Control & regulation of breathing for radiotherapy

Abstract

A computer implemented method for processing position data indicating a position of a subject in a radiotherapy device, the method comprising receiving 3D position data for the subject (202), process

Description

Radiotherapy can be described as the use of ionising radiation, such as X-rays, to treat a human or animal body. Radiotherapy is commonly used to treat tumours within the body of a patient or subject. In such treatments, ionising radiation is used to irradiate, and thus destroy or damage, cells which form part of the tumour. It is important that during radiotherapy treatment, radiation is delivered precisely to the desired area. For example, when delivering a radiation dose in the chest region, it is important to avoid or minimise radiation dose to the heart. The positions of some treatment sites are influenced by respiration. For example, this may be relevant when the treatment site is located in the breast, lungs, or under the diaphragm, such as the liver and pancreas. When a patient takes a breath in, the lungs expand, the heart moves away from the chestwall, and the diaphragm moves downwards, which may cause movement in all three dimensions. Existing techniques to improve the accuracy and preciseness of radiation delivery in the chest region include implementing either a breath hold or shallow breathing. The patient may be instructed to hold their breath or breath shallowly, for example by someone operating the beam treatment device. However, there is no real-time feedback delivered to the patient, and this relies on the patient following the instructions of the operator at the correct time. The only feedback delivered may be by medical images observed by the person operating the beam treatment device, for example three-dimensional MR images. They must therefore have detailed medical knowledge in order to interpret these images and instruct the patient accordingly. It would not be desirable to display these medical images to the patient directly as they would be unlikely to interpret them correctly or adjust their breathing as needed to result in accurate treatment. Elekta’s Active Breathing Coordinator is a respiratory gating system that uses a mouthpiece with a flow meter and valve to cause a patient to hold their breath, thereby reducing anatomical movement during treatment. A patient controlled balloon valve allows the patient to hold and maintain a breath-hold to a specific lung volume. This can be monitored by the patient and / or by a clinician controlling the treatment beam. However, this method is not suitable for shallow breathing. It also requires a mouthpiece to be used which may be uncomfortable for some patients. Another existing technique to implement shallow breathing is to use devices that constrict the chest to force shallow breathing. However, these devices may be uncomfortable for the patient, particularly for long periods of time. Such devices are especially unsuitable for anxious patients, or patients who have respiratory problems such as asthma. If parts of a patient are not in planned or expected locations, a lower than desirable dose may be applied to a tumour and a higher than desirable dose may be applied to organs at risk. The radiotherapy beam may be halted or gated to avoid this, but this can lead to delays in treatment times. This in turn can lead to increased discomfort of patients, especially when constricting or uncomfortable devices are used. There is a need for improved means of aligning parts of a patient with intended locations over time. It would be generally advantageous to monitor movement in all three dimensions and deliver feedback to a patient which enables improved adaptation of patient motion to a desired pattern or profile. It would also be advantageous to reduce usage of restrictive devices which can negatively impact patient comfort. It would also be advantageous to improve the accuracy of radiotherapy treatment and the efficiency of use of a radiotherapy device. Summary According to an aspect, there is provided a computer-implemented method for processing position data indicating a position of a subject in a radiotherapy device. The method comprises receiving three dimensional position data for the subject; processing the three dimensional position data to reduce it to a one dimensional signal; and outputting the one dimensional signal for display to the subject. The method may further comprise displaying the one dimensional signal to the subject in real time to provide real-time position feedback to the subject. Processing the three dimensional position data may comprise selecting one dimensional position data from the three dimensional position data, the one dimensional position data corresponding to a dominant axis of movement of the subject, wherein the one dimensional position data is used as the one dimensional signal. Processing the three dimensional position data comprises applying a weighting function to the three dimensional position data. The weighting function may comprise a weight for each of the three dimensions of the three dimensional position data. Processing the three dimensional position data may comprise multiplying respective position data for each of the three dimensions by the respective weight to determine weighted position data; and summing the weighted position data to determine the one dimensional signal. The method may further comprise obtaining a three dimensional acceptable range for the three-dimensional position data; processing the three dimensional acceptable range for the three dimensional position data to reduce it to a one dimensional range; and outputting the one dimensional range for display to the subject. Processing the three dimensional acceptable range for three dimensional position data to reduce it to a one dimensional range may comprise selecting the one dimensional range from the three dimensional acceptable range, the one dimensional range corresponding to a dominant axis of movement of the subject. Processing the three dimensional acceptable range may comprise applying an acceptable range weighting function to the three dimensional position data. The acceptable range weighting function may comprise a weight for each of the three dimensions of the three dimensional acceptable range. Processing the three dimensional acceptable range may comprise multiplying a respective acceptable range for each of the three dimensions by the respective weight to determine weighted acceptable ranges; and summing the weighted acceptable ranges to determine the one dimensional range. The three dimensional position data may comprise data for a first dimension, data for a second dimension, and data for a third dimension. The method may further comprise comparing the data for the first dimension to a first range; comparing the data for the second dimension to a second range; comparing the data for the third dimension to a third range; and determining that the position data for at least one of the first, second, and third dimensions is outside of the first, second, and third ranges respectively. The method may further comprise, in response to determining that the position data is outside of at least one of the first, second, and third ranges, outputting an indication that the user is outside of the acceptable range. The method may further comprise displaying a dynamic representation of the one dimensional position data and the acceptable range in real time to provide real-time position feedback to the subject. The acceptable range may be constant with time and displayed to the subject to indicate breath hold. The acceptable change may vary as a function of time. The acceptable range may be displayed to the subject to indicate a shallow breathing pattern. The method may further comprise determining the acceptable range based on pre-treatment measurements of the breathing of the subject. The three dimensional position data may comprise periodic movement data. The periodic movement data may correspond to a respiratory pattern of the subject. The three dimensional position data may be received from an MR imaging apparatus. According to an aspect, there is provided a computer-readable medium storing instructions which, when executed by a processor, cause the processor to perform any of the methods described herein. According to an aspect, there is provided a controller comprising a processor and a memory, the memory storing instructions which, when executed by the processor, cause the processor to perform any of the methods described herein. According to an aspect, there is provided a radiotherapy device comprising a controller. It further comprises a sensor communicatively coupled to the controller, the sensor being configured to measure and transmit the three dimensional position data to the controller. It further describes a display communicatively coupled to the controller, the display being configured to receive the one dimensional signal from the controller and to display the one dimensional signal. Brief description of the figures Specific embodiments are now described, by way of example only, with reference to the drawings, in which: Figure 1 depicts an exemplary radiotherapy system, according to some embodiments of the present disclosure. Figure 2 depicts a method for processing position information of a subject in a radiotherapy device according to some embodiments of the present disclosure. Figure 3 depicts a relationship between beam status, the instruction provided to the patient, and the respiratory cycle of the patient, including a task for the patient to hold their breath, according to some embodiments of the present disclosure. Figure 4 depicts a relationship between beam status, the instruction provided to the subject, and the respiratory cycle of the subject, including a task for the subject to hold their breath which is interrupted according to some embodiments of the present disclosure. Figure 5 depicts a relationship between beam status, the instruction provided to the patient, and the respiratory cycle of a patient, including a task for the patient to perform shallow breathing, according to some embodiments of the present disclosure. Figure 6 depicts a relationship between beam status, the instruction provided to the patient, and the respiratory cycle of a patient, including a task for the patient to perform shallow breathing which is interrupted, according to some embodiments of the present disclosure. Figures 7a to 7d depict an exemplary display to prompt a subject to hold their breath according to some embodiments of the present disclosure. Figures 8a to 8d depict an exemplary display to prompt a subject to breathe shallowly according to some embodiments of the present disclosure. Figure 9 depicts a block diagram of one implementation of a radiotherapy system according to some embodiments of the present disclosure. Figure 10 depicts an exemplary computer readable media according to some embodiments of the present disclosure. Detailed description A radiotherapy device, or sensors used in conjunction with a radiotherapy device, may be capable of measuring three-dimensional positions of a subject or parts of a subject over time. For example, the subject will typically exhibit a periodic respiratory motion. It is advantageous to monitor the movements associated with the subject’s breathing and provide alerts or indications when they should moderate their breathing to align more closely with a planned or expected movement profile (e.g. breathing profile). This enables closer alignment of movement of particular organs or parts of organs with that expected and used in treatment planning. However, there is a mismatch between the input data from monitoring the subject’s movement, which may be complex, three-dimensional, anatomical data, and the output data, i.e. a signal suitable for providing to the subject to enable the moderation of their breathing. If the input data were to be provided in its raw form, it may cause distress in the subject, and regardless, the subject is unlikely to be able to correctly interpret the data and respond appropriately. Therefore, the subject would not be able to adjust their breathing in order to allow the radiotherapy treatment to be administered to the desired areas. Due to the noise from magnetic resonance (MR) machines, voice coaching from a medical professional who can interpret the raw data may also be unfeasible. Moreover, if the processing of the input data to generate the output data is performed in an inaccurate or inappropriate manner, actions taken by the subject in response may not produce the desired alignment with the planned or expected breathing profile. The present disclosure provides techniques for processing the input data to generate output data which is suitable for regulation of motion or breathing. The output data may be used for testing compliance with a threshold, e.g. for providing feedback in support of a part of the subject being in an acceptable range of desired locations at desired times. The present disclosure provides methods and devices for processing position information of a subject or a part thereof in a radiotherapy device. Three dimensional position data is received for the subject or a part thereof. The three dimensional position data is processed to reduce it to a one dimensional signal. This may be performed, for example, by determining the dominant axis of motion and selecting the position data corresponding to this axis of motion as the one dimensional signal. In other examples, this may be performed by applying different weights to the components of motion along the different axes, these weights being optionally based on the relative contributions of the different components to the overall motion. The one dimensional signal is output for display to a subject. This one dimensional signal may be used to test compliance with a threshold, for example to determine whether the relevant part of the subject is within an acceptable range or tolerance of a planned or expected location as a function of time. As used herein, when a position of a subject is referred to, this may be used to refer to the position of a part of the subject, for example to the position of a part of the subject containing a target to be treated. Figure 1 depicts a radiotherapy device suitable for delivering, and configured to deliver, a beam of radiation to a subject during radiotherapy treatment. The device and its constituent components will be described generally for the purpose of providing useful accompanying information for the present invention. The device depicted in figure 1 is in accordance with the present disclosure and is suitable for use with the disclosed systems and apparatuses. While the device in figure 1 is an MR-linac, the implementations of the present disclosure may be any radiotherapy device, for example a linac device. The device 100 depicted in figure 1 is an MR-linac. The device 100 comprises both MR imaging apparatus 112 and radiotherapy (RT) apparatus which may comprise a linac device. The MR imaging apparatus 112 is shown in cross-section in the diagram. In operation, the MR scanner produces MR images of the subject, and the linac device produces and shapes a beam of radiation and directs it toward a target region within a subject’s body in accordance with a radiotherapy treatment plan. The depicted device does not have the usual ‘housing’ which would cover the MR imaging apparatus 112 and RT apparatus in a commercial setting such as a hospital. The MR-linac device depicted in figure 1 comprises a source of radiofrequency waves 102, a waveguide 104, a source of electrons 106, a source of radiation 106, a collimator 108 such as a multi-leaf collimator configured to collimate and shape the beam, MR imaging apparatus 112, and a patient support surface 114. In use, the device would also comprise a housing (not shown) which, together with the ring-shaped gantry, defines a bore. The moveable support surface 114 can be used to move a patient, or other subject, into the bore when an MR scan and / or when radiotherapy is to commence. The MR imaging apparatus 112, RT apparatus, and a subject support surface actuator are communicatively coupled to a controller or processor. The controller is also communicatively coupled to a memory device comprising computer-executable instructions which may be executed by the controller. The RT apparatus comprises a source of radiation and a radiation detector (not shown). Typically, the radiation detector is positioned diametrically opposed to the radiation source. The radiation detector is suitable for, and configured to, produce radiation intensity data. In particular, the radiation detector is positioned and configured to detect the intensity of radiation which has passed through the subject. The radiation detector may also be described as radiation detecting means, and may form part of a portal imaging system. The radiation source may comprise a beam generation system. Fora linac, the beam generation system may comprise a source of RF energy 102, an electron gun 106, and a waveguide 104. The radiation source is attached to the rotatable gantry 116 so as to rotate with the gantry 116. In this way, the radiation source is rotatable around the patient so that the treatment beam 110 can be applied from different angles around the gantry 116. Ina preferred implementation, the gantry is continuously rotatable. In other words, the gantry can be rotated by 360 degrees around the patient, and in fact can continue to be rotated past 360 degrees. The gantry may be ring-shaped. In other words, the gantry may be a ringgantry. The source 102 of radiofrequency waves, such as a magnetron, is configured to produce radiofrequency waves. The source 102 of radiofrequency waves is coupled to the waveguide 104 via circulator 118, and is configured to pulse radiofrequency waves into the waveguide 104. Radiofrequency waves may pass from the source 102 of radiofrequency waves through an RF input window and into an RF input connecting pipe or tube. A source of electrons 106, such as an electron gun, is also coupled to the waveguide 104 and is configured to inject electrons into the waveguide 104. In the electron gun 106, electrons are thermionically emitted from a cathode filament as the filament is heated. The temperature of the filament controls the number of electrons injected. The injection of electrons into the waveguide 104 is synchronised with the pumping of the radiofrequency waves into the waveguide 104. The design and operation of the radiofrequency wave source 102, electron source and the waveguide 104 is such that the radiofrequency waves accelerate the electrons to very high energies as the electrons propagate through the waveguide 104. The design of the waveguide 104 depends on whether the linac accelerates the electrons using a standing wave or travelling wave, though the waveguide typically comprises a series of cells or cavities, each cavity connected by a hole or ‘iris’ through which the electron beam may pass. The cavities are coupled in order that a suitable electric field pattern is produced which accelerates electrons propagating through the waveguide 104. As the electrons are accelerated in the waveguide 104, the electron beam path is controlled by a suitable arrangement of steering magnets, or steering coils, which surround the waveguide 104. The arrangement of steering magnets may comprise, for example, two sets of quadrupole magnets. Once the electrons have been accelerated, they may pass into a flight tube. The flight tube may be connected to the waveguide by a connecting tube. This connecting tube or connecting structure may be called a drift tube. The electrons travel toward a heavy metal target which may comprise, for example, tungsten. Whilst the electrons travel through the flight tube, an arrangement of focusing magnets act to direct and focus the beam on the target. To ensure that propagation of the electrons is not impeded as the electron beam travels toward the target, the waveguide 104 is evacuated using a vacuum system comprising a vacuum pump or an arrangement of vacuum pumps. The pump system is capable of producing ultra-high vacuum (UHV) conditions in the waveguide 104 and in the flight tube. The vacuum system also ensures UHV conditions in the electron gun. Electrons can be accelerated to speeds approaching the speed of light in the evacuated waveguide 104. The source of radiation is configured to direct a beam 110 of therapeutic radiation toward a patient positioned on the patient support surface 114. The source of radiation may comprise a heavy metal target toward which the high energy electrons exiting the waveguide are directed. When the electrons strike the target, X-rays are produced in a variety of directions. A primary collimator may block X-rays travelling in certain directions and pass only forward travelling X-rays to produce a treatment beam 110. The X-rays may be filtered and may pass through one or more ion chambers for dose measuring. The beam can be shaped in various ways by beam-shaping apparatus, for example by using a multi-leaf collimator 108, before it passes into the patient as part of radiotherapy treatment. In some implementations, the source of radiation is configured to emit either an X-ray beam or an electron particle beam. Such implementations allow the device to provide electron beam therapy, i.e. a type of external beam therapy where electrons, rather than X-rays, are directed toward the target region. It is possible to ‘swap’ between a first mode in which X-rays are emitted and a second mode in which electrons are emitted by adjusting the components of the linac. In essence, it is possible to swap between the first and second mode by moving the heavy metal target in or out of the electron beam path and replacing it with a so-called ‘electron window’. The electron window is substantially transparent to electrons and allows electrons to exit the flight tube. The subject or patient support surface 114 is configured to move between a first position substantially outside the bore, and a second position substantially inside the bore. In the first position, a patient or subject can mount the patient support surface. The support surface 114, and patient, can then be moved inside the bore, to the second position, in order for the patient to be imaged by the MR imaging apparatus 112 and / or imaged or treated using the RT apparatus. The movement of the patient support surface is effected and controlled by a subject support surface actuator, which may be described as an actuation mechanism. The actuation mechanism is configured to move the subject support surface in a direction parallel to, and defined by, the central axis of the bore. The terms subject and patient are used interchangeably herein such that the subject support surface can also be described as a patient support surface. The subject support surface may also be referred to as a moveable or adjustable couch or table. The radiotherapy apparatus I device depicted in figure 1 also comprises MR imaging apparatus 112. The MR imaging apparatus 112 is configured to obtain images of a subject positioned, i.e. located, on the subject support surface 114. The MR imaging apparatus 112 may also be referred to as the MR imager. The MR imaging apparatus 112 may be a conventional MR imaging apparatus operating in a known manner to obtain MR data, for example MR images. The skilled person will appreciate that such a MR imaging apparatus 112 may comprise a primary magnet, one or more gradient coils, one or more receive coils, and an RF pulse applicator. The operation of the MR imaging apparatus is controlled by the controller. The controller is a computer, processor, or other processing apparatus. The controller may be formed by several discrete processors; for example, the controller may comprise an MR imaging apparatus processor, which controls the MR imaging apparatus 110; an RT apparatus processor, which controls the operation of the RT apparatus; and a subject support surface processor which controls the operation and actuation of the subject support surface. The controller is communicatively coupled to a memory, e.g. a computer readable medium. The radiotherapy device and / or the controller may be configured to perform any of the method steps presently disclosed and may comprise computer executable instructions which, when executed by a processor cause the processor to perform any of the method steps presently disclosed, or when executed by the controller cause the controller to perform any of the method steps presently disclosed, or when executed by the radiotherapy device cause the radiotherapy device to perform any of the method steps presently disclosed. Any of the steps that the radiotherapy device and / or the controller is configured to perform may be considered as method steps of the present disclosure and may be embodied in computer executable instructions for execution by a processor. A computer-readable medium may comprise the above-described computer executable instructions. The linac device also comprises several other components and systems as will be understood by the skilled person. For example, in order to ensure the linac does not leak radiation, appropriate shielding is also provided. Figure 2 depicts a computer-implemented method for processing position data indicating a position of a subject in a radiotherapy device. The method may be performed by a radiotherapy device or by a controller of or communicatively coupled to the radiotherapy device. The patient position information is in three dimensions with different tolerances along different dimensions. Such three dimensional data may be configured to provide high-precision anatomical information such that it is typically rather detailed and complex. There is a need for techniques to reduce this complex information to a form suitable for regulation of subject motion. For example, there is a need for reducing the position information to a form suitable for testing compliance with a threshold, e.g. for determining whether the relevant part of the subject is within an acceptable range or tolerance of a planned or expected location as a function of time. At step 202, three dimensional position data for the subject is received. The three dimensional position data may be received from a sensor of or communicatively coupled to the radiotherapy device. The sensor may be configured to measure, determine or generate the three dimensional position data using any suitable technique / imaging modality. The sensor may comprise, by way of non-limiting example, one or more of an MR imaging apparatus, a kV imaging apparatus, an MV imaging apparatus, optical cameras and time of flight cameras. For example, a belt around the patient’s waist or chest with a block on it may be used to measure movement via optical cameras. In a further example, the patient may breathe into a mouthpiece to track inhalation and exhalation through the mouth. Use of an MR imaging apparatus may be particularly advantageous for monitoring the movement of parts of the anatomy of the subject as a function of time while the subject is positioned in the radiotherapy device. MR Imaging may be used to track the movement of, for example, a tumour, and determine when it is in an appropriate position for a radiation dose to be delivered. Typically, an MR image will be interpreted by a clinician. In some embodiments, machine learning methods may be used to extract the three dimensional position data from the MR image. As the patient breathes, there will typically be movement in all three dimensions to a greater or lesser extent. The dimensions may also be referred to as axes, axes of movement, or directions herein. The first, second, and third dimensions may be substantially perpendicular to one another. In an example, the first dimension is along a superior-inferior axis of the radiotherapy device or of an intended position of a subject, i.e. along the axis of rotation of the rotatable gantry 116. This axis may correspond to a direction into and out of a bore of the radiotherapy device, or a direction between the head and feet of the subject. When the patient inhales and exhales, the primary or dominant or greatest amplitude direction of movement is along the first dimension. Alternatively or in addition to comprising a component along the superior-inferior axis, the motion may comprise a second component perpendicular to the floor (i.e. vertically up / down) and / or a third component parallel to the floor (i.e. horizontally left / right). These components may have smaller amplitudes to the superior-inferior component. These components may have the same or similar frequency to the superior-inferior component. At step 204, the three dimensional position data is processed to reduce it to a one dimensional signal. The one dimensional position signal is more suitable for testing compliance with a threshold, e.g. for comparison to an acceptable range of positions. The display of this data may assist a subject with controlling their breath, for example performing a breath hold or shallow breathing. The one dimensional signal may correspond to a single spatial dimension, which may optionally be based on combining information from multiple spatial dimensions using weighting as described herein. The one dimensional signal may vary as a function of time. At step 206, the one dimensional signal is output for display to the subject. The one dimensional signal may be output by the controller to a component communicatively coupled to the controller, e.g. to a display. This communicative coupling may comprise wired or wireless means. At step 208, the one dimensional signal may be displayed in real-time as the subject moves to provide real-time position feedback to the subject. The one dimensional signal may, for example, be displayed on a display screen or using a projector. Advantageously, real-time feedback allows the subject to respond to the feedback as the radiotherapy treatment is being performed. For example, they may be able to resume a breath-hold to prevent movement of the diaphragm so that the dosage of ionising radiation is suitably high at the location of a tumour and can be minimised for other regions. The one dimensional signal may be displayed in any suitable manner. For example, a plot of the one dimensional signal as a function of time may be displayed. In other examples, a representation of the current value of the one dimensional signal relative to one or more thresholds may be displayed, the current value and optionally the one or more thresholds being updated in real time to vary as a function of time. While the current value of the one dimensional signal may in some examples be depicted using representations that extend in multiple dimensions, these representations may vary in such a way to only depict one dimensional motion. For example, the increase in radius of a circle may be used to represent an increase in the current value of the one dimensional signal. In a first embodiment, the position data for the first axis of movement only may be displayed to the subject in real-time. The processing may therefore comprise reducing the three dimensional data to only the data corresponding to the first (primary or dominant) axis of movement. The subject can adjust their breathing patterns in response to the real-time feedback displayed to them. For example, they may hold their breath or breathe shallowly for a given amount of time. Selecting one dimensional position data may comprise selecting the position data corresponding to the movement along the superior-inferior axis of the intended position of the subject, i.e. along the axis of rotation of the rotatable gantry 116 and such that the axis runs between the head and feet of the subject when they are lying down. This processing may be particularly fast and efficient, which may advantageously shorten the latency between measurement of the position data and adjustment of the movement / breathing of the subject. In a second embodiment, processing the three dimensional data may comprise applying a weighting function to the position data for the first, second, and third axes of movement. This allows the data to be presented in a single axis of movement. This data can then be output for display to the subject. The weighting function may comprise a weight for each of the three dimensions of the three dimensional position data. The processing of the three dimensional position data may comprise multiplying respective position data for each of the three dimensions by the respective weight to determine weighted position data, and summing the weighted position data to determine the one dimensional signal. In other words, the position data for the first dimension may be multiplied by a first weight, the position data for the second dimension may be multiplied by a second weight, and the position data for the third dimension may be multiplied by a third weight. The results of these multiplications may be referred to as weighted position data. The weighted position data may be summed to give the one dimensional signal. Since this processing incorporates data from multiple dimensions, and yet still outputs a one dimensional signal, it advantageously provides the output data in a suitable form for regulation of movement / breathing while minimising loss of the input information. It will be appreciated that the embodiment described above of selecting only the first dimension corresponds to an example in which weights of one, zero and zero are chosen for the first, second and third dimensions respectively. Therefore, these embodiments are combinable and generalisable. One, two or three of the weights may be non-zero. As such, the generated one dimensional signal may comprise data from one, two or three dimensions of movement. The magnitudes of the weights for the different dimensions may be calculated, generated or determined based on the contribution movement along that dimension makes to the overall movement of the subject or a part thereof. For example, the first weight may be larger than the second and third weights based on movement along the first dimension being dominant. A ratio of the weights for the different dimensions may be equal to correspond to or be in proportion to a ratio of the amplitude of motion for the different dimensions. The present disclosure provides techniques for efficiently reducing the three dimensional position data to a form suitable for outputting as a one dimensional signal, while retaining the contribution of each component to an extent based on the contribution that component makes to the overall motion. This enables improved processing of position data in optimising the use of the detailed, multi-dimensional data while still outputting a signal suitable for testing compliance with a threshold, e.g. suitable for display to a subject to feedback whether the subject or a part thereof is within an acceptable range of positions. In some examples, the weights may be based on measurements of the movement patterns of one or more subjects, for example based on movement of a particular subject to undergo radiotherapy treatment, or based on a population average of multiple subjects, or based on a reduced population average of subjects with particular dimensions, ages, health conditions etc. For example, for respiratory motion of a subject, the subject may be positioned in the radiotherapy device and their motion in three dimensions may be monitored as they breathe. Thus, a training period may be used to generate appropriate weights for each dimension. The relative amplitudes of the movement along the different dimensions may be determined. The relative magnitudes of the weights may be based on these relative amplitudes, in direct proportion or via a different function. In some examples, different weights may be calculated and used for different phases of breathing. This may improve the accuracy and relevance of the one dimensional signal across the whole breathing cycle. In other examples, the same weights may be calculated and used over the whole breathing cycle. This may enable faster and more efficient processing. As set out previously, the one dimensional signal generated based on the processing may be used to test compliance with a threshold, for example to determine whether the relevant part of the subject is within an acceptable range or tolerance of a planned or expected location as a function of time. This determination may correspond to determinations made as part of gating. The gating may be used to control whether a beam of ionising radiation is turned on or off. The three dimensional position of a monitored structure (i.e. the X, Y, and Z coordinates) may be understood as the relative movement from a reference position, i.e., the change in the X axis position (AX), change in the Y axis position (AY) and change in the Z axis position (AZ). The reference position may be selected from the position data in a breath cycle. For example, it may be one of: the position when a subject has fully inhaled while practicing deep breathing; the position when a subject has fully exhaled while practicing deep breathing; the centre or mean position during a breath cycle; the position when a subject has inhaled while practicing shallow breathing; the position when a subject has exhaled while practicing shallow breathing; or the position when a subject is undergoing a breath hold. The reference position may be determined before a treatment starts or in an initial period of a treatment. In order for the subject to regulate their breathing, an indication of the acceptable window of their motion associated with their breathing may be provided to them. This may be implemented in different ways. Examples may include an upper and / or lower threshold for deep breath-hold inhalation, an upper and / or lower threshold for deep exhalation or a (wider) range between upper and lower thresholds for shallow breathing. The threshold(s) may correspond to or be proportional to a value used for determining a beam hold state of the radiotherapy device, i.e. to a position of the subject dividing situations in which a motion manager / controller will determine that the radiotherapy beam should be on or off. Threshold gating may involve, for example, a logical AND of the three gating tolerances in three dimensions i.e., a determination as to whether the AX value is not outside the tolerance defined, the AY value is not outside the tolerance defined, and the AZ value is not outside the tolerance defined. Radiotherapy treatment may continue (i.e. the beam may not be gated) if all three of these conditions are true. For example, the AZ value may correspond to the superior-inferior axis, and there may be an upper threshold for deep breath-hold inhalation, such that if the subject exhales, the AZ value goes beyond that threshold. Similarly, there may be a lower threshold for deep exhalation, such that if the subject inhales, the AZ value goes beyond that threshold. The gating tolerance may be a range for shallow breathing, such that if any of the AX, AY, or AZ values are outside a particular range, it is an indicator that the subject is breathing more deeply. In some implementations, the percentage overlap of a region to be treated and a gating volume (an expansion of the region to be treated) may be compared to a tolerance overlap. If the percentage overlap does not exceed the tolerance overlap, then it may indicate that the subject is not in a suitable location for treatment to continue, and the beam may be gated in response. This gating based on percentage of overlap may be referred to as VOICE gating. The dominant motion may be derived from the AX, AY, AZ values, either by choosing a dominant axis or a vector based combination using the weighting described above. The thresholds described above may be continually adjusted. The thresholds may be dynamically updated during treatment, for example to correspond to the gating tolerances for a given radiotherapy treatment. In other words, if the controller determines that a condition for gating of the beam should be changed to be more or less strict, e.g. based on an altered beam strength or beam location or target location, the thresholds displayed to the subject may be dynamically changed in a corresponding manner. The threshold gating for turning a radiotherapy beam on and off may be determined separately from the signal that is displayed to the subject, or the same data may be used. In some implementations, the subject’s breathing is monitored prior to treatment or during the treatment to determine the weighting of the axes. The dominant motion indicator, which indicates the dimension along which the amplitude of motion is greatest, may be determined when the patient first engages with the system, i.e. when the patient is first disposed in the radiotherapy device. It is advantageous that the three dimensional data be processed in such a way that facilitates correlation between the behaviour of the patient, and in particular their breathing, and the output one dimensional data signal. This correlation helps to guide the patient to control and regulate their breathing, for example by implementing a breath hold or shallow breathing. Adjustment of the thresholds can then prompt the patient to control their breathing in various ways. By using the gating tolerances as the thresholds or acceptable range(s) for display to the subject, the guiding of the patient’s breathing can be linked directly to the condition for treatment to continue or be interrupted, which may lead to more efficient treatment workflows. This can also increase the speed and efficiency of the processing of the position data and reduce the latency and increase the responsiveness of the one dimensional signal provided for display to the patient. Complex motion trajectories may occur where the dominant motion has an inflexion. For example, this may be caused by the patient rotating their torso. In response to the change in the dominant axis, it may be determined that a “tipping point” has been met. In some implementations, the system may determine that the dominant axis has changed, i.e. may determine that the amplitude of motion is now greatest in the X dimension or the Y dimension rather than the Z dimension. The controller may dynamically adjust the processing of the three dimensional position data to account for this. For example, the processing of the data may comprise selecting the new dominant axis or adjusting the weights used for the different axes based on the new amplitudes of motion along the different dimensions. 5 While respiratory motion has been referred to by way of example, the techniques described herein can be applied to other motions, for example other periodic or quasiperiodic motions. In some examples, the techniques described herein may be applied to cardiac motion. Figure 3 depicts the relationship between beam status, the instruction provided to the patient, and the respiratory cycle of the patient, including a task for the patient to hold their 10 breath. The respiratory cycle of the patient may be measured via an imaging (e.g. MR imaging) system, which may be used to provide an indication of the position of the subject or a part thereof relative to a reference position. The position / movement of the subject may be parameterized based on spatial dimensions, which may be measured or estimated using the above-mentioned technique. LO 15 The bottom of figure 3 shows a graph including the volume of air in the lungs throughout the C\l respiratory cycle. As the patient inhales, the gradient of the line representing volume of air is positive, and as the patient exhales, the gradient of the graph is negative. The patient may be instructed to breathe normally as task 1, and if the patient does so, the inhale and exhale components of the respiratory cycle have an approximately constant amplitude and phase. 20 During task 2, the patient may be instructed to take deep breaths, and if the patient does so, the amplitude will increase in response to the increased volume of air being inhaled and exhaled. During task 3, the user may be instructed to hold their breath and therefore the volume of air in the lungs will be constant for as long as the patient holds their breath. As indicated in a treatment plan, it may be intended to irradiate the subject for the duration of 25 this breath hold that the beam status changes from off to on for this period. During the breath hold, the position of the radiation target should be approximately constant, such that the risk to the surrounding tissues is minimised. For example, if the breath is held for 15 seconds, the beam will only be on for that 15 seconds to ensure that the treatment is targeted correctly. 30 However, the subject may start to deviate from the tasks, for example by starting to exhale during the breath hold. The techniques described herein provide a real time indication to the subject that their measured position / volume of air in their lungs is not constant. For example, the line in the graph at the bottom of figure 3 may start to slope downwards during the breath hold window. This may alert the subject that they are deviating from the expected breathing pattern and allow them to correct for this by stopping exhaling to maintain an adequate breath hold. For example, the line may slope downwards temporarily, but remain in the shaded region indicating the acceptable range of position / motion. If the line goes outside the shaded region, this indicates that the position / motion is beyond a threshold and the beam may be gated. Tasks 1-3 may be repeated as necessary. Task 1 of normal breathing is followed by task 2 of taking deep breaths which is followed by task 3 of a breath hold. A recovery period (task 4), in which the subject regains a regular breathing pattern, may take place before repeating tasks 1-3. The cycle may be complete once the beam has been on for a cumulative time that is sufficient for treatment. Figure 4 depicts the relationship between beam status, the instruction provided to the patient, and the respiratory cycle of the patient, including a task for the patient to hold their breath which is interrupted. For example, the patient may sneeze, causing them to drop out of the breath hold only to resume it shortly after. When the patient is not in a breath hold, i.e., the volume of air in their lungs is not within a given range, the beam will be automatically configured to be turned off. Task 3 may last, for example, for 19 seconds, however the beam status is only on for 15 seconds of that. If the user continues to hold their breath when they have not been instructed to do so, the beam status may remain off. If the user begins a breath hold when they have not been instructed to do so, the beam status may remain off. Figure 5 depicts the relationship between beam status, the instruction provided to the patient, and the respiratory cycle of a patient, including a task for the patient to perform shallow breathing. In the period of shallow breathing, the volume of air in the lungs and the position of the subject may vary with a relatively small amplitude (i.e. relative to deeper breathing). In the graph at the bottom of figure 5, the top and bottom of the shaded region correspond to upper and lower thresholds respectively on acceptable positions of the subject to continue treatment. If the subject begins to breath more deeply, the amplitude of the line in the graph at the bottom of figure 5 may increase such that it gets closer to the boundaries of the shaded region. This serves as an alert to the subject that they should adjust their breathing to make it shallower, or at least no deeper. This real time feedback can enable the breathing of the subject to stay within an acceptable range such that treatment can be continued. If the breathing of the subject increases in amplitude such that the position of the subject goes beyond the threshold represented by the shaded region, the radiotherapy beam may be gated. Figure 6 depicts the relationship between beam status, the instruction provided to the patient, and the respiratory cycle of a patient, including a task for the patient to perform shallow breathing which is interrupted. For example, shallow breathing may be difficult to maintain for some patients. The radiotherapy beam may be gated off at the point at which the subject goes outside the range of acceptable positions. Figures 7a to 7d depict a display to the patient to prompt them to hold their breath. Figures 8a to 8d depict a display to the patient to prompt them to breathe shallowly. These are example representations of how the information about one dimensional position data and an acceptable range of movement might be displayed to a patient. In this example, the display may comprise a speedometer-type dial display representing the full range of the patient’s respiratory cycle (a full inhale and a full exhale), where the acceptable range for a breath hold is shown as a dark grey section in part of the dial. The needle represents the one dimensional position data, and moves in real time as the patient breathes. The needle may also be referred to as the respiratory marker. As the patient inhales, the needle may move clockwise around the display, and as the patient exhales, the second circle may move counter-clockwise. The region for breath hold or shallow breathing may be indicated within the dial, for example by a coloured or darkened block. When the needle is held within this region, the tumour is in the optimal location for treatment and the radiotherapy beam should be on and delivering radiation. In some implementations, the region indicated may change when the user is prompted to relax. To prompt the patient to shallow breathe, the display indicates a region that the needle should be kept in which is narrower than the total range of the dial. The region may be positioned close to the centre of the range of movement represented by the entire dial. To prompt the patient to hold their breath, the region that the needle should be kept in (shown in Figures 7a to 7d as a dark grey region) may be positioned at the top of the range of movement of the dial. In another example, the display may comprise a circle representing the full range of the patient’s respiratory cycle (a full inhale and a full exhale). Figure 8a to 8d depicts a display to the patient to prompt them to shallow breathe. In this example, the region indicated by a coloured or darkened block represents the shallow breathing window when the tumour is in the optimal location for treatment and the radiotherapy beam should be on and delivering radiation. The region is smaller than the circle representing the full range of the respiratory cycle, and may be positioned close to the centre of the range of movement. A ring that expands and contracts within the circle represents the one dimensional position data indicating the inhale / exhale position within the respiratory cycle. It may also be referred to as the respiratory marker. At Figure 7a and 8a, the patient may be instructed to relax and breathe normally. At Figure 7b and 8b, the patient may be instructed to breathe deeply and prepare to hold their breath. This may include a count down to when they will receive further instructions. At Figure 7c, the patient may be instructed to hold their breath, and at Figure 8c they may be instructed to instead breathe shallowly. The region indicated on the display will correspond to these instructions. When the patient breathes such that the representation of the one dimensional position data (the respiratory marker) is within the representation of the acceptable range (such as the darkened region of the dial or circle), there may be an indication that they have successfully performed shallow breathing or held their breath. For example, as shown at Figure 7d and 8d, a tick mark may be displayed to show that they are in the indicated region of movement. Alternatively, this indication may be based on the three dimensional position data received from the MR image. In some implementations, the movement in a second and third dimension are measured, and form part of the three dimensional position data but only a first dimension is displayed to the user. For example, the first dimension may be along the vertical axis of the patient. If the patient does not breath such that the three dimensional position data is within an acceptable range, they will not receive an indication that the breath hold has been successful. For example, Figures 7c and 8c show the respiratory marker outside of the indicated region, and there is no tick mark. In another example, the display may comprise a trace which moves vertically upwards as the patient inhales and vertically downwards as the patient exhales. The trace is in a fixed position on the horizontal axis and the display scrolls to the left. The range may be indicated on the trace by a coloured or patterned section of the graph. For a breath hold, a range at the top of the inhale position will be displayed. For shallow breathing, a larger range within the centre of the respiratory cycle will be displayed. Optionally, if the trace is within the acceptable range, an indication may be displayed to the user, for example as a tick. If the trace is outside the acceptable range, the tick may be removed. In some implementations, an image extracted from an MR system in real time may be overlaid with the display. For example, a first circle representing one dimensional position data in real time and a second circle representing the acceptable range for a breath hold may be overlaid on the image. The circle representing this position data will therefore move in real time, representing the inhale and exhale position of the patient’s breath cycle. When the patient is instructed to breathe shallowly, there may be a corresponding display. However, the representation of the acceptable range may not be a circle, but may instead be an oblong shape to represent the wider range of positions that are accommodated during shallow breathing. These representations may be coloured to help differentiate it from the background image and from one another. The MR image is intended for a clinician to interpret, and therefore the MR image alone is less suitable to be displayed to the patient since it is too complex. By overlaying this image with a simple graphical representation of their breathing position and the target region, the patient will be more easily able to adjust their breathing pattern for optimal treatment. The data displayed to the subject, i.e. displayed at step 208 referred to above, may be an analogue signal proportional to the breathing motion of the subject. The signal may be scaled prior to being displayed to the subject. The expected position of the thresholds can be calculated, for example based on prior measurements of the subject breathing, or based on population-level analysis. In some implementations, MR imaging and post processing of real-time images may be used to determine the three dimensional position of a monitored structure (for example, an organ or region of interest in the body). The X, Y and Z co-ordinates of the structure are thus known as a relative movement from a reference position (AX, AY &AZ). The patient only has control over their breathing, however their breathing may affect the movement of monitored structures. While the patient may be able to control how deeply or quickly they breathe, providing an indication that they should breathe such that an X displacement, Y displacement and Z displacement are within particular ranges may not be realistic or helpful for regulating the patient’s motion. The techniques described herein provide processing of complex three dimensional motion to output a one dimensional signal usable by a subject to regulate their breathing, for example to remain within a threshold. In some implementations, the patient is provided with a live video stream to help them regulate their breathing during treatment. In the live video stream, dynamic information may be provided, containing some trace or “Respiratory Signal” that correlates strongly with their breathing cycle. A poor correlation could lead to a lack of engagement or disconnect between the information presented and the patient’s ability to influence the anatomical position monitored through breathing. To guide the patient, there may be a “Respiratory Window”. The patient’s objective is to align their Respiratory Signal with the Respiratory Window. For example, in Figures 8a to 8d, the moving circle represents the Respiratory Signal, and the stationary circle represents the Respiratory Window for a deep breath hold. Radiation delivery (i.e., release of the gating hold signal to the radiotherapy device that delivers ionising radiation) may be computed based on a motion management strategy. For example, it may be computed based on at least one of threshold gating and VOICE gating as described above. In both threshold gating and VOICE gating, the motion of the monitored structure is known. Therefore the values AX, AY &AZ are all available for computation. The patient is able to see their behaviour (breathing) tightly correlating with the information provided to them by the system. The correlation is not only absolute (position) but with good temporal connection (low latency). Advantageously, these features mean that the subject is able to adjust their breathing in response to the biofeedback. Therefore the radiotherapy may be delivered more quickly and efficiently, with reduced break times needed where radiotherapy is not being delivered. The patient is also able to receive an indication of the acceptable window of their behaviour. Examples may include an upper threshold for deep breath-hold inhalation, a lower threshold for deep exhalation or a range for shallow breathing. The threshold may be proportional to the system’s Beam Hold state. The Beam Hold state is the state in which the Motion Manager decides that above criteria for Threshold Gating and VOICE Gating have been met and would allow the beam to be on (should it be possible) or not on (should there be other reasons for it not to be on). These two information elements of motion of the monitored structure and the acceptable window / range can be derived from the AX, AY and AZ values and the Beam Hold state conditions described above. The dominant motion can be derived from the A values. In some implementations, a dominant value may be chosen (for example, AZ corresponding to the superior-inferior axis of the radiotherapy device, along the intended position of a subject) or the dominant motion can be derived using a vector based combination of two or more of the A values. For example, the dominant motion may be a vector based combination of AY and AZ, corresponding to the direction perpendicular to the floor and the superior-inferior axis respectively. In some implementations, the thresholds (upper, lower or range as described above) can be continually adjusted based on the time-varying Beam Hold state conditions. Optionally, prior to the patient first engaging with the system, the system will first automatically determine the dominant motion indicator based on a monitored breathing pattern of the patient, and then apply the threshold indicators based on the Beam Hold state transitions. The system may then automatically adjust from this point forward for the patient, for example, based on changes in the radiotherapy delivery or treatment plan that change the motion that can be tolerated. While the methods disclosed herein are presented in a certain sequential order, this should not be taken to limit the methods to the orders presented. One or more of the method steps may be omitted or rearranged. The various steps may be performed in different orders. Various steps may be performed at the same time or substantially the same time. Herein, references to events occurring substantially at the same time may refer to events at least partially overlapping in time and / or events occurring at the same time within measurement uncertainties. Figure 9 illustrates a block diagram of one implementation of a radiotherapy system 900. The radiotherapy system 900 comprises a computing system 910 within which a set of instructions, for causing the computing system 910 to perform any one or more of the methods discussed herein, may be executed. The computing system 910 shall be taken to include any number or collection of machines, e.g. computing device(s), that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methods discussed herein. That is, hardware and / or software may be provided in a single computing device, or distributed across a plurality of computing devices in the computing system. In some implementations, one or more elements of the computing system may be connected (e.g., networked) to other machines, for example in a Local Area Network (LAN), an intranet, an extranet, or the Internet. One or more elements of the computing system may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. One or more elements of the computing system may be a personal computer (PC), a tablet computer, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. The computing system 910 includes controller circuitry 911 and a memory 913 (e.g., readonly memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.). The memory 913 may comprise a static memory (e.g., flash memory, static random access memory (SRAM), etc.), and / or a secondary memory (e.g., a data storage device), which communicate with each other via a bus (not shown). Controller circuitry 911 represents one or more general-purpose processors such as a microprocessor, central processing unit, accelerated processing units, or the like. More particularly, the controller circuitry 911 may comprise a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Controller circuitry 911 may also include one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. One or more processors of the controller circuitry may have a multicore design. Controller circuitry 911 is configured to execute the processing logic for performing the operations and steps discussed herein. The computing system 910 may further include a network interface circuitry 915. The computing system 910 may be communicatively coupled to an input device 920 and / or an output device 930, via input / output circuitry 917. In some implementations, the input device 920 and / or the output device 930 may be elements of the computing system 910. The input device 920 may include an alphanumeric input device (e.g., a keyboard or touchscreen), a cursor control device (e.g., a mouse or touchscreen), an audio device such as a microphone, and / or a haptic input device. The output device 930 may include an audio device such as a speaker, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), and / or a haptic output device. In some implementations, the input device 920 and the output device 930 may be provided as a single device, or as separate devices. In some implementations, computing system 910 includes training circuitry 918. The training circuitry 918 is configured to train a method as described herein. The model may comprise a deep neural network (DNN), such as a convolutional neural network (CNN) and / or recurrent neural network (RNN). Training circuitry 918 may be configured to execute instructions to train a model that can be used to perform a method as described herein. Training circuitry 918 may be configured to access training data and / or testing data from memory 913 or from a remote data source, for example via network interface circuitry 915. In some examples, training data and / or testing data may be obtained from an external component, such as image acquisition device 940 and / or treatment device 950. In some implementations, training circuitry 918 may be used to update, verify and / or maintain the model. In some implementations, the computing system 910 may comprise image processing circuitry 919. Image processing circuitry 919 may be configured to process image data 980 (e.g. images, or imaging data), such as medical images obtained from one or more imaging data sources, a treatment device 950 and / or an image acquisition device 940 as described herein. Image processing circuitry 919 may be configured to process, or pre-process, image data. For example, image processing circuitry 919 may convert received image data into a particular format, size, resolution or the like. In some implementations, image processing circuitry 919 may be combined with controller circuitry 911. In some implementations, the radiotherapy system 900 may further comprise an image acquisition device 940 and / or a treatment device 950, such as those disclosed herein (e.g. in relation to Figure 1). The image acquisition device 940 and the treatment device 950 may be provided as a single device. In some implementations, treatment device 950 is configured to perform imaging, for example in addition to providing treatment and / or during treatment. The treatment device 950 comprises the main radiation delivery components of the radiotherapy system described herein. Image acquisition device 940 may be configured to perform positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), etc. Image acquisition device 940 may be configured to output image data 980, which may be accessed by computing system 910. Treatment device 950 may be configured to output treatment data 960, which may be accessed by computing system 910. Computing system 910 may be configured to access or obtain treatment data 960, planning data 970 and / or image data 980. Treatment data 960 may be obtained from an internal data source (e.g. from memory 913) or from an external data source, such as treatment device 950 or an external database. Planning data 970 may be obtained from memory 913 and / or from an external source, such as a planning database. Planning data 970 may comprise information obtained from one or more of the image acquisition device 940 and the treatment device 950. The various methods described above may be implemented by a computer program. The computer program may include computer code (e.g. instructions) 1010 arranged to instruct a computer to perform the functions of one or more of the various methods described above. The steps of the methods described above may be performed in any suitable order. The computer program and / or the code 1010 for performing such methods may be provided to an apparatus, such as a computer, on one or more computer readable media or, more generally, a computer program product 1000, depicted in Figure 10. The computer readable media may be transitory or non-transitory. The one or more computer readable media 1000 could 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 could 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 disk, such as a CD-ROM, CD-R / W or DVD. The instructions 1010 may also reside, completely or at least partially, within the memory 913 and / or within the controller circuitry 911 during execution thereof by the computing system 910, the memory 913 and the controller circuitry 911 also constituting computer-readable storage media. In an implementation, the modules, components and other features described herein can be implemented as discrete components or integrated in the functionality of hardware components such as ASICS, FPGAs, DSPs or similar devices. A “hardware component” is a tangible (e.g., non-transitory) physical component (e.g., a set of one or more processors) capable of performing certain operations and may be configured or arranged in a certain physical manner. A hardware component may include dedicated circuitry or logic that is permanently configured to perform certain operations. A hardware component may comprise a special-purpose processor, such as an FPGA or an ASIC. A hardware component may also include programmable logic or circuitry that is temporarily configured by software to perform certain operations. In addition, 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). Unless specifically stated otherwise, as apparent from the following discussion, it is appreciated that throughout the description, discussions utilizing terms such as "receiving”, “determining”, “comparing ”, “enabling”, “maintaining,” “identifying,” “obtaining,” “detecting,” “generating,” “processing,” or the like, refer to the actions and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other implementations will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific example implementations, it will be recognized that the disclosure is not limited to the implementations described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. A computer-implemented method for processing position data indicating a position of a subject in a radiotherapy device, the method comprising:receiving three dimensional position data for the subject;processing the three dimensional position data to reduce it to a one dimensional signal; andoutputting the one dimensional signal for display to the subject.

2. The computer-implemented method of claim 1, comprising displaying the one dimensional signal to the subject in real time to provide real-time position feedback to the subject.

3. The computer-implemented method of claim 1 or claim 2, wherein processing the three dimensional position data comprises selecting one dimensional position data from the three dimensional position data, the one dimensional position data corresponding to a dominant axis of movement of the subject, wherein the one dimensional position data is used as the one dimensional signal.

4. The computer-implemented method of claim 1 or claim 2, wherein processing the three dimensional position data comprises applying a weighting function to the three dimensional position data.

5. The computer-implemented method of claim 4, wherein the weighting function comprises a weight for each of the three dimensions of the three dimensional position data, and processing the three dimensional position data comprises:multiplying respective position data for each of the three dimensions by the respective weight to determine weighted position data; andsumming the weighted position data to determine the one dimensional signal.

6. The computer-implemented method of any preceding claim, further comprising:obtaining a three dimensional acceptable range for the three-dimensional position data;processing the three dimensional acceptable range for the three dimensional position data to reduce it to a one dimensional range; andoutputting the one dimensional range for display to the subject.

7. The method of claim 6, wherein processing the three dimensional acceptable range for three dimensional position data to reduce it to a one dimensional range comprises selecting the one dimensional range from the three dimensional acceptable range, the one dimensional range corresponding to a dominant axis of movement of the subject.

8. The computer-implemented method of claim 6, wherein processing the three dimensional acceptable range comprises applying an acceptable range weighting function to the three dimensional position data.

9. The computer-implemented method of claim 8, wherein the acceptable range weighting function comprises a weight for each of the three dimensions of the three dimensional acceptable range, and processing the three dimensional acceptable range comprises:multiplying a respective acceptable range for each of the three dimensions by the respective weight to determine weighted acceptable ranges; andsumming the weighted acceptable ranges to determine the one dimensional range.

10. The computer-implemented method of any preceding claim, wherein the three dimensional position data comprises data for a first dimension, data for a second dimension, and data for a third dimension, and the method further comprises:comparing the data for the first dimension to a first range;comparing the data for the second dimension to a second range;comparing the data for the third dimension to a third range; anddetermining that the position data for at least one of the first, second, and third dimensions is outside of the first, second, and third ranges respectively.

11. The computer-implemented method of claim 10, the method further comprising:in response to determining that the position data is outside of at least one of the first, second, and third ranges, outputting an indication that the user is outside of the acceptable range.

12. The computer-implemented method of any preceding claim, comprising displaying a dynamic representation of the one dimensional position data and the acceptable range in real time to provide real-time position feedback to the subject.

13. The computer-implemented method of any of claims 6-12, wherein the acceptable range is constant with time and is displayed to the subject to indicate breath hold.

14. The computer-implemented method of any of claims 6-12, wherein the acceptable change varies as a function of time.

15. The computer-implemented method of any of claims 6-14, wherein the acceptable range is displayed to the subject to indicate a shallow breathing pattern.

16. The computer-implemented method of any of claims 6-15, comprising determining the acceptable range based on pre-treatment measurements of the breathing of the subject.

17. The computer-implemented method of any preceding claim, wherein the three dimensional position data comprises periodic movement data.

18. The computer-implemented method of claim 17, wherein the periodic movement data corresponds to a respiratory pattern of the subject.

19. The computer-implemented method of any preceding claim, wherein the three dimensional position data is received from an MR imaging apparatus.

20. A computer-readable medium storing instructions which, when executed by a processor, cause the processor to perform the method of any of claims 1-19.

21. A controller comprising a processor and a memory, the memory storing instructions which, when executed by the processor, cause the processor to perform the method of any of claims 1-19.

22. A radiotherapy device comprising:the controller of claim 21;a sensor communicatively coupled to the controller, the sensor being configured to measure and transmit the three dimensional position data to the controller; anda display communicatively coupled to the controller, the display being configured to receive the one dimensional signal from the controller and to display the one dimensional signal.

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