GB2558593A

GB2558593A - Cranial radiotherapy apparatus

Info

Publication number: GB2558593A
Application number: GB1700312.0A
Authority: GB
Inventors: Carlsson Per
Original assignee: Elekta AB
Current assignee: Elekta AB
Priority date: 2017-01-09
Filing date: 2017-01-09
Publication date: 2018-07-18
Anticipated expiration: 2037-01-09
Also published as: GB2558593B; GB201700312D0

Abstract

A radiotherapy apparatus 10 and method is claimed. The apparatus 10 comprising a treatment radiation source 20 ( which may comprise a linear accelerator), a magnetic resonance imaging (MRI) device 24 located in proximity to but outside the radiation field of the radiation source 20, and a moveable patient support 30 for supporting and translating a patient between a position in which a selected treatment area of the patient is capable of being imaged by the MRI device 24 (figure 1) and a position in which the selected treatment area is capable of receiving radiation from the radiation source 20 (figure 2). The apparatus 10 may include electromagnetic shielding for isolating the radiation source 20 and the MRI device 24.

Description

(54) Title of the Invention: Cranial radiotherapy apparatus Abstract Title: Cranial Radiotherapy Apparatus (57) A radiotherapy apparatus 10 and method is claimed. The apparatus 10 comprising a treatment radiation source 20 (which may comprise a linear accelerator), a magnetic resonance imaging (MRI) device 24 located in proximity to but outside the radiation field of the radiation source 20, and a moveable patient support 30 for supporting and translating a patient between a position in which a selected treatment area of the patient is capable of being imaged by the MRI device 24 (figure 1) and a position in which the selected treatment area is capable of receiving radiation from the radiation source 20 (figure 2). The apparatus 10 may include electromagnetic shielding for isolating the radiation source 20 and the MRI device 24.

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-1Cranial radiotherapy apparatus

FIELD OF THE INVENTION

The present invention relates to radiotherapy apparatus especially for, but not limited to, the treatment of tumours within the human head.

BACKGROUND ART

It has long been a challenge to provide radiotherapy to sites within the human head.

Since the stereotactic frame was developed by Lars Leksell in the late 1940s, and the development of the gamma knife, it has been an aim to provide radiotherapy doses to locations within the human head. The head has an unusually high concentration of vital and sensitive organs, such as the brain, the optic nerves, etc.. Thus, it is especially important when providing radiotherapy doses to the head that the doses are directed accurately.

Our earlier invention, disclosed in US 7729473, has a gamma knife arrangement with an investigative radiation source for generating a volumetric image, the gamma knife and investigative radiation source being spaced apart by a known distance so that a patient can be moved in between imaging and treatment positions. The patient can thus be moved so that the convergence point of the gamma knife is in the correct location for treatment, thanks to the volumetric image provided by the investigative radiation source.

The investigative radiation source set out by US 7729473 is an x-ray imaging system.

SUMMARY OF THE INVENTION

The present invention is directed to a radiotherapy apparatus having a treatment 25 radiation source, a magnetic resonance imaging device in proximity to but outside the radiation field of the treatment radiation source, and a moveable patient support for

-2supporting and translating a patient between a position in which a selected treatment area of the patient is capable of being imaged by the imaging device and a position in which the selected treatment area is capable of receiving radiation from the treatment radiation source.

This arrangement enables the use of recent imaging data, such as for the evaluation of organ and tumour or other disease status, in the treatment of a tumour or other disease. Thus, a treatment plan can be checked against an up-to-date image, so as to account for intra-tumour changes or haemorrhage and for adaptive planning in multi-fraction treatments.

An adapted plan could take into account, for example, tumour shrinkage. In addition a recent image could alert a medical professional to any potential problems such as haemorrhage.

An image can be taken before treatment, after treatment, or in a pause within a treatment session or fraction.

In existing treatment centres, obtaining a magnetic resonance (MR) image may require physically moving a patient from one department to another (in different parts of a hospital, for example). Workflow obstacles may thus result in significant delays between images being obtained and a treatment fraction being applied to the patient. This will also result in the patient being in a different position on the support.

The present invention thus smooths workflow paths, improving efficiency and reducing costs. The MR imaging equipment may also be used for imaging only - i.e. without a treatment phase - in facilities which lack an existing MR installation or where existing MR resources are stretched.

The treatment radiation source may be mounted on a first rotatable gantry.

The treatment radiation source is preferably a linear accelerator. The treatment source may be provided with a multi-leaf collimator. A second gantry may be provided opposite the first gantry, and a radiation detector may be provided on the second gantry in a position opposite and in line with the treatment radiation source.

The treatment radiation source may alternatively be based on radioactive isotopes. For example, the treatment radiation source may be a gamma knife.

-3The MR imaging device may be sized so that it is capable of imaging the head of the patient only. An advantage of such a size is that the imaging device may be located close to but outside the radiation field of the radiation source. Such a location enables the time delay between an image being made and irradiation to be minimised as far as possible, while also enabling the imaging device and radiation source to be operated without mutual interference. Furthermore, it is advantageous to minimise the distance moved by the selected treatment area between imaging and irradiation, so that the accuracy of the data from the imaging device is maximised at the time that irradiation takes place.

The radiotherapy apparatus may further be provided with electromagnetic shielding, for example a Faraday cage, which isolates the treatment radiation source and the MR imaging device. Shielding aims to ensure that electromagnetic noise from the treatment radiation source does not interfere with the imaging device or that low energy stray and scatter radiation from the treatment radiation source does not interfere with the MR imaging device.

The one or both rotatable gantries may be fixed to a drum or ring - referred to as a gantry base - which is rotated by a motor, so that the motor in turn moves the one or both rotatable gantries. The MR imaging device may be located at least partially within the drum or ring or gantry base. This arrangement allows a compact configuration, and also may reduce the difficulty of equipping an existing radiotherapy room with the apparatus of the present invention. The MR imaging device may be located substantially co-axially with respect to the gantry base; and the MR imaging device may be fixed to a non-moving support through an axial aperture of the gantry base.

The gantry base may be rotated continuously in either direction or kept still at a static position either during radiation or when radiation is paused. The gantry base (and thus the one or more gantries) may preferably have a pre-determined position during MR imaging for minimal interference between first gantry and the magnetic field inside the MR imaging device. The MR imaging device may be shimmed so that when the first gantry is in a pre-determined position the magnetic field of the MR imaging device is optimised. Thus, when the first gantry is in such a pre-determined position, the magnetic field of the MR imaging device is known to be optimised. Thus, any potential interference of the magnetic field of the MR imaging device by the treatment radiation source and related equipment is minimised and corrected for.

-4Thus, the moveable patient support may be adapted to translate a patient so that the patient's head is positioned within the gantry base, for MR imaging. The moveable patient support may further be adapted to translate a patient so that the patient's head is positioned entirely outside the gantry base, for receiving radiation from the radiation source.

The patient support may be moveable in a linear translation or a rotational translation, or a combination of the two. For example, a movement could be put into effect by movement of the patient support along track, and the track could be straight or curved. The important factor is that the patient remains in position on the patient support during the imaging and treatment phases, and during the transition between them. Thus, the position of the patient is known to be substantially the same throughout.

The patient support may be provided with fiducial location markers, visible to an imaging device, so that the location of the patient support can be verified. Such fiducial markers may be given a specific shape to aid recognition on an image produced by the imaging device. Alternatively (or in addition) the patient support may be constructed with distinctive features visible to the imaging device.

There may be a bridge or a separate support located close to the MR front to enable the translation distance from the positioning system to the MR. The bridge may have a guiding or docking device to enable accurate patient support positioning inside the MR despite large variations in patient weights that may occur. The bridge or support may also be adjustable in height if for example different imaging positions is desirable.

Alternatively, the radiotherapy apparatus may be arranged with an MR imaging device substantially at an end of the one or both gantries away from the gantry base. In such an arrangement, the MR imaging device and the gantry base are spaced apart by substantially the length of the one or both gantries. The patient support may thus translate a patient between a position in which the patient's head is within the MR imaging device and a position in which the patient's head is outside the MR imaging device.

The MR imaging device is preferably capable of having its magnetic field switched on and switched off relatively quickly. Preferably the magnetic field is only switched on when it is required, namely when imaging is desired, and switched off when treatment is taking place. Desirably, the switching on and off of the magnetic field can be done quickly, to minimise the

-5delay between the imaging stage and the treatment stage, for the reasons set out above. The switching on and off of the magnetic field may be achieved by powering on and off the MR imaging device itself, or by using shielding.

Alternatively the treatment radiation and MR imaging systems can be RF isolated from each other using a Faraday cage surrounding the magnet and leaving the linear accelerator parts outside the cage.

Alternatively the distance between treatment and the magnetic field of the MR imagine device is such that the decay and the level of the magnetic field means that any MR interference has a minimal effect on the dose delivered to the patient.

A second imaging device may be provided, which is suitable for imaging areas within the radiation field of the radiation. The second imaging device may be a computed tomography (CT) scanner or cone beam CT (CBCT) scanner.

The first gantry may be arranged so that radiation source projects its radiation so that a beam axis of the radiation is substantially orthogonal to an axis of rotation of the gantry (generally co-axial with both the torso of the patient and the drum), so that radiation is projected in substantially a single plane. Alternatively, the radiation source may direct its radiation at an acute angle to the axis of rotation of the gantry. Such an angle may be substantially fixed, or may be variable during a treatment. Setting an acute angle between the beam axis and the axis of rotation reduces the coincidence of opposite-directed beams, thus delivering a dose fall-off within the xy plane. Our co-pending UK patent application no. 1505877.9 describes this arrangement in more detail.

If a second imaging device is provided, the components of it may also be attached to the first or second gantry.

The present invention also relates to a method of applying radiotherapy to a patient comprising the steps of locating a patient on a moveable patient support, translating the patient into a position in which a selected treatment area is capable of being imaged by a magnetic resonance imaging device, obtaining a magnetic resonance volumetric image of the selected treatment area, translating the patient into a position in which the selected treatment area is capable of being receiving radiation from a radiation source comprising a linear accelerator, and applying radiation from the radiation source.

-6BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which;

Figure 1 shows a section of a radiotherapy apparatus, in which a patient is positioned 5 so that his head can be imaged;

Figure 2 shows a section of a radiotherapy apparatus, in which a patient is positioned so that his head can be treated; and

Figure 3 shows a section of a radiotherapy apparatus in perspective, in which a patient is positioned so that his head can be imaged.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to Figures 1 to 3, a radiotherapy apparatus 10 is provided. This has an annular gantry base 12 from which extend a first gantry 14 and a second gantry 16, the first 14 and second 16 gantries being substantially equally spaced apart from and parallel to an axis 18 around which the gantry base 12 is rotateable, carrying the two gantries with it. Thus, in the figures the apparatus is shown with the first gantry 14 uppermost and the second gantry 16 lowermost, but the gantry base 12 can be rotated as desired to position the gantries at any desired angular location. A linear accelerator (linac) 20 is mounted on the first gantry 14 and directed towards the axis 18 so that it issues a beam of radiation which intersects with the axis 18. A collimator set 21 is provided on the linac 20 in order to shape the beam to a desired cross-section in accordance with known dose delivery techniques. A radiation detector 22 is pivotally mounted on the second gantry 16, diametrically opposite the linac 20. At an end of the gantries 14 and 16 away from the gantry base 12 and substantially adjacent the gantries 14 and 16 is located a magnetic resonance (MR) imaging device 24. The MR imaging device 24 has a substantially cylindrical inner surface 26 whose axis is substantially co-axial with the axis 18 of the gantry base 12.

A patient support 30 is provided, on which a patient 32 may lie. The patient support 30 can be arranged so that the head 34 of the patient 32 is substantially in line with the axis 18 of the gantry base 12 and thus also of the MR imaging device 24. The patient support 30 is itself supported by and moveable relative to a support track 36. The support track 36 is

-7adjustable in height (and preferably other degrees of freedom) so that the head 34 of the patient 32 can be raised and lowered into a desired position as mentioned earlier, so that the head 34 is substantially in line with the axis 18 of the gantry base and MR imaging device 24. A support of the table top 37 can also be applied at the MR front in order to enable a thinner overlay and still have accurate positioning versus the MR.

The patient support 30 can be moved axially relative to the support track 36, so that the patient can be moved axially relative to the gantries 14 and 16 and the MR imaging device 24.

To protect the MR imaging device 24 from electromagnetic interference as well as stray fields generated by the linac 20 and its ancillaries, shielding 28 is provided between them in order to establish a faraday cage-like structure. This is in the form of a Copper or Aluminium tube centred on the axis 18 around the patient support 30, with a wide flange 28a at an end adjacent the MR imaging device 24. The conductive Copper or Aluminium provides the necessary shielding but is of a sufficiently low atomic number that its interaction with the beam produced by the linac 20 is within acceptable ranges. Alternatively, apertures could be provided in the Aluminium tube to allow unhindered passage of the beam, or the tube could be made sufficiently short that the beam does not need to pass through it. Aluminium or Copper is also non-ferromagnetic and thus presents less of a hazard when in close proximity to the MR imaging device.

The gantry base 12 is mechanised so that it can be rotated about its axis 18, thus allowing the gantries 14 and 16 to be rotated about the axis 18. The linac 20 can be moved during rotation of the gantry base 12 and gantries 14 and 16 to vary the angle with which it meets the axis 18. The radiation detector 22 can be moved correspondingly during rotation of the gantry base 12 and gantries 14 and 16. The pivotal mounting of the linac 20 and the radiation detector 22 enables them to be moved to mutually corresponding positions, so that the radiation detector 22 can detect at least part of the beam emitted by the linac 20 which has not been scattered or absorbed by a patient.

In use, a patient 32 lies down on the patient support 30 with his or her head away from the gantry base 12 and towards the MR imaging device 24. The height of the patient support 30 may be varied by adjusting the height of the support track 36 so that the head 34

-8of the patient 32 is substantially in line with the axis 18 of the gantry base 12 and MR imaging device 24.

When imaging of the head 34 is desired, the patient support 30 may be positioned by moving the patient support 30 along the support track 36 so that the head 34 is within the

MR imaging device 24, as shown in Figures 1 and 3. The first gantry 14 is in a pre-determined position in which the MR imaging device has been shimmed so as to optimise the magnet field homogeneity.

When treatment of the head 34 is desired, the patient support 30 may be positioned by moving the patient support 30 along the support track 36 so that the head 34 is in a position outside the MR imaging device 24 and wherein the part of the head 34 to be treated is in line with a radiation beam 38 generated by the linac 20, as shown in Figure 2. The radiation beam 38 will typically be collimated to a desired shape 40 within its maximum field 42 in order to deliver the prescribed dose profile.

In a position opposite the linac 20 is provided a radiation detector 22 which in use can detect the level of radiation which remains in the beam 38 after it has passed through or been scattered by the patient 32, and may also absorb any remaining radiation so that it does not escape. Alternatively, or in addition, a beam stop can be provided at this location.

It will of course be understood that many variations may be made to the abovedescribed embodiment without departing from the scope of the present invention.

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Claims

A radiotherapy apparatus having a treatment radiation source, a magnetic resonance imaging device in proximity to but outside the radiation field of the radiation source, and a moveable patient support for supporting and translating a patient between a position in which a selected treatment area of the patient is capable of being imaged by the imaging device and a position in which the selected treatment area is capable of receiving radiation from the radiation source.

A radiotherapy apparatus according to claim 1, in which the patient support may be translated linearly.

A radiotherapy apparatus according to claim 1, in which the patient support may be translated rotationally.

A radiotherapy apparatus according to any preceding claim, in which the patient support is supported by an additional support structure

A radiotherapy apparatus according to any preceding claim, wherein the treatment radiation source is mounted on a first gantry, and the first gantry is rotatable around a treatment axis.

A radiotherapy apparatus according to any preceding claim, wherein the first gantry is positioned in a pre-determined position during MR imaging.

A radiotherapy apparatus according to any preceding claim, in which the treatment radiation source is mounted on the first gantry so as to direct a beam of therapeutic radiation toward the treatment axis.

A radiotherapy apparatus according to any preceding claim, wherein the magnetic resonance imaging device is located on the treatment axis, displaced therealong relative to the treatment radiation source.

-109. A radiotherapy apparatus according to any preceding claim, wherein the magnetic resonance imaging device is sized so that it is capable of imaging the head of the patient only.

10. A radiotherapy apparatus according to any preceding claim, further comprising

5 electromagnetic shielding for isolating the treatment radiation source and the magnetic resonance imaging device.

11. A radiotherapy apparatus according to any preceding claim, wherein a second imaging device is provided, which is suitable for imaging areas within the radiation field of the radiation source.

10 12. A radiotherapy apparatus according to claim 11 in which the second imaging device is a CT imaging device.

13. A radiotherapy apparatus according to any preceding claim, wherein the first gantry is attached to a drum.

14. A radiotherapy apparatus according to claim 13, wherein the MR imaging device is

15 located substantially co-axially with respect to the drum and the MR imaging device is fixed to a non-moving support through an axial aperture of the drum.

15. A method of applying radiotherapy to a patient comprising the steps of

- locating a patient on a moveable patient support;

- translating the patient into a position in which a selected treatment area is

20 capable of being imaged by a magnetic resonance imaging device;

- obtaining a magnetic resonance volumetric image of the selected treatment area;

- translating the patient into a position in which the selected treatment area is capable of being receiving radiation from a radiation source comprising a linear

25 accelerator; and

- applying radiation from the radiation source.

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Amendments to the Claims have been filed as follows:CLAIMS

1. A radiotherapy apparatus having a treatment radiation source, a magnetic resonance imaging device sized to be capable of imaging the 5 head of a patient only, located in proximity to but outside the radiation field of the radiation source, a linearly moveable patient support for supporting and translating a patient between a position in which a selected treatment area of the patient is capable of being imaged by the imaging device and a position in which the

10 selected treatment area is capable of receiving radiation from the radiation source, and electromagnetic shielding for isolating the treatment radiation source and the magnetic resonance imaging device.
2. A radiotherapy apparatus according to claim 1, in which the patient support may be

15 translated rotationally.
3. A radiotherapy apparatus according to any preceding claim, in which the patient support is supported by an additional support structure
4. A radiotherapy apparatus according to any preceding claim, wherein the treatment radiation source is mounted on a first gantry, and the first gantry is rotatable around

20 a treatment axis.
5. A radiotherapy apparatus according to any preceding claim, wherein the first gantry is positioned in a pre-determined position during MR imaging.
6. A radiotherapy apparatus according to any preceding claim, in which the treatment radiation source is mounted on the first gantry so as to direct a beam of therapeutic

25 radiation toward the treatment axis.
7. A radiotherapy apparatus according to any preceding claim, wherein the magnetic resonance imaging device is located on the treatment axis, displaced therealong relative to the treatment radiation source.
8. A radiotherapy apparatus according to any preceding claim, wherein a second imaging device is provided, which is suitable for imaging areas within the radiation field of the radiation source.
9. A radiotherapy apparatus according to claim 8 in which the second imaging device is

5 a CT imaging device.
10. A radiotherapy apparatus according to any preceding claim, wherein the first gantry is attached to a drum.
11. A radiotherapy apparatus according to claim 10, wherein the MR imaging device is located substantially co-axially with respect to the drum and the MR imaging device

10 is fixed to a non-moving support through an axial aperture of the drum.

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Application No: GB 1700312.0