Static devices for use in radiotherapy and methods of designing such devices

Abstract

A compensation device for use in ion-based radiation therapy can include a disk with many protrusions that can be placed in a radiation beam to affect ions in the beam in different ways to generate an irradiation field from a broad beam. This is particularly useful for flash therapy because the time available to modulate the beam is limited. A method for designing such a compensation device is proposed, comprising the steps of: obtaining characteristics of an actual treatment plan including at least one beam; performing an initial treatment plan dose calculation to determine at least one parameter characteristic of a desired energy modulation of the actual plan; and calculating a shape for each of a plurality of elongated elements to modulate the dose of the delivered beam to mimic the dose of the initial treatment plan for each beam based on the at least one parameter.

Description

Technical Field

[0001] Technical Field

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

Background Art

[0002] Background

[0002] In ion-based radiation therapy, a patient is irradiated with a beam of protons or some other type of ion. By controlling the energy and direction of the ions, each ion can deposit its energy in a precisely controlled volume, making ion-based therapy advantageous. A common way to achieve a uniform or non-uniform irradiation field is to use pencil beam scanning, which directs many small beams of different directions and energy levels at 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]

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

[0004]

[0004] Passive devices, such as compensators, are known in ion-based radiation therapy for controlling the maximum range of ions by providing elements of various thicknesses formed from materials that attenuate the energy of the ions, thus shortening the path of the ions depending on the thickness of the compensator.

[0005]

[0005] The point at which ions impart the main part of their energy is known as the Bragg peak and is clearly defined near the end of the ion's trajectory. In addition to influencing the position of the Bragg peak by a compensator, devices are known for broadening the Bragg peak in the depth direction in order to achieve a uniform dose range across the target volume. To achieve this, a rotating disk with regions of different thicknesses is commonly used and is used to rotate at about 30 revolutions per second. Other devices include ripple filters, also called ridge filters, which are translucent devices having a regular pattern of ridges for modulating the beam to broaden the Bragg peak in the depth direction.

[0006]

[0006] In recent years, flash therapy has become of interest due to the promise of more efficient treatment in shorter and fewer fractions, thus saving hospital resources and also being more efficient from the patient's perspective. In flash therapy, the treatment irradiation is delivered instantaneously as a very short pulse at a very high dose rate, typically at a dose rate of 40 Gy / s or more. The time aspect is important to achieve the benefits associated with flash therapy. In such a short time, treatment using a scanned beam needs to be delivered at a single energy level, because any change in the energy level is on the order of seconds. Thus, the conventional pencil beam scanning method does not function. Furthermore, the rotating disks used in conventional passive treatments to generate an extended Bragg peak would also be infeasible.

[0007]

[0007] Simeonov et al. 3D range-modulator for scanned particle therapy: development, Monte Carlo simulations and experimental evaluation; 2017 Phys. Med. Biol. 62 7075 proposes a static element that includes disks of various thicknesses that effectively serve as compensators and has many thin pins of distinct shapes and different lengths arranged on the surface of the disks to modulate the required shift of the Bragg peak. This element combines the functions of a compensator and an energy filter in such a way that the PBS plan can be delivered with only a single energy layer per beam to shorten the delivery time. Based on the shape of the patient and the desired dose at the target, the element is designed by ray tracing combined with the concept of radiation path length. In fact, this involves following many lines of sight through the patient that align the depths at which the lines intersect the proximal and distal surfaces of the target. To serve as a compensator that conforms to the distal surface of the target, the disk part is designed with various thicknesses and the proximal-distal distance is used to calculate the length and shape of the pins in such a way that the field encompasses the entire target. This method enables a static device that can generate a uniform dose distribution that matches both the distal and proximal edges of the target. This device can be manufactured by three-dimensional printing.

Summary of the Invention

Problems to be Solved by the Invention

[0008]

[0008] It is required to be able to generate more complex dose distributions, for example, to enable the co-optimization of overlapping fields.

Means for Solving the Problems

[0009] Summary of the Invention

[0009] The present disclosure is a method for designing a compensation device for use in the delivery of ion-based radiation therapy, the compensation device comprising a substantially disk-shaped structure having a plurality of elongated elements on one side of the disk, the method comprising: · obtaining an initial treatment plan for pencil beam scanning; · obtaining the characteristics of an actual treatment plan, including at least one beam to be used to treat a patient; · determining at least one parameter characteristic of a desired energy modulation of the actual plan by performing a dose calculation of the initial plan; · calculating the shape of each of the plurality of elongated elements to modulate the dose of the beam delivered to mimic the dose of the initial plan for each beam, based on the at least one parameter; relates to a method comprising.

[0010]

[0010] The method may include calculating the dose of the actual plan and scoring the amount to be scored for pixels placed on a virtual grid projected upstream of the patient in the beam trajectory of at least one beam. The virtual grid enables the definition of a pixel grid.

[0011]

[0011] The step of calculating the shape also includes selecting the material of the one or more elongated objects. Alternatively, the material may be pre-selected. The combination of shape and material properties determines how much the elongated elements affect the beam.

[0012]

[0012] In some embodiments, the at least one parameter for determining the height and shape of the elongated object includes one or more of the following: · the energy layer index spectrum of the initial plan, · the energy spectrum of the initial plan, · the water equivalent depth spectrum at the end of the primary proton track of the initial plan.

[0013]

[0013] The actual plan may include a uniform radiation field. The actual plan can be used as the final treatment plan for delivery to the patient, either as is or after additional optimization steps after the compensating device has been designed. In the case of additional optimization steps, the method includes re-optimizing the actual plan, taking into account the compensating device in the re-optimization, to generate the final treatment plan used for delivery to the patient.

[0014]

[0014] To prepare for the manufacture of the resulting compensating device, the method may include obtaining element shape data indicative of the shape of each elongate element based on the actual plan, and using the element shape data to generate a file containing instructions for the design of the compensating device. For example, the file can be used to control a manufacturing process performed by a 3D printer.

[0015]

[0015] The actual plan or final treatment plan can be a pencil beam scanning plan at a single energy, i.e., without a spread-out Bragg peak, or a broad beam plan, i.e., a double scattering plan, a single scattering plan, or a wobbling plan. As described above, the term "pencil beam scanning" includes many different scanning methods including spot scanning, line scanning, or raster scanning.

[0016]

[0016] The present disclosure also relates to a method of manufacturing a compensating device for use in the delivery of ion-based radiation therapy, the method comprising performing the method according to any one of the preceding claims, and using the shape data resulting from the plan to generate a file containing instructions for the design of the compensating device.

[0017]

[0017] The present disclosure also relates to a computer program product including computer-readable code means which, when executed on a computer, cause the computer to perform the method according to any one of the above-described embodiments. The computer product may include a non-transitory storage device holding the code means.

[0018]

[0018] This disclosure also relates to a computer system including a program memory and processing means arranged to execute a program found in the program memory, wherein the program memory includes the computer program product described above.

[0019]

[0019] The compensating device is suitable for use in different types of ion-based radiotherapy. Since the compensating device is a passive component that operates without moving parts during treatment, it is well-suited for use in flash therapy. However, the compensating device can be used in conventional therapies. It can reduce the number of energy levels used during treatment and enable the entire target range using only one additional energy level.

[0020]

[0020] With the design method described herein, when designing compensator elements, complex criteria can be considered because any desired criterion can be represented as part of an initial optimization problem that includes variable RBE dose optimization, LET objectives, and beam-specific objective functions. Thus, co-optimization of overlapping fields becomes possible. Robust optimization can be applied to uncertainties in factors such as position and density, resulting in a plan that operates more reliably in different scenarios.

[0021] Brief Description of the Drawings The present invention will be described in more detail hereinafter by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2a

Figure 2b

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0023] Detailed Description of Embodiments

[0021] FIG. 1 shows an example of a passive modulation device 10 according to an embodiment of the present invention. The device basically includes a compensator element 11 which is a disk having various thicknesses over an area. The thickness is designed such that the input radiation field coincides with the distal end of the target. On the disk, many protrusions in the form of spike-like structures 13 of typically the same material as the compensator element are arranged. The protrusions 13 are typically arranged in a grid pattern on the disk, and each occupies an area of, for example, 1.5×1.5 mm of the disk. The protrusions 13 have different heights and shapes selected in such a way that the beam passing through the device is modulated so as to have a Bragg peak that includes the entire target in a desired manner. Of course, the size, shape and thickness of the compensator element, the arrangement of the protrusions on the compensator element and the size and height of the protrusions should be selected to match the target. 2 The protrusions 13 have different heights and shapes selected in such a way that the beam passing through the device is modulated so as to have a Bragg peak that includes the entire target in a desired manner. Of course, the size, shape and thickness of the compensator element, the arrangement of the protrusions on the compensator element and the size and height of the protrusions should be selected to match the target.

[0024]

[0022] FIG. 2a shows the device of FIG. 1 inserted between a radiation source 21 that emits a uniform radiation field 23 and a patient 25 that includes a target 27 shown simply as an ellipse. The energy spectrum of the radiation after passing through the device is modulated by the device 10 so as to generate a field that coincides with the shape of the target. In FIG. 2a, the target is shown as having a simple approximate circular shape, but according to the present invention, more complex shapes can be treated in the same way.

[0025]

[0023] Figure 2b corresponds to the situation of Figure 2a. The left figure shows the depth dose of the input beam upstream of the device. As can be seen, most of the dose is deposited at one specific depth corresponding to the energy of the protons in the beam. The right figure shows the depth dose after the beam has passed through the modulation device 10. As can be seen, the depth dose has a wider range corresponding to dose deposition across the entire target 27. Figures 2a and 2b show the modulation device 10 inserted into the beam at the protrusion 13 downstream of the disk 11, but the modulation device 10 can also be arranged in the opposite direction, i.e., at the protrusion upstream of the disk.

[0026]

[0024] Figure 3 is a flowchart of a method for designing a compensating element according to an embodiment of the present invention. Here, the method will be described for protons, but the method can be applied to any type of ion used in radiation therapy.

[0027]

[0025] In step S31, a conventional treatment plan, typically a pencil beam scanning plan, is obtained. The plan can be obtained by any suitable method known in the art. Typically, this is done by optimization based on an optimization problem that includes an objective function and / or constraints reflecting the desired characteristics, resulting in a dose distribution and an optimized treatment plan. This means that a virtual pixel grid is assumed at the cross-section of the beam upstream of the patient, and the energy spectrum and optionally the proton direction distribution for each pixel in the cross-section of the beam upstream of the patient are known. The characteristics of the radiation beam used for dose delivery to the patient are also determined. The radiation beam can be homogeneous or inhomogeneous, and in the simplest case, all ions initially have the same energy in a homogeneous beam.

[0028]

[0026] In step S32, optionally, the pixel grid is projected onto a plane outside the patient, and the pixels in the pixel grid correspond to the pixels in the cross-section described in step S31. Preferably, the position of the pixel grid corresponds to the position where the compensating element is to be placed during treatment. The distance to the patient can be freely selected, and in some implementations, a distance of 5 centimeters has been found to be an appropriate distance.

[0029]

[0027] The size of each pixel can be, for example, 1.5 mm × 1.5 mm. Considering a specific column of the input energy level of the field, the energy spectrum in each pixel is a linear function of the plan.

[0030]

[0028] In step S33, the dose is recalculated using a dose engine, for example, a Monte Carlo dose engine. During the recalculation, a specific quantity for each pixel in the pixel grid used when designing the compensation element is scored. For example, the proton energy of each pixel in the pixel grid can be accumulated in the energy spectrum for each pixel. The scored quantity can include, for example, one or more of the following: · Energy layer index spectrum for each pixel. · Water equivalent depth spectrum at the end of the proton track. · Proton energy.

[0031]

[0029] Based on the scored data for each pixel of the pixel grid, in step S34, it is determined to what extent the radiation beam used for dose delivery should be affected in the region corresponding to each pixel. For each pixel, the ions passing through the element should ideally have the same energy spectrum as that calculated in step S33. Based on the spectrum, the protrusion shape can be calculated for each pixel in step S35, resulting in an energy spectrum for each pixel in the dose delivery beam that is sufficiently similar to the energy spectrum calculated in step S33 to ensure sufficient quality in dose delivery. The same procedure can be applied to other selections of the scored data. The calculation of the protrusion shape can also include the selection of an appropriate material for the protrusion, i.e., a material that affects the ions passing through that pixel in the desired manner, along with the shape.

[0032]

[0030] The protrusions designed for each pixel need not be formed like pins or have any type of symmetry, although circular symmetry is easier to implement than more complex shapes. Instead, the protrusions can be any type of elongated object or set of elongated objects extending from the compensator element in the direction of the beam. The protrusions can be composed of many different protrusions within one pixel, such as spikes, pins, or elongated sheets. The lengths of the different portions of one or more elongated objects extending in one pixel differently affect the ions passing through that pixel and are selected to yield an energy spectrum of ions corresponding to the energy spectrum calculated in step S33. As described above, the dose delivery beam can be uniform, but the method can also be applied to more complex dose delivery beams as long as the characteristics of the dose delivery beam are known.

[0033]

[0031] The shape data obtained for each elongated object or set of objects can be used for triangulation to generate CAD files that can be used, for example, to manufacture the compensating device by three-dimensional printing. Instead, several additional optimization steps can be performed in step S36 to improve the resulting compensating device by taking into account possible scattering from the elongated objects before manufacturing the compensating device.

[0034]

[0032] One or more further additional optimization steps S37 can include performing a final PBS re-optimization that takes into account the shape of the compensating device by re-optimization after determining the shape of the compensating device for each beam. This helps to further fine-tune the plan. The final optimization is performed for each plan in a single energy layer. The final optimization can include multiple beams and any type of advanced objective function, such as a function related to RBE dose, LET, or robustness.

[0035]

[0033] Instead, the additional optimization of step S37 can be performed in multiple energy layers. If the design and effect of the compensation device are complete, the optimization plan should apply all weights to a single energy layer. If the layer weight spread exceeds a certain limit, this data can be used to adjust the shape of the compensation device. This procedure can be repeated until the hedgehog shape stabilizes between iterations. A similar approach should be applicable to the optimization of standard compensators for passive plans.

[0036]

[0034] The use of a pixel grid as predicted in step S32 is not necessary but is advantageous for simplifying the procedure. Note that the shape of the pixels can be appropriately selected. The pixels can be square or hexagonal, or can have any other feasible shape.

[0037]

[0035] As described above, the obtained compensation device can be used to form and modulate a field for any type of ion-based radiation therapy. In particular, the number of energy layers used can be reduced, and the delivery of the treatment can be made faster. Preferably, by designing the elongated object to ensure that the elongated object covers the entire three-dimensional target from one field, delivery using only one energy layer is made possible.

[0038]

[0036] FIG. 4 is a schematic diagram of a computer system capable of performing the optimization according to the present invention. The computer 41 includes a processor 43, a data memory 44, and a program memory 45. Preferably, there are also user input means 47, 48 in the form of a keyboard, a mouse, a joystick, voice recognition means, or any other available user input means. The user input means can be arranged to receive data from an external memory unit.

[0039]

[0037] The optimized PBS treatment plan is found in the data memory 44. The treatment plan can be generated by the computer 41 or received from another storage means by any method known in the art. The data memory also includes the dose delivery beam used in the actual treatment of the patient, i.e., the characteristics of the beam modulated by the compensation device.

[0040]

[0038] The data memory 44 also holds the characteristics of the modulation device, such as the material composition of the modulation device. If the material is known, the characteristics of the material can be stored. If the process involves selecting one of the many available materials to be used, the characteristics of all available materials, including the mass density and manufacturing limitations of the materials, should be stored. As understood, the data memory 44 is shown only schematically. There may be several data memory units each holding one or more different types of data, such as one data memory for the design of the compensation device.

[0041]

[0039] The program memory 45 holds a computer program arranged to control the processor to execute the design procedure according to the present invention. The program memory may also hold instructions on how to convert the design of the compensation device into instructions for a manufacturing machine, such as a three-dimensional printer arranged to manufacture the compensation device.

Claims

Claim 1 A method for computer-aided design of a compensating device for use in delivering ion-based radiation therapy, said compensating device comprising a substantially disk-shaped structure having a plurality of elongated elements on one side, said method comprising: said computer: a. obtaining an initial treatment plan, including beam characteristics in pencil beam scanning; b. scoring at least one parameter for desired energy modulation in an actual treatment plan by performing dose calculations on said initial treatment plan based on said beam characteristics; c. calculating the shape of each of said plurality of elongated elements to modulate the dose of said beam to be delivered so as to mimic the dose of said initial treatment plan based on said beam characteristics, based on said scored at least one parameter; A method comprising the steps of: Claim 2 Said scoring step includes calculating the dose of said actual plan and scoring quantities related to pixels located in a virtual grid projected upstream of the patient in the beam trajectory of the beam. The method according to claim 1. Claim 3 Said step of calculating the shape also includes selecting the material of said one or more elongated elements. The method according to claim 1 or 2. Claim 4 Said at least one parameter includes the energy layer index spectrum of said initial treatment plan for determining the shape of said elongated element. The method according to any one of claims 1 to 3. Claim 5 Said at least one parameter includes the energy layer index spectrum of said initial treatment plan for determining the height of said elongated element. The method according to any one of claims 4. Claim 6 Said at least one parameter includes the water equivalent depth spectrum at the end of the primary proton track of said initial treatment plan for determining the height of said elongated element. The method according to any one of claims 1 to 5. Claim 7 Said actual treatment plan includes a uniform radiation field. The method according to any one of claims 1 to 6. Claim 8 Said actual treatment plan is used as a final treatment plan. The method according to any one of claims 1 to 7. Claim 9 The method according to any one of claims 1 to 7, further comprising the step of re-optimizing the actual treatment plan, taking into account the compensation device in the re-optimization, to generate a final treatment plan for delivery to a patient.

10. The method according to any one of claims 1 to 9, comprising the steps of obtaining element shape data indicating the shape of each of the plurality of elongated elements based on the actual plan, and using the element shape data to generate a file containing instructions for the design of the compensation device.

11. The method according to claim 9, wherein the final treatment plan is a pencil beam scanning plan, a double scattering plan, a single scattering plan, or a wobbling plan.

12. A method comprising executing the method according to any one of claims 1 to 9 or claim 11, and generating a file containing instructions for the design of the compensation device using the shape data resulting from the initial treatment plan.

13. A program that, when executed by a computer, causes the computer to execute the method according to any one of claims 1 to 12.

14. A non-transitory storage medium storing the program according to claim 13.

15. A computer system comprising a program memory and processing means arranged to execute a program read from the program memory, wherein the program memory contains the program according to claim 13.

Images