The invention generally relates to planning intensity modulated proton therapy (IMPT). In particular the invention relates to optimizing an IMPT plan. More specifically, the invention relates to optimizing an IMPT plan with localized plan deficiencies.
In intensity modulated proton therapy (IMPT), target structures in a patient's body, such as tumors, are treated by subjecting them to irradiation by a beam of protons. The treatment is delivered in such a way that the dose that is delivered to the target structures (TSs) is as high as possible, while at the same time the dose delivered to the surrounding healthy tissue and structures, usually referred to as organs at risk (OARs), is as low as possible. A tradeoff between the two will have to be made. For this, clinical goals are provided. Clinical goals in planning the IMPT treatment will specify the requirements for dose to be delivered to a TS. The clinical goals may also include maximum value for the dose to be delivered to each OAR. Numerical optimization is typically used to determine the best total dose distribution to deliver. From this dose distribution the parameters for delivery are calculated that form the therapy plan.
IMPT plans define a pattern of locations where the protons beams are to be delivered, together with the intensity of the beam for each location. Because of the shape of the proton beam, a high dose is delivered to a relatively small volume. The location where the dose is delivered is referred to as a spot or proton spot.
Due to the shape of the Bragg peak of the proton beam, IMPT has the advantage that the treatment can be delivered with high accuracy. However, due to the characteristic beam shape used in IMPT, IMPT plans are particularly sensitive to errors such as range and setup uncertainties and organ deformations and movement. Failing to account for such errors in the IMPT plan may result in a delivered dose distribution that is inferior to the planned one.
Setup uncertainty is due to a positional shift of the patient, which may cause misalignment of dose contributions from different beam directions. Even with modern immobilization techniques, deviations of several millimeters are still possible. Range uncertainty corresponds to the uncertainty of the location of the Bragg peak in the patient. This uncertainty can e.g. stem from uncertainty in the Hounsfield units of the CT image that is typically used for planning and the conversion of these Hounsfield units to stopping power.
Robustness Analysis (RA) is a technique for simulating the effect of range uncertainty and setup errors on the dose distribution of the IMPT plan. In RA the dose distributions for various error scenarios are calculated. Setup error is simulated by using anatomical data of the patient and three independent parameters that mimic the whole body movement of the patient (corresponding to X, Y and Z shifts). Range error can be entered as a percentage of uncertainty.
Robust Optimization (RO) is a technique for optimizing IMPT plans. This technique takes into account setup and range errors in order to calculate an IMPT plan with a reduced sensitivity to error. In RO an overall plan objective value, which includes a clinical objective component and a patient setup error component, is minimized.
WO2017/109632 describes a robust optimization technique that also includes possible errors due to organ deformation and movement within the patient. In this technique, the RO objective value that is minimized, includes additional components for organ movement and organ deformation.
US2016/059039 describes a method for generating IMPT plans. In this method, dose distributions are calculated for each one of a plurality of uncertainty scenarios and robustness indeces for locations in target volumes of interest are computed. The entire treatment plan is then recalculated by minimizing an objective function based at least in part on deviations of the robustness indices from a prescribed robustness index.
In the current practice of IMPT planning, first a nominal plan is created that meets the clinical goals. This plan is then analyzed by RA. It is common for IMPT that the nominal plan will show localized areas with defects such as so-called hotspots or coldspots in the various simulated error scenarios. Robust optimization will improve the sensitivity to errors, and therefore resolve or reduce these deficiencies, but the overall quality of the plan is sacrificed in order to gain robustness. In cases where the nominal plan is acceptable and shows only small and/or few defects in the RA error scenarios, RO may lead to significant deterioration of the overall dose distributions. In these cases, it often happens that a physician will prefer to deliver the nominal plan without accounting for errors instead of delivering the RO plan. This means the treatment will then go ahead with the nominal plan and associated risks.
The current invention seeks to provide the physician with an alternative or additional way to optimize a preferred initial therapy play. The current invention further seeks to address the need to improve the robustness of an IMPT plan for localized dose deficiencies whilst avoiding, or at least reducing, degradation of the overall plan quality.
It is a further insight of the invention that patient movement does not just occur during patient setup, but may also occur during treatment delivery. IMPT treatment can take significant time to deliver, e.g. half an hour. Within that time frame the patient may shift slightly, but more importantly TSs and OARs may move and change. The uncertainty in position that is due to these shifts and changes is referred to as local residual error (LRE). The current invention additionally or alternatively seeks to improve robustness of an IMPT plan for localized areas that have a high risk of LRE induced dose errors.
Further advantages from the described invention will also be apparent to the skilled person. Thereto a method and system for optimizing an IMPT plan are provided. Also, a computer program product comprising instructions which, when executed, control a processor to perform the method for optimizing an IMPT plan is provided. Further, an arrangement for planning IMPT is provided.
The method for optimizing an IMPT plan, comprising the steps of: receiving an initial IMPT plan for a subject to be treated; receiving anatomical image data of the subject to be treated; and identifying critical proton spots in the initial plan using the anatomical image data. Critical proton spots are the proton spots that have a high risk of delivering a deviant dose, e.g. too high or too low in view of the clinical goals, in case an error, such as a setup, range or LRE error, occurs. The method also comprises the step of generating at least one local plan deficiency area (LPDA) associated with the identified critical proton spots. A local plan deficiency area corresponds to the area in the dose map where the clinical goals, or similar clinically defined dose criteria, are not met in case an error occurs. The method further comprises the steps of generating a local treatment plan for the LPDA by applying robust optimization to the LPDA; and generating an optimized treatment plan for delivery to the subject to be treated by combining the local treatment plan with the initial IMPT plan. The method is preferably computer-implemented or implemented by other suitable calculation means.
In an exemplary embodiment of the method, the critical proton spots are identified by applying RA to the initial plan. In this example, it can also be possible to identify the critical spots automatically based on automated RA and the received clinical goals.
According to another example of the method, critical proton spots are identified by calculating which proton spots have a local residual error risk value that is higher than a predetermined risk level.
In accordance with the method as described above and any of its exemplary embodiments, the LPDA may be generated based on the locations of the identified critical proton spots. For example, the LPDA may be generated by defining an area around each critical proton spot representative of a location uncertainty of the critical proton spot and merging the areas around adjacent critical proton spots. Alternatively, the LPDA may be generated from graphical user input. According to another alternative, and for the example where the critically proton spots are identified by applying RA, the LPDA may be generated by identifying the locations of the critical proton spots in the initial plan and the locations of the shifted critical spots in the error scenario where these spots do not meet the clinical goals and encompassing these in a single area.
In accordance with the method as described above and any of its exemplary embodiments, multiple LPDAs may be generated and a local treatment plan is generated for each LPDA.
The system for optimizing an IMPT plan comprises an input configured to receive an initial IMPT plan for a subject to be treated and an input configured to receive anatomical image data of the subject to be treated. The system also comprises an identification module configured to identify critical proton spots in the initial plan using the anatomical image data, and an area calculation module configured to generate at least one local plan deficiency area associated with the critical proton spots identified by the identification module. The system further comprises a local treatment plan generator configured to apply RO to the LPDA, thereby generating a local robust optimized treatment plan for the local plan deficiency area; and an optimized treatment plan generator configured to combine the local treatment plan with the initial IMPT plan to form an optimized intensity modulated proton therapy plan for delivery to the subject to be treated.
In an exemplary embodiment of the system, the identification module comprises a robustness analysis user interface. Additionally or alternatively, the area calculation module may comprise a user interface.
In a particularly advantageous embodiment, one or both of the robustness analysis user interface and the area calculation module user interface are part of a graphical user interface. In such an embodiment, the graphical user interface can, for example, comprise a display for providing a visual representation of the anatomical image data with at least one of the dose distribution and the proton spot locations.
The computer program product comprises instructions which, when executed, control a processor to perform the method for optimizing an IMPT plan as described above.
The arrangement for planning IMPT comprising an imaging device configured to provide an image of a subject to be treated, a contouring tool configured to provide anatomical image data based on the image provided by the imaging device and an input for receiving clinical goals for the intensity modulated proton therapy. The arrangement further comprises a system configured to generate an initial intensity modulated proton therapy plan based on the anatomical data and the clinical goals; and the system for optimizing the IMPT plan as described above.
An advantage of the current invention is that the physician has more options available for optimizing an IMPT plan. With the current invention he, or she, can also use local robust optimization of a smaller area of the plan.
A further advantage of the current invention lies in that localized areas of the IMPT plan with a high risk of resulting in an inferior delivered dose due to errors are made more robust without adversely affecting the dose distribution of the areas plan of the plan that do not have such a risk. Because the invention identifies the critical proton spots and translates these into local plan deficiency areas, the process of robust optimization can be performed on such a high risk localized area only, leaving the remaining parts of the plan unaffected.
Another advantage lies in that the IMPT plan can be made more robust with respect to possible patient movement and/or organ movement and deformation that occurs during treatment delivery. By identifying the critical spots that have a high risk for inferior dose delivery due to LRE, the areas corresponding to these spots can be subjected robust optimization.
In the following drawings:
b schematically illustrate an example where critical proton spots are identified by calculating which proton spots have a high risk for LRE.
The imaging device 102 of the arrangement can be a structural imaging device, such as a CT, MR or ultrasound scanner, a functional imaging device, such as a PET or SPECT scanner or any combination thereof. It has particular advantages to use a combined PET-CT scanner, because a PET-CT image will allow the physician to identify OARs from the structural CT image as well as cancerous TSs from the PET functional image.
The image of the subject to be treated that is provided by the imaging device 102 is used as input for a contouring tool 103. The contouring tool delineates the OARs and TSs that are identified in the image. These delineations form the contours that form the anatomical image data for the subject to be treated. This delineation is commonly referred to as contouring. The contouring tool 103 may identify the contours automatically, or it may have an interface where the physician or a trained clinician inputs the contours manually. The contouring tool 103 may also use a combination of manual and automated contouring.
In order to generate the plan for the IMPT, clinical goals for the treatment are needed. The arrangement provides an input 104 for these goals. The clinical goals can be determined by the physician based on the image provided by the imaging device 102, and may be based on clinical protocol. The clinical goals can be entered manually through a user interface, or, for example, uploaded automatically from a database using anatomical image data. Clinical goals will typically include maximum dose limits for the identified OARs and a minimum or average dose to be received by a TS.
The initial plan generator 105 is a system that is configured to generate an initial IMPT plan. For generating the initial plan, a commercially available product such as Auto Plan may be used. Generating the initial IMPT plan is usually an interactive process performed by a physician and will be described in more detail with reference to
The initial IMPT plan provided by the initial plan generator 105 and anatomical image data provided by the contouring tool 103 are then used as input for the system for optimizing the IMPT plan 106. For this, the system 106 has an input 108 configured to receive the initial IMPT plan for the subject to be treated and an input 109 configured to receive the anatomical image data of the subject to be treated. These inputs may also be combined into a single input. In the example of
The system further has an identification module 110 configured to identify the critical proton spots in the initial plan using the anatomical image data and an area calculation module 111 configured to generate at least one LPDA associated with the critical proton spots that have been identified by the identification module 110. Next, a local treatment plan generator 112 applies RO to the LPDA and thereby generates a local robust optimized treatment plan for the LPDA. The robust optimized local treatment plan can be generated in a manner that is similar to the generation of an overall robust optimized plan, except calculations are performed on the LPDA only. For generating the local robust optimized treatment plan, the system 106 may comprise an input for local clinical goals 114. This example is illustrated in
The system 106 also comprises an optimized treatment plan generator 113 that is configured to combine the local treatment plan with the initial IMPT plan. Hereby the optimized IMPT plan 107 for delivery to the subject to be treated is formed.
The embodiment of system for generating the initial IMPT plan illustrated in
The nominal plan generator 201 will generate a nominal IMPT plan in the manner that is commonly known in the art. This is an interactive process in which a dose distribution is calculated using numerical optimization based on the anatomical image data and the clinical goals provided by the physician. The physician assesses the dose distribution and adjusts the clinical goals until the dose distribution is acceptable for delivery to the subject to be treated. From this dose distribution the nominal plan generator 201 then calculates the parameters for delivery to form the nominal IMPT plan.
In a simple embodiment of a system for generating an initial IMPT plan 105, this system can consist of a nominal plan generator 201. In this simple case, the nominal plan is the initial plan. However, in a more extensive embodiment, it can be advantageous to also include a global RO unit 203 and a plan selector 204. The global RO unit 203 allows the physician to analyze the overall robustness of the nominal IMPT plan using an RA interface 206. With this interface, the physician can simulate the various error scenarios including range and setup error. The global RO unit can then use an RO calculator 207 on the nominal plan to calculate an RO plan. This may be preferred in cases where the RA shows many and/or extensive areas of dose deficiencies. Or the physician may simply wish to assess how much of the overall plan quality is sacrificed to reduce error sensitivity in the RO of the overall plan.
In order to make a choice as to which IMPT plan to use as the initial plan 205, the initial plan generator 105 comprises a plan selector 204. The plan selector presents the options of choosing between the nominal IMPT plan generated by the nominal plan generator 201 and the RO plan generated by the global RO unit 203. The plan that is chosen is then the initial plan 205 that is the output. It is particularly useful for the plan selector 204 to be operable independent of the global RO unit 203, meaning that a choice can be made irrespective of whether a global RO plan was calculated or not. The advantage of this is that the physician can bypass the RO of the full plan and directly choose the nominal plan as initial plan 205 if that is his preference.
In the method for optimizing the IMPT plan, an initial IMPT plan is received as input at 302. Such an initial IMPT plan may be the nominal IMPT plan, but it can also be an IMPT plan that has already undergone global RO. The initial plan can, for example, be determined by using the initial plan generator illustrated in
In the method illustrated in
Next, critical proton spots are identified in the initial plan using the anatomical image data 305. Critical proton spots are the proton spots that have a high risk of delivering a deviant dose, e.g. too high or too low in view of clinical goals, in case an error occurs. Such an error can be a range or setup error, an error due to organ motion or deformation, or an LRE.
In the method for optimizing an IMPT plan, critical proton spots may be identified in several ways.
In one example, the critical proton spots are identified by applying RA to the initial plan 310. This can be done interactively by the physician or automatically. In the option where RA is applied interactively by the physician, preferably a user interface is provided, more preferably in the form of a graphical user interface. Such an interface will allow the user to input the error scenario he wishes to simulate and he or she can the see the effect of the error on the dose distribution. The physician can the identify the areas in the dose distribution where the delivered dose would be deviant because it is too high or too low. An area with a dose that is too high would show as a hot spot, an area where the dose is too low as a cold spot. In such an interactive system, the proton spots could also be displayed and the physician could mark them as critical by clicking on them. In an alternative option, the user could be provided with a drawing tool for drawing around the area of dose deviation and the critical proton spots are then defined as the proton beams that would be delivered in that area. In the option where RA is performed as an automated process, the clinical goals are received 311 as additional input. Critical spots are then identified based on this automated process and the received clinical goals 301. In this case a spot is identified as critical in case, in one or more of the error scenarios, the dose that is delivered by the proton beam does not meet the clinical goals.
In a second example, the critical proton spots are identified by calculating which proton spots have local residual error risk value that is higher than a predetermined risk level 312. In this case, the predetermined risk level may be a preset threshold value, but it can also be received as an additional input value 313.
With the identified critical proton spots, at least one LPDA is created 306. A local treatment plan is then generated for the LPDA by applying RO to the LPDA 307. This treatment plan is local in nature, because it relates specifically to the LPDA and not to the IMPT plan as a whole. In generating this treatment plan, RO is applied specifically to the LPDA and not to the IMPT plan as a whole. In an advantageous embodiment the clinical goals that have been received as input are also used when RO is applied to the LPDA. This allows for a fully automated IMPT plan optimization process. Alternatively, additional or alternative clinical goals may be received at 307 for the process of applying RO to the LPDA.
The distribution of critical spots may also be such that it is preferred to generate multiple LPDAs. For example, a plan may show critical protons spots causing a hot spot and a cold spot in the delivered dose two separate locations in an RA error scenario, or multiple small hot or cold spots in the delivered dose different locations or for different error scenarios. In this case it could be preferred to generate an LPDA for each of these small areas of dose deviations. Alternatively, for example, there may also be two or more areas with critical proton spots with a high risk for LRE. In this case it could be preferred to generate an PLDA for each area of critical proton spots with a high risk for LRE. An IMPT plan may also have a combination of critical proton spots for areas of dose deviations in RA error scenarios with critical proton spots with a high risk for LRE. In such a case, it is preferred that the spatial locations and proximities of the various critical spots will determine whether a single LPDA should be generated or whether two or more LPDAs should be generated. If the critical proton spots are clustered in one smaller region, a single LPDA will suffice for all critical proton spots, regardless of their origin. However, if there are two or more spatially separate clusters, creating multiple LPDAs is preferred. In case multiple LPDAs are generated, a local treatment plan is generated 307 for each of the LPDAs by applying RO to each area. The result is that each LPDA has its own RO optimized local treatment plan.
When the local treatment plan or plans have been generated, it is, or they are, combined with the initial IMPT plan to generate the optimized IMPT treatment plan 308 for delivery to the subject to be treated. A possible way of combining a local treatment plan with the initial treatment plan is replacing the delivery parameter for the critical proton spots in the initial IMPT plan with the newly determined delivery parameters of the local treatment plan whilst leaving the delivery parameters for the other, remaining proton spots unchanged.
In the exemplary embodiment of
In the error scenario depicted in display 403 of the RA system of
Within the time span that IMPT takes to deliver, or, when the treatment is split into multiple fractions, the time span that a fraction of the IMPT takes to deliver, the subject that is treated may shift slightly, and TSs and OARs may move and change. LRE is the uncertainty in position that is due to these shifts and changes and the magnitude of the LRE during treatment delivery increases with time. This also means that the risk of delivering a deviant dose increases with time. Proton spots that are delivered earlier during the treatment will be affected less by LRE than proton spots delivered later on.
The current invention additionally or alternatively seeks to improve robustness of an IMPT plan for localized areas that have a high risk of LRE induced dose errors. For this purpose, the critical proton spots that have a high risk for LRE are identified. This process comprises two steps.
First, the potential critical proton spots are identified based on their location. For many locations in the patient's body, delivery of the proton spot in accordance with the initial plan will not result in the delivery of a deviant dose in case an LRE occurs. The proton spots that are delivered to these locations are low-risk with a low LRE risk value and are non-critical proton spots. Proton spots that can result in the delivery of a deviant dose in case an LRE occurs are typically located in proximity to an OAR and a TS.
After these potential critical proton spots have been identified based on location, the time of delivery is calculated. The probability that LRE occurs, and thereby the
LRE risk value, increases with the time taken to deliver the proton spot. Recent research suggests that the risk increases linearly with time and the risk can therefore be calculated by multiplying the delivery time with a predetermined proportionality risk constant. In order to determine the moment of delivery of each proton spot, the complete delivery of the treatment is simulated.
The combination of location of the proton spot with the moment of delivery during the treatment determines the LRE risk value of that proton spot. A visual representation of a simulation delivery is illustrated in
In the example of
Any of the method steps disclosed herein, may be recorded in the form of a computer program comprising instructions which when executed on a processor cause the processor to carry out such method steps. The instructions may be stored on a computer program product. The computer program product may be provided by dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions can be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which can be shared. Furthermore, embodiments of the present invention can take the form of a computer program product accessible from a computer-usable or computer-readable storage medium providing program code for use by or in connection with a computer or any instruction execution system. For the purposes of this description, a computer-usable or computer readable storage medium can be any apparatus that may include, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The medium can be an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, or apparatus or device, or a propagation medium. Examples of a computer-readable medium include a semiconductor or solid state memory, magnetic tape, a removable computer diskette, a random access memory “RAM”, a read-only memory “ROM”, a rigid magnetic disk and an optical disk. Current examples of optical disks include compact disk - read only memory “CD-ROM”, compact disk-read/write “CD-R/W”, Blu-Ray™ and DVD. Examples of a propagation medium are the Internet or other wired or wireless telecommunication systems.
Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. It is noted that the various embodiments may be combined to achieve further advantageous effects.
In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.
A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
Any reference signs in the claims should not be construed as limiting the scope.
Number | Date | Country | Kind |
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18191045.6 | Aug 2018 | EP | regional |
201841025833 | Jul 2019 | IN | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2019/068527 | 7/10/2019 | WO | 00 |