Patent Publication Number: US-2021178191-A1

Title: Radiotherapy system

Description:
TECHNICAL FIELD 
     Embodiments of the present disclosure relate to medical methods and apparatus, and particularly to a medical apparatus comprising a radiotherapy system, and corresponding methods. 
     BACKGROUND 
     BackgroundRecent developments in the field of radiotherapy have focussed on integrating an imaging system with the therapeutic system. The goal is to provide real-time, or near real-time, feedback on the location of an anatomical feature within the patient (e.g. a tumour) such that a therapeutic radiation beam can be more accurately controlled to target that feature, or therapy can be halted if the radiation beam has become misdirected (for example). 
     One suggested approach is to combine a linear accelerator-based therapeutic system with a magnetic resonance imaging (MRI) system within a single apparatus, known as an MRI-Linac. Such apparatus is described in a number of earlier applications by the present Applicant, including U.S. patent application Ser. No. 12/704,944 (publication no 2011/0201918) and PCT publication no 2011/127947. In the systems described in these earlier applications, a patient can be imaged and treated substantially simultaneously while lying in the same position. 
     MRI systems comprise one or more coils for generating the strong magnetic fields on which the MRI process relies. For example, the system may comprise one or more coils for generating a primary magnetic field; and one or more coils for generating a gradient magnetic field that is superposed on the primary magnetic field and allows spatial encoding of the protons so that their position can be determined from the frequency at which resonance occurs (the Larmor frequency). In addition, an MRI system which is combined with a radiotherapy system may comprise one or more active shielding coils, which generate a magnetic field outside the MRI system of approximately equal magnitude and opposite polarity to the magnetic field generated by the primary magnetic coil. The more sensitive parts of the system (such as the radiation head) may be positioned in this region outside the coils where the magnetic field is cancelled, at least to a first order. The coils define a relatively narrow bore, in which the patient (or part of the patient) is placed during imaging. 
     Radiotherapy involves the delivery of highly energetic ionizing radiation to a target region within the patient (e.g. a tumour). The ionizing radiation damages or kills the cells in its path indiscriminately; healthy cells and tissues are damaged as well as non-healthy (e.g. cancerous) cells and tissue. Healthy cells are able to recover quicker than non-healthy cells, and this often leads to treatment being delivered in multiple, separate treatment sessions (known as “fractions”) to allow the healthy cells to recover in between treatment sessions. However, it is a general goal that radiation dosage to healthy cells should be minimized or avoided where possible, and thus the radiation beam should be shaped and delivered in an extremely accurate manner. 
     In order to achieve the accuracy required of radiotherapy, patients are often “set up” on the treatment bed or table by a trained clinician or therapist. This involves positioning the patient in a position which is most advantageous for delivering the radiation to the target without impacting surrounding healthy tissue. Various supports, restraints and radiation shields may be positioned on and around the patient to ensure that the patient is comfortable, that movement is minimized, and that the impact of any stray radiation on healthy tissue is reduced. 
     This presents a difficulty in combining a radiotherapy system with an MRI system, owing to the narrow bore of the MRI system. That is, conventional radiotherapy systems may have a relatively open area around the treatment table or bed, so that the patient can be set up in the same position as they will ultimately be treated in. However, that is not possible in MRI—radiotherapy systems, where the patient is positioned within a narrow bore during treatment. Thus the patient must be set up for treatment on a table or bed outside the bore (e.g. on a patient support), prior to that bed being transferred to the bore. 
     A system for transferring the patient from the patient support to the bore is therefore required. 
     SUMMARY 
     Embodiments of the present disclosure seek to alleviate or overcome some or all of these problems. 
     Conventional MRI systems already comprise a system for transferring the patient into the bore for imaging purposes, of course. In these conventional systems, the bed or table is provided with rollers (e.g. wheels) which move in corresponding grooves or guides provided in the patient support and the bore of the MRI system. While this approach assists in reducing the friction between the bed and the patient support or bore, it presents difficulties when that MRI system is combined with a radiotherapy system. 
     It is beneficial for radiotherapy to be carried out in a consistent, predictable environment. The treatment is usually delivered in accordance with a treatment plan, which requires significant time and computing resources to generate. The treatment planning process is usually based on a planning image taken of the target region, where the target itself and surrounding sensitive structures (i.e. healthy organs and tissue which are particularly sensitive to radiation) are identified. The goal of treatment planning is to generate a treatment plan in which radiation dose to the target is maximized (e.g. is at least a defined minimum amount of radiation), radiation dose to the sensitive structures is minimized (e.g. is no more than a defined maximum amount of radiation), and radiation dose to healthy tissue is otherwise minimized or reduced to the extent possible. The treatment planning process may further take into account the limitations and abilities of the apparatus which is to deliver the treatment to the plan (e.g. available radiation power, radiation field size, etc). The treatment plan so generated (or the radiation dose profile achieved by the treatment plan) is output for review by a clinician, who may make changes or apply further constraints, requiring further iterations of the treatment planning process. 
     In order to reduce the complexities of the treatment planning process, it is beneficial if the background provided by the radiotherapy system is relatively uniform, or at least consistent from one treatment to the next. That is, ideally there should be no structural components which interfere with the beam or provide a source of stray radiation reflections. If such structural components are necessary, however, they should be consistent from one treatment to the next, such that the treatment planning process can take account of them more easily. 
     The problems with the conventional MRI system will now be apparent. The bed may be moved by different amounts into the bore, to account for different treatments, different target regions, and different patient anatomies. The rollers on the bed thus provide a structural component which varies inconsistently from one treatment to the next, and from one patient to the next. 
     In one aspect, the present disclosure provides a radiotherapy system, comprising: a bed, for supporting the patient; and a bridge, comprising one or more rolling elements for supporting the bed and allowing the bed to be moved along a surface of the bridge. The one or more rolling elements are located at respective fixed positions in the bridge. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present disclosure, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the following drawings, in which: 
         FIG. 1  shows a side view of a combined radiotherapy and MRI system in cross-section according to embodiments of the present disclosure; 
         FIG. 2  is a plan drawing of an MRI bridge according to embodiments of the present disclosure; 
         FIG. 3  is a perspective view of one aspect of the MRI bridge according to embodiments of the present disclosure; 
         FIG. 4  shows a perspective cut-away view of a patient bed or table according to embodiments of the disclosure; and 
         FIG. 5  shows a perspective view of one aspect of the patient bed or table according to embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a schematic illustration of a combined radiotherapy and MRI system  100  according to embodiments of the present disclosure, showing a side view of the system in cross-section. 
     The system comprises a structure  102  defining a bore  104  in which a patient or part of a patient may be positioned during treatment. For example, the structure may comprise one or more coils  106  for generating a magnetic field as will be described in greater detail below. It will be noted that, as  FIG. 1  shows the system  100  in cross-section, the structure  102  and the coils  106  are shown both above and below the bore  104 . 
     A bed  108 , for supporting the patient, can be positioned within the bore  104 , and may be movable in a longitudinal direction into and out of the bore  108  to enable the patient to enter and exit the apparatus  100  before and after treatment. It will be understood that different terms may be used to describe the bed without departing from the scope of the claims appended hereto. For example, the bed  108  may also be called a table, or support. Use of the term “bed” herein does not imply that the corresponding apparatus must comprise a mattress or other cushioning, for example. The primary function of the bed is to support the patient and, as will be described below, move with the patient into the bore  104  of the MRI apparatus during use. 
     A patient support  124  may be provided to support the bed  108  outside the bore  104 . In some embodiments, the patient support  124  may comprise one or more mechanisms for raising or lowering the bed  108  (when positioned on the support). For example, the height of the bed may be lowered to allow the patient to access or exit the bed  108  more easily before and after treatment. For treatment, the bed may be raised to a height at which the bed  108  can be transferred to the bore  104 . 
     A suitable surface  116  is provided within the bore  104  to support the bed  108  while it is positioned within the bore. Such a surface may be known in the art as a bridge  116 , and this term will be used hereinafter. The bridge  116  thus supports the bed  108  while it is located within the bore  104 . The bridge  116  may also project outside the bore  104  to a limited extent, towards the patient support  124 , such that the gap between the patient support  124  and the bridge  116  is relatively small, allowing the bed a smoother transition in its transfer from the support  124  to the bridge  116  and vice versa. 
     A low-friction surface (for example, one or more rolling elements such as rollers) and a driving mechanism (such as a driving piston, or a pulley) may be provided in the patient support  124  and/or the bridge  116  to enable such movement. This aspect will be discussed in more detail below, with respect to  FIGS. 2 to 5 . 
     The system  100  further comprises a radiotherapy apparatus which delivers doses of radiation to a patient supported by the bed  108 . The radiotherapy apparatus comprises a radiation head  110  housing a source of radiation and a collimating device  112 , which together generate a beam of therapeutic radiation  114 . The source of radiation may take any suitable form (e.g. a radioactive source such as cobalt  60 , a linear accelerator possibly in conjunction with an x-ray source, etc), and the beam may be formed of any suitable ionizing radiation, such as x-rays, electrons or protons (for example). The radiation will typically have an energy which is capable of having a therapeutic effect in a patient positioned on the bed  108 . For example, a therapeutic x-ray beam may have an energy in excess of 1 MeV. 
     The collimating device  112  may be any device suitable for collimating the radiation beam to take a desired shape (for example, to conform to the shape of a target within the patient). In one embodiment, the collimating device may comprise a primary collimator and a second collimator. The primary collimator collimates the radiation to form a uniform beam shape (cone-, fan- and pyramid-shaped beams are known in the art), while the secondary collimator acts on the beam so collimated to adjust the shape to conform to the cross-sectional shape or a target within the patient, e.g. a tumour. In one embodiment, the secondary collimating device comprises a multi-leaf collimator, known to those skilled in the art. Such a device comprises one or more banks of elongate leaves (and typically comprises two such banks on opposite sides of the beam), with each leaf being individually moveable into and out of the radiation beam in order to block that part of the beam from reaching the patient. In combination, the leaves collectively act to shape the beam according to a desired cross-section. 
     The radiation head may be mounted on a chassis (not illustrated), and configured such that the radiation beam  114  is directed towards the patient. The chassis may be rotatable around an axis, with the point of intersection of the radiation beam with the axis being known as the “isocentre” of the apparatus. In this way, radiation can be directed towards a patient on the bed  108  from multiple directions, reducing the dose which is delivered to healthy tissue surrounding the target for treatment. 
     The system  100  further comprises an MRI apparatus, for producing images of a patient positioned on the bed  108 . The MRI apparatus includes one or more magnetic coils  106  which act to generate a magnetic field for magnetic resonance imaging. That is, the magnetic field lines generated by operation of the magnetic coil  106  run substantially parallel to the central axis of the bore. The magnetic coils  106  may consist of one or more coils with an axis that runs parallel to, or is coincident with the axis of rotation of the chassis. The magnetic coils may be split into first and second magnetic coils, each having a common central axis, but separated by a window which is free of coils. In other embodiments, the magnetic coils  106  may simply be thin enough that they are substantially transparent to radiation of the wavelength generated by the radiation head  110 . In yet further embodiments, the magnetic coils  106  may have a varying pitch, such that the pitch is relatively wide where the coils  106  intersect with the radiation beam  114 , and relatively narrow in one or more regions outside the radiation beam  114 . The magnetic coils may comprise one or more coils for generating a primary magnetic field; one or more coils for generating a gradient magnetic field that is superposed on the primary magnetic field and allows spatial encoding of the protons so that their position can be determined from the frequency at which resonance occurs (the Larmor frequency); and/or one or more active shielding coils, which generate a magnetic field outside the apparatus of approximately equal magnitude and opposite polarity to the magnetic field generated by the primary magnetic coil. The more sensitive parts of the system  100 , such as the radiation head  110 , may be positioned in this region outside the coils where the magnetic field is cancelled, at least to a first order. 
     The coils  106  may be arranged within the structure  102 , which can additionally contain a system for keeping the coils cool (e.g. a cryogenic system based on liquid helium or similar). 
     The MRI system may further comprise an RF system (not illustrated) having an RF transmitter/receiver coil (also known as an imaging coil), which is brought close to the patient during imaging, transmits radio signals towards the patient, and detects the absorption at those frequencies so that the presence and location of protons in the patient can be determined. 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 multi-element phased array coils, for example. The imaging coil may be affixed to the structure  102 , or positioned close to the patient by a clinician. 
     In use, the MRI system can provide real-time imaging of a patient undergoing therapy, allowing accurate targeting of the treatment volume by the radiation beam  114  (for example through altered collimation by the collimating device  112 ), or automated shutdown if the patient moves significantly. 
     The system  100  further comprises a control apparatus  122 , which is coupled to one or more components of the system  100  and controls their operation. The control apparatus will typically comprise a suitably programmed computing device (i.e. comprising processing circuitry configured to implement code stored in a computer-readable medium such as memory), but may also comprise dedicated electronic circuits. 
     The control apparatus  122  may be configured to control the operation of the radiotherapy parts of the system  100 . For example, the apparatus  122  may control the source of radiation to generate a beam of therapeutic radiation having a particular energy, or comprising a particular radiation type; the apparatus  122  may control the collimator device  112  to conform the radiation beam  114  to a particular shape; the apparatus  122  may control the gantry, in order to rotate the radiation head  110  to one or more angles, such as a suitable angle for treatment; the apparatus may control movement of the bed  108  to a desired position for treatment of the patient. 
     The control apparatus  122  may also control the MRI parts of the system  100  so as to provide imaging information of the treatment volume of the patient. For example, the control apparatus  122  may control the magnetic coil  106  to generate a magnetic field of a certain strength, and a certain gradient; and the control apparatus  122  may control the imaging coil device to generate RF signals. 
     The control apparatus  122  may also control those parts of the system  100  relating to the position and movement of the bed  108 . For example, the control apparatus  122  may control the patient support to take a particular height; the control apparatus  122  may control the driving mechanism controlling the movement of the bed  108 . 
       FIG. 2  is a plan view of the bridge  116  according to embodiments of the disclosure. 
       FIG. 3  shows one aspect of the bridge  116  in more detail. 
     According to embodiments of the disclosure, the bridge  116  comprises one or more rolling elements  202 ,  204 . Note that this stands in contrast to conventional MRI systems, where rollers are provided in the bed and not the bridge. According to embodiments of the disclosure, rolling elements are provided in the bridge  116  (and potentially also the patient support  124 , see below) but not in the bed  108 . The bed  108  moves over the rolling elements  202 ,  204  (and in some cases is supported by them) in order to transport a patient into and out of the bore  104 . 
     The rolling elements are provided in fixed positions within the bridge  116 , and thus provide a consistent background for treatment planning purposes.  FIG. 2  further shows a radiation window or volume  210  through which the radiation beam  114  can pass when the radiotherapy apparatus is active. Note that the radiation window  210  may define a volume between two parallel planes, to account for the different directions the radiation beam may be directed in when the gantry is rotatable. In the illustrated embodiment, the rolling elements  202 ,  204  are arranged outside the radiation window  210 , so that the radiation beam  114  does not interact with the rolling elements and stray reflections of the radiation are reduced or minimized. In such embodiments, the rolling elements  202 ,  204  may be provided in positions which are adjacent to the radiation window  210 , but not inside the radiation window  210 , so that the bed  108  is firmly supported within the radiation window  210  (where accuracy of positioning is most important). In other embodiments, the rolling elements may be arranged within the radiation window  210  as well as outside the radiation window  210  (in which embodiments the fixed rolling elements still provide the benefit of a consistent background to the radiation). 
       FIG. 3  shows the arrangement of the rolling elements  202 ,  204  in more detail. It can be seen from the illustrated embodiment that first rolling elements  202  and second rolling elements  204  may be provided. The first rolling elements  202  are recessed into an upward-facing surface  206  of the bridge  116 , but project from that surface to provide the low-friction surface on which the bed  108  will move. The first rolling elements  202  are thus positioned beneath, and bear the weight of, the bed  108  during use. The first rolling elements  202  may be rotatable around an axis that lies parallel to the upward-facing surface  206  (and to the main upward-facing surface of the bed  108 ), and perpendicular to the direction of motion of the bed  108 . 
     The second rolling elements  204  are provided in a side-facing surface  208 , which lies perpendicular to the upward-facing surface  206 , such that the side-facing surface and the upward-facing surface together form a stepped profile. The second rolling elements  204  are also recessed into the side-facing surface  208 , but project from that surface to provide a low-friction surface which acts to guide the bed  108  in its movement between the patient support  124  and the bridge  116 . Thus, in contrast to the first rolling elements  202 , which bear the weight of the bed  108  during use, the second rolling elements  204 , together with the side-facing surface  208 , act to guide the motion of the bed between the patient support  124  and the bridge  116 . The second rolling elements  204  may be rotatable around an axis that lies parallel to the side-facing surface  208 , and perpendicular to the direction of motion of the bed  108  and the upward-facing surface  206 . 
     It is noted here that there is only one possible orientation of the patient support  124 , the bridge  116  and the bed  108 , in that the bed  108  must support a patient undergoing therapy, while the patient support  124  and the bridge  116  support the bed  108  (not necessarily at the same time). Thus there is a defined “upward” direction, which takes its conventional meaning with respect to gravity. Side-facing directions similarly have a conventional meaning, and can be defined relative to the upward direction (i.e. in that a side-facing direction may be defined as being transverse or, in some cases, perpendicular to the upward direction). 
       FIG. 2  shows the arrangement of rolling elements  202 ,  204  according to some embodiments. Thus the first rolling elements  202  may be arranged in pairs comprising one rolling element positioned at or near an edge of the bridge  116 , and another rolling element positioned at a corresponding position at or near the opposing edge of the bridge  116 . The bridge may comprise multiple such pairs of first rolling elements  202 . Similarly, the second rolling elements  204  may be arranged in pairs comprising one rolling element positioned at or near an edge of the bridge  116 , and another rolling element positioned at a corresponding position at or near the opposing edge of the bridge  116 . The bridge may comprise multiple such pairs of second rolling elements  204 . 
       FIG. 4  shows, in cut-away cross section, a bed  108  according to embodiments of the disclosure.  FIG. 5  shows an aspect of the bed  108  in greater detail. It will be understood by those skilled in the art that  FIG. 5  shows only one side of the bed  108 . A corresponding structure is provided on the opposing side of the bed  108 . 
     It will be seen that the bed  108  comprises a stepped profile which is complementary to the stepped profile of the bridge  116  described above with respect to  FIG. 3 . Thus, the bed comprises a downward-facing surface  306 , which engages with the first rolling elements  202  during use. In particular, as described above, the weight of the bed  108  is borne through the engagement of the downward-facing surface  306  with the first rolling elements  202 . The bed further comprises an inward side-facing surface  308 , which engages with the second rolling elements  204  during use. The interaction of the side-facing surface  208  with the second rolling elements  204  acts to guide the bed  108  in its motion between the patient support  124  and the bridge  116 . In particular, the bed is permitted to move in a longitudinal direction, defining the movement of the bed  108  between the patient support  124  and the bridge  116 , but is restricted by the interaction of the side-facing surface  308  with the second rolling elements  204  (and the interaction of a corresponding side-facing surface with second rolling elements on the opposing side of the bridge  116 ) from moving in a direction which is transverse or lateral to the longitudinal direction. 
     Different stepped profiles to those shown in  FIGS. 3 and 5  may be provided without departing from the scope of the claims appended hereto. For example, alternative stepped profiles may comprise a groove or channel in the bed  108 , within which the rolling elements of the bridge  116  or patient support  124  can be received. 
     It will further be noted from  FIG. 4  that a central portion  302  of the bed  108  (on which the patient rests during use) has a substantially uniform thickness. Thus the bed  108  presents a substantially consistent object which can be accounted for (or neglected) in the treatment planning process. 
     The rolling elements may comprise rollers (as illustrated), or any other suitable rolling mechanism. For example, the rolling elements may comprise ball bearings held in a fixed position but allowed to rotate. 
     The above description has focussed on rolling elements  202 ,  204  provided in the bridge  116 . However, it will be understood that similar arrangements of rolling elements may be provided in the patient support  124 . Thus, the arrangement of rolling elements shown in  FIGS. 2 and 3  may also be provided in the patient support  124 , to allow easy movement of the bed  108  from the patient support and on to the patient support  124 . 
     The present invention thus provides a radiotherapy system in which rolling elements are provided in the bridge, to facilitate movement of a bed within the system (e.g. between a patient support and the bridge). 
     Those skilled in the art will appreciate that various amendments and alterations can be made to the embodiments described above without departing from the scope of the invention as defined in the claims appended hereto.