate, and thus destroy or damage, cells which form part of the tumour. In this way, radiotherapy provides effective treatment of cancer.

A radiotherapy device typically comprises a gantry which supports a beam generation system, or other source of radiation, which is rotatable around a patient. In many devices suitable for providing radiotherapy, the source of radiation is configured to deliver radiation at an angle perpendicular to the gantry rotation angle, and although the gantry rotates through different angles, radiation is delivered in the same geometric plane throughout treatment. This is coplanar radiotherapy. Non-coplanar beam delivery allows for better dose conformity in radiotherapy treatments. In turn, better dose conformity leads to less dose being delivered to organs at risk (OARs), as well as helping to ensure the intended dose is delivered to the target region. Radiotherapy device designs have been proposed which enable a 'beam tilt. In these devices, the beam can be tilted to point out of the plane of rotation of the beam source, such that the beam is still pointed towards a common point, the isocentre, over a full gantry rotation.

However, many existing radiotherapy devices capable of delivering non-coplanar treatment, or proposed designs for such devices, are sub-optimal in several ways. Mechanical stability is important when designing a radiotherapy device, and devices which involve tilting a large, heavy source of radiation can jeopardise this mechanical stability. For these designs, it can also be difficult to provide a beam stopper across all the possible beam paths, which increases the shielding requirements for the hospital treatment room. Devices which make use of a gantry comprising a bore typically have improved mechanical stability, and in addition patient comfort may be increased when treatment is delivered via a device with a large bore. Patients receiving treatment via devices with large bores may feel less claustrophobic during treatment, compared to devices with smaller bores. However, devices with large bores typically require an increased distance between the beam shaper (for example a multi-leaf collimator) and the isocentre, which can lead to a sub-optimal sharpness of gradient in a resulting dose distribution.

The present invention seeks to address these and other disadvantages encountered in the prior art by providing an improved radiotherapy device capable of delivering non-coplanar treatment.

Summary

An invention is set out in the enclosed independent claim(s). Optional features are set out in the dependent claims.

Figures Specific embodiments are now described, by way of example only, with reference to the drawings, in which: Figure 1 depicts a radiotherapy device; Figures 2a-c depict a radiotherapy device according to the present disclosure; and Figures 3a-c depict a patient being positioned in a bore of a radiotherapy device according to figures 2a-c.

Detailed Description

In overview, and without limitation, the radiotherapy device disclosed herein comprises a bore for accommodating at least part of a patient. The bore comprises a tapered section which may, for example, taper from a first wider end toward a second, narrower end. An example shape suitable for the tapered section may be a frustoconical shape. The device also comprises a source of radiation coupled to the gantry and configured to deliver a non-coplanar beam of therapeutic radiation toward an isocentre, which is located within the tapered section.

Because the bore comprises a tapered section, the benefits of both a large diameter bore and a smaller diameter bore can be provided. The wider end of the tapered section facilitates entry of the patient into the bore. The patient can be moved laterally and rotated in a yaw direction to provide more flexibility in patient positioning, for example to adjust the angle at which the beam enters the patient's body. Centrally located targets (e.g. the patient's spine) can also be treated, for example by positioning the patient with their head in the narrow part of the bore, or feet-first with their legs in the narrow part of the bore e.g. to cover sites in the lower spine. Because the source of radiation is configured to direct radiation toward an isocentre, which itself is located in the tapered section, the beam shaper can be positioned closer to the isocentre. In other words, the beam shaper-toisocentre distance can be kept low.

Figure 1 depicts an MR-linac radiotherapy device suitable for delivering, and configured to deliver, a beam of radiation to a patient during radiotherapy treatment. The device and its constituent components will be described generally for the purpose of aiding understanding, and for providing useful accompanying information for the present invention. While the device in figure 1 is an MRlinac, the implementations of the present disclosure may be any radiotherapy device, for example a linac device.

The device 100 comprises both MR imaging apparatus 112 and radiotherapy (RT) apparatus which may comprise a linac device. The MR imaging apparatus 112 is shown in cross-section in the diagram. In operation, the MR scanner produces MR images of the patient, and the linac device 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. The depicted device does not have the usual 'housing' which would cover the MR imaging apparatus 112 and RT apparatus in a commercial setting such as a hospital.

The MR-linac device 1--depicted in figure 1 comprises a source of radiation, which may comprise a beam generation and shaping apparatus. The example beam generation and shaping apparatus depicted in figure 1 comprises a source of radiofrequency waves 102, a waveguide 104, a circulator 118, a source of electrons 106, and a collimator 108 such as a multi-leaf collimator configured to collimate and shape the beam. The MR-linac device 100 further comprises an MR imaging apparatus 112, and a patient support surface 114. In use, the device 100 would also comprise a housing (not shown) which, together with the ring-shaped gantry, defines a bore. The moveable support surface 114, otherwise known as a patient positioning surface (PPS), can be used to move a patient, or other subject, into the bore when an MR scan and/or when radiotherapy is to commence. The PPS is substantially rectangular in shape and comprises a central length axis 115. In the absence of an applied rotation, the central length axis 115 is parallel with the gantry rotation axis. The PPS may be rotatable, such as about a yaw rotation axis, such that the angle the central length axis makes with the gantry rotation axis is adjustable. The PPS may be rotatable about a roll rotation axis, which is coincident with the central length axis. The PPS may be rotatable about a pitch rotation axis, which is perpendicular both to the yaw rotation axis and the gantry rotation axis. The PPS may be moveable parallel with the central length axis / gantry rotation axis, such that the patient can be moved into, and out from, the bore of the device 100.

The MR imaging apparatus 112, RT apparatus, and a subject support surface actuator are communicatively coupled to a controller or processor. The controller is also communicatively coupled to a memory device comprising computer-executable instructions which may be executed by the controller.

The RT apparatus comprises a source of radiation and a radiation detector (not shown) and/or a beam stopper (not shown). Typically, the radiation detector is positioned diametrically opposite the radiation source. The radiation detector is suitable for producing, 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 also be described as radiation detecting means, and may form part of a portal imaging system. The beam stopper is positioned to stop the beam once it has passed through the isocentre, thereby reducing shielding requirements in the treatment room.

The radiation source may comprise a beam generation system. For a linac, the beam generation system may comprise a source of RF energy 102, an electron gun 106, and a waveguide 104. The radiation source is attached to the rotatable gantry 116 so as to rotate with the gantry 116. In this way, the radiation source 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 can continue to be rotated past 360 degrees. The gantry may be ring-shaped. In other words, the gantry may be a ring-gantry.

The source 102 of radiofrequency waves, such as a magnetron, is configured to produce radiofrequency waves. The source 102 of radiofrequency waves is coupled to the waveguide 104 via circulator 118, and is configured to pulse radiofrequency waves into the waveguide 104.

Radiofrequency waves may pass from the source 102 of radiofrequency waves through an RF input window and into an RF input connecting pipe or tube. A source of electrons 106, such as an electron gun, is also coupled to the waveguide 104 and is configured to inject electrons into the waveguide 104. In the electron gun 106, electrons are thermionically emitted from a cathode filament as the filament is heated. The injection of electrons into the waveguide 104 is synchronised with the pumping of the radiofrequency waves into the waveguide 104. The design and operation of the radiofrequency wave source 102, electron source and the waveguide 104 is such that the radiofrequency waves accelerate the electrons to very high energies as the electrons propagate through the waveguide 104.

The design of the waveguide 104 depends on whether the linac accelerates the electrons using a standing wave or travelling wave, though the waveguide typically comprises a series of cells or cavities, each cavity connected by a hole or 'iris' through which the electron beam may pass. The cavities are coupled in order that a suitable electric field pattern is produced which accelerates electrons propagating through the waveguide 104. As the electrons are accelerated in the waveguide 104, the electron beam path is controlled by a suitable arrangement of steering magnets, or steering coils, which surround the waveguide 104. The arrangement of steering magnets may comprise, for example, two sets of quadrupole magnets.

Once the electrons have been accelerated, they may pass into a flight tube (optional, and not shown). The flight tube may be connected to the waveguide by a connecting tube. This connecting tube or connecting structure may be called a drift tube. The electrons travel toward a heavy metal target which may comprise, for example, tungsten. Whilst the electrons travel through the flight tube, an arrangement of focusing magnets act to direct and focus the beam on the target.

To ensure that propagation of the electrons is not impeded as the electron beam travels toward the target, the waveguide 104 is evacuated using a vacuum system comprising a vacuum pump or an arrangement of vacuum pumps. The pump system is capable of producing ultra-high vacuum (UHV) conditions in the waveguide 104 and in the flight tube. The vacuum system also ensures UHV conditions in the electron gun. Electrons can be accelerated to speeds approaching the speed of light in the evacuated waveguide 104.

The source of radiation is configured to direct a beam 110 of therapeutic radiation toward a patient positioned on the patient support surface 114. The source of radiation may comprise a heavy metal target toward which the high energy electrons exiting the waveguide are directed. When the electrons strike the target, X-rays are produced in a variety of directions. A primary collimator may block X-rays travelling in certain directions and pass only forward travelling X-rays to produce a treatment beam 110. The X-rays may be filtered and may pass through one or more ion chambers for dose measuring. The beam can be shaped in various ways by beam-shaping apparatus, for example by using a multi-leaf collimator 108, before it passes into the patient as part of radiotherapy treatment.

In some implementations, the source of radiation is configured to emit either an X-ray beam or an electron particle beam. Such implementations allow the device to provide electron beam therapy, i.e. a type of external beam therapy where electrons, rather than X-rays, are directed toward the target region. It is possible to 'swap' between a first mode in which X-rays are emitted and a second mode in which electrons are emitted by adjusting the components of the linac. In essence, it is possible to swap between the first and second mode by moving the heavy metal target in or out of the electron beam path and replacing it with a so-called 'electron window'. The electron window is substantially transparent to electrons and allows electrons to exit the flight tube.

The subject or patient support surface 114 is configured to move between a first position substantially outside the bore, and a second position substantially inside the bore. In the first position, a patient or subject can mount the patient support surface. The support surface 114, and patient, can then be moved inside the bore, to the second position, in order for the patient to be imaged by the MR imaging apparatus 112 and/or imaged or treated using the RT apparatus. The movement of the patient support surface is effected and controlled by a subject support surface actuator, which may be described as an actuation mechanism. The actuation mechanism is configured to move the subject support surface in a direction parallel to, and defined by, the central axis of the bore. The terms subject and patient are used interchangeably herein such that the subject support surface can also be described as a patient support surface. The subject support surface may also be referred to as a moveable or adjustable couch or table.

The radiotherapy apparatus / device depicted in figure 1 also comprises MR imaging apparatus 112.

The MR imaging apparatus 112 is configured to obtain images of a subject positioned, i.e. located, on the subject support surface 114. The MR imaging apparatus 112 may also be referred to as the MR imager. The MR imaging apparatus 112 may be a conventional MR imaging apparatus operating in a known manner to obtain MR data, for example MR images. The skilled person will appreciate that such a MR imaging apparatus 112 may comprise a primary magnet, one or more gradient coils, one or more receive coils, and an RF pulse applicator. The operation of the MR imaging apparatus is controlled by the controller.

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; 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 subject support surface. The controller is communicatively coupled to a memory, e.g. a computer readable medium.

The linac device also comprises several other components and systems as will be understood by the skilled person.

Figures 2a, 2b and 2c depict a radiotherapy device 200 according to the present disclosure. The figures are cross-sectional views. Figure 2a is a top-down plan view, and figure 2b is a side view. Figure 2c is also a top-down view, with certain features visible in figure 2a removed to better depict the shape of a bore 260 of the device 200. The device 200 comprises a source of radiation 200, a beam shaper 220, a beam stopper 230, and a housing 270. Of course, the skilled person will appreciate that in practice the device 200 will have many other components, and that figures 2a, 2b and 2c are schematic diagrams that have been simplified to aid quick understanding.

The device 200 comprises a rotatable gantry (not depicted), to which the source of radiation 210, beam shaper 220 and beam stopper 230 are coupled. When the gantry rotates, each of these components rotates with it. The gantry has a gantry rotation axis 240, about which the various components affixed (or otherwise coupled) to the gantry can be rotated.

The source of radiation 210 is configured to deliver a beam of radiation. The beam of radiation is a therapeutic beam of radiation, suitable for the use in delivering radiation as part of a radiotherapy treatment plan. The source of radiation 210 is configured to deliver the beam of radiation toward an isocentre 214. The source of radiation 210 delivers radiation along a beam axis 212. The isocentre 214 may be described as a point or region in space which receives radiation at every gantry rotation angle; or similarly as the point or region in space at which the beam axes 212 at every gantry rotation angle intersect. From a purely mathematical perspective, it is possible to consider that the isocentre 214 is a point, however in reality due to mechanical tolerances, and the like, the isocentre 214 may be a circle or sphere. The isocentre 214 lies substantially along the gantry rotation axis 240, and accordingly the isocentre 214 may also be considered as the point at which the gantry rotation axis 214 and the beam axis 212 intersect.

The beam (or radiation) axis meets the gantry rotation axis 240 at an angle, a The angle 13 can be described as a beam angle. For coplanar treatment, the angle B would be 90 degrees. However, the radiation source 210 is configured to deliver a non-coplanar beam of radiation. Therefore, the radiation beam meets the gantry rotation axis 240 at a non-perpendicular angle, forming both an acute angle B with the gantry rotation axis 240, and an obtuse angle with the gantry rotation axis 240 (180°-8). As the gantry rotates, the beam (or radiation) axis 212 sweeps out a cone, with its apex located at the isocentre 214.

In an implementation, the source of radiation 210 is fixedly coupled to the gantry such that the acute angle B is a fixed angle. In other words, the source of radiation 210 may be configured to emit radiation at a fixed angle B with respect to the gantry rotation axis 240. This is in contrast with some prior devices, which seek to introduce non-coplanar funcitonality via a tiltable radiation source, which sometimes comes with the cost of reduced mechanical stability.

The device 200 comprises a beam shaper 220. The beam shaper 220 may also be described as a beam shaping apparatus, or a collimator. The beam shaper 220 is configured to modify the shape and size of the radiation beam produced by the radiation source 210. The beam shaper 220 is able to define and control the area that receives therapeutic radiation, ensuring accurate targeting of the tumor while sparing healthy surrounding tissue. An example of a beam shaper 220 is a multi-leaf collimator (M LC), and the skilled person will be familiar with the function of beam shapers such as MLCs.

As can best be appreciated from figure 2c, the device 200 comprises a bore 260. The bore 260 is an opening, which may be a central opening, comprised within the radiotherapy device 200. The bore 260 is a tunnel-like structure. The bore 260 is for accommodating at least part of a patient, for example the head and neck of a patient (as can be appreciated from figures 3a-c). Unlike prior radiotherapy device designs, the bore 260 comprises a tapered section 262. The tapered section 262 tapers from a first, wider end toward a second, narrower end. The bore 260 narrows from the first end toward the second end of the tapered section. The tapered section 262 of the bore 260 depicted in the figures is frustoconical in shape, and the tapered section 262 may therefore be described as a frustoconical section herein. However, the frustoconical shape is only one example of a suitable tapered shape; for example, the tapering may not be steady in gradient but might change in gradient over the length of the tapered section 262.

The tapered section 262 may define the shape of the entire bore 260, so that the entire bore is (e.g.) frustoconical in shape. Alternatively, as depicted in the figures, the bore 260 may further comprise a first portion 264 which interfaces with the wider end of the tapered section 262 and/or a second portion 266 which interfaces with the narrower end of the tapered section 262. The first portion 264 may by cylindrical in shape and may be defined by a first annular wall. The second portion 266 may also be cylindrical in shape and may be defined by a second annular wall. In this implementation, the first cylindrical portion 264 has a first diameter and the second cylindrical portion 266 has a second (smaller) diameter. Taking these sections into account, the bore 262 may comprise a funnel shape.

The tapered section 262 comprises a central axis which is co-incident with the gantry rotation axis 240. The first and second cylindrical portions 264, 266 may share this central axis. The bore 260 therefore has rotational symmetry about the gantry rotational axis 240.

The tapered section 262 comprises a substantially annular or ring-shaped wall 261. The annular wall 261 tapers from a first end of the tapered section, with a larger diameter, toward a second end of the tapered section, with a smaller diameter, to define the shape of the tapered section 262. The annular wall 261 may be described as a 'sloped', or 'angled', wall. As can be appreciated from figure 2c, as well as figures 3a-c, as a result of the tapered section 262 and (optionally) the cylindrical portions 264 and 266, the bore 260 becomes narrower in the direction the patient would be introduced into the device 200.

The shape of the bore 260 may be defined, wholly or in part, by the housing 270. The housing 270 comprises the substantially annular or ring-shaped wall 261, which defines the tapered section 262 of the bore. In an implementation comprising first and second cylindrical portions 264, 266, the housing 270 also comprises the first and second annular walls. In use, radiation passing along the radiation axis passes through the annular wall 261 of the housing as it travels toward the isocentre 214.

Advantageously, the isocentre 214 is located within the tapered section 262. This enables the beam-shaper-to-isocentre distance to be reduced when compared to device comprising a cylindrical bore. The device 200 may be configured such that the radiation axis 212 meets the tapered wall 261 at, or substantially at, 90°. Having the radiation axis 212 meet the tapered wall 261 at a perpendicular angle maximises space inside the bore 260 for a given beam shaper-to-isocentre distance.

The housing 270 is suitable for, and configured to, house the gantry and the components attached to it. The gantry is rotatable within the housing 270. The housing 270 is therefore stationary as the gantry rotates. The radiation beam, as it travels along the beam axis 212, passes through a wall of the housing 270. In the particular, the beam axis 212 passes through the sloped annular wall which defines the tapered section 262 of the bore 260. The housing 270 may also house other components, for example cooling components, one or more imaging apparatus, etc. The housing 270 may take several forms, and may comprise a hollow region in which the gantry and other components are located. The housing may comprise just a front fascia, and one or more substantially annular walls which define the bore 260. The housing 270 plays a role in improving patient comfort levels, as it prevents the patient from being able to see the radiation source as it rotates around them, which the patient might otherwise find alarming or disconcerting. The housing 270 also helps manage patient motion during treatment. Patients may need to remain still for accurate radiation delivery, and the housing 270 provides a structure to support immobilization devices and techniques.

The beam stopper 230 is coupled to the gantry at a position substantially opposite the source of radiation 210. The beam stopper is configured, and positioned, to intercept the beam of radiation 212 after it has passed through the isocentre 214. The beam stopper 230 acts to stop, block, or sufficiently attenuate the beam 212, which might otherwise be harmful to both patients and medical staff. In this way, the beam stopper 230 acts as a safety measure to prevent unnecessary exposure to radiation. The beam stopper 230 rotates with the gantry such that it is always located opposite the radiation source 210 throughout the gantry's range of rotation. The first cylindrical portion 264 of the bore 260 is advantageous since it provides the extra length required to introduce a beam stopper 230 at the appropriate place into the device 200, without unnecessarily increasing the width of the opening of the bore.

Traditionally, radiotherapy devices have cylindrical bores, which must be narrow enough to ensure the housing can house the gantry and the components coupled to the gantry. It has therefore been thought that a radiotherapy device comprising a short beam-shaper-to-isocentre distance -which is advantageous since a short distance provides a sharp penumbra of radiation in the treatment region -requires a narrow bore. Such a device comes with downsides, since the resulting bore may not be large enough to allow adequate rotation and re-positioning of the patient, for example so that a tumour or other target region of the patient's anatomy can be located at the isocentre. In this way, the number of available treatment sites is reduced. If such a device were to be additionally designed to deliver a non-coplanar beam of radiation, e.g. via adding a beam tilting functionality, the bore must become even narrower for a given beam-shaper-to-isocentre distance, resulting in a further reduction in the number of reachable treatment sites. Finally, adding a beam stopper on a machine with beam tilt makes the distance between the entrance of the bore and the isocentre longer, which again can reduce the number of treatment sites that can be reached. The device of the present disclosure addresses these problems by providing a tapered bore, with the isocentre positioned in the tapered section. The beam shaper can be brought close to the isocentre at the tapered section, while the wider end of the tapered section enables the patient to be easily maneuvered within the bore, thereby increasing the number of available treatment sites.

To make best use of this advantage, the beam shaping apparatus 220 may be positioned adjacent to the annular wall 261 of the tapered section 262. The beam shaping apparatus 220 may be positioned immediately adjacent to the annular wall 261, such that nothing is positioned between the beam shaper 220 and the annular wall 261. This is depicted in the figures (see e.g. figures 2a and 2b). A clearance of as low as 2cm between the beam shaper 220 and the tapered wall 261 is sufficient to enable to the beam shaper 220 to safely rotate with the gantry.

Figures 3a-c depict cross-sections through the radiotherapy device 200 described with respect to figures 2a-c. Figures 3a-c display the benefits of the bore described herein, by showing that a patient may be more easily rotated about a yaw axis and/or translated into the bore, for example via a patient positioning surface which forms part of the device. As can be seen in the figures, because the bore comprises a wider end, there is more room for the patient to be rotated, and for their position to be adjusted.

The patient positioning surface, PPS, may be configured to rotate about a yaw rotation axis. This yaw rotation axis may pass through the isocentre. With respect to the views shown in figures 3a-c, the yaw rotation axis is into the place of the diagram. The PPS has a central length axis, similar to the central length axis 115 shown in the PPS 114 described with respect to figure 1. Rotation of the PPS about the yaw rotation axis adjusts a yaw angle between the central length axis and the gantry rotation axis. The yaw angle may be substantially zero in figure 3a, but may be substantially 30 degrees in figure 3b. The yaw angle is measured in a substantially horizontal plane, i.e. the cross-sectional plane depicted in figures 3a-c.

In figure 3a, the patient is positioned to receive treatment at a target region located in their head, such as a brain tumour. Advantageously, the angle at which the target region may be presented to the radiation beam is adjustable, as can be appreciated from inspection of figure 3b. This functionality increases not only the number of treatment options available to clinicians for treating a particular tumour, but also the number of sites which may be treated.

At least part of the patient can be translated from the wider end of the bore, through the tapered section, and toward the narrower end. This increases the number of treatment sites which can be accessed, for example the patient's spine (see figure 3c), while ensuring that the beam shaper to isocentre distance of the device is relatively short. While a PPS is not depicted in figures 3a-c, it may have a central length axis such as that described with respect to the PPS 114 of figure 1, and the PPS may be further configured to translate in a direction parallel with its central length axis such that a patient positioned on the PPS may be translated into, and out from, the bore. Because the narrower end and the wider end of the bore are both open, i.e. because the bore is open-ended, the patient is less likely to feel enclosed, uncomfortable and claustrophobic while positioned in the bore, and the patient's comfort levels are thereby increased. Because the first and second end of the tapered section are open, at least part of the patient can be translated from the first end of the tapered section, through the tapered section, and through the second (narrower) end of the tapered section and into the second cylindrical portion.

While the benefits of improved patient positioning have been described primarily with respect to an improved angle of yaw rotation and degree to which the patient can be inserted into the bore, the skilled person will appreciate that a greater degree of patient positioning can be achieved in each of several degrees of freedom compared to a device with a narrow cylindrical bore, for example improved rotation in a pitch direction can be achieved, and greater range of lateral movement is enabled, for example the patient can be moved 'side to side' and also 'up and down' to a greater degree.

While the radiotherapy device depicted in figure 1 is an MR-linac, it should be understood that this invention is not limited to use with or incorporation with an MR-linac. The application relates to any suitable radiotherapy device, for example a traditional linac device. Such a device may comprise imaging apparatus enabling imaging modalities such as CT, CBCT, MR or the like; or the radiotherapy may be provided without any imaging functionality. Many benefits of the tapered bore, in particular, may be realised regardless of the imaging modality.

To summarise the advantages of certain examples described above, for dosimetric purposes it is advantageous to use a tilted beam line, i.e. to provide non-coplanar treatment, and to have the beam shaping apparatus close to the isocentre. This provides dose distributions with sharp gradients (or equivalently, narrow penumbra). In addition, a bore-type gantry is desirable for mechanical stability. To date, these advantages have been difficult to reconcile, since it was thought that such a device would require a very narrow bore, thus undesirably limiting the degree to which the patient can be moved and rotated within the bore, and undesirably reducing the number of sites in the body which may be treated. However, using a tapered (e.g. sloped) bore in a machine with a tilted beam enables the radius of the bore to be increased at the region where it is most impactful (i.e. the end in which the patient is introduced to the bore). This means the patient can be easily maneuvered. Because the isocentre is positioned in the tapered section of the bore, the beam shaper can still be positioned close to the isocentre, providing the dosimetric benefits described above. These multiple benefits are not limited to any particular type of radiotherapy machine or type of treatment, but are perhaps best realised when delivering radiotherapy to a patient's head and neck. In this case, the present device allows more flexibility to position the patient (e.g. wider range of lateral movement and rotations in the horizontal plane as depicted in figure 3b) when treating targets in the head, and treatment of centrally located targets (e.g. the spine) further down in the patient by positioning the patient with their head in the narrower part of the bore.

It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other implementations will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific example implementations, it will be recognized that the disclosure is not limited to the implementations described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims (24)

1. Claims 1. A radiotherapy device comprising: a rotatable gantry; a source of radiation coupled to the gantry and configured to deliver a non-coplanar beam of therapeutic radiation toward an isocentre; and a bore for receiving at least part of a patient, wherein the bore comprises a tapered section which tapers from a first, wider end toward a second, narrower end, and wherein the isocentre is located within the tapered section.
2. 2. The radiotherapy device of claim 1, wherein the tapered section is frustoconical.
3. 3. The radiotherapy device of claim 1 or claim 2, further comprising a housing which comprises the bore.
4. 4. The radiotherapy device of any preceding claim, wherein the tapered section is configured to receive the at least part of a patient.
5. 5. The radiotherapy device of claim 4, wherein the first end of the tapered section is for receiving the at least part of the patient.
6. 6. The radiotherapy device of claim 4 or claim 5, wherein the first end and the second end of the tapered section are open, such that the at least part of the patient can be translated from the first end, through the tapered section, and through the narrower end.
7. 7. The radiotherapy device of any preceding claim, the bore further comprising a first cylindrical portion which interfaces with the first end of the tapered section.
8. 8. The radiotherapy device of claim 7, the bore further comprising a second cylindrical portion which interfaces with the second end of the tapered section; wherein the first cylindrical portion has a first diameter and the second cylindrical portion has a second diameter, wherein the first diameter is greater than the second diameter.
9. 9. The radiotherapy device of any preceding claim, wherein the gantry is configured to rotate about a gantry rotation axis.
10. 10. The radiotherapy device of any claim 9, wherein the isocentre lies along the gantry rotation axis.
11. 11. The radiotherapy device of claim 9 or claim 10, wherein the source of radiation is configured to deliver the non-coplanar beam of therapeutic radiation along a beam axis, wherein the beam axis meets the gantry rotation axis at an acute angle.
12. 12. The radiotherapy device of claim 11, wherein the source of radiation is fixedly coupled to the gantry such that the acute angle is a fixed angle.
13. 13. The radiotherapy device of any of claims 9 to 12, wherein the tapered section comprises a central axis which coincides with the gantry rotation axis.
14. 14. The radiotherapy device of any preceding claim, the device further comprising a patient positioning surface, PPS.
15. 15. The radiotherapy device of claim 14, wherein the PPS is configured to rotate about a yaw rotation axis.
16. 16. The radiotherapy device of clam 14 or claim 15, wherein the PPS has a central length axis, and rotation of the PPS about the yaw rotation axis adjusts a yaw angle between the central length axis and the gantry rotation axis, wherein the yaw angle is measured in a substantially horizontal plane.
17. 17. The radiotherapy device of claim 16, wherein the yaw rotation axis passes through the isocentre.
18. 18. The radiotherapy device of claims 14 to 17, wherein the PPS has a central length axis, and the PPS is further configured to translate in a direction parallel with the central length axis such that a patient positioned on the PPS may be translated into the bore.
19. 19. The radiotherapy device of any preceding claim, further comprising a beam stopper coupled to the gantry at a position substantially opposite the source of radiation, the beam stopper being positioned to intercept the non-coplanar beam of therapeutic radiation after it has passed through the isocentre.
20. 20. The radiotherapy device of any preceding claim, wherein the tapered section is defined by an annular wall.
21. 21. The radiotherapy device of claim 20, further comprising a beam shaping apparatus positioned adjacent to the annular wall.
22. 22. The radiotherapy device of claim 20 or claim 21, wherein the non-coplanar beam of therapeutic radiation passes through the annular wall before reaching the isocentre.
23. 23. The radiotherapy device of any of claims 2D to 22, wherein the source of radiation is configured to deliver the non-coplanar beam of therapeutic radiation along a beam axis, and the beam axis meets the annular wall at a substantially perpendicular angle.
24. 24. The radiotherapy device of any preceding claim, wherein the at least part of the patient is the patient's head or neck.