System for adaptive radiotherapy treatment delivery

Abstract

Disclosed herein is a radiotherapy system comprising: a radiation delivery system for delivering radiation to a target region of a patient; a computer data store configured to store a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable; a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan; and a plan adaptation module.

Description

[0001] System for adaptive radiotherapy treatment delivery

[0002] This disclosure relates to radiotherapy, and in particular to a system and method for delivering adaptive radiotherapy to a patient.

[0003] Background

[0004] 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. In radiotherapy treatment, it is desirable to deliver a prescribed dose of radiation to a target region, e.g. a tumour, of a patient and to limit irradiation of other parts of the patient, e.g. healthy tissue and organs at risk (OARs).

[0005] The treatment planning procedure typically involves obtaining one or more medical images, such as a CT image of the patient, and segmenting them to identify the target region and OARs near the target region. The segmentation process can be performed manually or using auto-segmentation techniques. The clinician determines radiation treatment parameters, for example by prescribing a radiation dose to be delivered to the target region and maximum doses which can safely be delivered to the various OARs. The treatment planning procedure may then involve optimizing various radiation delivery variables to meet the prescribed radiation treatment parameters, for example determining the number of sessions (or 'fractions') over which radiotherapy should be conducted, the angles at which the radiation beam should be applied during each fraction, at what beam energy, the duration of application of the radiation beams at these angles, and the beam shape(s) at each angle of delivery. The clinician can be assisted by software during some or all of these steps. This aspect of treatment planning, conducted in advance of the patient's treatment (and sometimes between treatment fractions if there are gradual changes), can be described as 'offline' treatment planning.

[0006] However, the characteristics of the tumour, such as its shape and size, may change over the course of the multiple fractions of treatment. Similarly, other patient information and characteristics of the patient's anatomy can change between fractions, in both cases in a less foreseeable way. Accordingly, 'online' adaptive radiotherapy techniques may be used to update and re-optimise the radiotherapy treatment plan and / or delivery variables immediately prior to the patient's treatment. According to online adaptive radiotherapy techniques, the patient is imaged again immediately prior to treatment, and the treatment plan for that day's fraction may be adjusted and / or reoptimized according to the latest available medical images. Online adaptive radiation therapy techniques, as part of an online treatment workflow, therefore allow inter-fraction anatomical changes to be taken into account.

[0007] Additionally, the location or orientation of the tumour may change during a fraction session, which may be due to intra-fraction motion, such as patient breathing. In such cases, intra-fractional imaging during delivery can provide information that enables the implementation of 'real-time' adaptation in the form of either 'gating' of the radiation delivery, i.e. turning the beam on and off periodically, and / or providing an over-ride to the multi-leaf collimator control ('tracking') in order to shape the beam differently to the shape specified in the treatment plan.

[0008] However, current 'real-time' adaptation techniques involve adapting a fixed treatment plan. Such mechanisms require 'over-ride' features in the radiation delivery system in order to intercept and modify the execution of this original, fixed treatment plan. Such existing 'real-time' adaptation is effective, but only makes use of only some of the degrees of freedom available within the radiotherapy delivery system for control and optimisation of radiotherapy delivery. It is desirable to further optimise adaptive treatment, and to utilise further degrees of freedom of the delivery system for realtime adaptation in order to further improve the delivery of radiation to the tumour and reduce the delivery of radiation to adjacent healthy tissue.

[0009] The present invention seeks to address these and other disadvantages encountered in the prior art by providing an improved system and method for delivering radiotherapy to a patient.

[0010] Summary

[0011] An invention is set out in the independent claims. Optional features are set out in the dependent claims.

[0012] Figures

[0013] Specific examples are now described, by way of example only, with reference to the drawings, in which:

[0014] Fig. 1 shows a radiotherapy device or apparatus according to the present disclosure;

[0015] Fig. 2 shows a radiotherapy treatment workflow for fixed treatment plan delivery;

[0016] Fig. 3 shows a radiotherapy treatment workflow for fixed treatment plan delivery with gating and / or tracking;

[0017] Fig. 4 shows a radiotherapy system according to the present disclosure; Fig. 5 shows a radiotherapy treatment workflow for adaptive treatment plan delivery according to the present disclosure;

[0018] Fig. 6 shows a method of generating therapeutic radiation according to the present disclosure;

[0019] Fig. 7 shows a block diagram of one implementation of a radiotherapy system; and

[0020] Fig. 8 shows a computer readable medium or, more generally, a computer program product.

[0021] Overview

[0022] In a non-limiting overview provided to aid understanding, a system and method is provided that is capable of real-time adaptive radiotherapy, in which at least one radiation delivery variable of a current radiotherapy treatment plan is modified, during treatment, to generate a new current radiotherapy plan. The new current radiotherapy plan is saved in a computer data store (for example a computer memory), and may replace the existing treatment plan to form the basis of ongoing treatment. New plans may be regularly, or even continuously, updated based on real-time information about the target region, and saved in the computer data store to form the basis of ongoing treatment, allowing the new plans to be delivered using features such as control point interpolation provided by the delivery control module. This contrasts with current methods, which are not truly adaptive and do not generate and save a new treatment plan in this way, but instead simply use a direct control over-ride mechanism to bypass altogether the delivery control module and the 'control points' defined in the treatment plan.

[0023] Using this system and / or method, radiotherapy can be delivered in a manner that adapts to real-time anatomy or variation in earlier delivery and provides more accurate dose delivery and targeting of the tumour. More accurate targeting in turn means that treatment planning can use narrower positional margins, reducing the amount of radiation delivered to healthy tissue, and potentially reducing the number of fractions required, providing a better outcome for the patient.

[0024] Furthermore, the system and / or method of the present disclosure provides an approach to adaptive radiotherapy that can further improve delivery by generating future control points in a radiotherapy plan, which allows for adaptation beyond the limitations of a real-time over-ride-based system, and further allows for adaptation of the treatment plan for future treatment fractions based on real-time information from the present fraction.

[0025] Yet furthermore, by storing the generated plan in the computer data store that is used for the original plan, a separation of the adaptation architecture and delivery architecture can be achieved, allowing, for example, for a plan adaptation module to be fitted to existing delivery systems with only minor modification.

[0026] Further examples and advantages are set out below.

[0027] Detailed Description

[0028] Disclosed herein are systems, devices, methods and apparatuses relating to radiotherapy. With linear accelerator-based radiotherapy devices being highly complex and having many inter-related parts, the terms "system", "device", "apparatus", and "machine" may all be applied interchangeably to describe the radiotherapy device as a whole, or collections of components of the radiotherapy device. Likewise, the group of components that are primarily responsible for generating radiation and delivering it to a patient may be referred to interchangeably as "radiation delivery system", or "radiotherapy delivery apparatus", or "beam delivery apparatus" and the like, as will be understood by the skilled person.

[0029] Fig. 1 shows an exemplary radiotherapy (RT) device 100. The device and its constituent components will be well known to the skilled person but is described here generally for the purpose of providing useful accompanying information for the present disclosure. The radiotherapy device 100 is based on a linear accelerator (linac).

[0030] The device shown in Fig. 1 combines magnetic resonance (MR) imaging capability with a linac-based radiotherapy capability, and is known as an MR-linac device. MR-linacs are particularly well-suited for delivery of adaptive treatment, since MR images may be taken immediately prior to or during 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 Fig. 1 is in accordance with the present disclosure and is suitable for use with the disclosed systems and apparatuses. However, the present disclosure may be implemented in any radiotherapy device, for example, a linac-based radiotherapy device with CBCT imaging capability.

[0031] The device 100 in Fig. 1 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 patient, and the linac device produces and shapes a beam of radiation and directs it toward a target region within a patient'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.

[0032] The MR-linac device depicted in Fig. 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.

[0033] 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.

[0034] The radiation source may comprise a beam generation system. For a 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. In a 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 ring-gantry.

[0035] 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.

[0036] 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. These ion chambers measure the dose delivered by a beam, for example using monitor units (MU). The beam can be shaped in various ways by beam-shaping apparatus, for example by using a multileaf collimator 108, before it passes into the patient as part of radiotherapy treatment.

[0037] In some implementations, the source of radiation is configured to emit either an X-ray beam or a particle beam such as 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.

[0038] 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.

[0039] The radiotherapy apparatus / device depicted in Fig. 1 also comprises MR imaging apparatus 112. The MR imaging apparatus 112 is configured to obtain images of a patient or 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.

[0040] 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.

[0041] 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.

[0042] In conventional approaches to radiotherapy, a dose for the target / tumour is determined and prescribed, and that dose is then delivered in fractions across a number of sessions, which reduces the effects of radiation that is delivered to healthy tissue of the patient. Accordingly, a radiotherapy treatment plan is determined by clinicians in advance of beginning treatment. As set out above, that treatment plan may be delivered (e.g.) via traditional image-guided radiotherapy (IGRT), or via online adaptive techniques. In addition, off-line plan adjustments may take place. In traditional radiotherapy, a fixed treatment plan suitable for delivering a prescribed dose is prepared based on a CT scan taken some time before the course of treatment. Preparing the plan involves determining the number of sessions (or 'fractions') over which radiotherapy should be conducted, the angles at which the radiation beam should be applied during each fraction, at what beam energy the radiation beam should be applied, the beam shape(s) at each angle of delivery (etc.). The parameters to be used for each of those variables, which may be considered degrees of freedom of the radiation delivery system, are thus decided at the initial planning stage. The plan is delivered over the multiple fractions, with each fraction taking place on a different day and perhaps necessitating separate hospital visits for the patient.

[0043] A typical radiotherapy treatment plan for a particular fraction comprises a sequence of control points. Each control point specifies a measure of delivery progress - monitor units (MU or percentage MU). In other words, a fraction aims to deliver a certain dose to the tumour (for example 1000 MU), and each control point is to be delivered at a certain fraction of the total dose (for example, the first at OMU, a second at 50 MU, a third at 85 MU, etc). The MU is used as a measure of progress of the fraction, and interpolation between control points is sometimes necessary. For example, let us say that control point n has 100MU and the next control point n+1 has 110MU and that the current MU counter at a particular moment in time stands a 105MU. The desired delivery positions at that moment are typically derived by interpolating between control point n and control point n+1. This interpolation mechanism may decide the amount of MU to be delivered at various positions.

[0044] Each control point also specifies a set of delivery variables for each degree of freedom of the radiotherapy system. The positions may also be considered as, and referred to, as radiation delivery variables, or parameters. In a simple example, there may be only a single radiation delivery variable, a multi-leaf collimator (MLC) shape variable, in which case the control points can be described as a set of pre-determined MLC shapes scheduled to be delivered at certain points during a treatment fraction. However, the degrees of freedom, and hence radiation delivery variables, may include, for example, leaf and diaphragm positions that define a multi-leaf collimator (MLC) shape, the gantry angle, the beam energy and / or intensity, and the patient support surface position(s). It is useful to visualize the sequence of control points as a function, or a graph, of positions against MU, which specifies how the radiation is to be distributed using the degrees of freedom of the radiotherapy system. The discrete steps in the sequence, from one control point to the next, can approximate a smooth continuum of movement while radiating. However, discontinuities may also be specified with two adjacent control points having the same MU but different positions. In this case, the radiation must stop briefly while changing positions. This basic layout of a plan can be used in different ways. For example, intensity modulated radiotherapy (IMRT) plans alternate between radiating at a first fixed set of positions, then moving to a next set of positions, and repeating the process until all control points have been delivered. In contrast, volumetric modulated arc therapy (VMAT) treatment plans approximate a continuous dynamic motion. The systems and methods of the present disclosure are not limited to a particular treatment plan type or treatment mode or way of specifying a treatment plan.

[0045] In a traditional system with no patient imaging capability, the system is designed to input a plan and to deliver it to completion. It is also possible to re-plan and deliver a so-called partial plan in case something has gone wrong in the delivery of the intended plan. Such approaches are referred to herein as 'fixed treatment plan' delivery.

[0046] Fig. 2 shows a radiotherapy treatment workflow 200 for such fixed treatment plan delivery. At block 202, a CT scan of the patient is taken prior to any treatment. At block 204, planning is performed to generate a treatment plan to deliver the prescribed dose to the patient over a number of fractions. The treatment plan comprises a number of control points and delivery variables, as set out above. The treatment plan may be repeated in the same manner for each fraction of treatment. Block 206 represents the implementation of each of those fractions by a treatment system, such as a linac-based radiotherapy device. At block 208, the fixed plan from block 204 is delivered to the patient by the radiotherapy device.

[0047] Treatment provided according to conventional fixed plan delivery as shown in Fig. 2 does not feature any adaptation based on any variation that occurs after the initial CT scan at block 202. However, this fixed-plan delivery approach is suitable for some kinds of adaptation, especially inter-fraction adaptation. In this case, the plan can be adapted based on an image acquired just before delivery, as in online adaptive radiotherapy workflows. The adapted plan is then imported into the delivery part of the system. This adapted plan is fixed and is not updated during treatment, and is delivered to completion as in a traditional radiotherapy workflow.

[0048] Known techniques for dealing with intra-fraction motion include gating and tracking. Gating uses realtime imaging during irradiation to pause the beam when the target tumour moves significantly outside the intended position. Tracking makes use of real-time imaging to steer the MLC shape directly to point at the moving target tumour. In 'rigid tracking' the MLC shape is kept rigid, matching the plan, but moves with the target, while in 'deformable tracking' the shape can also change to match the tumour deformation. Such systems are still based on fixed-plan delivery but with the added possibility for the beam to be paused and / or for the MLC shape to be over-ridden in real time based on the imaging. Other degrees of freedom of the system still follow the fixed plan.

[0049] Fig. 3 shows a radiotherapy treatment workflow 300 for fixed treatment plan delivery with interfraction adaptation, and intra-fraction adaptation in the form of gating and / or tracking. At block 302, an initial pre-treatment CT scan is taken of the patient, as in block 202 of the workflow 200 of Fig. 2. Also like in Fig. 2, at block 304, a treatment plan with or for multiple fractions is devised based on the pre-treatment CT scan. Block 306 represents the implementation of each of those fractions by a treatment system, such as a linac-based radiotherapy device. In the workflow 300 of Fig. 3, a plan adaptation element is present in the radiotherapy device, represented by block 308. Imaging capability at block 310 is used to obtain an image 312 of the patient before delivery of each fraction. The plan adaptation element at block 308 adapts the original pre-determined fixed plan for that fraction based on the image 312, e.g. based on inter-fraction changes that have occurred since the original plan was prepared at block 304. The imaging capability at block 310 may also provide imaging 314 during delivery. Such real-time images may enable real-time MLC adjustment / tracking at block 316, which takes the form of over-riding the predetermined MLC variables provided by the fixed plan. At block 318, the fixed plan from block 304 is delivered to the patient, modified by inter-fraction adaptations and the MLC over-ride.

[0050] In an example, a control point in the original, fixed plan specifies a particular MLC shape to be delivered to a particular MU in the fraction. However, real-time imaging information 310 suggests that the tumour has changed shape slightly. An offset can be applied to the MLC shape specified at this control point to account for the change. However, importantly, in this prior workflow, the original and pre-determined fixed plan remains saved in memory, and is only adapted by 'over-rides' and interruptions. Accordingly, of the numerous available degrees of freedom and delivery variables of the treatment plan, only a limited number are adapted by conventional real-time adaptation techniques. For example, only the MLC shape can be adapted via over-rides. However, in such conventional adaptation, the control points of the plan are not affected, and control point interpolation does not take into account any intra-fraction variation.

[0051] Fig. 4 shows a radiotherapy system 400 according to the present disclosure which provides an improved approach to updating a treatment plan by enabling the generation and storage of a new radiotherapy treatment plan during delivery of radiation, enabling comprehensive real-time adaptive radiotherapy.

[0052] The radiotherapy system 400 comprises a computer data store 402, which functions as a plan data store. The computer data store 402 is a suitable computer-based memory. The computer data store 402 stores a current radiotherapy treatment plan 403. The current radiotherapy treatment plan 403, like the fixed treatment plans discussed herein, comprises a plurality of control points, each control point defining a value of at least one radiation delivery variable. An original current radiotherapy treatment plan 403 may be developed in a conventional manner based on pre-treatment CT imaging, as described above, and then stored in the plan data store 402.

[0053] The radiotherapy system 400 comprises a plan adaptation module 404. Optionally, the radiotherapy system 400 comprises an imaging system 406, such as the imaging systems capable of patient imaging described herein, such as MR imaging systems and / or CBCT imaging systems. The imaging system is suitable for and configured to obtain images of the target region of the patient.

[0054] The radiotherapy system 400 comprises a radiation delivery control module 408 and a radiation delivery system 410. The delivery control module 408 is configured to retrieve the current radiotherapy treatment plan 403 and control the radiation delivery system 410 to deliver radiation to the target region based on the current radiotherapy treatment plan 403. The plan adaptation module 404 is configured to, during delivery of radiation according to the current radiotherapy plan 403, receive information about the target region. The information about the target region may be obtained in 'real time', such as during delivery of radiation to the target region. The information may be based on imaging information acquired by the imaging system, such as a measure of target drift determinable from images; however, the information need not always be based on imaging information. The information may alternatively or additionally comprise information about the target region obtained using other instrumentation, such as optical or pressure sensor-based patient position monitoring equipment. The information may comprise information representing motion due to patient breathing. In some examples, the information about the target region comprises positional information measured during the delivery of radiation, the positional information relating to at least one of: a patient position, and a radiation delivery system position. For example, the radiation delivery system position may comprise positional information of at least one radiation delivery system component that is measured during delivery of radiation. The plan adaptation module 404 is further configured to, during delivery of radiation according to the current radiotherapy treatment plan 403, adapt the current radiotherapy treatment plan 403 based on the information to generate a new current radiotherapy treatment plan, wherein the adapting comprises modifying at least one radiation delivery variable of at least one control point of the current radiotherapy treatment plan, and to store the new current radiotherapy treatment plan in the plan data store 402.

[0055] Accordingly, the system 400 enables a versatile real-time adaptation of a radiotherapy plan, in which any degree of freedom of the plan may be adapted based on real-time information, and provides storage of that plan to enable it to be delivered by the radiotherapy delivery system. Using the systems and / or methods disclosed herein, a plan can be more comprehensively adapted in real-time compared with the known fixed plan, gating, and tracking techniques shown in the workflows 200, 300 of Figs. 2 and 3.

[0056] Fig. 5 shows an exemplary improved adaptive radiotherapy treatment workflow 500 which uses the system 400 of Fig. 4 to deliver adaptive treatment according to the present disclosure. Likewise, the system 400 of Fig. 4 may be used to implement the adaptive radiotherapy treatment workflow 500 of Fig. 5. The workflow 500 may be compared with the workflows 200, 300 of Figs. 2 and 3.

[0057] At block 502, a pre-treatment CT scan of the patient is obtained for planning purposes, as in blocks 202, 302 of Figs. 2 and 3. At block 504, an initial treatment plan is calculated as described above, which may be used as the initial current radiotherapy treatment plan 403 and stored in the computer data store 402. Block 506 represents the treatment system, in this example an MR-linac, which is to be used to deliver the multiple fractions of the initial treatment plan. The treatment system 506 features a plan adaptation module at block 508, which corresponds to the plan adaptation module 404 of Fig. 4. In the example of Fig. 5, the plan adaptation module 404 contains the plan data store 402, which stores the initial (or initial current) radiotherapy treatment plan. The radiotherapy system implementing the workflow 500 features imaging capability at block 510, which, as described in relation to Fig. 4, may be used to obtain information about the target. In this example, the imaging capability is an MR imaging capability. As noted above, in other examples, alternative or additional sources may be used to obtain information about the target.

[0058] The imaging at block 510 provides images 514 from before and / or during delivery to the plan adaptation module at block 508. The plan adaptation module at block 518 then generates a new current radiotherapy treatment plan as described in relation to Fig. 4. The new radiotherapy treatment plan may take into account inter-fractional change and / or intra-fractional change (such as due to breathing or drift) based on the images 514. Unlike the workflows 200, 300 of Figs. 2 and 3, in which the initial fixed plan is delivered at blocks 208, 318, in the workflow 500 of Fig. 5, the new current radiotherapy treatment plan is delivered at block 518. Thus, improved delivery based on realtime information may be achieved.

[0059] Unlike in the conventional workflows 200, 300 of Figs. 2 and 3, in which a fixed and pre-determined plan based on a pre-treatment CT image is delivered by the radiation delivery system with minor modification based on over-ride of variables at the delivery system, in the workflow 500 of Fig. 5, an adapted plan for that fraction and / or future fractions is generated at the plan adaptation module and provided to the radiation delivery system to execute, enabling more comprehensive adaptation. For example, if drift of the target region increases risk to an adjacent organ, then the treatment plan can be re-planned (e.g., with changed gantry angles) to better account for the organ at risk.

[0060] Furthermore, a significant distinction between the examples of Fig. 4 and 5 and the conventional workflows 200, 300 of Figs. 2 and 3 is the approach to plan storage. In the conventional workflows, the computer data store or memory that holds the initial, fixed plan is not modified or adapted. Instead, between retrieving the plan from memory and delivering it, variables are over-ridden or provided with a particular offset. The presently disclosed improved approach of Figs. 4 and 5 enables a plan to be comprehensively or fully updated in real-time and stored in place of the previous plan, allowing for continuous plan adaptation and providing an advantageous separation between the plan adaptation module architecture (or plan adaptation logic) and the radiation delivery system architecture (or radiation delivery system logic). The presently disclosed approach therefore allows different types of adaptive therapy to be delivered, especially as processor speeds improve over time. Furthermore, the radiation delivery system architecture need not be modified or updated in order to implement these types of adaptive therapy. Accordingly, workflow organisation and operator usability can be improved.

[0061] In some examples, plan generation is performed in parallel with delivery, speeding up the treatment process. In such examples, the starting point for the 'current radiotherapy treatment plan' may be provided in a simple form without specified control points, such as a treatment goal. The treatment goal may be, for example, to deliver a prescribed dose to the target region. Based on this treatment goal, for example an 'updated' plan comprising control points can be generated based on in-session imaging. In such examples, it is not necessary for a generated plan 'update' to specify a new current radiotherapy treatment plan in full, and is only necessary for the update to specify enough of a plan to keep delivery going until the next plan generation 'update'. 'Updates' will continue as such until the Initially prescribed dose is delivered.

[0062] The degrees of freedom, and hence radiation delivery variables, modifiable by the presently disclosed approach may include at least one of: the angles at which the radiation beam should be applied during each fraction, at what beam energy the radiation beam should be applied, the duration of application of the radiation beams at these angles, a weight of a particular beam, the beam shape(s) at each angle of delivery, leaf and diaphragm positions that define the multi-leaf collimator shape, and a patient position parameter such as a patient support surface position.

[0063] In some examples, adapting the current radiotherapy treatment plan comprises modifying a subset of the above plurality of delivery variables.

[0064] Using the presently disclosed approaches, conventional radiation therapy workflows can also be implemented. For example, fixed-plan delivery can be implemented by the examples of Figs. 4 and 5 by omitting any adaptation by the plan adaptation module. Existing workflows for drift corrections, or other such approaches which typically require restarting treatment with a new plan, can be implemented in an alternative manner by the system of Figs. 4 and 5 by delivering a fraction in a series of plan updates, instead of separate deliveries. Conventional gating and tracking approaches can also be implemented by plan updates.

[0065] Further optional features of the examples of Figs. 4 and 5 are described below.

[0066] In some examples, constraints may be placed by the system 400 on the allowed specification of plan updates or generation of new plans. For example, a constraint may be placed such that, of all of the available degrees of freedom, or delivery variables, adapting the current radiotherapy treatment plan is only enabled for a subset of those variables, such as variables related to MLC shape, which would thus implement a tracking-like adaptation. Advantageously, this may allow for incremental advances, gaining the benefits of a particular delivery paradigm while limiting complexity. Such examples may thereby have no more complexity than existing tracking over-ride systems, but will still benefit from the other advantages of the improved systems disclosed herein. In some examples, the system 400 comprises one or more secondary monitoring modules to monitor both adaptation and delivery. The monitoring of adaptation may be dependent on the type of adaptation being used and may be selected alongside the adaptation methods to be used for the treatment. Such monitoring may further improve the effectiveness and safety of the system.

[0067] In some examples the delivery control module may be configured to implement the delivery by skipping, underdosing and / or rearranging control points (for example, to avoid unnecessary exception handling), as well as reporting actual delivery to the plan adaptation module. In such examples, the delivery module may take into account actual delivery and correct for it in later plan updates, to achieve the intended treatment outcome more efficiently.

[0068] In some examples, the current radiotherapy treatment plan 403 comprises a treatment goal and adapting the current radiotherapy treatment plan comprises modifying the at least one radiation delivery variable based on the treatment goal. The treatment goal may comprise a prescribed dose, such as at least one of a prescribed minimum dose for the target region and a prescribed maximum dose for an organ at risk.

[0069] In some examples, adapting the current radiotherapy treatment plan 403 further comprises adding a control point to the current radiotherapy treatment plan and / or removing a control point from the current radiotherapy treatment plan. This is completely contrary to existing adaptive techniques, which involve only overriding the MLC shape associated with a control point which is currently being delivered. Such an approach enables the number of control points to be adapted to real-time changes, which can improve the efficiency of treatment and may reduce the number of fractions required. In an example, an optimisation process is constantly underway during treatment, which seeks to optimise the delivery of the remaining MU for that fraction based on a number of variables, including the number and schedule placement of the control points, plus the radiation delivery variables associated with each of the control points. The MU that has been delivered so far during treatment is recorded.

[0070] In an example, control points may be added to enable planning and delivery to operate in parallel. In one example, the system could be delivering a current set of 100 control points while planning for the next 100 control points, which would then be added to end of the current plan, preferably before delivery of the current control points is complete. In this way the plan may be extended repeatedly with new control points being added in time for continuous delivery. In some examples, the delivery control module 408 is further configured to retrieve the new current radiotherapy treatment plan and to control the radiation delivery system to deliver radiation to the target region based on the new current radiotherapy treatment plan. There may then follow further updates in which the new current radiotherapy treatment plan is adapted to generate a further new current radiotherapy treatment plan, and so on, thereby providing a continuous and iterative process in which the 'current' plan is continuously updated and re-saved in real time.

[0071] In some examples, the delivery control module 408 is further configured to, during delivery of radiation according to the current radiotherapy treatment plan, retrieve the new current radiotherapy treatment plan and to control the radiation delivery system to change to delivering radiation to the target region based on the new current radiotherapy treatment plan. Such an approach enables radiation to be continuously delivered while simultaneously changing to a new, adapted treatment plan.

[0072] In some examples, the plan adaptation module 404 is further configured to, during delivery of radiation according to the new current radiotherapy treatment plan, adapt the new current radiotherapy treatment plan based on further information about the target region to generate a further new radiotherapy treatment plan, and store the further new current radiotherapy treatment plan in the computer data store. In other words, the system 400 of Fig. 4 enables a plan to be adapted and updated multiple times during delivery of radiation, or during a session.

[0073] In some examples, adapting the current radiotherapy treatment plan further comprises modifying at least one radiation delivery variable of a range of the plurality of control points, and optionally further comprises removing control points subsequent to the range. Such an approach allows for, for example, an observed change in the patient to be accounted for in the remainder of the treatment plan, and for the optional removal of further subsequent control points, for example if the efficiency of radiation delivery will be improved by the adaptation of the plan to the extent that subsequent initially-planned control points will no longer be required. In some examples, the range of the plurality of control points that are modified corresponds to the control points that are yet to be delivered, or are scheduled to be delivered at a later point, in the fraction of radiotherapy that is being delivered (the present fraction of radiotherapy). In such examples, the present disclosure enables the system to adapt the radiotherapy plan for a particular fraction during, or within, that fraction. In some examples, the adapting is further based on the remaining dose to be delivered in the present fraction of radiotherapy.

[0074] In some examples, the adapting is further based on the remaining MU to be delivered in the present fraction of radiotherapy.

[0075] In some examples, the plan adaptation module is further configured to determine a drift of the target region based on the information and to adapt the current radiotherapy treatment plan in response to the drift.

[0076] In some examples, delivery of radiation according to the current radiotherapy plan is delivery of a current control point associated with the current radiotherapy treatment plan and the at least one control point of the current radiotherapy treatment plan (for which a delivery variable is modified) is a future control point scheduled at a future time point compared to the current control point. In such examples, the future control point may be scheduled for a future fraction scheduled for a future time point compared to the present or current fraction that is being delivered.

[0077] Fig. 6 shows a method 600 of generating therapeutic radiation according to the present disclosure. The method 600 is to be implemented using the system 400 of Fig. 4, and components of the system 400 correspond to respective components used in the method 600. Likewise, each of the features of the system 400 of Fig. 4 and the workflow 500 of Fig. 5 disclosed herein, including optional features, may optionally form a further part of the method 600.

[0078] At block 602, the method comprises, at a computer data store 402, storing a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable. In an example, an initial treatment plan is prepared and stored before a treatment fraction in the known way.

[0079] At block 604, the method comprises, by a delivery control module 408, retrieving the current radiotherapy treatment plan and controlling the radiation delivery system to deliver radiation to a target region of a patient based on the current radiotherapy treatment plan. In an example, the current radiotherapy treatment plan specifies a series of MLC shapes to be delivered at particular MU points in the fraction, and these dosages and beam shapes are delivered via the delivery system 518. At block 606, the method comprises, by a plan adaptation module 404, during delivery of radiation according to the current radiotherapy plan, receiving information about the target region. In an example, imaging information is received from an MR imager during treatment.

[0080] At block 608, the method comprises, by the plan adaptation module 404, during delivery of radiation according to the current radiotherapy plan, adapting the current radiotherapy treatment plan based on the information to generate a new current treatment plan, wherein the adapting comprises modifying at least one radiation delivery variable of at least one control point of the current radiotherapy treatment plan. In the example, the MR imaging information indicates that the patient has shifted slightly on the table and the position of the tumour has changed, as has the shape of the tumour as seen along the 'beam's eye view'. In prior adaptive methods, this change could be identified, but would necessitate (for example) a high amount of gating, or that the treatment be paused while a new fixed treatment plan is calculated for the fraction. In contrast, in the present method, the MLC position and shape can be adjusted not only for the current control point, but also for all future control points and for every delivery angle.

[0081] At block 610, the method comprises, by the plan adaptation module 404, during delivery of radiation according to the current radiotherapy plan, storing the new current radiotherapy treatment plan in the computer data store. In the example, the adapted MLC shapes and positions are saved in the computer data store 402 as the new current radiotherapy treatment plan.

[0082] In this way, the plan can be continually updated based on real-time imaging information. Treatment can then continue according to the latest available radiotherapy treatment plan. Not only current, but also future control points and their associated delivery variables can be adjusted based on the imaging information and (for example) the remaining MU to be delivered to the patient during the fraction.

[0083] The present method goes beyond the override of variables in an existing plan. Any of a range of delivery variables can be re-calculated and delivered, based on real-time information. The number of variables which can be updated is increased compared to existing methods (including variables associated with future control points, which may even be implemented in future fractions). The present methods provide a greater degree of adaptability, hence providing more accurate and personalised radiotherapy treatment to a patient. Further optional features of the examples of Figs. 4 to 6 of the present disclosure are now described.

[0084] In some examples, the new current radiotherapy treatment plan is generated during delivery of radiation such that delivery of treatment functions as a continuous delivery without restarting the MU count, or other general plan progress indicator, upon adapting the current radiotherapy treatment plan. For example, suppose the machine is delivering a plan of 1000MU and that there comes a point, for example at 400MU, where it becomes apparent that the target region has been drifting, although not excessively. With a fixed-plan delivery paradigm, the workflow would stop, recalculate, and update the delivery with a new plan of 600MU. However, in this example, the presently disclosed approach would recalculate the control points in the range between 400MU to 1000MU while continuing to deliver the current radiotherapy plan in parallel (provided the amount of drift remains acceptable enough that delivery can continue - if not, the current delivery could be stopped). The MU count may have increased further by the time the updated plan takes over, but the system will ensure that 1000MU will be delivered by plan completion. This is achieved despite the delivery and replanning overlap and regardless of the exact timing of the transition from old to new current radiotherapy treatment plan. Accordingly, in some examples, a monitor unit, MU, count determined by the system 400 is continuous across the current radiotherapy treatment plan and the new current radiotherapy treatment plan.

[0085] In some examples, generating a new current radiotherapy treatment plan comprises extending, truncating, or replacing at least some of the current radiotherapy treatment plan. In some examples, the delivery control module discards control points of the current or new current radiotherapy treatment plan that have already been delivered. Furthermore, the updates need not necessarily overlap with control points being delivered at the time, as in the drift correction example above. The system can also be used to extend the plan incrementally in just-in-time fashion.

[0086] In some examples, the system is arranged to communicate the running MU count to the plan adaptation module in real time. Advantageously, this helps to avoid unnecessary updating or modification of control points in the MU range which has already been delivered. For example, a dose monitor or ion chamber may monitor the MU, and a processor can be configured to keep a running total of the MU count, and communicate that to the plan adaptation module.

[0087] In some examples, the system is arranged to communicate at least some of the actual positions used during delivery to the plan adaptation module in real time. This provides a record of delivered treatment to the plan adaptation module and enables the plan adaptation module to generate a new current radiotherapy plan that will correct for imperfections in earlier delivery.

[0088] In some examples, when all control points of the current or new current radiotherapy plan have been delivered, the plan adaptation module signals the completion of treatment with an update and / or flag indicating that delivery of the current radiotherapy plan is complete. Such a mechanism enables the plan adaptation module to signal end-of-delivery to the delivery control module. The update and / or flag may indicate success / failure of the delivery and / or a termination reason associated with ending the delivery.

[0089] In some examples, the new current radiotherapy treatment plan comprises a delivery-enable and / or delivery-disable flag, which indicate respectively at what point(s) radiation should be enabled or disabled in the new current radiotherapy treatment plan. Advantageously, a flag is used to limit unnecessary communication between the planning architecture and the delivery architecture. Such a flag may also or alternatively be used to implement an approach corresponding to a "gating" approach, and / or to provide a time period during which radiation delivery is disabled in order to allow equipment to be moved.

[0090] In some examples, the system 400 comprises an interface for implementing plan updates based on the new current radiotherapy treatment plan. Advantageously, an interface provides separation between specification of a plan and the encoding and carrier mechanisms. It is preferred that planspecification (e.g., sequence of MU and positions) should ideally follow established treatment planning software as closely as possible for compatibility reasons, whereas the encoding (e.g., Protobuf, iCom, XML, etc.) and carrier (e.g., TCP / IP, ZeroMQ, etc.) mechanisms depend more on performance and efficiency requirements. It should also be understood that an interface can take many different forms, such as an embedded library within an adaptation module, and is not necessarily limited to a communication protocol. The interface may be arranged as a direct interface provided between the plan adaptation module 404 and the delivery control module 408, but need not necessarily be thus arranged. The interface may be used to communicate plan updates and replies, as well as "actual values" feedback from the delivery control module 408 to the plan adaptation module 404 in real-time. Advantageously, a particularly-defined interface allows adaptation solutions to be developed based on a common standard. The system 400 may also provide a user interface for manual intervention which enables a user to check, verify, and / or approve a generated new current radiotherapy treatment plan before it is retrieved by the delivery control module 408. Likewise, the system 400 may comprise a monitoring module to check and / or verify radiotherapy treatment plan implementation.

[0091] In some examples, a plan update in the form of generating a new current radiotherapy treatment plan may or may not significantly alter the control points being delivered at the time. In other words, radiation delivery can continue uninterrupted if still within tolerance, or otherwise the system will pause the radiation, move into the new position specified by the new current radiotherapy treatment plan, and resume radiation. Advantageously, conventional delivery systems are already capable of handling tolerance exceptions and recovering, and therefore are equipped to deal with any exceptions that may be triggered in the transition from one current plan to the next.

[0092] Preferably, the system 400 delivers control points in a time-efficient manner, while also taking account of the advance information that the control points provide. For example, suppose delivery is advancing at maximum dose rate with moving gantry, but is approaching a gantry angle where the MU per degree will have to double. It is not possible for the dose rate to increase beyond the maximum and it is also not possible for the gantry speed to change abruptly. So, the gantry should ideally start slowing down in advance to avoid unnecessary exception triggering and recovery. In this example case, if controlled correctly, the gantry would slow to half the previous speed. The dose rate would also slow proportionately but then double at the right moment, coordinated in the plan execution.

[0093] In some examples, the system comprises a watchdog or equivalent mechanism to ensure that communication lines are operating properly during delivery of the treatment plan. That prevents delivery from progressing if updates to the plan are blocked. In some examples, the new current radiotherapy treatment plan comprises an MU-authorization parameter, which indicates how far the MU count is allowed to advance without further updates (or without generating a new current radiotherapy treatment plan). If the system progresses to the MU count provided by the MU- authorization parameter without receiving a new current radiotherapy treatment plan, delivery may be paused or stopped. The plan adaptation module may receive MU-count updates in real time and can therefore authorize delivery for a suitable portion of MU ahead. An advantage of this approach is that it protects delivery against communication problems in both directions. Delivery will pause or stop in case of MU-count communication failure or in case of plan update failure. Advantageously, in examples disclosed herein, generating a new current radiotherapy treatment plan is handled separately from plan execution. The processing time needed for the plan generating / update itself may grow proportionately with the length of the update sequence. Plan execution, on the other hand, will likely work in fixed real-time clock cycles, so may be disrupted if updates block execution, even if momentarily. Separate handling combined with feeding of control points internally, for example via shared memory or just-in-time in smaller sequences, may help to improve computing performance.

[0094] In some examples, the plan adaptation module 404 comprises the computer data store 402. In some examples, the delivery control module 408 comprises the computer data store 402. In some examples, the plan adaptation module 404 is configured to store the new current radiotherapy treatment plan in the computer data store 402 by sending the new current radiotherapy treatment plan to the delivery control module 408. In some examples, at least one of the plan adaptation module 404 and the delivery control module 408 comprises the computer data store 402 and a direct interface is provided between the plan adaptation module 404 and the delivery control module 408, as described above.

[0095] In some examples, particularly those in which the initial current radiotherapy treatment plan comprises a treatment goal or prescribed dose without specifying control points, a radiotherapy system disclosed herein comprises a radiation delivery system for delivering radiation to a target region of a patient, a computer data store configured to store a current radiotherapy treatment plan, and a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan. In these examples, the system further comprises a plan adaptation module configured to, during delivery of radiation according to the current radiotherapy plan: receive information about the target region, based on the current radiotherapy treatment plan, generate a new current radiotherapy treatment plan, and store the new current radiotherapy treatment plan in the computer data store.

[0096] In some examples, particularly those used to generate a plan in parallel with delivery, a radiotherapy system disclosed herein comprises a computer data store configured to store a current radiotherapy treatment plan, and a plan adaptation module configured to, during delivery of radiation generate a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable, and store the current radiotherapy treatment plan in the computer data store. In these examples, the system further comprises a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan.

[0097] The radiotherapy treatment plans described herein, such as the new current radiotherapy treatment plan examples, may correspond, in particular, to a radiation delivery plan.

[0098] In some examples, the radiotherapy treatment plans described herein comprise information representative of interpolation of delivery variables between control points, which may include interpolated values for radiation delivery variables.

[0099] In some examples, the plan adaptation module 404 may generate a new current radiotherapy treatment plan in the form of a "plan update". The plan update may specify a value for at least one radiation delivery variable. Accordingly, in some examples, the new current radiotherapy treatment plan is a plan update, and the delivery control module 408 is configured to modify the current radiotherapy treatment plan during delivery based on the plan update. The plan update need not specify a full treatment plan.

[0100] The plan adaptation module 404 may communicate or send a plan update to the delivery control module 408, which may appropriately store a corresponding new current radiotherapy treatment plan in the computer data store 402, and / or the plan adaptation module 404 may communicate the plan update to the computer data store 402 itself. Hence, the approaches described herein for storing the new current radiotherapy treatment plan in the computer data store 402 may comprise generation and / or communication and / or sending of a plan update by the plan adaptation module 404. In some examples, the delivery control module 408 is configured to append the plan update to the current radiotherapy treatment plan during delivery, such as by scheduling a control point specified in the plan update after the last control point of the current radiotherapy treatment plan.

[0101] In some examples, the delivery control module 408 may be arranged to reply to the plan adaptation module 404 regarding a particular plan update. The reply may comprise an indication of acceptance / rejection for the plan update, which may further indicate a reason for rejecting a plan update. Additionally or alternatively, the reply may comprise optimisation feedback. As described above, generating a new current radiotherapy treatment plan may comprise extending, truncating, or replacing at least some of the current radiotherapy treatment plan. In some examples, the system 400 is arranged to merge new plan input parameters provided by the plan adaptation module 404 in a plan update with the current plan parameters to form the new current radiotherapy treatment plan. For example, parameters specified in a plan update may be used to extend, or replace, or be concatenated with, parameters of the current radiotherapy treatment plan, and that may be done without restarting the MU count of current delivery. As explained herein, those parameters may be part of a control point or set of control points. Such merging, etc., may be implemented either at the plan adaptation module 404 or the delivery control module 408. Advantageously, message sizes can be reduced by, e.g., a plan update specifying to combine control points to be updated with control points to be inherited from the last current plan into a new current plan.

[0102] In some examples, the delivery control module 408 is configured to determine timing and / or speed information for delivering the new current radiotherapy treatment plan using the radiation delivery system In such examples, a timing calculation step may be performed in order to enable the current or new current radiotherapy treatment plan to be delivered in the shortest possible or desirable time. Such an approach may be implemented each time a plan update or new current radiotherapy treatment plan is generated, and may be implemented by the delivery control module 408 and / or the plan adaptation module 404. Such examples are particularly advantageous in dynamic techniques such as VMAT, especially with fast gantry motions.

[0103] In the timing calculation step, calculation of optimum or preferable speeds for any point in delivery may depend on what comes next in the plan. Accordingly, the timing calculation step may be performed in advance of delivery so that later control logic can focus on the point of delivery in the plan. It is typically more efficient for these calculations to be performed once on every plan update rather than on every control clock cycle.

[0104] In some examples, the system 400 may calculate timing information, such as dose rate and speed, and add this information to the current or new current radiotherapy treatment plan. Such a calculation may take into account limits to the deceleration of the gantry (or table). This constraint means, for example, that the gantry must slow down early because of a later constraint in a later control interval (reverse constraints). Similarly, limits to acceleration imposes constraints coming from a control interval and imposing a limit to the gantry speed in later control intervals (forward constraints). In some examples, there may also or alternatively be a lower limit on all moving degrees of freedom if the is a minimum dose rate constraint.

[0105] A timing calculation step is beneficial because plan transitions can potentially trigger tolerance exceptions and position recovery, which can significantly slow the delivery. This depends on the specific constraints applicable at any given time. For example, if dose rate or gantry speed is the limiting factor at some point in the delivery, then changing a plan to move the relevant leaves more will not likely cause an exception. However, if leaf movement is the limiting factor, then demanding more leaf movement in a plan update may well trigger an exception. One way to minimize such exception handling is for plans to specify additional parameters, for example, to help the optimization to reserve some capacity to increase movement without triggering any exception. An example of this is for plan updates to specify maximum intended speeds (either for the whole plan or at each control point). Some target regions move more than others so the intended maximum speeds can be set by adaptation according to the treatment and / or the specifics of the case. Note that these would be maximum speeds expected in target region motions, not to be confused with optimum axis speeds in delivery.

[0106] It may be useful for plan adaptation module 404 to have visibility of the optimization, to see what optimization decisions are made in delivery and to see where the limiting constraints are, and so plan adaptation module 404 may be arranged accordingly. It may be useful for the delivery control module 408 to provide real-time feedback of the actual values (actual MU, actual axis positions, etc., with timestamps), for the plan adaptation module 404 to be able to reconstruct the dose to the target region, possibly also using information about the target region in the dose reconstruction.

[0107] In some examples, an authorised-MU may be specified by or to the system 400. The authorised-MU is an amount of MU that the system 400 is authorised to deliver. Authorized-MU is proposed here as a way to safeguard against communication failures, for example between adaptation and delivery, but can be useful in a variety of different conditions where applications external to the delivery must participate together in time-critical communication with delivery (for example, secondary monitoring). The delivery control module 408 may be arranged to allow radiation to progress only up to the lowest of all received authorised-MU values. This mechanism protects against a wide variety of failure conditions, including failures in the outgoing messages, failures in the incoming messages and failures in external applications themselves. This is because radiation needs all three of these to work properly for the authorized MU to stay ahead of the actual MU. A failure in any one of them would halt one or other authorized MU source and thereby stop the radiation after exceeding the difference between the actual MU and authorized MU.

[0108] In some examples, the new current radiotherapy treatment plan comprises an indication of an authorised monitor unit, MU, count that the delivery control module 408 is authorised to deliver.

[0109] In some examples, the delivery control module 408 comprises a real-time control sub-module and a plan update implementation sub-module. The real-time control sub-module is arranged to work with real-time clock cycles, whereas the plan update implementation sub-module is arranged to perform the steps necessary for implementing plan updates (such as checking the plan, and other preprocessing steps) in parallel with delivery. A bridging approach may be used between the two submodules. In an example, the bridging involves the two sub-modules communicating via shared memory, for example, to copy the new current radiotherapy treatment plan to a region of memory and send a reference to it to the real-time environment. An alternative approach to bridging is for the plan update implementation sub-module to split the new current radiotherapy treatment plan into fragments and send each fragment one by one separately in sequence to the real-time control submodule as needed. Advantageously, using two sub-modules enables a scalable solution allowing for large intermittent updates or frequent small updates without disrupting any delivery flow.

[0110] In some examples, the system 400 may transition from the current radiotherapy treatment plan to the new current radiotherapy treatment plan using an approach that comprises delaying the transition to pause the beam when a transition would otherwise cause the delivery to go out of tolerance.

[0111] In some examples, interpolation is used to interpret the new current radiotherapy treatment plan to decide the desired axis position(s) of the radiation delivery system for the current M U count.

[0112] In some examples, the new current radiotherapy treatment plan and / or plan update comprises a state decision point. This is the point at which delivery could switch either way between radiating (possibly while in motion) and recovery states, for example, for move-only in the plan or to get back into position following a plan update that goes out of tolerance.

[0113] In some examples, the new current radiotherapy treatment plan and / or plan update comprises control information for the control of the dose rate and axes for radiation vs. recovery states. Dose rate and axes positions must stay in sync while radiating, whereas the axes can move independently in position recovery. Control can be optimized by also taking account optimization information calculated earlier in a and / or the plan update.

[0114] In some examples, the plan adaptation module 404 is arranged to determine the delivery progress. Such examples may advantageously improve the efficiency of planning / adaptation algorithms by allowing the adaptation to focus on the relevant part of the plan at any given time. For example, it is no longer relevant to adapt the range of MU which has already been delivered.

[0115] Further examples of adaptation approaches enabled by the present disclosure are as follows:

[0116] • Adapt the remainder of a plan to completion for slow or intermittent change to the target region (with intention that the plan update will then run to completion, but still allow the possibility for further changes, as required).

[0117] • Adapt only for a brief MU range ahead, for more rapid changes to the target region (on the grounds that further updates are inevitable within a short time).

[0118] • Similarly, incremental planning, perhaps also combined with adaptation, could focus on planning ahead for a brief MU range ahead, ideally keeping in sync with the delivery. So, excluding the MU range which has already been delivered and whatever MU range has not yet been specified, there is a relevant current-plan MU range (plus corresponding control point range).

[0119] For these examples reason, it is useful but not necessary that:

[0120] • Delivery progress is visible to the plan adaptation module.

[0121] • Plan updates need not necessarily adapt or specify delivery to completion.

[0122] • Plan updates need not necessarily adapt or specify control points in the MU range that is already delivered and therefore no longer relevant.

[0123] • Delivery reaching the end of the current control points need not necessarily end the delivery.

[0124] In some examples, delivery ends when dose coverage is completed, which may be indicated by the adaptation module. However, other constraints may also apply, such as a maximum allowed MU for a delivery, which may force termination.

[0125] In some examples, MU scaling may be implemented. Dose to a target region is not necessarily in proportion to the MU output of the machine. The relationship between dose and MU is complex and requires time-consuming calculations to come to a plan. Changes to a plan could in principle require a change of MU to get to the right dose to the target region. Therefore, it can be useful to introduce a measure of delivery progress that is in proportion to dose (for example, a percentage of intended dose coverage) instead of in proportion to MU (for example, MU or percentage of total MU). In this case, the current and / or new current radiotherapy treatment plan can also indicate the scaling between dose and MU at every control point. This determines the increases to dose in line with increases to the MU according to the scaling in effect in control point intervals. In this way, changes that would otherwise require changes to MU in the control points can be indicated with a change to the MU scaling values while keeping the same dose values in the control points.

[0126] In another exemplary implementation of the system 400 and workflow 500, the approach may be generalised such that a radiotherapy system disclosed herein comprises a radiation delivery system for delivering radiation to a target region of a patient; a delivery control module configured to control the radiation delivery system to deliver radiation to the target region based on a current radiotherapy treatment plan; and a plan adaptation module configured to, during delivery of radiation according to the current radiotherapy treatment plan: receive information about the target region; based on the current radiotherapy treatment plan and the information about the target region, generate a plan update, the plan update comprising information representative of at least one delivery variable; and communicate the plan update to the delivery control module, wherein the delivery control module is further configured to modify and / or replace the current radiotherapy treatment plan based on the plan update to generate a new current radiotherapy treatment plan, and to deliver radiation to the target region based on the new current radiotherapy treatment plan.

[0127] Said exemplary implementation may further comprise any one or more of the optional features described elsewhere herein.

[0128] In some examples, the plan update comprises at least one of: at least one radiation delivery variable of at least one control point of a new current radiotherapy treatment plan; a range of control points each specifying a respective monitor unit value; information representative of monitor unit scaling; a flag indicating that delivery is complete; a flag indicating whether or not to deliver radiation; and / or a value of an authorised monitor unit amount for delivery.

[0129] In approaches of the present disclosure, an example delivery workflow for plan updates is as follows:

[0130] • Initialize delivery (initial current plan has no control points).

[0131] • Plan updates can commence (plan updates may also commence after confirmation and start).

[0132] • Confirm delivery (the delivery is authorized to go ahead).

[0133] • Start (radiation delivery starts). End delivery on completion of adaptation.

[0134] An example delivery workflow for conventional fixed plan delivery, on the other hand, is as follows:

[0135] • Load delivery plan (initializes the delivery).

[0136] • Start direct external control if applicable.

[0137] • Confirm and start.

[0138] • Delivery ends when the delivery reaches the prescribed MU at the end of the control points.

[0139] In some examples of the approaches of the present disclosure, in delivery initialization, the initial state for a particular patient may have no control points to begin with (a 'null' plan). In such examples, the first plan update is functionally no different from any other plan updates, and provides an "update" from an initial null state.

[0140] Advantageously, using approaches disclosed herein, a radiotherapy treatment plan can be adapted in a manner that need not specify the plan to completion and need not specify the already delivered range.

[0141] Advantageously, approaches disclosed herein can make adaptive radiotherapy modular, separating management and optimization of the delivery side (plan execution, speed of delivery, etc.) from management and optimization of the planning and adaptation side (plan optimization, image processing, adaptive algorithms, etc.). Advantageously, the approaches disclosed herein can be used to adapt a plan using any suitable adaptation algorithm for deciding and / or changing the course of delivery during delivery. In current approaches, the adaptation side of the system must manage adaptation while also implementing delivery functionality (because direct external override bypasses the delivery logic in the delivery system).

[0142] Advantageously, approaches disclosed herein can facilitate incremental planning during delivery, namely planning in parallel with delivery.

[0143] Advantageously, approaches disclosed herein enable fast delivery of treatment by reducing gaps in treatment that may otherwise be needed to adapt a plan, and further may adapt a plan with an appropriate level of granularity as needed. The systems disclosed herein may comprise a radiotherapy device including radiotherapy delivery apparatus, also referred to as a radiation delivery system, such as those of Figs. 1 and 7. Accordingly, the system may comprise a computing system, image acquisition device, treatment device, input device and / or output device like those of Fig. 7.

[0144] Fig. 7 illustrates a block diagram of one implementation of a radiotherapy system 700. The radiotherapy system 700 comprises a computing system 710 within which a set of instructions, for causing the computing system 710 to perform any one or more of the methods discussed herein, may be executed.

[0145] The computing system 710 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.

[0146] The computing system 710 includes controller circuitry 711 and a memory 713 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.). The memory 713 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).

[0147] Controller circuitry 711 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 711 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 711 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 711 is configured to execute the processing logic for performing the operations and steps discussed herein.

[0148] The computing system 710 may further include a network interface circuitry 718. The computing system 710 may be communicatively coupled to an input device 720 and / or an output device 730, via input / output circuitry 717. In some implementations, the input device 720 and / or the output device 730 may be elements of the computing system 710. The input device 720 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 730 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 720 and the output device 730 may be provided as a single device, or as separate devices.

[0149] In some implementations, the computing system 710 may comprise image processing circuitry 719. Image processing circuitry 719 may be configured to process image data 780 (e.g. images, or imaging data), such as medical images obtained from one or more imaging data sources, a treatment device 750 and / or an image acquisition device 740. Image processing circuitry 719 may be configured to process, or pre-process, image data. For example, image processing circuitry 719 may convert received image data into a particular format, size, resolution or the like. In some implementations, image processing circuitry 719 may be combined with controller circuitry 711.

[0150] In some implementations, the radiotherapy system 700 may further comprise an image acquisition device 740 and / or a treatment device 750, such as those disclosed herein in the examples of Figs. 1 to 3. The image acquisition device 740 and the treatment device 750 may be provided as a single device. In some implementations, treatment device 750 is configured to perform imaging, for example in addition to providing treatment and / or during treatment. The treatment device 750 comprises the main radiation delivery components of the radiotherapy system, such as the linac.

[0151] Image acquisition device 740 may be configured to perform positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), or other suitable imaging techniques. Image acquisition device 740 may be configured to output image data 780, which may be accessed by computing system 710. Treatment device 750 may be configured to output treatment data 760, which may be accessed by computing system 710.

[0152] Computing system 710 may be configured to access or obtain treatment data 760, planning data 770 and / or image data 780. Treatment data 760 may be obtained from an internal data source (e.g. from memory 713) or from an external data source, such as treatment device 750 or an external database. Planning data 770 may be obtained from memory 713 and / or from an external source, such as a planning database. Planning data 770 may comprise information obtained from one or more of the image acquisition device 740 and the treatment device 750. Accordingly, computing system 710 is arranged to implement the methods disclosed herein relating to handling treatment plans and treatment quality criteria.

[0153] The various methods described above may be implemented by a computer program. The computer program may include computer code (e.g. instructions) 810 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 810 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 800)), depicted in Fig. 8. The computer readable media may be transitory or non-transitory. The one or more computer readable media 800 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 810 may also reside, completely or at least partially, within the memory 713 and / or within the controller circuitry 711 during execution thereof by the computing system 710, the memory 713 and the controller circuitry 711 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.

[0154] 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.

[0155] 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).

[0156] 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", "calculating", "displaying", "storing", 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.

[0157] 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

Claims1. A radiotherapy system comprising: a radiation delivery system for delivering radiation to a target region of a patient; a computer data store configured to store a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable; a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan; and a plan adaptation module configured to, during delivery of radiation according to the current radiotherapy plan: receive information about the target region; adapt the current radiotherapy treatment plan based on the information to generate a new current radiotherapy treatment plan, wherein the adapting comprises modifying at least one radiation delivery variable of at least one control point of the current radiotherapy treatment plan; and store the new current radiotherapy treatment plan in the computer data store.

2. The system of any preceding claim, wherein the current radiotherapy treatment plan comprises a treatment goal based on a prescribed dose and adapting the current radiotherapy treatment plan comprises modifying the at least one radiation delivery variable based on the treatment goal.

3. The system of any preceding claim, wherein adapting the current radiotherapy treatment plan further comprises adding a control point to the current radiotherapy treatment plan and / or removing a control point from the current radiotherapy treatment plan.

4. The system of any preceding claim, wherein the at least one radiation delivery variable represents one of: a gantry angle, at what beam energy the radiation beam should beapplied, the duration of application of a radiation beam at gantry angle, a weight of a particular beam, or a patient position parameter.

5. The system of any preceding claim, wherein the delivery control module is further configured to retrieve the new current radiotherapy treatment plan and to control the radiation delivery system to deliver radiation to the target region based on the new current radiotherapy treatment plan.

6. The system of any preceding claim, wherein the delivery control module is further configured to, during delivery of radiation according to the current radiotherapy treatment plan, retrieve the new current radiotherapy treatment plan and to control the radiation delivery system to change to delivering radiation to the target region based on the new current radiotherapy treatment plan.

7. The system of any preceding claim, wherein the plan adaptation module is further configured to, during delivery of radiation according to the new current radiotherapy treatment plan, adapt the new current radiotherapy treatment plan based on further information about the target region to generate a further new radiotherapy treatment plan, and store the further new current radiotherapy treatment plan in the computer data store.

8. The system of any preceding claim, wherein adapting the current radiotherapy treatment plan further comprises modifying at least one radiation delivery variable of a range of the plurality of control points, and optionally further comprises removing at least one control point subsequent to the range.

9. The system of claim 8, wherein the range of the plurality of control points corresponds to the control points that are yet to be delivered in a present fraction of radiotherapy.

10. The system of any preceding claim, wherein the adapting is further based on the remaining dose to be delivered in a present fraction of radiotherapy.

11. The system of any preceding claim, the system further comprising an imaging system for obtaining images of the target region of the patient, and wherein the information about the target region is based on imaging information acquired by the imaging system.

12. The system of any preceding claim, wherein the information about the target region comprises positional information measured during the delivery of radiation, the positional information relating to at least one of: a patient position, and a radiation delivery system position.

13. The system of any preceding claim, wherein the plan adaptation module is further configured to determine a drift of the target region based on the information and to adapt the current radiotherapy treatment plan in response to the drift.

14. The system of any preceding claim, wherein delivery of radiation according to the current radiotherapy plan is delivery of a current control point associated with the current radiotherapy treatment plan; and wherein the at least one control point of the current radiotherapy treatment plan is a future control point scheduled at a future time point compared to the current control point.

15. The system of any preceding claim, wherein the plan adaptation module is configured to store the new current radiotherapy treatment plan in the computer data store by sending the new current radiotherapy treatment plan to the delivery control module.

16. The system of any preceding claim, wherein the new current radiotherapy treatment plan is a plan update, and wherein the delivery control module is configured to modify the current radiotherapy treatment plan during delivery based on the plan update.

17. The system of any preceding claim, wherein the delivery control module is configured to determine timing and / or speed information for delivering the new current radiotherapy treatment plan using the radiation delivery system.

18. The system of any preceding claim, wherein a monitor unit, MU, count determined by the system is continuous across the current radiotherapy treatment plan and the new current radiotherapy treatment plan.

19. The system of any preceding claim, wherein the new current radiotherapy treatment plan comprises an indication of an authorised monitor unit, MU, count that the delivery control module is authorised to deliver.

20. A method of generating therapeutic radiation, the method comprising: at a computer data store, storing a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable; by a delivery control module, retrieving the current radiotherapy treatment plan and controlling the radiation delivery system to deliver radiation to a target region of a patient based on the current radiotherapy treatment plan; and by a plan adaptation module, during delivery of radiation according to the current radiotherapy plan: receiving information about the target region; adapting the current radiotherapy treatment plan based on the information to generate a new current treatment plan, wherein the adapting comprises modifying at least one radiation delivery variable of at least one control point of the current radiotherapy treatment plan; and storing the new current radiotherapy treatment plan in the computer data store.

21. The method of claim 20, wherein the current radiotherapy treatment plan comprises a treatment goal based on a prescribed dose and adapting the current radiotherapy treatment plan comprises modifying the at least one radiation delivery variable based on the treatment goal.

22. The method of any of claims 20 or 21, wherein adapting the current radiotherapy treatment plan further comprises adding a control point to the current radiotherapy treatment plan and / or removing a control point from the current radiotherapy treatment plan.

23. The method of any of claims 20 to 22, wherein the at least one radiation delivery variable represents one of: a gantry angle, a weight of a particular beam, or a patient position parameter.

24. The method of any of claims 20 to 23, wherein the method further comprises, at the delivery control module, retrieving the new current radiotherapy treatment plan and controlling the radiation delivery system to deliver radiation to the target region based on the new current radiotherapy treatment plan.

25. The method of any of claims 20 to 24, wherein the method further comprises, at the delivery control module, during delivery of radiation according to the current radiotherapy treatment plan, retrieving the new current radiotherapy treatment plan and controlling the radiation delivery system to change to delivering radiation to the target region based on the new current radiotherapy treatment plan.

26. The method of any of claims 20 to 25, wherein the method further comprises, at the plan adaptation module, during delivery of radiation according to the new current radiotherapy treatment plan, adapting the new current radiotherapy treatment plan based on further information about the target region to generate a further new radiotherapy treatment plan, and storing the further new current radiotherapy treatment plan in the computer data store.

27. The method of any of claims 20 to 26, wherein adapting the current radiotherapy treatment plan further comprises modifying at least one radiation delivery variable of a range of the plurality of control points, and optionally further comprises removing control points subsequent to the range.

28. The method of claim 27, wherein the range of the plurality of control points corresponds to the control points that are yet to be delivered in a present fraction of radiotherapy.

29. The method of any of claims 20 to 28, wherein the adapting is further based on the remaining dose to be delivered in a present fraction of radiotherapy.

30. The method of any of claims 20 to 29, wherein the information about the target region comprises imaging information acquired by an imaging system for obtaining images of the target region of the patient.

31. The method of any of claims 20 to 30, wherein the information about the target region comprises positional information measured during the delivery of radiation, the positional information relating to at least one of: a patient position, and a radiation delivery system position.

32. The method of any of claims 20 to 31, wherein the method further comprises, at the plan adaptation module, determining a drift of the target region based on the information and adapting the current radiotherapy treatment plan in response to the drift.

33. The method of any of claims 20 to 32, wherein delivery of radiation according to the current radiotherapy plan is delivery of a current control point associated with the current radiotherapy treatment plan; and wherein the at least one control point of the current radiotherapy treatment plan is a future control point scheduled at a future time point compared to the current control point.

34. The method of any of claims 20 to 33, the plan adaptation module storing the new current radiotherapy treatment plan in the computer data store comprises sending the new current radiotherapy treatment plan to the delivery control module.

35. The method of any of claims 20 to 34, wherein the new current radiotherapy treatment plan is a plan update, and wherein the method further comprises, by the delivery control module, modifying the current radiotherapy treatment plan during delivery based on the plan update.

36. The method of any of claims 20 to 35, further comprising determining, by the delivery control module, timing and / or speed information for delivering the new current radiotherapy treatment plan using the radiation delivery system.

37. The method of any of claims 20 to 36, wherein a monitor unit, MU, count determined by the system is continuous across the current radiotherapy treatment plan and the new current radiotherapy treatment plan.

38. The method of any of claims 20 to 37, wherein the new current radiotherapy treatment plan comprises an indication of an authorised monitor unit, MU, count that the delivery control module is authorised to deliver.

39. A computer-readable medium containing instructions that, when executed by a processor, cause the performance of the method of any of claims 20 to 38.

40. A radiotherapy system comprising: a radiation delivery system for delivering radiation to a target region of a patient; a computer data store configured to store a current radiotherapy treatment plan; a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan; and a plan adaptation module configured to, during delivery of radiation according to the current radiotherapy plan: receive information about the target region; based on the current radiotherapy treatment plan, generate a new current radiotherapy treatment plan; and store the new current radiotherapy treatment plan in the computer data store.

41. A radiotherapy system comprising: a radiation delivery system for delivering radiation to a target region of a patient; a computer data store configured to store a current radiotherapy treatment plan; a plan adaptation module configured to, during delivery of radiation: generate a current radiotherapy treatment plan, the current radiotherapy treatment plan comprising a plurality of control points, each control point defining a value of at least one radiation delivery variable, and store the current radiotherapy treatment plan in the computer data store; and a delivery control module configured to retrieve the current radiotherapy treatment plan and control the radiation delivery system to deliver radiation to the target region based on the current radiotherapy treatment plan.

42. A radiotherapy system comprising: a radiation delivery system for delivering radiation to a target region of a patient; a delivery control module configured to control the radiation delivery system to deliver radiation to the target region based on a current radiotherapy treatment plan; and a plan adaptation module configured to, during delivery of radiation according to the current radiotherapy treatment plan: receive information about the target region; based on the current radiotherapy treatment plan and the information about the target region, generate a plan update, the plan update comprising information representative of at least one delivery variable; and communicate the plan update to the delivery control module, wherein the delivery control module is further configured to modify and / or replace the current radiotherapy treatment plan based on the plan update to generate a new current radiotherapy treatment plan, and to deliver radiation to the target region based on the new current radiotherapy treatment plan.

43. The system of claim 42, wherein the plan update comprises at least one of: at least one radiation delivery variable of at least one control point of a new current radiotherapy treatment plan; a range of control points each specifying a respective monitor unit value; information representative of monitor unit scaling; a flag indicating that delivery is complete; a flag indicating whether or not to deliver radiation; and / or a value of an authorised monitor unit amount for delivery.

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