Method for generating a radiotherapy plan, computer program and computer system for generating a radiotherapy plan, and radiotherapy delivery system

Abstract

A method for optimizing a radiation therapy plan for delivering charged particles to a patient by pencil beam scanning, comprising optimizing the treatment plan using an optimization problem designed to allow spots to vary in at least one of shape and orientation, and optionally size, allowing optimized spots to cover the target in the best possible way with a sharp rim along the outer edge of the target. The invention also relates to a computer program product and a computer system for use in such planning, as well as a treatment delivery system for delivering such a plan.

Description

Technical Field

[0001] The present invention relates to the planning and delivery of ion beam therapy.

Background Art

[0002] In ion beam therapy, charged particles such as ions such as protons or helium or carbon ions are used. The overall aim is to deliver a dose to the target volume while minimizing the unwanted dose to nearby critical organs and healthy tissue. In particular, the present invention relates to charged particle therapy using scanned focused ion beams known as pencil beam scanning (PBS). In PBS, separate beams are directed at the patient in a large number of discrete or quasi-discrete spots, or by line scanning. In order to cover the target in three dimensions while minimizing the dose delivered outside the target, a large number of spots are delivered at each of a large number of different energy levels.

[0003] The region near the edge of the beam where the dose rate drops to a low value is known as the penumbra. It is desirable to keep the penumbra as narrow as possible.

[0004] The reduction of the dose near the boundary of the target must be as steep as possible towards its edge in order to ensure a sufficient dose throughout the target while protecting the surrounding tissue as much as possible. The reduction of the dose depends on the lateral shape and size of the spot, with a greater reduction for smaller spots. Thus, current clinical practice when designing spots is to make them small, taking into account the beam transport system, and, conventionally, as circular as technically possible. Conventionally, dose planning for proton beam therapy aims to make the spots uniformly circular and of the same size. To achieve this, the beam is typically adjusted using focusing elements upstream of the patient.

[0005] Various attempts have been made to further improve the dose distribution near the edge of the target. In these attempts, typically, apertures specific to different types of static irradiation fields are used. Such apertures have to be specially made for each patient, which is expensive and not practical. It is also possible to use a dynamically adjustable collimating device such as a multi-leaf collimator (MLC), but this is not very common for PBS systems. MLCs are also expensive. Apertures also increase the generation of neutron background dose during treatment, which is also a problem. Also, all types of apertures only affect the spots at the edge of the treatment irradiation field. Summary of the Invention

[0006] It is an object of the present invention to enable the generation and delivery of particle-based radiation therapy having improved target coverage and, in particular, improved characteristics near the edge of the target.

[0007] The present invention relates to a computer-based method for generating a radiation therapy plan for delivering charged particles to a patient by pencil beam scanning, the method comprising optimizing the treatment plan using an optimization problem designed to allow the particles to be delivered in spots that differ in at least one of shape and orientation.

[0008] According to the present invention, therefore, for a specific beam energy, the shape and / or orientation of the spot can be changed to generate spots that cover the target cross-section together for that energy, while at the same time achieving a reduction in the periphery. This can be done for each individual spot, for each energy layer, or for each beam. Another organization of spot deformation is to repeat energy layers or beams in which the spots for each energy layer (or for each beam) have different shapes and / or orientations. This can be set within an energy layer or a beam. In a preferred embodiment, it is possible to make the spot shape circular or elliptical. In other embodiments, the spot shape may be further varied to include, for example, triangular or rectangular spots, or spots having any suitable geometric shape. Of course, the shape may not be geometrically perfect due to technical limitations. For example, a circular spot may not be perfectly circular. The term "circular" herein should be construed to mean something close to circular that can be generated by the delivery system. For even greater flexibility, the size of the spot may also be changed.

[0009] For the shape and / or orientation, one or more predetermined values or combinations of values may be allowed. By limiting the number of possible combinations, delivery is made easier and faster. Alternatively, the shape and / or orientation may be allowed to be freely changed for maximum flexibility. This allows the spots to be positioned and oriented to cover the target in the best possible way. It also allows the positioning of the edges of the spots with the best-defined boundaries to be aligned and oriented with respect to the target boundary to cause the most rapid possible reduction at the target boundary.

[0010] The optimization problem may be set up to allow changing the spot in at least one part of the target while maintaining the spot uniformly in at least another part of the target. This allows for maximum flexibility in the areas where this is feasible and other areas can be planned in a simpler way. For example, it may be advantageous to change the spot near the outer edge of the target while maintaining the spots further away from that edge uniformly, e.g., uniformly circular. This allows for adaptation of the coverage to the actual shape of the target and faster delivery of the spot at the center of the target as well as sharp peripheral parts at the outer edge of the target.

[0011] One efficient way to achieve different spot shapes and / or orientations is to use an aperture system such as a collimator configured to adjust the spot fluence. Alternatively, an electro-optical focusing system may be used to shape the spot. In the latter case, there is no neutron dose generated by the collimator, which is particularly beneficial for pediatric applications.

[0012] A combination of an aperture device and an electromagnetic focusing system may also be used. For this purpose, the plan obtained by the method must include a method for controlling the aperture device.

[0013] The greatest flexibility is achieved when spot shaping is done for each individual spot for each energy layer. Each spot can then be stretched to an optimal shape, typically an ellipse, and positioned and oriented in the best possible way according to the curvature of the target beam direction image projection. Typically, the spot at the center of the target is maintained circular because it is a spot near the boundary that affects the periphery around the target.

[0014] Alternatively, a limited number of spot shapes can be enabled, such as one circular spot shape having a vertical major axis and two elliptical spot shapes. One circular spot shape having a predetermined major axis, as well as a number of predetermined elliptical spot shapes and sizes, are also possible. These embodiments may allow for a simpler plan and / or a simplified and accelerated delivery compared to embodiments where the shape, size, and / or orientation of the spots can be freely varied.

[0015] For example, for one nominal energy, various spots can be grouped into separate energy layers such that there is one layer containing an elliptical spot having a first orientation, one layer containing an elliptical spot having a second orientation, and one layer containing a circular spot.

[0016] Also, the optimization problem may be designed to determine the delivery order of the spots taking into account the delivery time.

[0017] The present invention also relates to a computer program product including computer-readable code means for causing a processor to perform the method according to any one of the preceding claims when executed in a processor of a computer. The computer program product may comprise non-transitory storage means holding the computer-readable code means.

[0018] The present invention also relates to a computer system comprising a processor, a data memory, and a program memory configured to hold a computer program in such a way that it can be executed in the processor, wherein the program memory includes the computer program product according to the above.

[0019] The present invention also relates to a radiation therapy delivery system for delivering charged particles to a patient by means of PBS, the particles being delivered in spots, the system comprising a processor for controlling the delivery of the therapy, the system further comprising change means for changing at least one of the shape and orientation of the spot during delivery, the processor being configured to control said change. The change means may include an electro-optical system and / or a controllable aperture device configured to change the shape and / or orientation of the spot during delivery as discussed above. The system may also be configured to organize the spots for most efficient delivery.

[0020] The radiation therapy delivery system according to any one of the preceding claims may further comprise a memory, the memory holding a treatment plan, the processor being configured to control the delivery system according to the treatment plan, the treatment plan having been generated using a method according to any of the embodiments disclosed in the present application.

[0021] Hereinafter, the present invention will be described in more detail by way of example with reference to the accompanying drawings.

Brief Description of the Drawings

[0022]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0023] FIG. 1 schematically discloses, in a beam view, an energy layer in a target 1 covered by spots 3, 5 according to an embodiment of the present invention. As shown in the figure, at the center away from the boundary of the target, there is a substantially circular spot 3 positioned adjacent to each other so as to cover the central region of the target. The spot 5 near the boundary of the target is elliptical, and the shape of each spot 5 is configured to cover the region between the round spot and the boundary of the target. The spots 3, 5 may be generated by any form of pencil beam scanning including discrete scanning, quasi-discrete scanning, line scanning, or by any other suitable method.

[0024] In the situation shown in FIG. 1, both the shape and orientation of the spots 3, 5 can be freely changed. As described above, the plan may be set up to allow only a limited set of shapes, sizes and / or orientations. For example, two elliptical shapes with a vertical major axis or four elliptical shapes with a major axis at 45° to each other may be allowed. It may be possible to change the shape and / or orientation. The size of the spot may also be changed. For example, all spots may be of the same size, but different shapes and / or orientations may be allowed, or it may be possible to adapt the size to a part of the target, for example, between another spot and the boundary of the target.

[0025] Figure 2 illustrates the overall planning method according to the present invention. In the first step S21, an optimization problem is defined. The optimization problem may be defined by any suitable method, but is set up to enable changing the spot in at least one of shape, size, or orientation. In the second step S22, optimization is performed using the optimization problem defined in step S21. In an optional third step S23, the energy layers included in the optimized plan are organized in a way that is as efficient as possible for delivery. For example, all spots having the same characteristics in terms of shape, size, and orientation are delivered continuously such that only a change in spot shape occurs once for each set of characteristics. Alternatively, spots having the same set of characteristics may be grouped together in an energy layer such that there is one energy layer per type of spot. Alternatively, this organization of spots may be done in the delivery system.

[0026] Also, the optimization problem may be set up to enable changing the spot only in one or more portions of the target while keeping the spots in the remaining one or more portions uniform. Typically this means enabling changing these boundary spots (i.e., the spots near the boundary of the target) to match the contour of the target as closely as possible while keeping the spots within the boundary spots uniform (e.g., circular and of the same size).

[0027] Figure 3 is a schematic diagram of a computer system capable of implementing the treatment planning method of the present invention. The computer 31 includes a processor 33, a data memory 34, and a program memory 36. Preferably, there are also one or more user input means 38, 39 in the form of a keyboard, mouse, joystick, voice recognition means, or any other available form of user input means. Also, the user input means may be configured to receive data from an external memory unit.

[0028] The data memory 34 contains the data necessary to implement the present method, such as the desired dose distribution and the segmented patient image. The program memory 36 holds a computer program configured to cause a computer to perform the method steps according to some embodiments of the present invention outlined in FIG. 2.

[0029] Of course, the data memory 34 and the program memory 36 are schematically illustrated and considered. There may be several data memory units each holding one or more different types of data, or alternatively there may be one data memory holding all the data in a suitably structured manner, which also holds the program memory. Both the program and the data may be present in one or more memories within the computer system or in another unit accessible from the computer system.

[0030] FIG. 4 is a schematic of a system 60 for radiotherapy and / or treatment planning. Of course, such a system may be designed in any suitable manner, and the design shown in FIG. 4 is only an example. The patient 61 is positioned on the treatment table 63. The system comprises an imaging / treatment device having a radiation source 65 mounted within a gantry 67 for irradiating the patient positioned on the treatment table 63 with radiation. Typically, the treatment table 63 and the gantry 67 are movable relative to each other in several dimensions to deliver radiation to the patient as flexibly and accurately as possible. These components and their functions are well known to those skilled in the art.

[0031] Typically, there are many passive devices provided for shaping the beam in the lateral and depth directions, which will not be considered in more detail here. Means are arranged for delivering radiation in the form of a pencil beam. In this example, the system also comprises modification means 89 for influencing the path of the particles of the beam in the beam line and means for modifying the magnetic field, for example by generating a magnetic field or an electric field or a combined magnetic field / electric field.

[0032] The changing means 89 is configured to change at least one of the shape and orientation of the spot and optionally the spot size during delivery. In a preferred embodiment, the changing means comprises an electro-optical system configured to change the path of the charged particles to generate different spots. Instead of or in addition to the electromagnetic system, the changing means may comprise aperture shaping means in the form of a collimator or block configured to change the shape and / or orientation of the spot during delivery.

[0033] The computer 71 comprises a processor 73, a data memory 74 and a program memory 76. Preferably, there is also one or more user input means 78, 79 in the form of a keyboard, a mouse, a joystick, voice recognition means or any other available user input means. Also, the user input means may be configured to receive data from an external memory unit.

[0034] The data memory 74 may contain clinical data and / or other information used to obtain a treatment plan. Typically, the data memory 74 includes one or more patient images used in the treatment plan according to an embodiment of the present invention. The program memory 76 holds at least one computer program configured to cause the processor to control the delivery system according to the optimization results. Also, if the spot organization for delivery is not performed by the planning system shown in step S23, the processor 73 may perform this step, i.e., determine a suitable order for spot delivery to minimize the delivery time.

[0035] Of course, data memory 74 and program memory 76 are only schematically illustrated and considered. There may be several data memory units each holding one or more different types of data, or alternatively there may be one data memory holding all data in a suitably structured manner, which holds the program memory. One or more memories may also be stored in other computers. Also, this computer may be configured to perform optimization.

[0036] Although deformations in spot shape and orientation for circular and / or elliptical spots are illustrated above, of course the spot can be given any suitable shape using an aperture device designed for different shapes, including triangular, rectangular, or any other geometric shape that can help cover a particular target in the best possible way.

Claims

1. A computer-based method for generating a radiotherapy plan for delivering charged particles to a target (1) in a patient (61) by pencil beam scanning, wherein the charged particles are delivered as a plurality of spots (3, 5) covering a cross-section of the target (1), the method includes optimizing the radiotherapy plan using an optimization problem, the optimization problem is designed to optimize the radiotherapy plan by allowing the spots (3, 5) to differ in at least one of shape and orientation and positioning and orienting the spots (3, 5).

2. The computer-based method according to claim 1, wherein the optimization problem is designed to allow two or more predetermined sets of values for the shape and / or orientation for the spots (3, 5).

3. The computer-based method according to claim 1, wherein the optimization problem is designed to allow the spots (3, 5) to be freely changed in at least one of shape and orientation.

4. The computer-based method according to any one of claims 1 to 3, wherein the optimization problem is designed to allow the shape and / or orientation of the spots (3, 5) to be changed in at least one part of the target (1) while maintaining the shape and / or orientation of the spots (3, 5) uniformly in at least another part of the target (1).

5. The computer-based method according to claim 4, wherein the optimization problem is designed to allow the shape and / or orientation of the spots (5) to be changed in a part near the boundary of the target while maintaining the shape and / or orientation of the spots (3) uniformly in the central part of the target (1).

6. The computer-based method according to any one of claims 1 to 5, further comprising the step of determining the order of delivery of the spots (3, 5) in consideration of the delivery time.

7. The computer-based method according to any one of claims 1 to 6, wherein the treatment plan is configured to control an aperture device and / or an electro-optical system during delivery of the charged particles to change the shape and / or orientation of the spot.

8. The computer-based method according to any one of claims 1 to 7, wherein the optimization problem is configured to also be able to change the size of the spots (3, 5).

9. A computer program including computer-readable code means for causing a processor of a computer (31) to execute the computer-based method according to any one of claims 1 to 8 when executed in the processor (33) of the computer.

10. Non-transitory storage means (36) holding the computer program according to claim 9.

11. A computer system (31) comprising a processor (33), a data memory (34), and a program memory (36) configured to hold the computer program according to claim 9 in a manner executable by the processor (33).

12. A radiation therapy delivery system (60) for delivering charged particles to a patient (61) by PBS, wherein the charged particles are delivered in spots, The radiation therapy delivery system includes a processor (73) for controlling the delivery of the charged particles, a memory (74), and a changing means for changing at least one of the shape and orientation of the spot during the delivery of the charged particles. The memory (74) holds a treatment plan generated using the computer-based method according to any one of claims 1 to 8, and the processor (73) is configured to control the radiation therapy delivery system (60) according to the treatment plan. The radiation therapy delivery system, wherein the processor (73) is configured to control the changing means.

13. The radiation therapy delivery system according to claim 12, wherein the changing means includes an electro-optical system.

14. The radiation therapy delivery system according to claim 12, wherein the changing means includes a controllable aperture device configured to change the shape and / or orientation of the spot during delivery of the charged particles.

15. The computer-based method according to claim 1, wherein the optimization problem is designed to align and orient spots (5) to conform to the boundary of the target at the boundary of the cross-section of the target.

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