Methods for treatment plan verification

Abstract

A method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment The method comprises obtaining a pre-treatment cone beam computed tomography, CBCT, image of a patient. The method further comprises adapting a treatment plan, based on the CBCT image. The method further comprises delivering a first portion of the adapted treatment plan to the patient. The method further comprises obtaining dose data from the delivery of the first portion. The method further comprises determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data. If the dosimetric value is within an acceptable range, the method further comprises delivering a second portion of the adapted treatment plan. Or, if the dosimetric value is outside the acceptable range, the method further comprises stopping the delivery of the adapted treatment plan.

Description

[0001] METHODS FOR TREATMENT PLAN VERIFICATION

[0002] Field of the Invention

[0003] The present disclosure relates to methods for treatment plan verification. More specifically, the present invention relates to a method for radiotherapy treatment plan verification, and data processing apparatuses, computer programs, and non-transitory computer-readable storage mediums configured to execute methods for radiotherapy treatment plan verification.

[0004] Background of the Invention

[0005] Radiation therapy or radiotherapy may be described as the use of ionising radiation to damage or destroy unhealthy cells in both humans and animals. The ionising radiation may be directed to tumours on the surface of the skin or deep inside the body. Common forms of ionising radiation include X-ray, gamma rays and charged particles. An example of a radiotherapy technique is Gamma Knife*, where a patient is irradiated using a number of gamma rays that converge with higher intensity and high precision at a targeted region (e.g., a tumour). Another example of radiotherapy comprises using a linear accelerator (“linac”), whereby a targeted region is irradiated by high-energy radiations or particles (e.g., electrons, high-energy photons, and the like). In another example, radiotherapy may be provided using a heavy charged particle accelerator (e.g., protons, carbon ions, and the like).

[0006] The placement and dose of the radiation beam may be accurately controlled to provide a prescribed dose of radiation to the target region (e.g., the tumour) and to reduce damage to surrounding healthy tissue (known as organs at risk or OARs). An aspect of treatment planning concerns determining suitable characteristics of radiation to be delivered to produce a safe and effective dose. A treatment plan may be determined by a treatment planning system.

[0007] Adaptive Radiation Therapy (ART) is a form of radiotherapy that adjusts the treatment plan throughout the course of treatment based on changes in the patient’s anatomy or tumour. For example, changes may result from tumour shrinkage / growth, patient weight loss / gain, organ motion (bladder filling, bowel movements, lung expansion), and setup variations. Online ART adapts a treatment plan duringthe treatment session (or just before the session) by incorporating online pretreatment imaging and re-planning. A new reference image, such as a cone beam computed tomography (CBCT), computed tomography (CT) or MRI scan, is acquired each day and

[0008] P151368PC01 2025P00097 WO used to modify the original treatment plan to better conform the dose distribution to the current patient anatomy. This has the potential to reduce the treatment margins and ensure coverage by those margins.

[0009] Therefore, it is desirable to provide an improved method of radiotherapy treatment plan verification especially in the case when online replanning does not allow for independent plan verification (also known as plan quality assurance or QA) due to (1) LINAC occupancy and (2) treatment time constraint.

[0010] Summary of the Invention

[0011] It is an aim of the present disclosure to at least partially address one or more of the challenges mentioned above. The invention is defined in the independent claims, to which reference should now be made. Further features are set out in the dependent claims.

[0012] According to a first aspect of the present disclosure, there is provided a method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment. The method comprises obtaining a pre-treatment cone beam computed tomography (CBCT) image of a patient. The method further comprises adapting a treatment plan, based on the CBCT image. The method further comprises delivering a first portion of the adapted treatment plan to the patient. The method further comprises obtaining dose data from the delivery of the first portion. The method further comprises determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data. If the dosimetric value is within an acceptable range, the method further comprises delivering a second portion of the adapted treatment plan. Or, if the dosimetric value is outside the acceptable range, the method further comprises stopping the delivery of the adapted treatment plan.

[0013] In some embodiments, the first portion of the adapted treatment plan is a smaller proportion of the adapted treatment plan than the second portion.

[0014] In some embodiments, the first portion and the second portion collectively comprise the entirety of the adapted treatment plan.

[0015] In some embodiments, the first portion is calculated based on the number of Monitor Units, MU, per treatment field needed for photons exiting the patient to be detected by a detector.

[0016] P151368PC01 2025P00097 WO In some embodiments, the first portion is calculated based on the number of MU per treatment field needed for a threshold number of photons exiting the patient to be detected by a detector.

[0017] In some embodiments, the threshold number of photons is based on the number of photons required to produce a 3D dose back-projection into the CBCT image.

[0018] In some embodiments, obtaining dose data from the delivery of the first portion comprises recording an exit dose using a detector.

[0019] In some embodiments, the detector is a megavoltage, MV, flat panel detector.

[0020] In some embodiments, the dosimetric value associated with quality assurance of the adapted treatment plan comprises a gamma index.

[0021] In some embodiments, if the dosimetric value is outside the acceptable range, the method further comprises sending an alert to a user.

[0022] In some embodiments, the pre-treatment CBCT image comprises a quantitative CBCT, image.

[0023] According to a second aspect of the present disclosure, there is provided a data processing apparatus comprising a memory storing computer-executable instructions, and a processor configured to execute the instructions to carry out a method in accordance with any of the embodiments described above.

[0024] According to a third aspect of the present disclosure, there is provided a computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out a method in accordance with any of the embodiments described above. The computer program may be a computer program product comprising a computer readable medium, the computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform a method in accordance with any of the embodiments described above.

[0025] P151368PC01 2025P00097 WO According to a fourth aspect of the present disclosure, there is provide a computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out a method in accordance with any of the embodiments described above.

[0026] Other features of the disclosure are described below.

[0027] The invention may be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations thereof. The invention may be implemented as a computer program or a computer program product, i.e. a computer program tangibly embodied in a non-transitory information carrier, e.g. in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, one or more hardware modules.

[0028] A computer program may be in the form of a stand-alone program, a computer program portion, or more than one computer program, and may be written in any form of programming language, including compiled or interpreted languages, and it may be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a data processing environment.

[0029] The invention is described in terms of particular embodiments. Other embodiments are within the scope of the following claims. For example, the steps of the invention may be performed in a different order and still achieve desirable results.

[0030] Elements of the invention have been described using the terms “processor” etc. The skilled person will appreciate that such functional terms and their equivalents may refer to parts of the system that are spatially separate but combine to serve the function defined. Equally, the same physical parts of the system may provide two or more of the functions defined. For example, separately defined means may be implemented using the same memory and / or processor as appropriate.

[0031] Brief Description of the Drawings

[0032] Embodiments of the invention will now be further described by way of example only and with reference to the accompanying drawings, wherein like reference numerals refer to like parts, and wherein:

[0033] P151368PC01 2025P00097 WO Figure 1 is a flow chart illustrating process steps in a method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment.

[0034] Figure 2 is a schematic of an example treatment plan.

[0035] Figure 3 is a radiotherapy system, suitable for use with embodiments of the invention.

[0036] Figure 4 is a radiotherapy device or apparatus, suitable for use with embodiments of the invention.

[0037] Figure 5 is a flow chart illustrating a computer implemented method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment

[0038] Detailed Description

[0039] Embodiments of the invention provide methods for treatment plan verification (also known as treatment plan quality assurance (QA)) of a newly adapted plan during a fraction of an online ART treatment, prior to delivery of that very fraction. The paradigm shift from offline to online treatment planning calls for new approaches to create confidence in the newly adapted treatment plans while patient is lying on treatment table. Traditional approaches based on phantoms and radiochromic films are not suitable for online treatment planning. Additionally, there is now a crucial time constraint to guarantee patient comfort and minimal patient motion / deformation during the plan QA process so any QA must be quick, yet accurate and representative of both new plan and patient daily anatomy.

[0040] Embodiments of the invention aim to solve the aforementioned unmet clinical need raised by the new paradigm shift towards online ART workflow. Embodiments of the invention propose a new deliveryapproach where the delivery of the newlyadapted plan is splitintotwo phases. Inthefirst phase, a portion of the newly optimized treatment plan is delivered to make it sure that (a) the treatment plan meets the criteria it has been optimized for and (b) patient has not moved and no significant deformation has happened during the development of the newly adapted treatment plan. If the treatment plan meets the criteria and the patient has not moved, the remaining portion of the newly optimized treatment plan can be delivered as the second phase.

[0041] P151368PC01 2025P00097 WO Embodiments of the invention may comprise one or more of the following steps:

[0042] 1. Acquiring a pre-treatment CBCT to be used for plan adaptation.

[0043] 2. Optimizing a new treatment plan (plan adaptation) while patient lies on the treatment table.

[0044] 3. Calculating, as a function of gantry angle the minimum number of dose (or Monitor Units (MU)) per each treatment field sufficient to have “enough” photons exiting the patients and recorded by the megavoltage flat panel (MV FP).

[0045] 4. Calculating dose deposited to the patient when Monitor Units (MUs) of the first part / portion of the adapted plan will be delivered (this step may be performed while delivering the MUs of the first part of the adapted plan as in step 5).

[0046] 5. Delivering the MUs calculated at step 3.

[0047] 6. Recording the exit dose using the MV FP.

[0048] 7. Back-projecting 2D images from the MV FP into total dose on the CBCT acquired at step 1 by meansofa physical model calculation or an Al prediction-based approach (this choice may be influenced by back-projection speed).

[0049] 8. Evaluating a metric for traditional dosimetric comparison (e.g. 3D gamma index).

[0050] 9. Setting a threshold to consider the metric defined at step 8 as acceptable (this could be body site or technique specific). The threshold may be predetermined / set previously. 10. If the result from step 8 is within the acceptability range / threshold defined at step 9, then a user can proceed with the delivery of the remaining MUs (i.e. the difference between the MUs planned in the adapted plan and those already delivered in this QA check based on a partial delivery).

[0051] 11. If the result from step 8 is not within the acceptability range defined at step 9, then user will stop the delivery of the second part of the adapted plan and investigate the root cause of this mismatch, e.g. patient movement or adapted treatment plan error.

[0052] At a high level, the method takes as input an adapted treatment plan and associated pretreatment daily CBCT, acquires dose data from a partial delivery of MUs and outputs a dosimetric value associated with the QA of the newly adapted plan. The proposed method goes beyond currently proposed approaches based on CBCT second acquisition after plan adaptation phase, proposing not to image the patent again but delivering a very small part of the adapted treatment plan to capture possible adapted plan mistakes as well as, as a byproduct of the approach, possible patient movements / deformations.

[0053] P151368PC01 2025P00097 WO Embodiments of the invention fill the gap in plan QA in the context of online ART. This creates confidence in medical physicists and radiation oncologists who historically were used to having longtime between the treatment planning phase and the treatment delivery. Such an approach is no longer feasible in the context of online ART. Embodiments of the invention merge the concept of anatomical patient check after the treatment adaptation phase and dosimetric consistency between actually delivered and expected doses from newly adapted plan.

[0054] Various aspects and details of these principal concepts will be described below with reference to Figures 1 to 5.

[0055] Referring initially to Figure 5, this Figure is a flow chart illustrating a first example of a computer implemented method 500 for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment. Method 500 comprises, at step 502, obtaining a plurality of elements including a pre-treatment CBCT image of a patient. The pre-treatment CBCT image may comprise a quantitative CBCT image. Step 502 also comprises obtaining an adapted treatment plan, the treatment plan having been adapted based on the CBCT image. The adaptation of the treatment plan may include updates to allow for the impact of daily anatomical differences on target and OAR segmentations, and tailoring of radiation dose distribution to the daily anatomy. Step 502 also comprises obtaining dose data from delivery of a first portion of the adapted treatment plan to the patient. As discussed in greater detail below with reference to the method 100, the first portion of the adapted treatment plan may, together with a second portion, collectively comprise the entirety of the adapted treatment plan. The first portion of the adapted treatment plan may be a smaller proportion of the adapted treatment plan than the second portion, and in some examples, the first portion of the adapted treatment plan may deliver a non-therapeutic radiation dose to the patient. In some examples, obtaining dose data from the delivery of the first portion may comprise obtaining an exit dose recorded using a detector. The detector may be a MV flat panel detector. The associated dose recorded into the MV FP during the delivery of the first part of the treatment plan may be stored and transferred to a software workstation. In some examples, obtaining dose data may comprise back-projecting from the MV FP 2D images into total dose on the 3D daily CBCT by means of a physical model calculation or Al prediction-based approach

[0056] Referring still to Figure 5, in step 504, the method 500 comprises determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data. As discussed in greater detail below with reference to the method 100, the dosimetric value may be

[0057] P151368PC01 2025P00097 WO a gamma index. Other possible metrics may include target or OAR DVHs or other plan quality indices like conformity or radiobiological indices. Once the delivered dose of the first part of the adapted treatment plan has been back projected onto the daily qCBCT, dosimetric comparison between doses planned in the newly adapted plan and actually delivered in the first part of the plan can be made by means of traditional dose comparison metrics.

[0058] The method 500 then comprises taking action accordingto whether or not the dosimetric value is within an acceptable range. Method 500 may thus comprise assessing whetherthe dosimetric value is within an acceptable range. The acceptable range may be determined based on the body site of the radiotherapy treatment, and / or the radiotherapy treatment technique being used. In some examples, a threshold may be set to define an acceptable range for the dosimetric value. If the dosimetric value is within an acceptable range, the method 500 comprises validating the adapted treatment plan as acceptable to be fully delivered to the patient in step 506. In some examples, validating the adapted treatment plan as acceptable to be fully delivered to the patient may comprise initiating delivery of a second portion of the adapted treatment plan. The second portion may comprise the remaining portion of the plan, and delivery may be initiated for example by sending an appropriate message, notification, or instruction. In some examples, the method 500 may further comprise initiating delivery of the first portion of the adapted treatment plan to the patient.

[0059] If the dosimetric value is outside the acceptable range, the method 500 may comprise not validating the adapted treatment plan as acceptable to be fully delivered to the patient. This may comprise causing delivery of the adapted treatment plan to be stopped.

[0060] Figure 1 is a flow chart illustrating process steps in another computer implemented method 100 for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment.

[0061] Method 100 comprises, at step 102, obtaining a pre-treatment CBCT image of a patient. The pretreatment CBCT image may comprise a quantitative CBCT image. To capture the daily anatomic variability of patient target and organs at risk(OARs), a CBCT is routinely acquired with the primary goal to be used in Image Guided RadioTherapy (IGRT). With the paradigm shiftto online ART, CBCT becomes a planning tool and the current evolution towards quantitative CBCT (qCBCT) is paving the road to a one-stop-shop CBCT to be used for both IGRT and online ART without the need for additional info from planning CT (pCT).

[0062] P151368PC01 2025P00097 WO Method 100 comprises, at step 104, adapting a treatment plan, based on the CBCT image. This may occur while the patient lies on the treatment table. For example, plan adaptation based on qCBCT aims at incorporating daily anatomical differences into target and OAR segmentations and tailoring radiation dose distribution to the daily anatomy. With the current end-to-end time slot of 15 min for a single online ART fraction, it is impossible to guarantee all the traditional plan QA checks of a newly adapted plan based on treatment deliveries to phantom and use of films. Furthermore, the patient is lying on the treatment table, not only occupying the delivery space, but also calling for a fast plan QA check to minimize their discomfort and possible movements / deformations (e.g. bladder filling).

[0063] Method 100 comprises, at step 106, delivering a first portion of the adapted treatment plan to the patient. The first portion of the adapted treatment plan may be a smaller proportion of the adapted treatment plan than the second portion. The first portion may be calculated based on the number of MU per treatment field needed for photons, or a threshold number of photons, exiting the patient to be detected by a detector. The threshold number of photons may be determined based on the number of photons required to (accurately) produce a 3D dose back-projection into the CBCT image. In some examples, the first portion may be 1% or less, 5% or less, 10% or less, 20% or less, etc. of the MUs of the adapted treatment plan.

[0064] In some embodiments, step 106 may comprise calculating, as a function of gantry angle, the minimum number of dose (or MU) per each treatment field sufficient to have “enough” photons exiting the patients and recorded by the MV flat panel (FP). Based on the concept of in vivo exit dosimetry (see (1) Routine individualised patient dosimetry using electronic portal imaging devices. Nijsten SM, Mijnheer BJ, Dekker AL, Lambin P, Minken AW. Radiother Oncol. 2007 Apr;83(1):65-75.; and (2) A literature review of electronic portal imaging for radiotherapy dosimetry, van Elmpt W, McDermott L, Nijsten S, Wendling M, Lambin P, Mijnheer B. Radiother Oncol. 2008 Sep;88(3):289-309.) MV FP can be used to record radiation exiting the patient when a given treatment field is delivered and reaching the MV FP. Traditionally, this has been done by recording the entire dose exiting the patient to be used as an offline benchmark of the planned and expected delivered doses. As a result of that application, no change can be made anymore in the delivered treatment but, eventually, a change can be proposed only to the next fractions, assuming there are still or enough fractions to be delivered and the calculated error / mismatch can be corrected (we know we can only add radiation dose, we cannot remove radiation dose in

[0065] P151368PC01 2025P00097 WO the case by mistake a specific structure has received a radiation dose level higher than its toxicity).

[0066] Embodiments of the invention split the treatment delivery into two parts: the first part is defined based on the MU(1 , i) being a subset of total MU(i) of the i-th treatment field at a given entry angle (e.g. in Intensity Modulated RT - IMRT - or Volumetric Modulated Arc Therapy - VMAT) from the adapted treatment plan so that MU(1,i) produces enough photons exiting the patient at that given gantry angle recorded by the MV FP to be used fora robust 3D dose back-projection into the daily qCBCT. This can be accomplished by modifying the treatment planning system (TPS) to calculate not only the dose deposited to the patient but also the dose reaching the MV FP after exiting the patient.

[0067] In some embodiments, step 106 may comprise calculating dose deposited to the patient when MUs of the first part of the adapted plan is delivered (this may be done while delivering the MUs of the first part of the adapted plan). Based on the MU(1 ,i) defined above, the TPS will calculate the dose deposited to the patient when MU(1,i) i=1 , ...N will be delivered. This will be a subset of the total dose from the adapted plan and will be used as a benchmark from the back-projected actually delivered dose in the first part of the plan. To minimize the total online ART time slot, this calculation may be parallelized with the delivery of the MU(1 ,i).

[0068] Once calculated MU(1,i) for i=1, ...N being N the total number of treatment fields, the calculated MUs can be delivered to the patient by using the selected treatment delivery during plan optimization, e.g. IMRT orVMAT.

[0069] Method 100 comprises, at step 108, obtaining dose data from the delivery of the first portion. This step may comprise recording an exit dose using a detector. The detector may be a MV flat panel detector. The associated dose recorded into the MV FP during the delivery of the first part of the treatment plan is then stored and transferred to a software workstation.

[0070] Step 108 may comprise back-projecting from the MV FP 2D images into total dose on the 3D daily CBCT acquired prior to treatment adaptation by means of a physical model calculation or Al prediction-based approach (this choice may be made as a function of back-projection speed). The 2D dose recorded from the MV FP and transferred to a software workstation will be processed to back-project it as a total dose of the delivered first part of the treatment plan (from each i-th treatment segment field) on the daily qCBCT. This is a time-consuming process that is

[0071] P151368PC01 2025P00097 WO traditionally done offline when using the total delivered dose (in this case the sum of first and second parts of the adapted plan) with the limitation of just discovering possible errors / mistakes without the possibility to online act on them. Embodiments of the invention, based on splitting the overall plan into two parts, allows for QA of the adapted plan itself and dosimetrically capture of possible patient movements / deformations. In fact, any of these causes will result in a mismatch between the planned dose during the new plan adaptation on the daily qCBCT and the actually delivered dose back projected on the very same daily qCBCT.

[0072] Method 100 comprises, at step 110, determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data. The dosimetric value may be a gamma index. Other possible metrics may include target or OAR DVHs or other plan quality indices like conformity or radiobiological indices. Once the delivered dose of the first part of the adapted treatment plan has been back projected onto the daily qCBCT, dosimetric comparison between doses planned in the newly adapted plan and actually delivered in the first part of the plan can be made by means of traditional dose comparison metrics. For example, by means of gamma pass rate (e.g. 97% at 2% / 2mm and / or 99% at 3% / 3mm), Planning Target Volume (PTV) coverage (e.g. 95% of the PTV covered by reference isodose) or Dose Volume Histogram (DVH) of OARs (e.g. 60% of the volume covered by a dose less than 80% of the maximum at that very same OAR).

[0073] Method 100 comprises, at step 112, assessing whether the dosimetric value is within an acceptable range. The acceptable range may be determined based on the body site of the radiotherapy treatment, and / or the radiotherapy treatment technique being used.

[0074] Step 112 may comprise setting a threshold to consider the metric defined at step 110 as acceptable (this could be body site or technique specific). An acceptability threshold may be defined as a function of body district, treatment technique (e.g. conventional RT versus Stereotactic RadioSurgery - SRS - or Stereotactic Body RT - SBRT) and / or other inputs. This will allow to in vivo assess if the actual delivered dose will be acceptable due to the lack of adapted plan mistake and patient movement / deformation during the plan adaptation phase.

[0075] If yes, method 100 comprises, at step 114, delivering a second portion of the adapted treatment plan. The first portion and the second portion may collectively comprise the entirety of the adapted treatment plan, for example, the first portion may be 5% of the MUs of the adapted treatment plan and the second portion may be the other 95%.

[0076] P151368PC01 2025P00097 WO If the result from step 110 is within the acceptability range defined at step 112, then a user can proceed with the delivery of the resulting MUs (the difference between the MUs planned in the adapted plan and those already delivered in this QA check based on a partial delivery). Based on the output of step 112, if the newly adapted plan is deemed acceptable to be fully delivered, then the MU to be delivered in second delivery part MU(2,i) = MU(i)-MU(1 ,i), i.e. the remaining MU(i) at the i-th treatment plan field from what has already been delivered, can be delivered.

[0077] Optionally, the same concept as in first part of the delivery can be applied to the second part of the delivery, where potential dose mismatch can be discovered and potentially accounted for in the next fraction, if any. Potential errors / mismatch in second part of the delivery will not be likely to come from plan adaptation mistakes, but from actual plan delivery, e.g. from an erratic delivery of MUs, from leaf position errors (e.g. in the Multi Leaf Collimator - MLC) or from patient movements / deformation in the second part of the treatment delivery. These could be taken into account in an offline ART. Examples of suitable ART include: segment aperture morphing (SAM) with or without beam weight re-optimization, e.g. Ahunbay, Ergun E., et al. "An on-line replanning scheme for interfractional variations a." Medical physics 35.8 (2008): 3607-3615; an adaptive sequencer such as C. Kontaxis, G. Bol, J. Lagendijk, B. Raaymakers, Towards adaptive IMRT sequencingforthe MR-linac, Physics in Medicine & Biology, 60 (2015) 2493.

[0078] If no, method 100 comprises, at step 116, stopping the delivery of the adapted treatment plan, and optionally, at step 118, sending an alert to a user.

[0079] If the result from step 110 is not within the acceptability range defined at step 112, then a user may stop the delivery of the second part of the adapted plan and investigate the root cause of this mismatch, e.g. patient movement or adapted treatment plan error. Alternatively, the delivery of the second part of the plan may be stopped automatically. Based on the output of step 112, if the newly adapted plan is not acceptable to be fully delivered, then the root cause of the dosimetric mismatch should be investigated. A first action may be to take a new CBCT to evaluate possible patient movements / deformations. If no significant patient movement / deformation is found, a second action may be to investigate adapted treatment plan quality and stop treatment delivery to the patient until the reason for this dosimetric mismatch has been found.

[0080] Figure 2 shows a simplified representation of what a treatment plan or an adapted treatment plan may look like. Example contours of the body 208, prostate 210, rectum 212 and bladder 214 can

[0081] P151368PC01 2025P00097 WO be seen. Figure 2 shows four multi-leaf collimator (MLC) apertures which shape the radiation beams 206 of the linac to match the outline of the tumour from different angles. By moving the individual leaves of the MLC, the MLC blocks certain parts of the beam, allowing only specific sections to pass through. MLCs allow for precise delivery of radiation to the tumour, sparing nearby healthy tissue. This precision is important in techniques like Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), where the beam intensity can be modulated to match the tumour’s 3D shape. Isodose lines 204abc are contour lines representing areas within the body 208 receiving the same dose of radiation. MLCs help tailor the radiation beam so that the isodose lines tightly conform to the shape of the tumour, all the beams 206 combine to generate the dose distribution. In this simplified representation, only four MLC apertures / beams are shown. In practice there would usually be more than four beams, e.g. nine, and in some cases several segment for the same field, i.e. beam angle. Or, if VMAT is used, the gantry of the linac moves around the patient, delivering radiation in a continuous arc. The MLC apertures may change over time as the treatment is delivered, to sculpt the dose distribution, which is shown as an isodose distribution (isodose lines 204abc). As such, the generated at least one treatment plan may comprise one or more of: an indication of how many radiation beams 206 are needed, howthe MLC leaves should be positioned forthe treatment, the isodose contours 204abc, and a likely anatomical state 208, 210, 212, 214 of the patient.

[0082] Example methods according to the present disclosure allow a time-efficient and robust treatment plan verification method. This combination of speed and quality supports the delivery of radiotherapy treatment in the form of online ART.

[0083] The robust treatment plans and speed afforded by methods of the present disclosure support the provision of online ART, in which daily CBCT is used to capture patient imaging at the start of each visitof the treatment fraction. This up-to-date imaging data can enable clinicians to track changes in patient anatomy, includingfor example, tumour shrinkage overthe course of the radiotherapy treatment, allowing for online target localisation and plan adaptation without the constraints of diagnostic CT imaging. The adapted treatment plans based on the CBCT are verified by methods according to the present disclosure. This may result in many additional medical treatment benefits (including improved accuracy of radiotherapy treatment, reduced exposure to unintended radiation, reduced treatment duration, higher tumor control, etc.). The methods presented herein may be applicable to a variety of medical treatment and diagnostic settings or radiotherapy treatment equipment and devices.

[0084] P151368PC01 2025P00097 WO Figure 3 is a block diagram of an implementation of a radiotherapy system 300, suitable for executing methods according to embodiments (e.g. method 500 and / or method 100). The example radiotherapy system 300 comprises a computing system 310 within which a set of instructions, for causing the computing system 310 to perform the method (or steps thereof) discussed herein, may be executed. The computing system 310 may implement a treatment plan verification system arranged to verify treatment plans, e.g. as described in relation to methods 500 and / or 100. The computing system 310 may also be referred to as a computer. In particular, the methods described herein maybe implemented by a processor or controller circuitry 311 of the computing system 310.

[0085] The computing system 310 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.

[0086] The computing system 310 includes controller circuitry 311 and a memory 313 (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 313 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). Memory 313 may be used to store or buffer image data until required for processing.

[0087] Controller circuitry 311 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 311 may comprise a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long

[0088] P151368PC01 2025P00097 WO instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Controller circuitry 311 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 311 is configured to execute the processing logic for performing the operations and steps discussed herein.

[0089] The computing system 310 may further include a network interface circuitry 315. The computing system 310 may be communicatively coupled to an input device 320 and / or an output device 330, via input / output circuitry 316. In some implementations, the input device 320 and / or the output device 330 may be elements of the computing system 310. The input device 320 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 / ora haptic input device. The output device 330 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 320 and the output device 330 may be provided as a single device, or as separate devices.

[0090] In some implementations, the computing system 310 may comprise image processing circuitry 314. Image processing circuitry 314 may be configured to process image data 370 (e.g., images, imaging data, projections, projection data), such as medical images (e.g. CBCT) obtained from one or more imaging data sources, a treatment device 350 and / or an image acquisition device 340. Image processing circuitry 314 may be configured to process, or pre-process, image data 370. For example, image processing circuitry 314 may convert received image data into a particular format, size, resolution or the like. Image processing circuitry 314 may be configured to perform image reconstruction. In some implementations, image processing circuitry 314 may be combined with controller circuitry 311.

[0091] In some implementations, the radiotherapy system 300 may further comprise an image acquisition device 340 and / or a treatment device 350. The image acquisition device 340 and the treatment device 350 may be provided as a single device. In some implementations, treatment device 350 is configured to perform imaging, for example in addition to providing treatment and / or during treatment.

[0092] P151368PC01 2025P00097 WO Image acquisition device 340 may be configured to perform positron emission tomography (PET), computed tomography (CT), magnetic resonance imaging (MRI), single positron emission computed tomography (SPECT), X-ray, and the like.

[0093] Image acquisition device 340 may be configured to output image data 370, which may be accessed by computing system 310. Treatment device 350 may be configured to output treatment data 360, which may be accessed by computing system 310.

[0094] Computing system 310 may be configured to access or obtain treatment data 360, planning data 380 and / or image data 370. Treatment data 360 may be obtained from an internal data source (e.g., from memory 313) or from an external data source, such as treatment device 350 or an external database. Planning data 380 may be obtained from memory 313 and / or from an external source, such as a planning database. Planning data 380 may comprise information obtained from one or more of the image acquisition device 340 and the treatment device 350.

[0095] The various methods described above (e.g. methods 500 and / or 100) may be implemented by a computer program. The computer program may include computer code (e.g., instructions) arranged to instruct a computer to perform the functions of one or more of the various methods described above. For example, the steps of the methods described in relation to Figure 1 may be performed by the computer code. The steps of the methods described above may be performed in any suitable order. The computer program and / or the code 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. The computer readable media may be transitory or non-transitory. The one or more computer readable media 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 may also reside, completely orat least partially, within the memory 313 and / orwithin the controller circuitry 311 during execution thereof by the computing system 310, the memory 313 and the controller circuitry 311 also constituting computer-readable storage media.

[0096] P151368PC01 2025P00097 WO In an implementation, the modules, components and other features described herein may be implemented as discrete components or integrated in the functionality of hardware components such as ASICS, FPGAs, DSPs or similar devices.

[0097] 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 (such as the steps outlined in method 500 and / or 100) 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.

[0098] In addition, the modules and components may be implemented as firmware or functional circuitry within hardware devices. Further, the modules and components may 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).

[0099] Figure 4 depicts a radiotherapy apparatus, suitable for use with embodiments. The cross-section through radiotherapy apparatus 400 includes a radiation head 410 and a beam receiving apparatus 402, both of which are attached to a gantry 404. The radiation head 410 includes a radiation source 412, which emits a beam of radiation 406. The radiation head 410 also includes a beam shaping apparatus 418, which controls the size and shape of the radiation field associated with the beam.

[0100] The beam receiving apparatus 402 is configured to receive radiation emitted from the radiation head 410, for the purpose of absorbing and / or measuring the beam of radiation. In the view shown, the radiation head 410 and the beam receiving apparatus 402 are positioned diametrically opposed to one another.

[0101] The gantry 404 is rotatable and supports the radiation head 410 and the beam receiving apparatus 402 such that they are rotatable around an axis of rotation 408, which may coincide with the patient longitudinal axis. The gantry provides rotation of the radiation head 410 and the beam receiving apparatus 402 in a plane perpendicular to the patient longitudinal axis (e.g., a sagittal plane). Three gantry directions XG, YG, ZGmay be defined, where the YGdirection is perpendicular with gantry axis of rotation. The ZGdirection extends from a point on the gantry corresponding to

[0102] P151368PC01 2025P00097 WO the radiation head, towards the axis of rotation of the gantry. Therefore, from the patient frame of reference, the ZGdirection rotates around as the gantry rotates.

[0103] Radiotherapy apparatus 400 also includes a support surface 420 (e.g. the treatment table) on which a subject (or patient) is supported during radiotherapy treatment. The radiation head 410 is configured to rotate around the axis of rotation 408 such that the radiation head 410 directs radiation towards the subject from various angles around the subject in order to spread out the radiation dose received by healthy tissue to a larger region of healthy tissue while building up a prescribed dose of radiation at a target region.

[0104] The radiotherapy apparatus 400 is configured to deliver a radiation beam towards a radiation isocentre, which is substantially located on the axis of rotation 408 at the centre of the gantry 404 regardless of the angle at which the radiation head 410 is placed.

[0105] The rotatable gantry 404 and radiation head 410 are dimensioned so as to allow a central bore 422 to exist. The central bore 422 provides an opening, sufficient to allow a subject to be positioned therethrough without the possibility of being incidentally contacted by the radiation head 410 or other mechanical components as the gantry rotates the radiation head 410 about the subject, also known as patient collision.

[0106] The radiation head 410 emits the radiation beam 406 along a beam axis 424 (or radiation axis or beam path), where the beam axis 424 is used to define the direction in which the radiation is emitted by the radiation head. The radiation beam 406 is incident on the beam receiving apparatus 402, which may include at least one of a beam stopper and a radiation detector. The beam receiving apparatus 402 is attached to the gantry 404 on a diametrically opposite side to the radiation head 410 to attenuate and / or detect a beam of radiation after the beam has passed through the subject.

[0107] The radiation beam axis 424 may be defined as, for example, a centre of the radiation beam 406 or a line of maximum radiation intensity within the radiation beam.

[0108] The beam shaping apparatus 418 delimits the spread of the radiation beam 406. The beam shaping apparatus 418 is configured to adjust the shape and / or size of a field of radiation produced by the radiation source. The beam shaping apparatus 418 does this by defining an aperture (also referred to as a window or an opening) of variable shape to collimate the radiation

[0109] P151368PC01 2025P00097 WO beam 406 to a chosen cross-sectional shape. In this example, the beam shaping apparatus 418 maybe provided by a combination of a diaphragm and an MLC. Beam shaping apparatus 418 may also be referred to as a beam modifier.

[0110] The radiotherapy apparatus 400 may be configured to deliver both coplanar and non-coplanar (also referred to as tilted) modes of radiotherapy treatment. In coplanar treatment, radiation is emitted in a plane which is perpendicular to the axis of rotation of the radiation head 410. In non-coplanar treatment, radiation is emitted at least at an angle which is not perpendicular to the axis of rotation. In order to deliver coplanar and non-coplanar treatment, the radiation head 410 may move between at least two positions, one in which the radiation is emitted in a plane which is perpendiculartotheaxisof rotation (coplanar configuration) and one in which radiation is emitted in a plane which is not perpendicular to the axis of rotation (non-coplanar configuration).

[0111] In the coplanar configuration, the radiation head is positioned to rotate about a rotation axis and in a first plane. In the non-coplanar configuration, the radiation head is tilted with respect to the first plane such that a field of radiation produced by the radiation head is directed at an oblique angle relative to the first plane and the rotation axis. In the non-coplanar configuration, the radiation head is positioned to rotate in a respective second plane parallel to and displaced from the first plane. The radiation beam is emitted at an oblique angle with respect to the second plane, and therefore as the radiation head rotates the beam sweeps out a cone shape.

[0112] The beam receiving apparatus 402 remains in the same place relative to the rotatable gantry when the radiotherapy apparatus is in both the coplanar and non-coplanar modes. Therefore, the beam receiving apparatus 402 is configured to rotate about the rotation axis in the same plane in both coplanar and non-coplanar modes. This may be the same plane as the plane in which the radiation head rotates.

[0113] The radiotherapy apparatus 400 includes a controller 430, which is programmed to control the radiation source 412, beam receiving apparatus 402, beam shaping apparatus and the gantry 404. Controller 430 may perform functions or operations such as treatment planning, treatment plan verification, treatment execution, image acquisition, image processing, motion tracking, motion management, and / or other tasks involved in a radiotherapy process.

[0114] Controller 430 is programmed to control features of apparatus 400 according to a radiotherapy treatment plan for irradiating a target region, also referred to as a target tissue, of a patient. The

[0115] P151368PC01 2025P00097 WO treatment plan includes information about a particular dose to be applied to a target tissue, as well as other parameters such as beam angles, dose-histogram-volume information, the number of radiation beams to be used duringtherapy, the dose per beam, and the like. Controller 430 is programmed to control various components of apparatus 400, such as gantry 404, radiation head 410, beam receiving apparatus 402, and support surface 420, according to the treatment plan.

[0116] Hardware components of controller 430 may include one or more computers (e.g., general purpose computers, workstations, servers, terminals, portable / mobile devices, etc.); processors (e.g., central processing units (CPUs), graphics processing units (GPUs), microprocessors, digital signal processors (DSPs), field programmable gate arrays (FPGAs), special-purpose or specially-designed processors, etc.); memory / storage devices such as a memory (e.g., read-only memories (ROMs), random access memories (RAMs), flash memories, hard drives, optical disks, solid-state drives (SSDs), etc.); input devices (e.g., keyboards, mice, touch screens, mics, buttons, knobs, trackballs, levers, handles, joysticks, etc.); output devices (e.g., displays, printers, speakers, vibration devices, etc.); circuitries; printed circuit boards (PCBs); or other suitable hardware. Software components of controller 430 may include operation device software, application software, etc.

[0117] The radiation head 410 may be connected to a head actuator414, which is configured to actuate the radiation head 410, for example between a coplanar configuration and one or more non-coplanar configurations. This may involve translation and rotation of the radiation head 410 relative to the gantry. In some implementations, the head actuator may include a curved rail along which the radiation head 410 may be moved to adjust the position and angle of the radiation head 410. The controller 430 may control the configuration of the radiation head 430 via the head actuator 414.

[0118] The beam shaping apparatus 418 includes a shaping actuator 416. The shaping actuator is configured to control the position of one or more elements in the beam shaping apparatus 418 in orderto shape the radiation beam 406. In some implementations, the beam shaping apparatus 418 includes an MLC, and the shaping actuator 416 includes means for actuating leaves of the MLC. The beam shaping apparatus 418 may further comprise a diaphragm, and the shaping actuator 416 may include means for actuating blocks of the diaphragm. The controller 430 may control the beam shaping apparatus 418 via the shaping actuator 416.

[0119] P151368PC01 2025P00097 WO A treatment plan may comprise positioning information of beam shaping apparatus 418. The positioning information of beam shaping apparatus 418 may comprise information indicating a configuration of one or more elements of beam shaping apparatus 418, such as leaf configuration of an MLC of beam shaping apparatus 418, a configuration of a diaphragm of beam shaping apparatus 418, a configuration of an opening (e.g., window or aperture) of the MLC, and / or the like.

[0120] 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”, “generating”, “adapting”, “reducing”, “obtaining”, “parameterizing”, “training”, or the like, refer to the actionsand processesof 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.

[0121] While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the inventions. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of methods and apparatus described herein may be made.

[0122] The following are certain enumerated embodiments further illustrating various aspects the disclosed subject matter.

[0123] 1. A method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment, the method comprising:

[0124] obtaining a pre-treatment cone beam computed tomography, CBCT, image of a patient; adapting a treatment plan, based on the CBCT image;

[0125] delivering a first portion of the adapted treatment plan to the patient;

[0126] obtaining dose data from the delivery of the first portion;

[0127] determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data; and

[0128] if the dosimetric value is within an acceptable range, delivering a second portion of the adapted treatment plan; or

[0129] P151368PC01 2025P00097 WO if the dosimetric value is outside the acceptable range, stopping the delivery of the adapted treatment plan.

[0130] 2. The method of claim 1, wherein the first portion of the adapted treatment plan is a smaller proportion of the adapted treatment plan than the second portion.

[0131] 3. The method of claim 1 or 2, wherein the first portion and the second portion collectively comprise the entirety of the adapted treatment plan.

[0132] 4. The method of any precedingclaim, wherein the first portion is calculated based on the number of Monitor Units, MU, per treatment field needed for photons exiting the patientto be detected by a detector.

[0133] 5. The method of claim 4, wherein the first portion is calculated based on the number of MU per treatment field needed for a threshold number of photons exiting the patient to be detected by a detector.

[0134] 6. The method of claim 5, wherein the threshold number of photons is based on the number of photons required to produce a 3D dose back-projection into the CBCT image.

[0135] 7. The method of any preceding claim, wherein obtaining dose data from the delivery of the first portion comprises recording an exit dose using a detector.

[0136] 8. The method of any of claims 4 to 7, wherein the detector is a megavoltage, MV, flat panel detector.

[0137] 9. The method of any preceding claim, wherein the dosimetric value associated with quality assurance of the adapted treatment plan comprises a gamma index.

[0138] 10. The method of any precedingclaim, wherein, if the dosimetric value is outside the acceptable range, the method further comprises sending an alert to a user.

[0139] 11. The method of any preceding claim, wherein the pre-treatment CBCT image comprises a quantitative CBCT, image.

[0140] P151368PC01 2025P00097 WO 12. A data processing apparatus comprising a memory storing computer-executable instructions, and a processor configured to execute the instructions to carry out the method of any preceding claim.

[0141] 13. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 1 to 11.

[0142] 14. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1 to 11.

[0143] P151368PC01 2025P00097 WO

Claims

24Claims1. A method for radiotherapy treatment plan verification during a fraction of an online adaptive radiotherapy treatment, the method comprising:obtaining: a pre-treatment cone beam computed tomography, CBCT, image of a patient, an adapted treatment plan, which has been adapted based on the CBCT image, and dose data from delivery of a first portion of the adapted treatment plan to the patient; determining a dosimetric value associated with quality assurance of the adapted treatment plan, based on the dose data; andif the dosimetric value is within an acceptable range, validating the adapted treatment plan as acceptable to be fully delivered to the patient.

2. The method of claim 1 , wherein validating the adapted treatment plan as acceptable to be fully delivered to the patient comprises initiating delivery of a second portion of the adapted treatment plan.

3. The method of claim 1 or 2, further comprising: if the dosimetric value is outside the acceptable range, not validating the adapted treatment plan as acceptable to be fully delivered to the patient.

4. The method of any preceding claim, wherein not validating the adapted treatment plan as acceptable to be fully delivered to the patient comprises causing delivery of the adapted treatment plan to be stopped.

5. The method of any preceding claim, wherein the first portion of the adapted treatment plan delivers a non-therapeutic radiation dose to the patient.

6. The method of any preceding claim, further comprising initiating delivery of the first portion of the adapted treatment plan to the patient.

7. The method of any preceding claim, wherein the first portion of the adapted treatment plan is a smaller proportion of the adapted treatment plan than the second portion.P151368PC01 2025P00097 WO8. The method of any preceding claim, wherein the first portion and the second portion collectively comprise the entirety of the adapted treatment plan.

9. The method of any preceding claim, wherein the first portion is calculated based on the number of Monitor Units, MU, per treatment field needed for photons exiting the patientto be detected by a detector.

10. The method of claim 9, wherein the first portion is calculated based on the number of MU per treatment field needed for a threshold number of photons exiting the patient to be detected by a detector.

11. The method of claim 10, wherein the threshold number of photons is based on the number of photons required to produce a 3D dose back-projection into the CBCT image.

12. The method of any preceding claim, wherein obtaining dose data from delivery of the first portion comprises obtaining an exit dose recorded using a detector.

13. The method of any of claims 9 to 12, wherein the detector is a megavoltage, MV, flat panel detector.

14. The method of any preceding claim, wherein the dosimetric value associated with quality assurance of the adapted treatment plan comprises a gamma index.

15. The method of any of claims 3 to 14, wherein, if the dosimetric value is outside the acceptable range, the method further comprises sending an alert to a user.

16. The method of any preceding claim, wherein the pre-treatment CBCT image comprises a quantitative CBCT, image.

17. A data processing apparatus comprising a memory storing computer-executable instructions, and a processor configured to execute the instructions to carry out the method of any preceding claim.

18. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 1 to 16.P151368PC01 2025P00097 WO19. A computer-readable medium comprising instructions which, when executed by a computer, cause the computer to carry out the method of any of claims 1 to 16.

20. A radiotherapy system comprising a computing system, the computing system comprising instructions for causing the computing system to perform the method of any of claims 1 to 16.P151368PC01 2025P00097 WO

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