Static device for radiotherapy treatment and method for designing such a device

Abstract

The present invention relates to a static device for radiotherapy treatment and a method for designing such a device. A compensating device for ion-based radiotherapy may include a disk with multiple protrusions that can be placed in a radiation beam to affect the ions in the beam in different ways, thereby creating an irradiation field from a wide beam. This is particularly useful in FLASH therapy because the time available for modulating the beam is limited. A method for designing such a compensating device is proposed, comprising the steps of obtaining characteristics of an actual treatment plan including at least one beam; determining at least one parameter characteristic of the desired energy modulation of the actual plan by performing a dose calculation of an initial plan; and based on the at least one parameter, calculating the shape of each of a plurality of elongated elements to modulate the dose of the transmitted beam to simulate the dose of the initial plan for each beam.

Description

Technical Field

[0001] The present invention relates to a passive device for use in radiation therapy treatment and a method of designing such a device. Background Art

[0002] In ion-based radiotherapy treatment, a patient is irradiated with a beam of protons or some other type of ions. Ion-based treatments are advantageous because, by controlling the energy and direction of the ions, the volume in which each ion deposits its energy can be controlled with high precision. A common way to achieve a uniform or non-uniform irradiation field is to use pencil beam scanning, in which many small beams of different directions and energy levels are directed to different points within the target. The term pencil beam scanning includes many different scanning methods, such as point scanning, or line scanning, or raster scanning.

[0003] However, in some cases it is desirable to shape and modulate the field using a static broad beam with a single energy in combination with different types of active or passive devices for shaping the field.

[0004] It is known to use passive devices such as compensators in ion based radiation therapy to control the maximum range of ions by providing an element of varying thickness made of a material that attenuates the energy of the ions, thereby shortening the path of the ions according to the thickness of the compensator.

[0005] The point where the ions deposit most of their energy is called the Bragg peak and is well defined near the end of the ion trajectory. In addition to influencing the position of the Bragg peak with the aid of a compensator, devices are known for extending the Bragg peak in the depth direction to achieve uniform dose coverage over the target volume. To achieve this, a rotating disk with regions of varying thickness is typically used, and rotation speeds of approximately 30 revolutions per second have been used. Other devices include a corrugated filter, also called a ridge filter, which is a device comprising a disk with a regular ridge pattern that will modulate the beam to broaden the Bragg peak in the depth direction.

[0006] In recent years, FLASH therapy has attracted interest because it promises effective treatment in shorter and fewer fractions, with the added benefit of saving hospital resources and being more efficient from the patient's perspective. In FLASH therapy, therapeutic irradiation is delivered in very short pulses at very high dose rates, typically in fractions of a second at dose rates of 40 Gy / s or more. The time aspect is crucial to achieving the advantages associated with FLASH therapy. With such short times, treatment with scanned beams must be performed at a single energy level, as each change in energy level takes on the order of a second. Therefore, conventional pencil beam scanning methods will not work. Furthermore, the use of spinning disks to create the spread-out Bragg peaks in conventional passive therapies would also not be feasible.

[0007] Simeonov et al.: 3D range-modulator for scanned particle therapy: development, Monte Carlo simulations and experimental evaluation; 2017 Phys. Med. Biol. 62 7075 (Simonov et al.: 3D range-modulator for scanned particle therapy: development, Monte Carlo simulations and experimental evaluation; 2017 Phys. Med. Biol. 62 7075), a static element is proposed, which includes a disc of varying thickness that effectively acts as a compensator, and a plurality of fine pins with well-defined shapes and different lengths are arranged on the surface of the disc to modulate the necessary shift of the Bragg peak. The element combines the functions of a compensator and an energy filter, allowing PBS plans to be delivered with only a single energy layer per beam to reduce the delivery time. The element is designed by means of ray tracing combined with the concept of radiation path length based on the geometry of the patient and the desired dose of the target. In practice, this involves following multiple lines of sight through the patient, recording the depth at which the line intersects the proximal and distal surfaces of the target. The disk portion is designed with varying thickness to act as a compensator that conforms to the distal surface of the target, and the proximal-distal distance is used to calculate the length and shape of the pin so that the field will cover the entire target. This method enables a static device to create a uniform or near-uniform dose distribution that conforms to both the distal and proximal edges of the target. The device can be manufactured by 3D printing.

[0008] It is desirable to be able to create more complex dose distributions, for example, to be able to jointly optimize overlapping fields.

[0009] The co-pending patent application EP20192106.1 discloses a method of designing a compensation device for ion-based radiotherapy treatment delivery, the device comprising a substantially disk-shaped structure comprising a plurality of elongated elements on one side of the disk. The design method involves adjusting the shape of each of the elongated elements based on characteristics of an actual treatment plan, determining at least one parameter characteristic of a desired energy modulation of the actual plan by performing a dose calculation of an initial plan, and calculating the shape of each of the plurality of elongated elements based on the at least one parameter to modulate the dose of the delivered beam to simulate the dose of the initial plan for each beam. Summary of the invention

[0010] The object of the present invention is to provide a method for designing a compensation device as described above.

[0011] The present disclosure relates to a method of designing a compensating device for use in ion-based radiation therapy treatment delivery, the device comprising a substantially disk-shaped structure comprising a plurality of elongated elements on one side of the disk, the method comprising the following steps

[0012] Obtain a model of the compensation device, whose properties are defined by a set of model parameters,

[0013] obtaining an optimization problem, the optimization problem defining a planning objective,

[0014] Optimizing the values ​​of a set of planning parameters to achieve a planning goal, the plan parameters including the parameters in the set of model parameters.

[0015] Typically, the planning parameters also include standard planning parameters, such as point weights. Planning goals are typically defined as ensuring a uniform dose to the target while sparing other tissues, and in particular organs at risk. The step of obtaining an optimization problem may include formulating the optimization problem based on the current patient anatomy, or using a pre-formulated optimization problem.

[0016] Obtaining a suitable optimization problem and using it to optimize the compensating device enables fast and reliable design of the compensating device as defined. It also enables other favorable aspects to be considered in the design process, such as robustness, linear energy transfer (LET)-based objectives, or relative biological effectiveness (RBE)-based objectives.

[0017] The method may also include selecting a material for the elongated body or elongated bodies. Alternatively, the material may have been pre-selected. The combination of shape and material properties determines how the elongated element affects the bundle. An elongated body is typically defined by the shape and size of its base and its height.

[0018] The plan resulting from the optimization process can be used as the final plan delivered to the patient, either as is or after an additional optimization step after the compensating device has been designed. In the latter case, the method comprises the following steps: re-optimizing the standard plan parameters and taking into account the parameters of the compensating device. This is preferably done without involving the plan parameters of the compensating device in the optimization.

[0019] In order to prepare the resulting compensation device for production, the method may comprise the steps of obtaining element shape data indicating the shape of each elongated element based on the planned parameters of the compensation device, and using the element shape data to generate a file comprising instructions for designing the compensation device. The file may be used to control a manufacturing process, for example performed by a 3D printer.

[0020] The treatment plan may be a pencil beam scanning plan or a broad beam plan, such as a double scatter plan or a single scatter plan utilizing a single energy, ie without a spread-out Bragg peak. As mentioned above, the term pencil beam scanning covers many different scanning methods, including point scanning, line scanning or raster scanning.

[0021] The present disclosure also relates to a method of manufacturing a compensation device for ion-based radiotherapy treatment delivery, comprising performing any of the aforementioned methods and using shape data derived from the plan to generate a file including instructions for designing the compensation device, and using the file to control the manufacture.

[0022] The present disclosure also relates to a computer program product comprising computer readable code means, which, when executed in a computer, causes the computer to perform the method according to any one of the aforementioned embodiments. The computer product may include a non-transitory memory storing the code means.

[0023] The present disclosure also relates to a computer system comprising a program memory and processing means arranged to execute a program found in the program memory, said program memory comprising a computer program product according to above.

[0024] The compensation device is suitable for different types of ion-based radiotherapy treatments. It is ideally suited for use in FLASH therapy, as it is a passive component that operates without any moving parts during treatment; however, it can also be used in conventional therapies. This will allow a reduction in the number of energy levels used during treatment, even enabling full target coverage with just one energy level.

[0025] The design approach described in this paper allows complex criteria to be taken into account when designing compensator elements, since any desired criterion can be expressed as part of the initial optimization problem, including variable RBE dose optimization, LET targets, and beam-specific objective functions. Thus, joint optimization of overlapping fields can be achieved. Robust optimization with respect to uncertainties in factors such as patient position and density can also be applied, which will lead to plans that work more reliably under different field contexts.

[0026] The method may also include designing a channel array device to be used with the compensator device, the channel array device comprising a substantially disk-shaped structure including the channel array.

[0027] In some embodiments, the channel array device may be designed after the compensation device, taking into account the design of the compensation device. In this case, the method may further include

[0028] Get the model of the channel array device, whose properties are defined by the model parameter set,

[0029] obtaining an optimization problem that defines a planning objective for the channel array device given the planning parameters obtained for the compensation device,

[0030] Optimizing values ​​of a set of planning parameters to achieve a planning goal, the planning parameters including parameters in the set of model parameters for the channel array device.

[0031] In other embodiments, the compensation device and the channel array device are optimized together in one process. In this case, the method includes the following steps: obtaining an optimization problem defining a joint planning goal for the compensation device and the channel array device acting together, and optimizing the values ​​of a set of joint planning parameters of the compensation device and the channel array device to achieve the joint planning goal,

[0032] In all embodiments, a starting guess of the channel array parameters can be obtained using ray tracing methods and simple geometric considerations, where the channel area is proportional to the expected flux at the location of the channel. The channel array device can be manufactured in the same manner as the compensation device, or manufactured together with the compensation device, or manufactured in a separate operation.

[0033] The purpose of the channel array device is to reduce the amount of modulation of the incident proton flux required to meet the planning goals. The depth and size of the channel determines how many incident protons pass through the array device disk in the area near each channel. This will affect the dose in the area downstream of the channel. In the ideal case, it is thereby possible to have a uniform incident flux and still achieve a dose distribution where a laterally modulated flux would be required without the channel array device. This allows the first disclosed compensation device to be used for wide beam irradiation. The shape and arrangement of the channels can be determined by ray tracing methods or by optimization methods.

[0034] The ray tracing method applies the flux of the existing plan as a starting point. The particle flux distribution of the existing plan is then used to calculate the size and distribution of the channel gaps required to reproduce the flux of the existing plan for a given incident flux.

[0035] Typically, the planning parameters also include standard planning parameters, such as point weights. The planning goal is usually defined as ensuring a uniform dose to the target while not harming other tissues, and in particular organs at risk. Additional planning goals can be that the solution should produce an incident flux that is as uniform as possible or have any other desired shape. The step of obtaining the optimization problem can include formulating the optimization problem based on the anatomy of the current patient, or using a pre-formulated optimization problem.

[0036] The combined use of a channel array device and a compensation device allows also 3D conformal dose to be delivered for wide beam irradiation.

[0037] The present disclosure also relates to a computer program product comprising computer readable code means, which, when executed in a computer, will cause the computer to perform the method according to any one of the aforementioned embodiments. The computer product may include a non-transitory memory storing the code means.

[0038] The present disclosure also relates to a computer system comprising a program memory and processing means arranged to execute a program found in the program memory, said program memory comprising a computer program product according to above. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention will be described in more detail below by way of examples and with reference to the accompanying drawings.

[0040] Figure 1 An example of the device disclosed in this specification is illustrated.

[0041] Figure 2a Illustration of how to Figure 1 The equipment is used in radiation therapy.

[0042] Figure 2bThe dose depth of the incident beam upstream of the device and the resulting depth dose distribution in the patient are shown.

[0043] Figure 3a The diagram can be used with Figure 1 The devices shown in the figure are used together with a channel array device.

[0044] Figure 3b Graphics Figure 3a Channel array devices such as Figure 1 Components of the compensator device of the device shown.

[0045] Figure 4 is a flow chart of a method for designing a modulation device.

[0046] Figure 5 is a flow chart of a method for designing a channel array device.

[0047] Figure 6 is a flow chart of a method for designing a modulation device and a channel array device together.

[0048] Figure 7 is a schematic diagram of a computer system in which the method of the present invention can be implemented. DETAILED DESCRIPTION

[0049] Figure 1 An example of a passive modulation device 10 according to an embodiment of the invention is shown. The device comprises a compensator element 11 which is essentially a disc having a varying thickness across its area. The thickness is designed to conform the incident radiation field to the far end of the target. On the disc, a plurality of protrusions in the form of spike-shaped structures 13 are arranged, typically of the same material as the compensator element. The protrusions 13 are typically placed on the disc in a grid pattern, each occupying, for example, 1.5×1.5 mm of the disc. 2 The protrusions 13 have different heights and shapes, selected so that the beam passing through the device will be modulated to have a Bragg peak that covers the entire target in the desired manner. Of course, the size, shape and thickness of the compensator element, the arrangement of the protrusions on the compensator element and their size and height should be selected to match the target, including a suitable margin.

[0050] Figure 2a The device shown is inserted between a radiation source 21 emitting a uniform radiation field 23 and a patient 25. Figure 1 The device is shown simplified as an ellipse and includes a target 27. The radiation field is modulated by the device 10 so that the energy spectrum of the radiation will create a dose field that conforms to the shape of the target after passing through the device. Figure 2a In the figure, the target shown has a simple approximately circular form, but according to the invention, more complex shapes can also be processed.

[0051] Figure 2b Corresponds to Figure 2a The left diagram depicts the depth dose for the incident beam upstream of the device. It can be seen that most of the dose will be deposited at a specific depth, corresponding to the energy of the protons in the beam. The right diagram depicts the depth dose after the beam has passed through the modulation device 10. It can be seen that the depth dose has a wider range, corresponding to dose deposition throughout the target 27. Although Figure 2a and Figure 2b The modulation device 10 inserted into the bundle is shown with the protrusion 13 downstream of the disc 11, but it could also be placed in the opposite direction, ie with the protrusion upstream of the disc.

[0052] According to the present invention, the modulation device is optimized by directly optimizing its geometric parameters. These parameters generally include the thickness of the compensator 11 and the width and length of each of the protrusions. The width and cross-sectional shape can vary over the length of each protrusion. The pixel grid pattern can be included in the optimization problem as a constraint, or can be an optimization parameter in the optimization problem. The pixel grid pattern defines the base of each of the protrusions, where they are connected to the compensator 11. Alternatively, the base of each protrusion can be freely selected in the optimization.

[0053] The protrusion designed for each pixel does not have to be shaped as a pin or have any type of symmetry, although circular symmetry can be easier to achieve than more complex shapes. Instead, it can be any type of elongated body or collection of elongated bodies extending from the compensator element in a direction parallel to the beam. It can be composed of many different protrusions within a pixel, such as spikes, pins, or elongated sheets. The different fractional lengths of one or more elongated bodies extending in a pixel are such that ions passing through the pixel will be affected differently, resulting in a spectrum of absorbed energy.

[0054] Figure 3a A channel array device having an array of open channels or channels is shown, which can be used with Figure 1 , Figure 2a and Figure 2bThe channel array device is preferably made of a high Z material and is shaped as a disk with an array of narrow channels or channels extending through the disk to a specific depth for each channel. Each channel can have any suitable cross-section, such as circular or square. The size is tuned to block a certain amount of proton flux. The removal of protons will result in an uneven dose at shallow depths. Due to scattering effects and the initial emissivity of the beam, as the depth increases, the doses from adjacent channels will merge further downstream of the channel array device to produce a sufficiently smooth dose in the target. Dose inhomogeneity at shallow depths is actually beneficial because it actually enhances the FLASH effect sought in upstream risk organ tissue. The channel array device can be designed in any suitable manner, but is preferably designed by optimization, which will be discussed in more detail below.

[0055] Figure 3b Shown for use with compensation equipment Figure 3a The arrangement of the channel array device of FIG. 1 may be a modulation device 10 as discussed above. Figure 3b In the embodiment, the channel array device is placed upstream of the compensation device, but it can also be placed downstream.

[0056] When used with the modulation device 10, the channels of the channel array device can, but need not be, placed in the same grid pattern as the protrusions of the modulation device, so that each channel is aligned with the longest part of one protrusion in the direction of the beam. When used with a compensation device that does not include an array or grid pattern, the channels can be placed in any suitable manner.

[0057] The modulation device and the channel array device may be two separate units used together as discussed above, but they may also be joined together, or manufactured as an integrated unit.

[0058] Figure 4 4 is a flow chart of a method that can be used to design a modulation device 10. The input data S41 of the method includes a set of planned parameters for the modulation device, including in some embodiments the thickness of the disk 11, the shape and size of the base of each of the protrusions 13, and the length of each protrusion. Alternatively, the shape and / or size of the base of the protrusions can be predefined and added as a constraint. As described above, the protrusions can have any suitable shape, and can even have different shapes and / or sizes relative to their base and their length.

[0059] Initially, an optimization problem S42 used to optimize the modulation device is also obtained. The optimization problem comprises an objective function and / or constraints related to how the modulation device should affect the incident radiation. In step S43, an optimization is performed based on the optimization problem.

[0060] As an example, the optimization problem of a modulation device can be set up as described by the following steps:

[0061] • Define a Cartesian grid (with equal spacing in the horizontal and vertical directions) that defines the lateral positions of the elongated bodies.

[0062] - Place elongated bodies at grid points (pixels) inside the field.

[0063] The given elongated body has a pyramidal shape with a quadratic base and is truncated at a certain height.

[0064] The sides of the pyramid base are equal to or smaller than the pitch of the Cartesian grid.

[0065] The geometry of each pyramid is specified by the size of the base, the height and size of the quadratic surface, and the apex of the truncated pyramid.

[0066] Each pyramid is placed on a solid volume representing a compensator with the same base size and height as the grid spacing, whose values ​​are optimized.

[0067] • During the optimization process, the geometric parameters of the pyramid are varied until the optimal geometry is found.

[0068] • Geometry parameters are optimized together with other parameters, such as point weights, which are optimized separately.

[0069] The above specifications are given as examples. The channel array device can be part of the overall optimization or can also be optimized separately. A suitable parameter for optimization is the diameter of the hole.

[0070] The resulting shape data S44 of each elongated body or set of bodies may be used for triangulation to generate a CAD file which may be used to produce the compensation device, e.g. by 3D printing. Alternatively, some additional optimization steps S45 may be performed to improve the resulting compensation device before production, i.e. by taking into account possible scattering from the elongated bodies before outputting the final shape data in S46.

[0071] After determining the geometry of the compensation device for each beam, one or more other additional optimization steps may be included, performing a final PBS re-optimization in which the fixed geometry of the compensation device is considered. This will help to further tune the plan. The final optimization is performed using a single energy layer for each plan. This final optimization can include multiple beams and any type of advanced objective function, such as those related to RBE dose, LET, or robustness.

[0072] Alternatively, additional optimization can be performed using multiple energy layers. If the design and effect of the compensating device are perfect, then the optimized plan should place all weights in a single energy layer. If the layer weight dispersion exceeds a certain limit, then this data can be used to adjust the geometry of the compensating device. The process can be iterated until the geometry of the compensating device stabilizes between iterations. A similar approach should be possible for the optimization of the standard compensator of the passive plan.

[0073] As described above, the resulting modulation device can be used to shape and modulate the field of any type of ion-based radiotherapy treatment. In particular, it will be possible to reduce the number of energy slices used, making the delivery of the treatment faster. Preferably, by designing the elongated bodies so that they ensure coverage of the entire three-dimensional target from one field, delivery using only one energy slice is enabled.

[0074] Figure 5 is a flow chart of a method that can be used to design a channel array device 31. In this embodiment, the channel array device 31 is designed to be used with an existing modulation device or compensation device. The input data S51 of the method is the geometry of the compensation device or modulation device 10 used with the channel array device, and the proton flux distribution of the scanning beam or wide beam. The input data also includes a set of model parameters of the channel array device, such as the thickness and the number and size of the channels. An optimization problem is also obtained, which defines the planning objectives of the channel array device 31 given the planning parameters obtained for the compensation device 10. The compensation or modulation device can be combined with Figure 1 The modulation device 10 discussed can be combined with Figure 4 The compensation or modulation device may be designed by the methods discussed in the above-mentioned co-pending applications or by any other method.The treatment plan may be a FLASH plan involving a broad beam proton flux distribution or a FLASH plan delivered using pencil scanning.

[0075] In step S53, the channel array device 31 is optimized based on the input data S51 and the optimization problem S52, which has properties defined by the model parameter set, including, for example, the thickness of the channel array device and the channel size. The geometry of the compensation device is used to determine the number of channels and their positions. The number of channels and their positions can also be determined independently of the geometry of the compensation device. The thickness of the channel array plate should be sufficient to completely block incident particles that do not pass through the channel gaps.

[0076] The channel can be cylindrical in shape with the axis along the beam direction, or any other suitable shape. For cylindrical channels, the diameter is determined by a geometric ray tracing method, where the transmission is proportional to the cross-sectional area of ​​the channel. The channel diameter can also be determined by a direct optimization method, where the diameter is a free variable that is optimized along with other free variables of the optimization problem such as the point weights of the compensation device and the geometric shape parameters.

[0077] As a final step S54, the shape information of each channel is used to generate control data that can be used to manufacture the device. This may involve using the triangulated shape information to generate a CAD file that can be used to manufacture the device. For example, the CAD file can be sent to a 3D printer, and an optional step S55 will print the device based on the information in the CAD file. Of course, another suitable manufacturing method may be used.

[0078] Figure 6 is a flow chart of an alternative method in which a channel array device 31 is designed together with a compensator device or a modulator device 10. The channel array device has a Figure 5 The same properties discussed. In this embodiment, the input data S61 includes a set of joint planning parameters for obtaining a combination of a compensator device and a channel array device, including the shape and size of the compensator or modulator device and the channel array device and their distance during treatment. In view of the joint planning parameters, the optimization problem S62 defines a joint planning target for the combination of the modulator device 10 and the channel array device 31. In step S63, the modulator device 10 and the channel array device 31 are optimized together to achieve the joint planning target. In step S64, control data is generated based on the parameters determined in the optimization in the same manner as in step S54. As before, step S65 is an optional step for manufacturing the modulator device 10 or other compensator device and the channel array device 31.

[0079] In all embodiments, the modulation device 10 and the channel array device 31 may be positioned at a distance from each other or adjacent to each other substantially concentrically with respect to the direction of the beam.

[0080] Figure 7 is a schematic overview of a computer system in which the optimization according to the invention can be implemented. The computer 51 comprises a processor 53, a data memory 54 and a program memory 55. Preferably, there are also one or more user input components 57, 58 in the form of a keyboard, a mouse, a joystick, a voice recognition device and / or any other available user input device. The user input device may also be arranged to receive data from an external memory unit.

[0081] The optimized PBS treatment plan is found in the data store 54. The treatment plan may be generated in the computer 51, or received from another storage device in any manner known in the art. The data store also includes the characteristics of the dose delivery beam to be used in the actual treatment of the patient, i.e., the beam to be modulated by the compensation device.

[0082] The data memory 54 also stores properties of the modulation device, such as its material composition. If the material is known, its properties can be stored. If the process involves selecting one from a large number of available materials to be used, the properties of all available materials should be stored, including their mass density and manufacturing limitations. As will be understood, the data memory 54 is only shown schematically. There may be several data memory cells, each storing one or more different types of data, for example, one data memory for the design of a compensation device, etc.

[0083] The program memory 55 stores a computer program arranged to control the processor to perform the design process according to the invention. The program memory may also store instructions for how to convert the design of the compensation device into instructions for a manufacturing machine, such as a 3D printer arranged to produce the compensation device. Like the data memory 54, the program memory may also be implemented as one or several units, as the case may be.

Claims

1. A computer-based method for designing a compensation device (10) for ion-based radiotherapy treatment delivery, the device comprising a structure substantially in the shape of a disk, the structure comprising a plurality of elongated elements on one side of the disk, the method comprising the following steps obtaining (S41) a model of the compensation device, the properties of which are defined by a set of model parameters, wherein the model parameters include the thickness of the disc-shaped structure and the width and length of the elongated element, formulating (S42) an optimization problem based on the patient's anatomy, the optimization problem defining a planning goal, the planning goal being defined as ensuring a uniform dose to the target while sparing other tissues and organs at risk, Optimizing (S43) values ​​of a set of planning parameters of the compensation device to achieve the planning goal using the optimization problem, the planning parameters comprising the set of model parameters, wherein the optimization is performed with respect to one or more of a variable RBE dose optimization, a LET target, and a beam-specific objective function.

2. The method according to claim 1, wherein: The optimizing step (S43) also includes selecting a material for the one or more elongated elements.

3. The method according to claim 1, wherein: The actual plan (S44) includes a uniform radiation field.

4. The method according to claim 3, wherein: The actual plan is used as the final plan.

5. The method according to claim 4, further comprising the steps of: The actual plan is re-optimized (S45) taking into account the compensation device (10) in the re-optimization to produce a final plan (S46) for delivery to the patient.

6. The method according to claim 3, comprising the step of obtaining element shape data indicating the shape of each elongated element based on the actual plan, and using the element shape data to generate a file including instructions for designing the compensation device.

7. The method according to claim 1, wherein: The final treatment plan (S44, S46) is a pencil beam scanning plan or a double scattering plan or a single scattering plan.

8. The method according to any one of claims 1-7 further includes designing a channel array device (31) to be used with the compensation device (10), the channel array device including an element having a channel array and being substantially shaped like a disk, the method further including, in order to design the channel array device, obtaining a model of the channel array device whose properties are defined by a set of model parameters, obtaining (S52) an optimization problem for the channel array device, the optimization problem defining a planning objective of the channel array device (31) in view of the planning parameters obtained for the compensation device (10), optimizing the values ​​of the planning parameter set of the channel array device to achieve the planning objective of the channel array device, the planning parameters including the parameters in the model parameter set of the channel array device.

9. The method according to any one of claims 1-7 further comprises designing a channel array device (31) to be used with the compensation device (10), the channel array device (31) comprising a substantially disk-shaped element having a channel array, the method further comprising, in order to design the channel array device, obtaining an optimization problem (S62) defining a joint planning objective for the compensation device (10) and the channel array device (31) to act together, and optimizing (S63) the values ​​of a set of joint planning parameters of the compensation device (10) and the channel array device (31) to achieve the joint planning objective.

10. A method of manufacturing a compensation device (10) for ion-based radiation therapy treatment delivery, comprising: Executing the method according to any one of claims 1 to 9, using the shape data obtained from the plan (S44) to generate (S54; S64) A file comprising instructions for the design of a compensation device, and using said file to control said manufacturing.

11. A computer program product comprising computer-readable code means which, when executed in a computer, cause the computer to perform the method according to any one of claims 1 to 9.

12. The computer program product of claim 11, comprising a non-transitory memory storing the code means.

13. A computer system (51) comprising a program memory (55) and a processor (53), the processor (53) being arranged to execute a program found in the program memory, the program memory comprising a computer program product according to claim 12.

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