Static device for use in radiation therapy treatment and design method for the same

Abstract

A compensating device for use in ion-based radiation therapy may include a disk having a number of protrusions that may be placed in a radiation beam to affect the ions in the beam in different ways to create a radiation field from a wide beam. This is particularly useful in FLASH therapy because the time available or modulating the beam is limited. A method for designing such a compensating device is proposed, the method comprising the steps of obtaining characteristics of an actual treatment plan including at least one beam; determining at least one parameter characteristic of a desired energy modulation of the actual plan by performing a dose calculation for an initial plan; and calculating a shape for each of a plurality of elongated elements to modulate the dose of the delivered beam based on the at least one parameter to simulate the dose of the initial plan per 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 radiation therapy treatment, the patient is irradiated with a beam of protons or some other type of ions. Ion-based treatments are advantageous because the volume in which each ion stores its energy can be controlled with high precision by controlling the energy and direction of the ions. A common way to achieve a uniform or non-uniform radiation field is to use pencil beam scanning, where 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 spot scanning or line scanning or raster scanning.

[0003] However, in some cases it may be 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 that shape the field.

[0004] It is known to use passive devices such as compensators in ion based radiotherapy treatments to control the maximum range of the ions by providing elements of varying thickness made of a material that will attenuate the energy of the ions, thereby shortening their path according to the thickness of the compensator.

[0005] The point where the ion stores a major part of its energy is called the Bragg peak and is well defined near the end of the ion's trajectory. In addition to influencing the position of the Bragg peak by means of a compensator, devices are also known that expand the Bragg peak in the depth direction to achieve uniform dose coverage within the target volume. To achieve this, a rotating disk with areas of varying thickness is typically used and rotations of about 30 revolutions per second have been used. Other devices include a corrugated filter, also called a ridge filter, which is a semi-transparent device comprising a disk with a regular pattern of ridges that will modulate the beam to broaden the Bragg peak in the depth direction.

[0006] In recent years, FLASH therapy has become a source of 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 as well. In FLASH therapy, the therapeutic radiation is given in very short pulses at very high dose rates, typically a fraction 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. Due to such short times, treatment with a scanned beam must be given at a single energy level, since each change in energy level is of the order of a second. Therefore, conventional pencil beam scanning methods do not work. Further, the spinning disks used to create the extended Bragg peak in conventional passive therapy are also not feasible.

[0007] Simeonov et al., in "3D range-modulator for scanned particle therapy: development, Monte Carlo simulations and experimental evaluation" published in "Phys. Med. Biol. 62 7075 (Physics in Medicine and Biology)" in 2017, proposed a static element, which includes a disk of different thicknesses that effectively acts as a compensator, and a number of fine pins with well-defined shapes and different lengths are set on the surface of the disk to modulate the necessary displacement of the Bragg peak. This element combines the functions of the compensator and the energy filter in such a way as to allow PBS plans to transmit only a single energy layer per beam to reduce the delivery time. The element is designed based on the patient's geometry and the required dose in the target by means of ray tracing combined with the concept of radiation path length. In practice, this involves following many lines of sight through the patient and registering the depths at which these lines of sight intersect the proximal and distal surfaces of the target. The disk sections are designed with different thicknesses to act as compensators that adapt to the distal surface of the target, and the proximal-distal distance is used to calculate the length and shape of the pins so that the field will cover the entire target. This approach enables a static device to create a 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 achieve co-optimization of overlapping fields. Summary of the invention

[0009] The present disclosure relates to a method of designing a compensation device for ion-based radiation therapy treatment delivery, the device comprising a substantially disk-shaped structure including a plurality of elongated elements on one side of the disk, the method comprising the following steps:

[0010] Obtain initial treatment plan with pencil beam scanning

[0011] Obtaining characteristics of an actual treatment plan including at least one beam to be used to treat the patient

[0012] Determine at least one parameter characteristic of the required energy modulation for the actual plan by performing a dose calculation for the initial plan

[0013] - Based on the at least one parameter, calculating a shape of each of the plurality of elongated elements to modulate a dose of the delivered beam to simulate an initially planned dose per beam.

[0014] The method may include calculating the actual planned dose and scoring an amount for pixels placed on a virtual grid projected upstream of the patient in the beam trajectory of the at least one beam. The virtual grid implements a definition of a pixel grid.

[0015] The step of calculating the shape also includes selecting a material for the one or more elongated bodies. Alternatively, the material may be pre-selected. The combination of shape and material properties determines how the beam is affected by the elongated element.

[0016] In some embodiments, the at least one parameter used to determine the height and shape of the elongated body includes one or more of the following:

[0017] · Initial planned energy layer index spectrum

[0018] Energy spectrum of the initial plan

[0019] • Water equivalent depth spectrum at the end of the initially planned main proton trajectory.

[0020] The actual plan may include a uniform radiation field. The actual plan may be used as a final plan for delivery 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 includes a step of re-optimizing the actual plan, which takes into account the compensating device in the re-optimization to produce a final plan for delivery to the patient.

[0021] In order to prepare for the production of the resulting compensation device, the method may include the following steps: 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 the design of the compensation device. The file can be used to control a manufacturing process, for example, a manufacturing process performed by a 3D printer.

[0022] The actual or final treatment plan may be a pencil beam scanning plan or a broad beam plan, i.e. a double scattering plan or a single scattering plan or a wobbling plan, which has a single energy, i.e. without an extended Bragg peak. As mentioned above, the term "pencil beam scanning" covers many different scanning methods, including spot scanning, line scanning or raster scanning.

[0023] The present disclosure also relates to a method of manufacturing a compensating device for ion-based radiotherapy treatment delivery, comprising performing a method according to any of the preceding claims, using shape data derived from a plan to generate a file comprising instructions for the design of the compensating device.

[0024] 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 above embodiments. The computer product may include a non-transitory storage storing the code means.

[0025] 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 the above.

[0026] The compensation device is suitable for use in different types of ion-based radiotherapy treatments. It is well suited for FLASH therapy as it is a passive component that does not require any moving parts to operate during treatment; however, it can also be used in conventional therapies. It will be able to reduce the number of energy levels used during treatment, or even achieve complete target coverage using just one energy level.

[0027] The design approach described in this paper allows for complex criteria to be considered 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 position and density can also be applied, which will lead to plans that work more reliably under different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be described in more detail below by way of examples and with reference to the accompanying drawings.

[0029] Figure 1 An example of the device disclosed in this specification is shown

[0030] Figure 2a Picture shows Figure 1 How the device can be used in radiation therapy.

[0031] Figure 2b The dose depth of the incident beam upstream of the device and the resulting depth dose distribution in the patient are illustrated.

[0032] Figure 3 is a flow chart of a method according to an embodiment of the present invention.

[0033] Figure 4 is a schematic diagram of a computer system in which the inventive method may be performed. DETAILED DESCRIPTION

[0034] Figure 1An 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 different thickness across its area. The thickness is designed to conform the incident radiation field to the far end of the target. There are provided on the disc a number of protrusions 13 in the form of spike-like structures, which are typically of the same material as the compensator element. The protrusions 13 are typically placed in a grid pattern on the disc, each taking up, for example, 1.5 x 1.5 mm of the disc. 2 The protrusions 13 have different heights and shapes, which are selected in such a way that the light beam passing through the device is modulated so that the Bragg peak covers the entire target in the desired manner. Of course, the size, shape, thickness of the compensator element, the arrangement of the protrusions on the compensator element and their size and height should be selected to meet the target.

[0035] 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 10 is simplified to the form of an ellipse and includes a target 27. The radiation field is modulated by the device 10 in such a way that the energy spectrum of the radiation after passing through the device will create a field that conforms to the shape of the target. Figure 2a In FIG. 1 , the target is shown to have a simple nearly circular form, but more complex shapes can also be handled according to the present invention.

[0036] Figure 2b Corresponds to Figure 2a The left figure depicts the depth dose of the incident beam upstream of the device. It can be seen that most of the dose is deposited at a specific depth, which corresponds to the energy of the protons in the beam. The right figure 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, which corresponds to the dose deposition across the target 27. Although Figure 2a and Figure 2b The modulation device 10 is shown inserted into the light beam with the protrusion 13 downstream of the disc 11, but it can also be placed in the opposite direction, ie with the protrusion upstream of the disc.

[0037] Figure 3 is a flow chart of a method for designing a compensation element according to an embodiment of the present invention. Although the method is described here for protons, it can be applied to any type of ions used in radiation therapy.

[0038] In step S31, a conventional treatment plan is obtained, typically a pencil beam scanning plan. The plan can be obtained by any suitable means known in the art. Typically, this is accomplished by optimization based on an optimization problem that includes an objective function and / or constraints reflecting desired properties and results in a dose distribution and an optimized treatment plan. This means that it is assumed that a virtual pixel grid in a cross section of the beam upstream of the patient, the energy spectrum and, optionally, the proton direction distribution for each pixel in a cross section of the beam upstream of the patient will be known. The characteristics of the radiation beam to be used to deliver a dose to the patient are also determined. The radiation beam can be uniform or non-uniform, but in the simplest case is a uniform beam in which all ions initially have the same energy.

[0039] In step S32, optionally, a pixel grid is projected out of the plane in which the patient is located, the pixels in the pixel grid corresponding to the pixels in the cross section mentioned in step S31. The positions of the pixel grid preferably correspond to the positions where the compensating elements will be placed during treatment. The distance to the patient can be freely selected; in some embodiments, 5 cm has been found to be a suitable distance.

[0040] For example, each pixel may be 1.5 mm x 1.5 mm in size. The energy spectrum at each pixel is a direct function of the plane, given the specific sequence of incident energy levels of the field.

[0041] In step S33, the dose is recalculated using a dose engine, such as a Monte Carlo dose engine. During the recalculation, certain quantities are scored for each pixel in the pixel grid for use in designing compensation elements. For example, the proton energy in each pixel in the pixel grid can be accumulated in an energy spectrum per pixel. For example, the quantities scored can include one or more of the following:

[0042] Energy layer index spectrum per pixel

[0043] Water equivalent depth spectrum at the end of the proton trajectory

[0044] Proton energy

[0045] Based on the scoring data for each pixel of the pixel grid, in step S34 it is determined how the radiation beam to be used for dose delivery should be affected in the area corresponding to each pixel. For each pixel, ideally, the ions that have passed through the element should have the same energy spectrum as calculated in step S33. Based on this energy spectrum, a protrusion shape can be calculated for each pixel in step S35, which will produce an energy spectrum per pixel in the dose delivery beam that is sufficiently similar to the energy spectrum calculated in step S33 to ensure sufficient dose delivery quality. The same procedure can be applied to other selections of scored data. The calculation of the protrusion shape can also include selecting an appropriate material for the protrusion, i.e. a material that, together with the shape, affects the ions passing through the pixel in a desired manner.

[0046] The protrusion designed for each pixel does not have to be shaped as a pin or have any type of symmetry, although circular symmetry may be easier to achieve than more complex shapes. Instead, it can be any type of elongated body or group of elongated bodies extending from the compensator element in the direction of the beam. Within one pixel, it can consist of many different protrusions, such as spikes, pins or elongated sheets. The lengths of different parts of one or more elongated bodies extending in one pixel are chosen in such a way that ions passing through the pixel are affected differently resulting in an energy spectrum of the ions corresponding to the energy spectrum calculated in step S33. As mentioned above, the dose delivery beam can be uniform, but the method is also applicable to more complex dose delivery beams as long as its properties are known.

[0047] The resulting shape data for each elongated body or each group of elongated bodies can be used for triangulation to generate a CAD file, which can be used to produce the compensation device, for example, by 3D printing. Alternatively, some additional optimization steps can be performed in step S36 to improve the resulting compensation device before production, i.e. by taking into account possible scattering from the elongated bodies.

[0048] One or more further additional optimization steps S37 may include: After determining the geometry of the compensation device per beam, performing a final PBS re-optimization in which the geometry of the compensation device is taken into account. This will help to further fine-tune the plan. The final optimization is performed with a single energy layer per plan. The final optimization can include multiple beams and any type of high-level objective function, such as functions related to RBE dose, LET or robustness.

[0049] Alternatively, the additional optimization of step S37 can be done over multiple energy layers. If the design and effect of the compensating device is perfect, the optimized plan should place all weights in a single energy layer. If the layer weights extend beyond a certain limit, this data can be used to adjust the geometry of the compensating device. This procedure can be iterated until the hedgehog-like geometry stabilizes between iterations. A similar approach should be applicable to the optimization of standard compensators for passive planning.

[0050] As foreseen in step S32, the use of a pixel grid is not necessary, but is beneficial to simplify the procedure. It should be noted that the shape of the pixels can be selected as desired. The pixels can be square or hexagonal or have any other feasible shape.

[0051] As described above, the resulting compensation device can be used to shape and modulate the field of any type of ion-based radiation therapy. In particular, it can reduce the number of energy layers used, allowing faster delivery of the treatment. Preferably, the elongated bodies are designed to enable delivery using only one energy layer so that they ensure coverage of the entire three-dimensional target from one field.

[0052] Figure 4 is an overview diagram of a computer system in which the optimization according to the invention can be performed. A computer 41 comprises a processor 43, a data memory 44 and a program memory 45. Preferably, user input means 47, 48 are also present, in the form of a keyboard, a mouse, a joystick, a voice recognition device or any other available user input means. The user input means may also be arranged to receive data from an external memory unit.

[0053] The optimized PBS treatment plan is found in data storage 44. The treatment plan may be generated in computer 41 or may be received from another storage device in any manner known in the art. The data storage also includes the characteristics of the dose delivery beam to be used for the actual treatment of the patient, i.e., the beam that will be modulated by the compensation device.

[0054] The data store 44 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 material to use from a number of available materials, the properties of all available materials should be stored, including their mass density and manufacturing limitations. As will be understood, the data store 44 is shown only schematically. There may be several data store units, each storing one or more different types of data, for example, one data store for the design of a compensation device, etc.

[0055] The program memory 45 stores a computer program arranged to control the processor to perform a design procedure according to the invention. The program memory may also store instructions on how to convert the design of the compensation device into instructions for a manufacturing machine, for example a 3D printer arranged to produce the compensation device.

Claims

1. A method of designing a compensating device for use in ion-based radiation therapy treatment delivery, the device comprising a substantially disk-shaped structure including a plurality of elongated elements on one side of the disk, the method comprising the steps of: a. Obtaining the initial treatment plan for pencil beam scanning by optimizing the optimization problem and obtaining the dose distribution and optimized treatment plan, b. obtaining characteristics of an actual treatment plan including at least one beam to be used to treat the patient, c. determining at least one parameter characteristic of the required energy modulation of the actual plan by performing a dose calculation of the initial treatment plan, d. based on the at least one parameter, calculating the shape of each of the plurality of elongated elements to modulate the dose of the delivered beam, thereby simulating the initially planned dose of each beam, wherein the at least one parameter for determining the height and shape of the elongated element comprises one or more of the following: an energy layer index spectrum of the initial plan, an energy spectrum of the initial plan, a water equivalent depth spectrum at the end of the main proton trajectory of the initial plan, and Therein, the method further comprises the following steps: re-optimizing the actual treatment plan, taking the compensation device into account in the re-optimization to generate a final treatment plan to be delivered to the patient.

2. The method according to claim 1, wherein: A dose of the actual treatment plan is calculated and a quantity is scored for pixels placed on a virtual grid projected upstream of the patient in a beam trajectory of the at least one beam.

3. The method according to claim 1 or 2, wherein: The step of calculating the shape further comprises selecting a material for the one or more elongated elements.

4. The method according to claim 1 or 2, wherein: The actual treatment plan comprises a uniform radiation field.

5. The method according to claim 1 or 2, wherein: The actual treatment plan is used as the final treatment plan.

6. The method according to claim 1 or 2, comprising the step of obtaining element shape data indicating the shape of each elongated element based on the actual treatment 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 is a pencil beam scanning plan or a double scatter plan or a single scatter plan or a wobbling plan.

8. A method of manufacturing a compensating device for use in ion-based radiotherapy treatment delivery, comprising performing a method according to any preceding claim, using shape data derived from a plan to generate a file comprising instructions for the design of the compensating device.

9. 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 preceding claims.

10. The computer program product according to claim 9, comprising a non-transitory storage holding said code means.

11. A computer system comprising a program memory and processing means arranged to execute a program in the program memory, the program memory comprising a computer program product according to claim 9.

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