GB2549916A

GB2549916A - Radiotherapeutic apparatus

Info

Publication number: GB2549916A
Application number: GB1713354.7A
Authority: GB
Inventors: Neil Bourne Duncan; Charles Knox Christopher
Original assignee: Elekta AB
Current assignee: Elekta AB
Priority date: 2011-03-30
Filing date: 2011-03-30
Publication date: 2017-11-01
Anticipated expiration: 2031-03-30
Also published as: GB201713354D0; GB2549916B

Abstract

Radiotherapeutic apparatus comprising: magnetic coils 16 disposed around a patient support 10 for creating a magnetic field, where the coils 16 have a longitudinal axis I and the magnetic field is created parallel to the longitudinal axis I; a radiation source 6 producing a beam of radiation directed toward the patient support 10 and which is mounted on a rotatable support 28 to rotate radiation source 6 around patient support 10; and a slip ring located around patient support 10 for conveying electrical power to radiation source 6 and where the slip ring is broken into a plurality of arc segments or contact points 88;and a plurality of power cables 70, each running from a respective arc segment 88 to a power source, with each power cable 70 comprising a section parallel to the longitudinal axis I and extending from its respective arc segment 88 to a point beyond the longitudinal extent of the coils 16. Rotatable support 28 may comprise at least one brush contact arranged to contact the slip ring to convey electrical power to the radiation source 6. Radiation source 6 may be a linear accelerator. The apparatus may further comprise a magnetic field detecting imaging means.

Description

Radiotherapeutic Apparatus

FIELD OF THE INVENTION

The present invention relates to apparatus for the delivery of radiotherapy.

BACKGROUND ART

Radiotherapeutic apparatus is well-known, and consists of a source of radiation which emits a beam of radiation that is directed toward a patient in order to destroy or otherwise harm cancerous cells within the patient. Usually, the beam is collimated in order to limit its spatial extent to a desired region within the patient, usually the tumour or a subsection of the tumour. The source can be a linear accelerator for high-energy (MV) x-radiation, or an isotopic source such as Co-60.

The source is often rotated around the patient in order to irradiate the desired region from a number of different directions, thereby reducing the dose applied to healthy tissue around the desired region. The shape of the defined desired region can change dynamically as the source rotates, in order to build up a complex dose distribution for tumours with more challenging shapes and/or which are located near to sensitive areas.

As the dose distribution becomes more closely tied to the exact shape of the tumour, and as the accuracy of the dose delivery improves, it has become necessary to know the current position of the patient, their internal organs, and the tumour with greater accuracy. As a result, low-energy x-ray sources are often provided on the apparatus in addition to the high-energy therapeutic source, to allow for x-ray or CT imaging of the patient before or during treatment. Portal imagers are often provided, which detect the therapeutic beam after attenuation by the patient. Both provide a degree of information as to the patient, but are subject to the inherent limitations of x-ray imaging, in particular the poor contrast obtained in areas of soft tissue. Generally, x-ray imaging is able to provide good contrast between areas of bone, soft tissue, and air, which allows for the detection of the gross patient position but has difficulty in detecting internal movements of the patient and the sub-structure within the soft tissue.

Efforts have therefore been directed towards combining a radiotherapy source with an MRI imager. MRI provides contrast within soft tissue, and is therefore suitable. However, there are significant practical problems in combining these two very different technologies.

SUMMARY OF THE INVENTION

One such practical problem is the delivery of power to the source. Linear accelerators have significant power demands, typically in the region of 10-14kW. Delivered via a standard 415V three-phase supply, this therefore involves current flows of up to 30A. Isotopic sources also need power in order to operate collimators and the like, although their current demands will usually be somewhat lower.

Given that the source needs to rotate around the patient, this power will usually be delivered by way of a slip ring arrangement. This involves conducting the current via an at least part-circumferential path around (or within) the MRI coils, which will create stray magnetic fields that interfere with the MRI field(s) and degrade the image quality.

The present invention therefore provides a radiotherapeutic apparatus comprising a patient support, magnetic coils disposed around the patient support for creating a magnetic field therewithin, wherein the magnetic coils have a longitudinal axis, and the magnetic field therewithin is parallel to the longitudinal axis, a radiation source producing a beam of radiation directed toward the patient support and mounted on a rotatable support thereby to rotate the radiation source around the patient support, a slip ring for conveying electrical power to the radiation source and located around the patient support, wherein the slip ring is broken into a plurality of arc segments, and a plurality of power cables, each running from a respective arc segment of the slip ring to a power source, each power cable comprising a section extending from its respective arc segment to a point beyond the longitudinal extent of the magnetic coils, the section being arranged parallel to the longitudinal axis.

The rotatable support can comprise at least one brush contact, arranged to contact the slip ring and thus convey electrical power to the radiation source.

The radiation source can be a linear accelerator.

An imaging means is ideally provided, for detecting the magnetic field and deriving an image therefrom.

In this way, power cabling adapted to carry currents of 25A or more can be brought to the radiation source without an adverse effect on the magnetic imaging system.

BRIEF 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 radiotherapy apparatus according to the present invention, combining an MRI and linear-accelerator;

Figure 2 shows a schematic arrangement of a second embodiment of the power supply cable for the radiation source of such an apparatus;

Figure 3 shows a longitudinal view of the second embodiment; and

Figure 4 shows a schematic arrangement of the elements making up a radiotherapy apparatus according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a system 2 according to embodiments of the present invention, comprising a radiotherapy apparatus 6 and a magnetic resonance imaging (MRI) apparatus 4.

The system includes a couch 10, for supporting a patient in the apparatus. The couch 10 is movable along a horizontal, translation axis (labelled "I"), such that a patient resting on the couch is moved into the radiotherapy and MRI apparatus. In one embodiment, the couch 10 is rotatable around a central vertical axis of rotation, transverse to the translation axis, although this is not illustrated. The couch 10 may form a cantilever section that projects away from a support structure (not illustrated). In one embodiment, the couch 10 is moved along the translation axis relative to the support structure in order to form the cantilever section, i.e. the cantilever section increases in length as the couch is moved and the lift remains stationary. In another embodiment, both the support structure and the couch 10 move along the translation axis, such that the cantilever section remains substantially constant in length, as described in our earlier patent application published as WO 2009/007737, the contents of which are incorporated by reference and to which the skilled person is referred for a full understanding of the described embodiment.

As mentioned above, the system 2 also comprises an MRI apparatus 4, for producing near real-time imaging of a patient positioned on the couch 10. The MRI apparatus includes a primary magnet 16 which acts to generate the so-called "primary" magnetic field for magnetic resonance imaging. That is, the magnetic field lines generated by operation of the magnet 16 run substantially parallel to the central translation axis I. The primary magnet 16 consists of one or more coils with an axis that runs parallel to the translation axis I. The one or more coils may be a single coil or a plurality of coaxial coils of different diameter. In one embodiment (illustrated), the one or more coils in the primary magnet 16 are spaced such that a central window 17 of the magnet 16 is free of coils. In other embodiments, the coils in the magnet 16 may simply be thin enough that they are substantially transparent to radiation of the wavelength generated by the radiotherapy apparatus. The magnet 16 may further comprise one or more active shielding coils, which generates a magnetic field outside the magnet 16 of approximately equal magnitude and opposite polarity to the external primary magnetic field. The more sensitive parts of the system 2, such as the accelerator, are positioned in this region outside the magnet 16 where the magnetic field is cancelled, at least to a first order.

The MRI apparatus 4 further comprises two gradient coils 18, 20, which generate the so-called "gradient" magnetic field that is superposed on the primary magnetic field. These coils 18, 20 generate a gradient in the resultant magnetic field that allows spatial encoding of the protons so that their position can be determined, for example the gradient coils 18, 20 can be controlled such that the imaging data obtained has a particular orientation. The gradient coils 18, 20 are positioned around a common central axis with the primary magnet 16, and are displaced from one another along that central axis. This displacement creates a gap, or window, between the two coils 18, 20. In an embodiment where the primary magnet 16 also comprises a central window between coils, the two windows are aligned with one another.

An RF system causes the protons to alter their alignment relative to the magnetic field. When the RF electromagnetic field is turned off the protons return to the original magnetization alignment. These alignment changes create a signal which can be detected by scanning. The RF system may include a single coil that both transmits the radio signals and receives the reflected signals, dedicated transmitting and receiving coils, or multielement phased array coils, for example. Control circuitry controls the operation of the various coils 16, 18, 20 and the RF system, and signal-processing circuitry receives the output of the RF system, generating therefrom images of the patient supported by the couch 10.

As mentioned above, the system 2 further comprises a radiotherapy apparatus 6 which delivers doses of radiation to a patient supported by the couch 10. The majority of the radiotherapy apparatus 6, including at least a source of radiation 30 (e.g. an x-ray source and a linear accelerator) and a multi-leaf collimator (MLC) 32, is mounted on a chassis 28. The chassis 28 is continuously rotatable around the couch 10 when it is inserted into the treatment area, powered by one or more chassis motors. In the illustrated embodiment, a radiation detector 36 is also mounted on the chassis 28 opposite the radiation source 30 and with the rotational axis of the chassis positioned between them. The radiotherapy apparatus 6 further comprises control circuitry, which may be integrated within the system 2 shown in Figure 1 or remote from it, and controls the radiation source 30, the MLC 32 and the chassis motor.

The radiation source 30 is positioned to emit a beam of radiation through the window defined by the two gradient coils 18, 20, and also through the window defined in the primary magnet 16. The radiation beam may be a cone beam or a fan beam, for example.

In other embodiments, the radiotherapy apparatus 6 may comprise more than one source and more than one respective multi-leaf collimator.

In operation, a patient is placed on the couch 10 and the couch is inserted into the treatment area defined by the magnetic coils 16, 18 and the chassis 28. The control circuitry 38 controls the radiation source 30, the MLC 32 and the chassis motor to deliver radiation to the patient through the window between the coils 16, 18. The chassis motor is controlled such that the chassis 28 rotates about the patient, meaning the radiation can be delivered from different directions. The MLC 32 has a plurality of elongate leaves oriented orthogonal to the beam axis; an example is illustrated and described in our EP-A-0,314,214, the content of which is hereby incorporated by reference and to which the reader is directed in order to obtain a full understanding of the described embodiment. The leaves of the MLC 32 are controlled to take different positions blocking or allowing through some or all of the radiation beam, thereby altering the shape of the beam as it will reach the patient. Simultaneously with rotation of the chassis 28 about the patient, the couch 10 may be moved along a translation axis into or out of the treatment area (i.e. parallel to the axis of rotation of the chassis). With this simultaneous motion a helical radiation delivery pattern is achieved, known to produce high quality dose distributions.

The MRI apparatus 4, and specifically the signal-processing circuitry, delivers realtime (or in practice near real-time) imaging data of the patient to the control circuitry. This information allows the control circuitry to adapt the operation of the MLC 32, for example, such that the radiation delivered to the patient accurately tracks the motion of the target region, for example due to breathing.

Clearly, the radiotherapy apparatus 6 will have a significant power consumption, mainly due to the need to power the linear accelerator 30, but also the collimator 32 and the like. This needs to be transmitted to the rotating chassis 28, which would normally be achieved via a slip ring. These consist of a number of longitudinally spaced conductive circular rings to which power is fed from a fixed connection and from which power is drawn via a brush contact that can slide (or slip) circumferentially around the ring. The brush contacts can be mounted on the chassis 28 and thus power is transmitted from a fixed supply to the rotating chassis. This allows the chassis to rotate continuously around the couch 10. The alternative, a flexible conduit linking the chassis 28 or the radiotherapy apparatus 6 to a fixed point, requires that there be limitations on the range of angular movement of the radiotherapy apparatus 6. A slip ring has the problem that the current drawn (even from a 415V supply) could have a significant disruptive effect on the magnetic fields produced by the primary coil 16 and the gradient coils 18, 20, if it is not properly controlled. The slip rings, by their nature, extend around the couch 10 and thus have a coil form and are capable of creating a magnetic field. Their coil strength is not large, but the currents flowing in them may be substantial and thus the magnetic field created by those currents may be significant relative to the magnetic fields being created by the primary coil 16 and the gradient coils 18, 20. This could therefore adversely affect the quality of the images produced by the MRI system.

Various aspects of the cable configuration could be changed.

Figures 2 and 3 show an embodiment of the invention. Instead of power being supplied by a single cable 50, it is supplied by an array of cables spaced along the path of the single cable 50 as it rotates. Cable 70 is supported by a rigid support (not shown, for clarity). Cable 72 is supported in a position alongside cable 70 in an arrangement that differs by a rotation of between 5° and 10° around the axis I from the arrangement of cable 70. Further cables 74, 76, 78, 80, 82 etc are placed in arrangements that are further rotated around the axis I so that a cage of longitudinally-extending cables extends around apparatus 2. Each cable is connected to the power supply 52 and terminates at an associated contact point 88 accessible to the radiotherapy apparatus 6. Thus, there are a series of contact points 88 spaced circumferentially around the apparatus, fed by power cables that extend in a longitudinal direction. As illustrated, the radiotherapy apparatus 6 has a short length of cable 90 extending radially outwardly to a pick-up 92 which makes electrical contact to one or more of the contact points 88. It is preferred that the pick-up makes contact to at least two contact points 88 so that there is a continuous electrical power supply to the radiotherapy apparatus 6 as it rotates.

Figure 4 shows the schematic arrangement of the system. A treatment planning system 100 is loaded with the desired dose distribution and the various apparatus constraints and produces a treatment plan consisting of beam shapes and doses to be delivered from specific rotational directions. This is passed to a control apparatus 102 which sends instructions to the radiotherapy apparatus 104 to rotate the linear accelerator 106 to the desired position using the drive motor 108 and set the collimator(s) 110 as required. The control apparatus 102 also instructs the MRI primary coils 112, gradient coils 114 and rf system 116 as required in order to obtain images of the patient prior to, during, and/or after treatment

Thus, embodiments of the invention are able to provide a satisfactory power supply to a rotating radiotherapy apparatus without at any time allowing current to be conducted in a circular path around the longitudinal axis.

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

Claims

1. Radiotherapeutic apparatus comprising; a patient support; magnetic coils disposed around the patient support for creating a magnetic field therewithin, wherein the magnetic coils have a longitudinal axis, and the magnetic field therewithin is parallel to the longitudinal axis; a radiation source producing a beam of radiation directed toward the patient support and mounted on a rotatable support thereby to rotate the radiation source around the patient support; a slip ring for conveying electrical power to the radiation source and located around the patient support, the slip ring broken into a plurality of arc segments; and a plurality of power cables, each running from a respective arc segment of the slip ring to a power source, each power cable comprising a section extending from its respective arc segment to a point beyond the longitudinal extent of the magnetic coils, the section being arranged parallel to the longitudinal axis.

2. The radiotherapeutic apparatus according to claim 1, wherein the rotatable support comprises at least one brush contact, arranged to contact the slip ring and thus convey electrical power to the radiation source.

3. The radiotherapeutic apparatus according to claim 1 or claim 2, wherein the radiation source is a linear accelerator.

4. The radiotherapeutic apparatus according to any one of the preceding claims further comprising an imaging means for detecting the magnetic field and deriving an image therefrom.

5. The radiotherapeutic apparatus according to any one of the preceding claims, wherein the power cabling is adapted to carry currents of at least 25 A.