Patient positioning device for a radiotherapy system

Abstract

A method for calibrating a radiotherapy positioning device having a patient support surface movable by a mechanism, the method comprising obtaining outputs of a patient support surface position sensor and a mechanism position encoder at a plurality of positions of the support surface and using the outputs to determine a relationship between the sensor and encoder outputs.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to apparatuses, devices, systems and methods for radiotherapy, in particular, but not exclusively, apparatuses and / or systems for patient positioning. BACKGROUND

[0002] Radiotherapy can be described as the treatment of the human or animal body using ionising radiation, such as X-rays. Radiotherapy is commonly used to treat tumours in a human or animal patient or subject. In such treatment, the cells making up part of the tumour are destroyed or damaged by irradiation with ionising radiation.

[0003] Precise control of the patient position is very important for effective radiotherapy. The patient is moved to a desired position using a complex patient positioning system in order to be irradiated appropriately by the treatment beam. In some systems, the patient can be translated and rotated in multiple possible dimensions of movement. In combination with a treatment plan and a moveable treatment beam, this approach allows optimisation of the delivery of radiation to the tumour and can minimise the amount of healthy tissue exposed to radiation. SUMMARY

[0004] The invention is described in the claims. BRIEF DESCRIPTION OF DRAWINGS

[0005] Reference will now be made, by way of example only, to the accompanying drawings in which:

[0006] Figure 1 A radiotherapy system is shown;

[0007] Figure 2 A patient positioning apparatus in a first configuration is shown;

[0008] Figure 3 A patient positioning apparatus in a second configuration is shown; Figure 2

[0009] Figure 4 A schematic view of a patient support surface is shown;

[0010] Figure 5 A method for calibrating a patient positioning apparatus is shown;

[0011] Figure 6 A method for calibrating a patient positioning apparatus is shown;

[0012] Figure 7 A rotatable patient support surface is shown; and

[0013] Figure 8 A method for calibrating a patient positioning apparatus is shown. DETAILED DESCRIPTION

[0014] ​Figure 1 A radiation therapy system or device is shown that is adapted to deliver and configured to deliver a radiation beam to a patient during radiation therapy. To provide useful attendant information to the present disclosure, a generalized description of the device and its constituent components will be provided. Figure 1 A device according to the present disclosure is shown and is adapted for use with the disclosed systems and apparatuses. While Figure 1 The device in is a magnetic resonance linac (MR-linac), but embodiments of the present disclosure can be any radiation therapy device, such as a linac device.

[0015] Figure 1 The device 100 shown is a magnetic resonance linac. The device 100 includes a magnetic resonance imaging apparatus 112 and a radiation therapy (RT) apparatus that can include a linac device. The magnetic resonance imaging apparatus 112 is shown in partial cutaway perspective in the figure. In operation, the magnetic resonance scanner produces magnetic resonance images of a patient, the linac apparatus produces and shapes a radiation beam according to a radiation therapy plan, and directs it to a target region within the patient. Figure 1 A conventional “shell” covering the magnetic resonance imaging apparatus 112 and the radiation therapy apparatus in a commercial setting, such as a hospital, is not shown in.

[0016] Figure 1 The magnetic resonance linac device shown includes a radio frequency (RF) wave source 102, a waveguide 104, an electron source 106, a radiation source 103, a collimator 108 (e.g., a multi-leaf collimator configured to collimate and shape the beam), a magnetic resonance imaging apparatus 112 (shown in partial cutaway), and a patient support surface 114. In use, the device also includes a shell (not shown) that defines a bore with the ring gantry. The patient support surface 114 is movable and can be used to support a patient and move the patient or other subject into the bore at the start of an MR scan and / or radiation therapy. The magnetic resonance imaging apparatus 112, the radiation therapy apparatus, and the patient support surface actuator are communicatively coupled to a controller or processor. The controller is also communicatively coupled to a memory device including computer executable instructions that are executable by the controller.

[0017] The radiation therapy apparatus includes the radiation source 103 and a radiation detector (not shown). Typically, the radiation detector is positioned diametrically opposite the radiation source 103. The radiation detector is adapted and configured to produce radiation intensity data. In particular, the radiation detector is positioned and configured to detect radiation intensity that has passed through a subject. The radiation detector can also be described as a radiation detection apparatus and can form part of a portal imaging system.

[0018] The radiation source 103 can include a beam generation system. For a linear accelerator, the beam generation system can include a radio frequency wave source 102, an electron source 106 (e.g., an electron gun), and a waveguide 104. The radiation source 103 is attached to a rotatable gantry 116 so as to rotate with the gantry 116. In this way, the radiation source 103 can rotate around the patient so that the treatment beam 110 can be applied from different angles around the gantry 116. In preferred embodiments, the gantry can continue to rotate. In other words, the gantry can rotate 360 degrees around the patient and can in fact continue to rotate beyond 360 degrees. The gantry can be toroidal. In other words, the gantry can be a toroidal gantry.

[0019] The radio frequency wave source 102 (e.g., a magnetron) is configured to generate radio frequency waves. The radio frequency wave source 102 is coupled to the waveguide 104 via a circulator 118 and is configured to send pulses of radio frequency waves into the waveguide 104. The radio frequency waves can enter the radio frequency input connection tube or pipe from the radio frequency wave source 102 through a radio frequency input window. The electron source 106 is also coupled to the waveguide 104 and is configured to inject an electron beam into the waveguide 104. In the electron source 106, electrons are thermionically emitted from a heated filament wire when the filament wire is heated. The temperature of the filament wire controls the number of electrons injected. The injection of electrons into the waveguide 104 is synchronized with the pumping of the radio frequency waves into the waveguide 104. The design and operation of the radio frequency wave source 102, the electron source 106, and the waveguide 104 is such that the radio frequency waves accelerate the electrons to very high energies as the electrons propagate through the waveguide 104.

[0020] The design of the waveguide 104 depends on whether the linear accelerator uses standing waves or traveling waves to accelerate the electrons, although the waveguide generally includes a series of compartments or cavities, each cavity connected by a hole or “iris” through which the electron beam can pass. The cavities are coupled so as to produce the appropriate electric field pattern that accelerates the electrons propagating through the waveguide 104. The electron beam path is controlled by a suitable arrangement of steering magnets or steering coils around the waveguide 104 as the electrons are accelerated in the waveguide 104. The arrangement of steering magnets can include, for example, two sets of quadrupole magnets.

[0021] Once the electrons are accelerated, they enter a flight tube. The flight tube can be connected to the waveguide by a connection tube. This connection tube or connection structure can be referred to as a drift tube. The electrons travel toward a heavy metal target that can include, for example, tungsten. As the electrons travel through the flight tube, an arrangement of focusing magnets directs and focuses the beam on the target.

[0022] To ensure that the propagation of the electrons is not impeded as the electron beam travels toward the target, a vacuum system including a vacuum pump or vacuum pump arrangement is used to evacuate the waveguide 104. The pump system is capable of producing ultra-high vacuum (UHV) conditions in the waveguide 104 and the flight tube. The vacuum system also ensures the ultra-high vacuum conditions in the electron gun. The electrons can be accelerated to speeds close to the speed of light in the evacuated waveguide 104.

[0023] The radiation source 103 is configured to direct a treatment beam 110 of therapeutic radiation towards a patient positioned on a patient support surface 114. The radiation source 103 can thus also be referred to as a therapeutic radiation source. The radiation source 103 can comprise a heavy metal target towards which high-energy electrons exiting a waveguide are directed. When the electrons hit the target, X-rays are generated in various directions. A primary collimator can block X-rays travelling in certain directions and only let X-rays travelling forward pass through to create the treatment beam 110. The X-rays can be filtered and dose measurements can be made by one or more ion chambers. The beam can be shaped in various ways by a beam shaping device (e.g. by using a multi-leaf collimator 108) before it enters the patient as part of a radiation therapy.

[0024] In some embodiments, the radiation source 103 is configured to emit an X-ray beam or an electron particle beam. Such embodiments allow the apparatus to provide electron beam therapy (i.e. a type of external beam therapy) in which electrons (rather than X-rays) are directed as therapeutic radiation towards a target region. By adjusting components of the linear accelerator, it is possible to “switch” between a first mode in which X-rays are emitted and a second mode in which electrons are emitted. In essence, by moving a heavy metal target into or out of the electron beam path and replacing it with a so-called “electron window”, it is possible to switch between the first and second modes. The electron window is substantially permeable to electrons and allows electrons to exit the flight tube.

[0025] 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 be positioned on the patient support surface. The patient support surface 114 and the patient can then be moved to the second position inside the bore so that the patient can be imaged by the magnetic resonance imaging device 112 and / or imaged or treated using the radiation therapy device. The bore can thus be located around a portion of a space suitable for receiving at least a portion of a patient (i.e. a patient receiving space). Movement of the patient support surface is effected and controlled by a patient support surface actuator, which can be described as an actuation mechanism. These components can together be described as a patient positioning system or a patient positioning apparatus, which can comprise further components. The actuation mechanism is configured to move the patient support surface in a direction parallel to and defined by a central axis of the bore. The terms subject and patient are used interchangeably herein, such that the patient support surface can also be described as a subject support surface. The patient support surface can also be referred to as a movable or adjustable couch or table.

[0026] Figure 1The radiation therapy apparatus / device shown in FIG. 1 also includes a magnetic resonance imaging device 112. The magnetic resonance imaging device 112 is configured to obtain images of a subject positioned on (i.e., placed on) the patient support surface 114. The magnetic resonance imaging device 112 can also be referred to as a magnetic resonance imager. The magnetic resonance imaging device 112 can be a conventional magnetic resonance imaging device that operates in a known manner to obtain magnetic resonance data (e.g., magnetic resonance images). Those skilled in the art will recognize that such a magnetic resonance imaging device 112 can include a main magnet, one or more gradient coils, one or more receive coils, and a radio frequency pulse applicator. Operation of the magnetic resonance imaging device is controlled by a controller.

[0027] The controller is a computer, processor, or other processing device. The controller can be made up of multiple discrete processors. For example, the controller can include a magnetic resonance imaging device processor that controls the magnetic resonance imaging device 110, a radiation therapy device processor that controls operation of the radiation therapy device, and a subject support surface processor that controls operation and actuation of the patient support surface. The controller is communicatively coupled to a memory (e.g., a computer readable medium).

[0028] The linear accelerator device also includes several other components and systems that will be understood by those skilled in the art. For example, to ensure that the linear accelerator does not leak radiation, appropriate shielding is also provided.

[0029] Figure 2 And Figure 3 A patient positioning device 300 is shown. Figure 2 An angled back view of the patient positioning device 300 is shown. Figure 3 An angled front view of the patient positioning device 300 is shown. The patient positioning device 300 includes a patient support device 310 and a support structure 320. The support structure 320 is configured to support the patient support device 310 on a floor (e.g., the floor of a treatment room). The support structure 320 can be configured to provide this support in part by contacting the floor and / or a base 328 that can be embedded within the floor. The support structure 320 can be configured to provide this support in part by contacting the floor and / or a base 328 that can be embedded within the floor. Figure 2 And Figure 3 In the embodiment depicted in FIG. 1, the support structure includes a first (or upper) support leg 322, a support element 324, and a second (or lower) support leg 326.

[0030] The patient positioning device 300 also includes a rotation mechanism. The rotation mechanism is configured to tilt (i.e., rotate) the patient support device 310. This rotation is made with respect to a horizontal plane, or equivalently with respect to the floor of the treatment room, to adjust a tilt angle, e.g., a pitch angle. In Figure 2 And Figure 3In the depicted embodiment, the rotation mechanism includes a drive member 332 and an actuation mechanism 330. The rotation mechanism can also include a coupling element 325 that couples the drive member 332 to the patient support device 310. The rotation mechanism is configured to apply a force to the underside of the patient support device 310 via the drive member 332, thereby rotating the patient support device 310 relative to the support structure 320.

[0031] The patient support device 310 is configured to support a patient. The patient support device 310 includes a patient support surface 312 and a patient support base 314. In use of the device, a patient can lie on the patient support surface 312. In other words, in use, the patient contacts the upper surface of the patient support device 310. The patient support surface 312 is coupled to the patient support base 314 using a linear guide. As is known to those skilled in the art, a linear guide is arranged to relatively rigidly hold two components by a coupling mechanism that allows reciprocating translational motion of the components relative to one another along a particular axis, but will prevent lateral and / or torsional motion of the two components relative to one another. The patient support surface 312 is linearly movable relative to the patient support base 314 in a direction parallel to the longitudinal axis of the patient support device 310. The direction of this linear motion is indicated by the double-headed arrow 350. Movement of the patient support surface 312 relative to the patient support base 314 is controlled by a linear actuator.

[0032] As shown in FIG. 3, the patient support base 314 is coupled to the patient support surface 312 via a linear guide. The linear guide includes an elongate bearing guide 316 mounted to the patient support surface 312. In some examples, the elongate bearing guide is mounted to the patient support base 314 instead, and in other examples, the elongate bearing guide is mounted to each of the patient support surface 312 and the patient support base 314. Likewise, more than one pair of elongate bearing guides can form the linear guide. At least one bearing is provided for movement relative to the elongate bearing guide to enable linear movement. The bearing can be mounted or attached to one of the patient support surface 312 or the patient support base 314, or can not be mounted or attached to either the patient support surface 312 or the patient support base 314, as is the case when the system is being assembled, disassembled, or tested. Regardless of which arrangement is used, the respective components allow the patient support surface 312 to be coupled to the patient support base 314 and to linearly translate relative to the patient support base 314. Figure 3 Figure 2 As shown in FIG. 3, the patient support base 314 is coupled to the patient support surface 312 via a linear guide. The linear guide includes an elongate bearing guide 316 mounted to the patient support surface 312. In some examples, the elongate bearing guide is mounted to the patient support base 314 instead, and in other examples, the elongate bearing guide is mounted to each of the patient support surface 312 and the patient support base 314. Likewise, more than one pair of elongate bearing guides can form the linear guide. At least one bearing is provided for movement relative to the elongate bearing guide to enable linear movement. The bearing can be mounted or attached to one of the patient support surface 312 or the patient support base 314, or can not be mounted or attached to either the patient support surface 312 or the patient support base 314, as is the case when the system is being assembled, disassembled, or tested. Regardless of which arrangement is used, the respective components allow the patient support surface 312 to be coupled to the patient support base 314 and to linearly translate relative to the patient support base 314. Figure 3

[0033] ​​Separate from the linear guides described above, the patient positioning device 300 can be configured to rotate the patient support surface 312 relative to one or both of the pitch and roll rotation axes. In such an embodiment, the axis of linear movement of the patient support surface 312 relative to the patient support base 314 can be parallel to the roll rotation axis. In alternative embodiments, the axis of linear movement of the patient support surface 312 relative to the patient support base 314 and the roll rotation axis can not be parallel. The roll rotation movement and / or the pitch rotation movement can be controlled via linear actuators or suitable actuation mechanisms 330.

[0034] Additionally or as an alternative to the longitudinal movement, the patient positioning surface can also be configured to move laterally. This movement can be perpendicular to the longitudinal movement and can be controlled by movement of the support structure 315 relative to a lateral carriage 317. This movement can be achieved by actuators in a known manner and can also utilize one or more linear guides. In summary, the patient support surface 312 can be configured to move in any one, all or a combination of three translational degrees of freedom: height, longitudinal movement and lateral movement.

[0035] The support structure 320 is configured to bear the weight of the patient support device 310 and the patient positioned on the patient support surface 312. A number of embodiments of the support structure 320 are contemplated. In the embodiment shown, the support structure 320 comprises an upper element coupled to the underside of the patient support device 310 and a lower element coupled to the base. The upper element can be a first support leg 322 and the lower element can be a second support leg 326 coupled to the base. The first support leg 322 and the second support leg 326 are coupled to each other by a support element 324. In this context, the support element 324 can be referred to as a support block or an anchoring element. Figure 2 and Figure 3 In the embodiment shown, the support structure 320 comprises an upper element coupled to the underside of the patient support device 310 and a lower element coupled to the base. The upper element can be a first support leg 322 and the lower element can be a second support leg 326 coupled to the base. The first support leg 322 and the second support leg 326 are coupled to each other by a support element 324. In this context, the support element 324 can be referred to as a support block or an anchoring element.

[0036] The patient support device 310 can be rotatably coupled to the support structure 320 to allow rotation about a rotation axis. In a simple embodiment, the support structure 320 can be coupled to the patient support device 310 via the engagement between a shaft and one or more bearings that receive the shaft. For example, one or more bearings can be mounted to the underside of the patient support device 310 and configured to receive a shaft that forms part of the support surface. For example, the upper region of the first support leg 322 can ultimately form a double-ended shaft, where each end of the shaft is received in a bearing mounted to the base of the patient support device 310. In this embodiment, the orientation of the shaft and the bearings defines the rotation axis about which the patient support device 310 can rotate relative to the support structure 320. Other embodiments include a ball joint or any other mechanical linkage that allows the patient support device 310 to rotate relative to the support surface through a rotation axis.

[0037] The second (or lower) support leg is coupled to the base 328. The second support leg 326 can be fixedly attached to the base 328. Alternatively, the coupling can be achieved via a lower coupling element, and the second support leg 326 can be configured to rotate relative to the lower coupling element as part of a height adjustment mechanism. The lower coupling element extends upwardly away from the base 328, allowing the second support leg 326 to be coupled to the lower coupling element. This arrangement defines a rotation axis that is parallel to the rotation axis about which the patient support apparatus 310 rotates relative to the first support leg 322.

[0038] The support structure 320 can further comprise a height adjustment mechanism (not shown in the figures). The height adjustment mechanism is configured to adjust the height, i.e. the vertical distance, of the patient support apparatus 310 above the floor or base. The height adjustment mechanism comprises one or more motor mechanisms. An upper motor mechanism can be positioned within, form part of and / or be coupled to the support element 324. A lower motor mechanism can be positioned within, form part of and / or be coupled to the lower coupling element.

[0039] The height adjustment mechanism can be formed by one or more different mechanisms. In Figure 2 and Figure 3 In the embodiment shown, the height adjustment mechanism is configured to adjust the vertical distance between the support element 324 and the patient support apparatus 310 by actuating the rotation of the first support leg 322 relative to the base 328. As a result, the height of the patient support apparatus 310 above the floor is increased. The height adjustment mechanism comprises a rotation mechanism or motor configured to generate a rotational movement of the first support leg 322 relative to the support element 324. This can be a rotary hydraulic motor. The rotary motor is housed within the support element 324. It will be appreciated that by rotating the first support leg 322 clockwise from the perspective shown in Figure 2 As a result, the height of the patient support apparatus 310 above the floor / base is increased.

[0040] Optionally, an additional rotary motor can be provided. This rotary motor can be referred to as a "lower" rotary motor in contrast to the "upper" rotary motor described above. The lower rotary motor is also housed within the support element 324 and is configured to drive a rotation relative to the support element 324 and the lower leg 326. As a result, the height adjustment mechanism can also be configured to adjust the vertical distance between the support element 324 and the base 328 and / or the floor of the treatment room by actuating the second support leg 326 using this lower rotary motor. Thereby, the height of the patient support apparatus 310 is adjusted. By driving the rotation synchronously using the upper and lower rotary motors, the vertical height of the patient support surface 312 can be adjusted.

[0041] For example, the height adjustment mechanism can include a lower rotary mechanism or motor, such as a rotary hydraulic motor, configured to produce rotational movement of the second support leg 326 relative to the support structure 324. It will be appreciated that by rotating the second support leg 326 counterclockwise from the perspective shown, the height of the patient support device 310 above the base is increased. Figure 2 The height adjustment mechanism is configured to control the height of the patient support device 310 above the floor of the treatment room. As mentioned above, the patient support device 310, and in particular the base of the patient support device 310, is rotatably coupled to the support structure 320 to allow rotation about a rotational axis. By adjusting the height of the patient support device 310 above the floor of the treatment room using the height adjustment mechanism, the height of this rotational axis can also be adjusted.

[0042] The height adjustment mechanism is configured to control the height of the patient support device 310 above the floor of the treatment room. As mentioned above, the patient support device 310, and in particular the base of the patient support device 310, is rotatably coupled to the support structure 320 to allow rotation about a rotational axis. By adjusting the height of the patient support device 310 above the floor of the treatment room using the height adjustment mechanism, the height of this rotational axis can also be adjusted.

[0043] Described herein is a support structure 320 and a height adjustment mechanism that includes a mechanism capable of rotating one or more support legs about a rotational axis to adjust the height of the patient support device 310. However, the height adjustment mechanism can take many forms. For example, the height adjustment mechanism can include an arrangement of hydraulic pistons positioned and configured to adjust the height of the patient support device 310. Alternative embodiments can involve a scissor lift mechanism. Those skilled in the art will appreciate other possible ways of adjusting the height of the patient support device 310. Regardless of the particular embodiment of the support structure 320 and / or the height adjustment mechanism, a rotary mechanism is coupled to the support structure 320 and configured to apply a force to the underside of the patient support device 310 in order to rotate the patient support device 310 relative to the support structure 320.

[0044] In some embodiments, the positioning device 300 further includes a skirt 345 configured to cover the support structure 320 and the rotary mechanism. The skirt 345 can be connected between the base 328 and the patient support device 310. The skirt 345 has flexibility and in particular can have a wave-like configuration, i.e. configured to extend, compress or fold into a wrinkle resembling a wave. Thus, the patient and the clinician can be protected from possible injuries due to the moving mechanisms described herein. With this design, in particular by the rotary mechanism being attached to and supported by the support structure, it is simpler to provide this protection using a simple skirt 345. In Figure 2 and Figure 3 In Figs. 3 and 4, the skirt 345 is shown folded or compressed downwardly from the patient support device 310 so that the support structure 320 and the rotary mechanism can be seen.

[0045] Figure 4is a schematic view of an arrangement 400 for linear translation of a patient support surface 401. The patient support surface is arranged to be moved by a movement mechanism 402. The patient support surface 401 can be coupled to the movement mechanism 402 via an intermediate component (not shown). An encoder 403 is provided to record and / or output the internal position of the movement mechanism 402. The patient support surface 401 is arranged such that the movement mechanism 402 is able to move the patient support surface 401 along a track 405 in a direction A-B. Figure 4 The patient support surface 401 is arranged to be moved in either direction indicated by the double headed arrow between A-B. At either end of the track 405 are end stops 407, 409 which prevent the patient support surface 401 from moving further in a particular direction and set a limit to the movement of the patient support surface 401 in that particular direction. Each end stop 407, 409 can be a mechanical block arranged such that the patient support surface 401 will abut it. A sensor 411 is provided to determine the position of the patient support surface 401 along the track 405. The sensor 411 can be an absolute linear sensor such as a linear magnetic encoder available from Renishaw, MicroE or Heidenhain. The sensor 411 can also be referred to as a magnetic scale. Thus, the sensor 411 directly indicates the position of the patient support surface 401.

[0046] The patient support surface 401 can be similar or identical to the patient support surface 312 of Figure 2 and Figure 3 . Figure 4 may be considered a simplified depiction of a patient positioning device 300. The movement mechanism 402 can likewise be any of the translation mechanisms disclosed herein, for example a linear or rotary actuator. For example, the movement mechanism 402 can comprise a mechanism for mechanically translating the motion of an actuator component into motion of the patient support surface 401. The movement mechanism 402 can comprise a motor with a gearbox, and / or a transmission, and / or a solenoid. The track 405 and the directions A-B can extend along any of the longitudinal and lateral directions described herein or along the height direction Z.

[0047] The encoder 403 can record the position of a component of the movement mechanism 402, such as the position of a linear actuator or a rotating component of a motor, or record the number of revolutions of a rotating component in a particular direction. Thus, the component of the movement mechanism 402 can be referred to as an internal component of the movement mechanism 402. The encoder can be a rotary encoder, such as an optical rotary encoder, such as those available from Posial, Hengstler, or Heidenhain. In an ideal system, as the movement mechanism 402 moves the patient support surface 401, the change in position or orientation of the internal component of the mechanism precisely corresponds to a change in position of the patient support surface 401, and the reading of the encoder 403 can give a direct indication of the position of the patient support surface 401. However, typically one or more internal components of the movement mechanism 402 will exhibit characteristics such as backlash, and the change in position or orientation of the internal component will not directly correspond to a change in position of the patient support surface 401. Thus, the encoder can not always directly indicate the position of the patient support surface 401.

[0048] The absolute linear output or reading of the sensor 411 is typically a true indication of the position of the patient support surface 401 compared to the reading of the encoder 403. Thus, the output of the sensor 411 can be considered to provide an absolute measurement of the position of the patient support surface 401 along the track 405, while the output of the encoder 403 can be considered to provide an approximate or relative measurement of the change in position of the patient support surface 401.

[0049] The sensor 411 measures the absolute position of the patient support surface 401 with a particular spatial resolution. As the patient support surface 401 is driven along the track 405 by the movement mechanism 402, the sensor 411 is only sensitive to changes in position that exceed the resolution of the sensor 411. Similarly, as the movement mechanism 402 drives the patient support surface 401 along the track, the encoder 403 records changes in the position of the internal component of the movement mechanism 402 with a particular resolution. Typically, the minimum change in internal position that the encoder is able to resolve will result in a change in position of the patient support surface that is smaller than the minimum change in position of the patient support surface that the sensor 411 is able to resolve. Thus, in terms of measuring the position of the patient support surface 401, the resolution of the sensor 411 can be considered to be lower than the encoder 403.

[0050] Thus, the sensor 411 and the encoder 403 each provide different advantages and disadvantages. Disclosed herein is a system and / or method of combining the sensor 411 and the encoder 403 readings in a manner that mitigates the disadvantages of each of the sensor and the encoder and promotes the advantages of each of the sensor and the encoder.

[0051] Figure 5 It is shown Figure 4a further simplified schematic of the arrangement 400, and a method 550 for calibrating a patient positioning device. For simplicity, the movement mechanism 402, the encoder 403, and the track 405 are not shown.

[0052] In a first step S555, the method 550 comprises taking readings from the sensor 411 and the encoder 403 at a first position of the patient support surface. The absolute position of the patient support surface 401 can be determined from the readings of the sensor 411. Accordingly, the relative position of the patient support surface in terms of encoder 403 readings can be converted to absolute position based on the readings of the sensor 411.

[0053] In a second step S557, the method 550 comprises moving the patient support surface 401 to a second position using the movement mechanism 402, and taking readings from the sensor 411 and the encoder 403 at the second position. The absolute position of the patient support surface 401 at the second position can be estimated or determined based on the readings of the sensor 411. Accordingly, the relative position of the patient support surface at the second position in terms of encoder 403 readings can be converted to absolute position based on the readings of the sensor 411.

[0054] In a third step S559, the method 550 comprises analysing the readings to determine a relationship between each encoder reading and a corresponding position of the patient support surface. Since the encoder readings or outputs are known for both positions, and the absolute position is also known for each of these two positions, an appropriate interpolation, extrapolation or determination can be made such that the encoder readings for other positions can be converted to a measurement or estimate of the absolute position.

[0055] Beneficially, the determined relationship between each encoder reading and a corresponding position of the patient support surface allows the encoder readings to be used as a direct measurement or estimate of the position of the patient support surface. Accordingly, the higher resolution of the encoder 403 can be used to provide a more accurate position estimate than the sensor 411. Furthermore, the reliability of the absolute linear sensor 411 can be used to guarantee the integrity of the positions determined from the encoder 403.

[0056] In the methods disclosed herein, the output of the sensor 411 can be related to the position of the patient support surface 401 according to the following equation:

[0057] P = cE' + d (1)

[0058] where P is the true position of the patient support surface 401, E' is the output or reading of the sensor 411, and c is determined by the manufacturing process of the sensor 411 and typically has a very high accuracy. In many implementations, c is in fact equal to 1. d is an offset caused by the mounting and / or cutting position of the sensor 411.

[0059] In the method disclosed herein, the output of encoder 403 can be correlated with the position of patient support surface 401 according to the following equation:

[0060] P = aE + b (2)

[0061] Where P is the actual position of the patient support surface 401, E is the output or reading of the encoder 403, 'a' is determined by at least one characteristic of the moving mechanism 402 or the patient positioning device, and 'b' is the offset caused during assembly. Parameter 'a' may represent a characteristic of one or more internal components of the moving mechanism 402, such as a characteristic of a transmission and / or gearbox. In some examples, parameter 'a' may represent the length of a guide, the angle of a component portion, and / or the position of a screw. In each example, parameter 'a' may have a theoretical reference value depending on the specifications of the component represented. Due to manufacturing and / or installation processes, the value of parameter 'a' may differ from the theoretical reference value.

[0062] like Figure 5 As shown in method 550, determining the relationship between each encoder reading and the corresponding position may include using the readings obtained in steps S555 and S557 to solve the simultaneous equations (1) and (2).

[0063] Figure 6 It shows Figure 5 A further simplified schematic diagram of the arrangement 400, and a method 650 for calibrating the patient positioning device. Method 650 is... Figure 5 An exemplary implementation of method 550, wherein optional additional steps are added.

[0064] In the first step S651, the patient support surface 401 is positioned at one end of the track 405, abutting against end stops 407, 409. The end of the track 405 can be considered a zero position, i.e., P = 0. Assuming c equals 1, the value of the offset parameter d at P = 0 can be calculated. The value of d is constant within the range of motion of the patient support surface, meaning that P can be determined for any value of E, thus providing a measurement of the true position of the patient support surface 401 along the track 405. In some examples, the offset value f may be known and the first step S651 may not be necessary.

[0065] In the second step S655, the patient support surface 401 is moved to a first position different from the end or zero position in the first step S651 using the moving mechanism 402. This first position is a first calibration position. At this first position, according to... Figure 5 In the first step, S555 obtains readings from sensor 411 and encoder 403. The readings provide the values ​​of E and E′ at the first position.

[0066] In a third step S657, the patient support surface 401 is moved to a second position different from the first position using the movement mechanism 402. The second position is a second calibration position. At the second position, readings are obtained from the sensor 411 and the encoder 403 according to Figure 5 the second step S557. The readings provide values for E and E' at the second position.

[0067] In a fourth step S659, parameters defining a relationship between the position of the patient support surface and the readings of the encoder are determined. The readings of the two calibration positions are used to solve the simultaneous equations (1) and (2) and a and b are determined. Optionally, the determined value of a is compared to a theoretical reference value. The theoretical reference value can be stored or pre-set in a computer memory, e.g. a look-up table. Optionally, if the value of a does not match the theoretical reference value, the method can comprise raising, generating or activating an alarm indicating that the calibration was not successful. If the value of a does not match the theoretical reference value, the method can also comprise restarting the method 650.

[0068] In a fifth step S663, the method comprises moving the patient support surface 401 to a third position different from the first and second positions using the movement mechanism 402. The third position is an examination point position. Readings are obtained from the sensor 411 and the encoder 403 and each respective reading is converted to a respective estimate or calculation of the position of the patient support surface 401 using equations (1) and (2) and the previously determined values of a, b, c and d. The fifth step S663 can also be performed as part of the method 550 Figure 5 wherein the examination point position can be estimated twice based on respective readings of the sensor 411 and the encoder 403 in combination with the determined relationship.

[0069] Thereby, two independent sources of estimates of the position are obtained at the examination point position. The estimate obtained using equation (1) can be the true position of the patient support surface 401. If the calibration method is valid and a and b have been determined with sufficient accuracy, the estimate obtained using equation (2) can also be the true position of the patient support surface 401. The two estimates of the position are compared in the fifth step S663, e.g. by determining the difference between the two values or by obtaining a ratio of the two values. If the difference or ratio does not match what is expected, e.g. if there is a large difference between the two estimates, it can indicate that something has gone wrong. Optionally, it is determined whether the comparison between the two estimates is within a predefined tolerance. If the comparison determines that the two estimates are outside the predefined tolerance, an alarm can be raised or activated and / or the calibration method can be restarted. Possible problems include: an unexpected change or malfunction in the movement mechanism 402, that the previous calibration steps of the method were not performed correctly or accurately, and that any one of the sensor 411 or the encoder 403 is malfunctioning in some way.

[0070] If the comparison determines that the two estimates are within a predefined tolerance range, the patient support device is considered to be correctly calibrated. Furthermore, by using a higher-resolution encoder 403 to determine the absolute position of the patient support surface 401 instead of using a lower-resolution sensor 411, improved accuracy and control of the patient support device can be achieved. Moreover, each time the patient support surface 401 moves to a new position, independent estimation and verification can be performed via comparison in step five, S663. This method allows for continuous verification of the calibration of the patient positioning device during use. Advantageously, a method is provided in which an alarm or indication is immediately issued if a positioning error occurs during use (e.g., when positioning a patient).

[0071] Therefore, each of the X, Y, and Z axis movements of the patient positioning device can be calibrated, and the movement of the patient support surface can be continuously monitored and / or verified to ensure that the patient positioning device remains correctly calibrated in each direction of movement.

[0072] The rotational motion of the patient positioning device can also be calibrated according to the method disclosed herein.

[0073] Figure 7 The illustrated arrangement 700 includes a rotatable patient support surface 701. The patient support surface 701 may be equivalent to other patient support surfaces 401, 312 disclosed herein, and may be part of any patient positioning device disclosed herein. In fact, Figure 4 and Figure 7 Arrangements 400 and 700 can be the same device. Each figure is only a simplified depiction of the scale used to illustrate the possible movements of the patient support surface.

[0074] The patient support surface 701 can rotate in the direction shown by the double-headed arrow between +Y and -Y. This rotation is called pitch rotation. Although pitch motion is discussed herein for illustrative purposes, the patient support surface 701 can also rotate about other axes perpendicular to the axis of pitch rotation, such as tilt rotation and yaw rotation, and the methods and systems disclosed herein are equally applicable to these directions of rotation.

[0075] The rotation of the patient support surface 701 is measured as an angle relative to the dashed line CD, which extends parallel to the floor where the patient positioning device is located. Sensor 705 is used to measure the rotation, tilt, or deflection of the patient support surface 701. Sensor 705 is an absolute sensor, such as... Figure 4 to Figure 6The sensor 705 can be a inclinometer and / or be arranged to measure the absolute rotational position of the patient support surface relative to the direction of gravity towards the earth. The movement mechanism 707 is arranged to cause rotation of the patient support surface 701. The movement mechanism 707 can be any of those disclosed herein and can comprise components such as gears, linear or rotational actuators and / or variable speed drives. The movement mechanism 707 comprises an encoder 709 (not shown - in this example it is internal to the movement mechanism 707) which is arranged to measure the internal position of the movement mechanism 707, similar to the encoder 403 of Figure 4 to Figure 6

[0076] Calibration of the rotational movement of the patient support surface can be considered in a similar way to the calibration method for linear translation disclosed in Figure 4 to Figure 6 Rather than measuring position along a linear trajectory, the different angular / rotational positions or orientations of the patient support surface are measured. Figure 7 The sensor 705 provides an absolute measurement of position in a similar way to the sensor 411 of Figure 4 and the encoder 709 of Figure 7 provides an indirect relative measurement of position in a similar way to the encoder 403 of Figure 4 Again, the encoder 709 typically has a higher equivalent resolution than the sensor 705.

[0077] The sensor 705 provides an unbiased absolute measurement. Thus, the rotational position of the patient support surface 701 is given by:

[0078] P = E' (3)

[0079] where E' is the output or reading of the sensor 705.

[0080] Due to the complexity of the rotational movement mechanism, the relationship between the output of the encoder 709 and the rotational position of the patient support surface 701 depends on a function f(E) as follows:

[0081] P = f(E) (4)

[0082] The function f(E) has n parameters to be calibrated, each of which can relate to a characteristic of the movement mechanism 707 or patient positioning apparatus. Each of the n parameters has a theoretical reference value. Typically, f(E) comprises n trigonometric functions, each of which has a parameter which is one of the n parameters to be calibrated. The plurality of trigonometric functions of d(E) are combined in a way which best describes the type of rotational movement to be characterised and / or calibrated. For example, when calibrating the pitch rotation of the patient support surface 701, 9 parameters can be used, and / or when calibrating the roll rotation of the patient support surface 701, 10 parameters can be used. ​

[0083] Equations (3) and (4) can be seen as analogous to equations (1) and (2) describing linear translational motion.

[0084] It will be appreciated that the exact form of f(E) can be chosen to best describe or characterize the corresponding type of rotation of the patient support surface 701. In a similar way to the parameter a of equation (2), each of the n parameters of the function f(E) can represent one or more design characteristics of the movement mechanism 707, such as the length of a guide, the angle of a component part, and / or the position of a screw. Due to production and / or installation processes, the parameters can differ from theoretical reference values. A mathematical optimization algorithm can be used to estimate the actual values of the parameters in order to best fit f(E) according to equation (4).

[0085] Figure 8 A simplified schematic view of the arrangement 700 is shown, as well as the method 850. The sensor 705 is shown as a linear scale spanning the maximum rotation range of the patient support surface 701, +Y to -Y. In some examples, +Y is +3 degrees and -Y is -3 degrees. In other examples, different rotation range limits will be set for a particular patient positioning device. Figure 7

[0086] In a first step S855, the method comprises rotating the patient support surface 701 to a first rotational position or orientation using the movement mechanism 707. The first position is a first calibration position. At the first position, according to equation (3), E = f(E') = a. Figure 5 The first step S555 of the method comprises taking readings from the sensor 705 and the encoder 709. The readings provide values of E and E' at the first position.

[0087] In a second step S857, the patient support surface 701 is rotated to a second rotational position different from the first position. The second position is a second calibration position. At the second position, according to equation (3), E = f(E') = a. Figure 5 The second step S557 of the method comprises taking readings from the sensor 705 and the encoder 709. The readings provide values of E and E' at the second position.

[0088] Further steps similar to the previous two steps S855, S857 should be performed, such that the number of different positions at which readings are taken corresponds to the number of parameters n that must be calibrated for f(E) in equation (4). Figure 8 A third step S858 is shown in the method 850, representing the last such calibration step.

[0089] ​In a subsequent step S859, parameters defining the relationship between the position of the patient support surface and the encoder readings are determined. After obtaining readings from the sensor 705 and the encoder at n positions, the n parameters of f(E) can be determined by solving equations (3) and (4) as a system of equations. In each case, the sensor 705 provides the true angular position or orientation of the patient support surface 701.

[0090] As with the method 650 of FIG. 6, each of the n parameters can be compared to a theoretical reference value. If the parameter does not match the theoretical reference value, an alarm can be raised or activated indicating a calibration failure and / or that the calibration process can be restarted. The theoretical reference value can be stored or preset in a computer memory, for example a lookup table. Figure 6

[0091] In a final step S863, the method comprises moving the patient support surface 701 to a checkpoint position using the movement mechanism 707. Readings are obtained from the sensor 705 and the encoder 709 and each respective reading is converted to a respective estimate or calculation of the rotational position of the patient support surface 701 using equations (3) and (4) and the previously determined values of the n parameters.

[0092] As described above in relation to linear translational motion, two independent estimates of the position are obtained in this step. The estimate obtained using equation (3) can be the true rotational position of the patient support surface 701. If the calibration method is valid and the n parameters have been determined with sufficient accuracy, the estimate obtained using equation (4) can also be the true position of the patient support surface 701. In the final step S863, the estimates of the position are compared, for example by determining the difference between the two values or by taking the ratio of the two values. If the difference or ratio does not correspond to what is expected, for example if there is a large difference between the two estimates, it can indicate that something has gone wrong. Alternatively, it is determined whether the comparison between the two estimates is within a predefined tolerance. If the comparison determines that the two estimates are outside the predefined tolerance, an alarm can be raised or activated and / or the calibration method can be restarted. Possible errors include: a failure of the movement mechanism, the previous calibration steps of the method have not been performed correctly or accurately, and any one of the sensor 705 or the encoder 709 is malfunctioning in some way.

[0093] ​If the comparison determines that the two estimates are within a predefined tolerance, the patient support device is considered to be correctly calibrated. Furthermore, by using the higher resolution encoder 709 to determine the absolute position of the patient support surface 701, rather than using the lower resolution sensor 705, it is possible to achieve improved accuracy and control of the patient support device. Furthermore, each time the patient support surface 701 is moved to a new position, the independent estimate and verification by the comparison of the final step S863 can be made. This approach allows the calibration of the patient positioning device to be continuously verified during use. Beneficially, a method is provided in which, if a positioning error occurs during use, for example when positioning a patient, an alert or indication is immediately issued.

[0094] While each of the methods 550, 650, 850 are described herein with respect to particular examples, each method can be combined with another method or applied to another example. For example, the method 550 can be applied to linear translation motion, or the method 850 can be applied to rotational motion, as long as the relationship between the encoder output and the position of the patient support surface is appropriately determined. Figure 8 The method 850 can be applied to linear translation motion, or Figure 5 The method 550 can be applied to rotational motion.

[0095] Described herein is a method for calibrating a radiotherapy positioning device having a patient support surface movable by a mechanism, the method comprising obtaining outputs of a patient support surface position sensor and a mechanism position encoder at a plurality of positions of the support surface, and using these outputs to determine a relationship between the sensor and encoder outputs.

[0096] Those skilled in the art will realize that many modifications, alterations and combinations can be made with respect to the examples described above without departing from the scope of the disclosed concept, and that such modifications, alterations and combinations will be viewed as being within the ambit of the disclosed concept.

[0097] Those skilled in the art will also realize that the scope of the application is not limited to the examples described herein, but is defined by the appended claims.

[0098] The various methods described above can be implemented by a computer program. The computer program can include computer code arranged to instruct a computer to perform the functions of one or more of the various methods described above. Computer programs and / or code for performing such methods can be provided either at a device, such as a computer, on one or more computer readable media, or more generally, computer program products. The computer readable media can be transitory or non-transitory. The one or more computer readable media can be, for example, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or a propagation medium for data transmission, for example for downloading the code over the Internet. Alternatively, the one or more computer readable media can take the form of one or more physical computer readable media, such as semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory (RAM), a read-only memory (ROM), a rigid magnetic disc, and an optical disc, such as a CD-ROM, CD-R / W or DVD.

[0099] In one implementation, the modules, components and other features described herein can be implemented as discrete components or functions implemented in hardware circuitry, such as an ASIC, an FPGA, a DSP or similar device.

[0100] A "hardware component" is a tangible (e.g., non-transitory) physical component (e.g., a combination of one or more processors) that is capable of performing certain operations and can be configured or arranged in a certain physical manner. A hardware component can include customized hardware circuitry that is permanently configured to perform certain operations. A hardware component can be or include an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other customized hardware component. A hardware component can also include programmable logic or circuitry that is temporarily configured by software to perform certain operations.

[0101] Accordingly, the phrase "hardware component" should be understood to encompass a tangible entity that is physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a certain manner or to perform certain operations described herein.

[0102] Additionally, the modules and components can be implemented as firmware or functional circuitry within hardware devices. Further, the modules and components can be implemented in any combination of hardware devices and software components, or only in software (e.g., code stored or otherwise embodied in a machine-readable medium or in a transmission medium).

[0103] A computer readable medium comprising computer readable instructions which, when executed by a processor, cause the processor to perform any of the methods described herein is described. The computer readable medium can be a tangible and / or non-transitory medium.

Claims

1. A method for calibrating a radiotherapy patient positioning device, the patient positioning device comprising: a patient support surface; a sensor for measuring a position of the patient support surface; a movement mechanism for moving the patient support surface; and an encoder for encoding an internal position of the movement mechanism, wherein a minimum change in the internal position that the encoder is able to resolve will result in a change in the position of the patient support surface that is smaller than a minimum change in the position of the patient support surface that the sensor is able to resolve; the method comprising: taking readings from the sensor and the encoder at a first position of the patient support surface; moving the patient support surface to a second position using the movement mechanism and taking readings from the sensor and the encoder at the second position; and analyzing the readings to determine a relationship between each encoder reading and a corresponding position of the patient support surface; wherein the method further comprises: moving the patient support surface to a third position using the movement mechanism; making a first estimate of the third position, the first estimate being based on readings from the sensor; making a second estimate of the third position using the determined relationship, the second estimate being based on readings from the encoder; and comparing the first estimate and the second estimate of the third position. Comparing the first estimate and the second estimate comprises determining whether the first estimate is within a predefined tolerance of the second estimate.

2. The method of claim 1, wherein, If the first estimate is not within the predefined tolerance of the second estimate, activating an alarm.

3. The method of claim 2, further comprising: The sensor is arranged to measure an absolute position of the patient support surface along a linear track.

4. The method according to any of the preceding claims, wherein, The sensor is arranged to measure an absolute rotational position of the patient support surface.

5. The method of any one of claims 1 to 3, wherein, The sensor is arranged to measure an absolute rotational position of the patient support surface relative to a direction of gravity towards the Earth.

6. The method of claim 5, wherein, The sensor is an inclinometer.

7. The method of claim 5, wherein, Determining a relationship between an output of the encoder and a position of the patient support surface comprises determining at least one parameter, the at least one parameter being representative of a characteristic of the patient positioning device.

8. The method of claim 1, wherein, The at least one parameter comprises a plurality of parameters, each parameter being representative of a respective characteristic of the patient positioning device.

9. The method of claim 8, wherein, The method further comprises taking readings from the sensor and the encoder at a plurality of positions, wherein the number of the plurality of positions is at least equivalent to the number of parameters of the plurality of parameters.

10. The method of claim 9, wherein, The at least one parameter is representative of a characteristic of the movement mechanism.

11. The method of any one of claims 8-10, wherein, The characteristic is one of: movement mechanism backlash, encoder offset.

12. The method of any one of claims 8-10, wherein, 13. A system for calibrating a radiotherapy patient positioning device, the radiotherapy patient positioning device comprising: a patient support surface; a sensor for measuring a position of the patient support surface; a movement mechanism for moving the patient support surface; and an encoder for encoding an internal position of the movement mechanism, wherein a minimum change in the internal position that the encoder is able to resolve will result in a change in the position of the patient support surface that is smaller than a minimum change in the position of the patient support surface that the sensor is able to resolve; ​ an encoder for encoding an internal position of the movement mechanism, wherein a minimum change in the internal position that the encoder is able to resolve will result in a change in position of the patient support surface that is smaller than a minimum change in position of the patient support surface that the sensor is able to resolve; the system is arranged to perform a method comprising: taking readings from the sensor and the encoder at a first position of the patient support surface; moving the patient support surface to a second position using the movement mechanism and taking readings from the sensor and the encoder at the second position; and analyzing the readings to determine a relationship between each encoder reading and a corresponding position of the patient support surface; wherein the method further comprises: moving the patient support surface to a third position using the movement mechanism; making a first estimate of the third position, the first estimate being based on readings from the sensor; making a second estimate of the third position using the determined relationship, the second estimate being based on readings from the encoder; and comparing the first and second estimates of the third position.

14. A computer readable medium containing instructions which, when executed by a processor, cause a radiotherapy system to perform the method of any of claims 1 to 12.

Images