Radiation treatment planning with ion arcs.

Abstract

A method for generating an ion-based radiation therapy plan includes a spot weight optimization procedure tailored to generate a plan involving an arc as a combination of one or more sub-arcs and possibly a static beam, where the one or more sub-arcs are overlapped or have different orientations. The method includes jointly selecting a first and a second set of energy levels.

Description

[Technical field]

[0001] The present invention relates to planning ion-based radiation therapy, and in particular to planning treatments involving ion arcs. [Background technology]

[0002] In particle-based radiation therapy, a patient is irradiated with charged particles such as protons, helium, or carbon ions. The particles are controlled in such a way that most of the energy is deposited at a specific depth in the patient so that the entire target is covered. The depth of the Bragg peak in the patient can be controlled by adjusting the kinetic energy of the particles. The lateral position of the Bragg peak can be controlled using electromagnets to deflect the focused beam. This allows for highly localized dose delivery at a well-controlled location in the patient. A particular combination of kinetic energy and lateral deflection of the beam is called a spot. The relative number of particles delivered to a spot is commonly called the spot weight. The use of spots at many different locations in three-dimensional space can completely cover the target volume with the desired dose distribution. This procedure is called active scanning ion beam therapy, also known as pencil beam scanning.

[0003]

[0003] The kinetic energy of a spot is often, but not necessarily, distributed over several discrete energies. A group of spots with the same kinetic energy but different lateral deflections is often called an energy layer. Thus, all spots within one energy layer have the same energy layer. To cover a desired volume of the patient, different energy layers with different energy levels are defined such that particles of a particular energy layer deposit their energy at a given (water equivalent) depth of the patient. The energy layers are selected in such a way that the Bragg peaks are distributed over the volume to be treated.

[0004]

[0004] The spot weights for each energy layer are determined in the treatment planning system through optimization, and the spot weights are iteratively varied to achieve a desired goal or constraint on dose level or other related quantity. The case where the spot weights are allowed to vary freely through the beam is called Intensity Modulated Ion Therapy. In the general case of protons, it is called Intensity Modulated Proton Therapy (IMPT).

[0005]

[0005] Ion arc therapy involves the emission of a series of multiple main irradiation directions, e.g., 10 or more, 50 or more, or 100 or more irradiation directions, each with several energy layers, e.g., up to 20. The adjustment between each energy layer and each irradiation direction is time consuming. Typically, only one energy layer is delivered per direction. The arc can be delivered via a continuous moving arc where the radiation is delivered during the movement, or controlled by a series of static beams, which represent a trajectory with a stop where the beam is turned on. The arc is defined by control points, and each pair of control points defines the initial and final energy levels, as well as the start and stop angles of the irradiation. Two adjacent control points can vary in irradiation angle, energy level, or both. To ensure that the irradiation is delivered approximately from the main irradiation direction, the start and stop angles are typically close to each other. The control points are selected to achieve a short delivery time while still maintaining a high quality plan that ensures effective treatment of the patient. Summary of the Invention

[0006]

[0006] It is an object of the present disclosure to provide an ion arc treatment plan that allows for time-efficient delivery to the patient while ensuring proper dose distribution.

[0007]

[0007] Accordingly, an aspect of the present disclosure relates to a computer-implemented method of creating an ion-based radiation therapy plan for treating a patient, the method including a spot weight optimization procedure arranged to create a plan involving an arc with a first portion being a first sub-arc, the sub-arc defined by a first set of control points defining a first set of energy levels distributed over a first trajectory involving different irradiation angles that shift the beam in a first direction, the plan further involving a second portion involving a second set of control points different from the first set of control points, the second set of control points defining a second set of energy levels, The second part is a static beam and the second set of control points defines several energy levels from one irradiation angle, or the second portion is a second sub-arc, and the second set of control points defines a second trajectory along a second direction different from the first direction; or the second portion involves a second sub-arc of movement in the first direction, and the relative movement between the gantry and the patient through the arc represents more than a full revolution around the patient; or the second portion involves a second sub-arc that at least partially overlaps the first sub-arc; The method includes selecting both a first and a second set of energy levels.

[0008]

[0008] A plan can be set up such that delivery time is reduced by appropriate adjustment of the energy layers, while proper dose distribution can be ensured by adjusting the radiation into an arc having a first and second portion, where at least the first portion is a sub-arc. Since the energy levels are selected together for the entire plan, they can complement each other throughout the treatment area. This allows the energy levels to be grouped into a first and second set to minimize the time required to change the energy levels during delivery. The first and second portions can be delivered in any suitable order, i.e., the second portion can be delivered before the first portion. When the first and second portions are involved in sub-arcs moving in the same direction, at least one of the first or second sub-arcs can represent a full revolution, and the other sub-arc can represent a full revolution or a partial revolution around the patient. Alternatively, both sub-arcs can represent partial revolutions that collectively represent more than a full revolution.

[0009] In some embodiments, the second portion involves a static beam that includes at least two different energy levels that are irradiated from the same direction. A static beam allows for a higher number of energy levels compared to the energy layers included in the sub-arc that are delivered from one irradiation angle, with typically one energy level being used for each main irradiation direction.

[0010]

[0010] In other embodiments, the second portion involves a second sub-arc in a different direction from the first sub-arc, and a second set of energy levels is distributed through a second trajectory. In some cases, the direction of the second sub-arc can be opposite to the first direction. By turning on the beam during the gantry movement in both directions, it will save time when the gantry moves back and forth. For example, it is feasible to independently select the first and second directions when translation and rotation are combined for optimal coverage of the target.

[0011]

[0011] In yet another embodiment, the second portion involves a second sub-arc that at least partially overlaps with the first sub-arc trajectory, and the second direction is the same as the first direction. This is feasible, for example, when the relative movement between the gantry and the patient represents a full rotation around the patient. In such a case, each of the first and second sub-arcs may represent a full revolution or a part of a revolution. In addition, in an embodiment in which the irradiation angle is changed using the gantry, the patient may be moved during treatment in a direction different from the movement of the irradiation device. This may be achieved by moving the support on which the patient is positioned. This may involve raising and lowering a chair or moving the examination table horizontally. In this case, the first and / or second sub-arc would represent a spiral rather than a circle around the patient. Overlapping sub-arcs of the same direction may also be achieved by moving the gantry back and forth so that it can move in the same direction multiple times.

[0012]

[0012] When the second sub-arc and the first sub-arc have overlapping portions in either the same or opposite directions, the irradiation angles of the sub-arcs can be the same or can be selected to complement each other. For example, the irradiation angle of the second sub-arc can be shifted to achieve a different main irradiation direction in the second sub-arc than in the first sub-arc. Additionally, the energy level in the second sub-arc can be mirrored with respect to the first sub-arc. This means that the irradiation angle that is involved in a high energy level for the first sub-arc will have a low energy level in the second arc, and vice versa.

[0013]

[0013] As can be understood, the method is not limited to only a first and a second part, any number of parts of the same or different types can be combined. For example, a first sub-arc can be combined with several second parts of different types, such as a first sub-arc followed by a static beam and a second sub-arc, or a static beam followed by a first sub-arc, followed by another static beam, and / or followed by a second sub-arc.

[0014]

[0014] The method may include grouping the energy layers of each portion into at least a first and a second sector, and the energy level in each sector is adjusted to reduce delivery time. This typically involves grouping the energy layers into sectors in such a way that the energy level decreases in each sector to reduce the number of increases in energy level in a sub-arc, since in many systems increases take longer than decreases. In the case of mirroring, sectors from the first arc may also be used for the second arc, and the energy levels are mirrored in each sector.

[0015]

[0015] The selection of energy layers is performed simultaneously for all sub-arcs and static beams. In some embodiments, the steps of selecting the first and second sets of energy layers, and possibly further sets, both include a pre-selection step, where the energy layers are selected prior to the spot weight optimization procedure. The pre-selection of energy layers can be performed to use the same sectors in the first and second sub-arcs. The sectors in the first and second sub-arcs can also be shifted with respect to each other to achieve greater flexibility in optimization while maintaining short delivery times. The pre-selection can be performed by treating the first and second sub-arcs as one single arc. Alternatively, the energy level selection is performed as part of the spot weight optimization procedure based on a dose-based optimization goal.

[0016] The pre-selection may be based on any suitable criteria, for example one of the following: Maximize the target volume covered Minimize overlap of covered target volumes Maximizing a goodness measure of the covered target volume

[0017]

[0017] The method according to the present disclosure may be combined with further techniques to improve the resulting plan. For example, robust optimization may be applied. A particularly useful addition is to apply energy level reduction techniques to the first and second sets of energy levels in order to reduce the total number of further energy levels. Examples of energy level reduction techniques are discussed, for example, in European Patent Application No. 18165472.4 by the same applicant.

[0018]

[0018] Aspects of the present disclosure also relate to a computer program product comprising computer readable code means which, when executed in a computer, causes the computer to perform a method according to any one of the preceding claims. The computer program product may be stored in any suitable manner, but is preferably stored on a non-transitory storage medium. Aspects of the present disclosure also relate to a computer having a processor and a program memory, the program memory including the computer program product stored in such a manner that it can be executed in the processor.

[0019]

[0019] The method according to the present disclosure allows for the creation of time-efficient treatment plans by minimizing the need for time-consuming energy layer changes without sacrificing the flexibility required to ensure proper dose distribution. Such changes are typically known to be time-consuming until scanning the patient through several revolutions when changing to higher energies, and using one energy layer per irradiation direction can be faster than changing the energy layer multiple times from the same or nearby directions. The method can also be combined with robust optimization, so that the generated plans are robust to uncertainties, for example, in the patient setup, the patient anatomy, and the interpretation of densities in different voxels of the patient. This is an important feature of any particle treatment plan.

[0020]

[0020] The invention is explained in more detail below, by way of example and with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0021] [Figure 1a] 11A-11C illustrate different possible combinations of sub-arcs and static beams according to an embodiment of the present invention. [Figure 1b] 11A-11C illustrate different possible combinations of sub-arcs and static beams according to an embodiment of the present invention. [Figure 1c] 11A-11C illustrate different possible combinations of sub-arcs and static beams according to an embodiment of the present invention. [Figure 1d] 11A-11C illustrate different possible combinations of sub-arcs and static beams according to an embodiment of the present invention. [Diagram 2] FIG. 1 illustrates the selection of energy levels in two sub-arcs planned to construct an arc, according to one embodiment. [Diagram 3] 1 is a flow chart illustrating some embodiments of an ion arc treatment planning method. [Figure 4] FIG. 1 illustrates a computer system on which the method according to the present invention may be implemented. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022]

[0021] The present invention is suitable for planning any type of ion-based radiotherapy arc plan. In some of the examples below, protons are mentioned as examples, but it should be understood that the method is not limited to protons.

[0023]

[0022] An arc may be defined as a beam that defines a trajectory on the patient. As explained above, an arc is typically defined by a series of control points, each successive pair of which defines a start and stop angle and a first and a last energy layer. To form an arc, at least two control points must define different irradiation directions to define different irradiation angles. In other words, each possible subset of three adjacent control points in a set of control points always has at least two successive control points with different irradiation angles relative to the patient. This means that the beam enters the patient from at least two different directions and at at least two different points due to the relative movement between the beam and the patient. The movement may represent a rotation, which may be a full or partial revolution, or a translation, or a combination of the two. A conventional arc rotates or moves in a single direction relative to the patient, and as a full revolution or less.

[0024]

[0023] The arc may be continuous in the sense that the beam is on during the movement and therefore between the control points. The control points may be grouped into pairs. A pair of control points defines a gantry angle window through which the irradiation is delivered. In other words, if the current and next control points are included in the same pair of control points, the irradiation is on between the control points. If the current and next control points belong to different pairs of control points, the irradiation may be turned off between these control points to provide the patient with the specified irradiation before moving to the next pair of control points. The control points belonging to the same pair typically have the same energy level, and the energy level is typically changed between the pair of control points. The irradiation of the energy layer and the change between the energy layers and therefore between the energy levels both take time, so it is desirable to reduce the number of energy layers for the arc. For many machines, the time to switch energy levels in one direction takes substantially more than the other direction, for example, changing from high energy to low energy is faster than changing from low energy to high energy. Alternatively or in addition to reducing the energy layers, the order of the energy layers may be selected to minimize the time it takes to change and deliver overall.

[0025]

[0024] The arc is achieved by relative movement between the beam and the patient. This may be achieved by rotating the gantry and / or by influencing the direction of the beam by some other means such as magnets. It may also be achieved by moving the patient relative to the beam, for example by positioning the patient on a movable support such as a rotating chair or examination table. Such movable patient supports are known in the art.

[0026]

[0025] Figures 1a, 1b, 1c, 1d show different combinations of sub-arcs and / or static beams that can be implemented according to embodiments of the present invention. In each example, the arcs are created by relative movement between the gantry and the patient, which can be created by rotating the gantry, or by moving the patient support with the patient thereon, or both. Rotating patient supports in the form of chairs or examination tables are known in the art. It is also possible to move the beam relative to the patient by other means, for example using magnets.

[0027]

[0026] Figure 1a shows an example where the first and second parts of the arc are both sub-arcs, R1, R2, covering the same part of the patient's circumference with opposite trajectories. As shown in the figure, the first sub-arc uses pairs of control points centered on three different irradiation angles A1, A2, A3, and uses energy layers R1E1, R1E2, R1E3 for angles A1, A2, A3, respectively. In this example, the second sub-arc R2 uses the same irradiation angles A1, A2, A3, but different energy layers R2E1, R2E2, R2E3 for angles A1, A2, A3. As will be appreciated, the sub-arcs can also follow the same trajectory in the same direction, and if a rotating gantry is used, this would save time to create the second sub-arc during the return movement, instead of returning the gantry before delivering the second sub-arc.

[0028]

[0027] Figure 1b shows a different example where the first and second parts of the arc are both sub-arcs R1, R2 covering the same part of the patient's circumference with opposite trajectories or optionally with trajectories in the same direction. As shown in the figure, the first sub-arc uses three different irradiation angles A1, A2, A3 and uses energy layers R1E1, R1E2, R1E3 for angles A1, A2, A3 respectively. The second sub-arc R2 in this example uses different irradiation angles A1', A2', A3' and energy layers R2E1, R2E2, R2E3.

[0029]

[0028] Figure 1c shows an example where the first part is a sub-arc R1' that covers a part of the patient's circumference and the second part is a static beam S1. The sub-arc R1' involves several control points that define the irradiation angle in the same manner as in Figure 1a. The static beam involves several energy layers S1E1, S1E2, S1E3, S1E4 delivered from one irradiation angle.

[0030] FIG. 1d shows a first sub-arc R1″, the first part of which covers all around the patient, and a second part of which is a second revolution around the patient in the same direction, the second sub-arc R2″, covering the same orbit. As will be appreciated, the directions of R1″ and R2″ can also be opposite. In the case of a rotating patient support, it is more feasible to continue the rotation in the same direction. If the gantry rotates, it may be more feasible to reverse the rotation for the second sub-arc. The first and second sub-arcs R1″, R2″ will be involved with the control points in a similar manner to FIG. 1a or FIG. 1b. That is, the control points may define the same irradiation angle in both cases, but each irradiation angle for each sub-arc may involve a different energy layer, or may define a different irradiation angle for the second sub-arc R2″ than the first sub-arc R1″.

[0031]

[0030] According to the present disclosure, the arc may include one or more sub-arcs, which differ in direction and / or involved energy layers. According to one embodiment of the present disclosure, the first portion of the delivery is in the form of a first sub-arc having a first set of energy layers. The second portion of the delivery involves at least a second portion having a second set of energy layers different from the first set.

[0032] The second portion may be in the form: A second sub-arc having a different direction than the first sub-arc. The second sub-arc may follow the same trajectory as the first sub-arc but in a different direction, or may proceed at an angle from the first sub-arc. One or both sub-arcs may be non-linear and follow any suitable non-linear trajectory. A second sub-arc with the same direction as the first sub-arc, but with a different set of energy layers. This is particularly appropriate when the first sub-arc represents a full revolution around the patient, or when the first and second sub-arc cover the same area of ​​the patient in some other way. Combining higher energy with lower energy from the same irradiation direction is often preferable for the quality of the plan. However, if different energies from the same or adjacent directions are delivered in succession, this can result in slower delivery times, since the arc will include many energy switches up and down from the same or adjacent directions. Therefore, it is often faster to perform a full revolution with one set of energy layers, and then deliver the second set of energy layers through a second revolution that builds the second sub-arc. This can be appropriate even if the first and / or second sub-arc cover only a part of the circumference, meaning that the beam is off for part of the revolution. Static beam delivered from one angle. Static beams are used to deliver multiple energy layers. This is particularly suitable where there are multiple energy layers for one direction, but significantly fewer energy layers for other directions. Directions requiring multiple energy layers can be selected for delivery of the static beam. This results in a dynamic arc that stops in a particular direction, delivers a larger number of energy layers, and then continues.

[0033]

[0032] In the first and second alternatives above, the result may be considered as a multi-arc comprising a first and a second sub-arc. In the third alternative, the result may be considered as a hybrid arc comprising a first sub-arc and a static beam. The term "arc" in this document is intended to cover both multi-arcs and hybrid arcs according to this definition.

[0034]

[0033] As will be appreciated, any combination of the above, in any order, is possible. For example, a treatment may be configured with a static beam followed by a sub-arc, or vice versa. As another example, an arc may have several sub-arcs, with a static beam between all or some of them. These sub-arcs may have the same or opposite trajectories, or completely different trajectories. An arc may also comprise two or more sub-arcs, representing the same full revolution with a static beam between them.

[0035]

[0034] Figure 2 shows, by way of example, possible ways of adjusting the energy levels for the available irradiation directions in the first and second sub-arcs. In Figure 2, the energy levels of the first sub-arc for each respective irradiation direction are marked as circles, and the upward energy jumps of the first arc are shown as solid lines. For the second sub-arc, the energy levels are marked as circles with crosses, and the upward energy jumps are shown as dashed lines. In this example, it is assumed that the first arc is delivered in a direction from 0 degrees to 360 degrees, and the second arc is delivered in the opposite direction. This is appropriate, for example, when the gantry delivers the first arc during the first direction and then delivers the second sub-arc while returning to the initial position. As shown in the figure, the first sub-arc includes several changes to lower energy levels, but only three changes to higher energy levels: 11, 12, and 13. Each successive sequence of changes to lower energy levels constitutes a sector. For the first sub-arc, sectors 14, 15, 16, and 17 are separated by dotted lines. The number of changes to higher energy levels that signal the start of a new sector is kept low because such changes take longer than changes to lower energy levels. The second sub-arc similarly contains several changes to successively lower energy levels, but only three changes to higher energy levels: 21, 22, and 23. In this way, the energy levels of the first and second sub-arc can be selected to complement each other.

[0036]

[0035] In a second option, the number of turns / direction changes can be set by the user (e.g., 2 or 3) or selected by an algorithm based on goodness measures such as target coverage and delivery time. This can be combined with a maximum number of turns to have an upper limit, or with a combined goodness measure that takes into account the number of turns. The resulting arc can also include a portion of a full turn, i.e., the resulting arc can have, for example, two 1 / 3 turns, if this is beneficial.

[0037]

[0036] In a third option, the direction of the static beam within the hybrid arc can be specified by a user or determined automatically by an algorithm based on a goodness measure, typically involving a combination of dosimetry and time scales.

[0038]

[0037] Different methods for selecting a static beam direction include the following. Ray tracing of the patient combined with a goodness measure. The goodness measure can be based on density variations in the path of the trace (depth-wise or lateral-wise due to small perturbations). It can also be based on how sharp the path to the target is with respect to the OAR. · Consider all static beams simultaneously to avoid selecting close angles for static beams, since close beams usually do not contribute to the robustness to the same extent. Machine learning or deep learning Defining several candidate beam directions with candidate energy tiers and performing a first step of spot weight optimization to determine which beam direction and tier has the best chance to meet the optimization goal. For example, a beam direction with many highly utilized energy tiers can be selected, possibly taking into account the angle of the tier to avoid many close angles.

[0039]

[0038] A static beam can be combined with several arc pivot / rotation directions, after which it should preferably be stopped to achieve the best delivery time. For example: Located at the turning point of a change in direction of rotation where there will already be a delay or stop. Located before a switch to an energy level where the energy switch time is longer than other switches. As mentioned before, many machines suffer from longer switch times from lower to higher energies and if a static beam can be placed in location for an upward switch this can be beneficial from a delivery time standpoint.

[0040]

[0039] Figure 3 shows different embodiments of the planning method according to the invention. In a first optional step S31, the number of sub-arcs to be included in the planning is pre-determined. Alternatively, a minimum and / or a maximum value for the number of sub-arcs can be pre-determined or the selection can be left to an optimization procedure.

[0041]

[0040] In a second optional step S32, the number of static beams to be included in the plan, or the minimum and / or maximum number of static beams, is pre-determined. The beam angles of the static beams may also be pre-determined. Alternatively, the selection of the number and / or beam angles may be left to an optimization procedure. In a third optional step S33, the energy levels to be used in the sub-arcs and static beams are pre-selected. How to perform this pre-selection is discussed below. Alternatively, the energy levels may also be left to an optimization procedure.

[0042]

[0041] An optimization problem S34 is provided, which is adjusted to optimize goodness measures such as target coverage and delivery time. In step S35, optimization is performed based on the optimization problem. If pre-determination and pre-selection steps S31, S32, S33 have been performed, the results from these steps are also used as inputs to the optimization. The result of the optimization is a treatment plan that defines an arc with one or more sub-arcs and optionally one or more static beams in terms of control points including irradiation angles and energy levels.

[0043]

[0042] Steps S31, S32, and S33 may be included or omitted independently of one another and may be performed in any suitable order.

[0044]

[0043] Multiple energy tiers are selected by simultaneously analyzing the target and patient geometry for all revolutions, or based on goals such as dose or LET. This can be done by a pre-selection method or as part of spot weight optimization.

[0045]

[0044] Pre-selection methods include, for example: · Mirroring any second sub-arc: Create a solution where the first and second sub-arc have an upward energy jump at the same location. More generally, the most expensive energy level change should be at the same location, and as will be appreciated, this typically increases the energy level. As an example, energy tiers can be selected first for the first sub-arc, grouped into sectors with descending energy levels. When selecting energy tiers for the second sub-arc, the sectors are placed between the same irradiation angles as the first sub-arc. Alternatively, the selection of the sector locations can be done simultaneously across the two sub-arcs. Shift Mirroring: For every two subarcs, the energy level change is selected such that the most expensive energy level change, typically an upward jump, for one subarc is located at the midpoint between the most expensive energy level change of the other subarc. Optimized solution space: All arcs use a solution space that uses upward energy jumps at the same locations, but the energy between the upward jumps is selected such that multiple sub-arcs improve the solution space in an optimal manner. Optimization of the solution space can be based on: i. Maximizing the covered target volume ii. Minimizing overlap of covered target volumes iii. Maximizing the different goodness measures outlined above, which affect, for example, delivery time or plan quality Treating multi-arcs as a large single arc: each arc is added to the end of the previous sub-arc to create a large single arc, selecting upward energy spikes for every arc regardless of the position of the spikes in other sub-arcs, but in such a way that the combined set of energy layers meets appropriate goodness measures in terms of target coverage and time, as before.

[0046]

[0045] As part of spot weight optimization based on an optimization goal, selecting an energy layer involves, for example: Energy layer reduction techniques, as disclosed for example in US 11027148 B2 and EP 3549636 B1. The optimization starts with a higher number of energy layers than is desired at the end of the optimization. The number of energy layers in use is then reduced during the optimization, for example by filtering, where the less utilized energy layers are removed, or by penalization techniques, where the optimization includes a penalty for the number of utilized energy layers, or by a combination of filtering and penalization. These energy layer reduction techniques are then applied simultaneously to all the different parts. Beam splitting techniques, as discussed in US Patent Application Publication No. 2021 / 0121150A1. The optimization starts with a limited number of static beams, and each beam is iteratively split into several sub-beams during spot weight optimization. In this process, the energy layer from the original beam is redistributed through the new sub-beams until the sub-beams are placed close enough to form a continuous arc. In the current invention, the energy layer can be redistributed over at least two portions, one of which is a sub-arc. Other methods

[0047]

[0046] As a final step following these methods for selecting energy tiers, the total number of energy tiers can be further reduced by the use of energy tier reduction techniques, which reduces delivery time and is beneficial in clinical workflow.

[0048]

[0047] Figure 4 shows a schematic diagram of a computer system on which the optimization according to the invention can be carried out. The computer 41 comprises a processor 43, a data memory 44 and a program memory 45. Preferably, one or more user input means 47, 48 are also present in the form of a keyboard, a mouse, a joystick, voice recognition means and / or any other available user input means. The user input means may also be arranged to receive data from an external memory unit.

[0049]

[0048] The program memory 45 holds a computer program adapted to control the processor to execute the optimization procedure according to the present invention. As with the data memory 44, the program memory may be implemented as one or several units as seen fit. The data memory 44 holds input data that may be used in the treatment planning and output data resulting from the planning. The input data includes patient data and information related to the patient's clinical objectives. The output data includes control point information such as energy levels, angles, spot weights, and MU.

Claims

1. 1. A computer-implemented method of generating an ion-based radiation therapy plan for treating a patient, the method comprising: a spot weight optimization procedure adapted to generate the plan as involving an arc with a first portion being a first sub-arc, the sub-arc being defined by a first set of control points defining a first set of energy levels distributed over a first trajectory involving different exposure angles that cause a beam to deviate in a first direction, the plan further involving a second portion involving a second set of the control points different from the first set of control points, the second set of control points defining a second set of energy levels; a. the second portion is a static beam and the second set of control points defines several energy levels from one illumination angle; or b. the second portion is a second sub-arc and the second set of control points defines a second trajectory along a second direction different from the first direction; or c. the second portion engages a second sub-arc of movement in the first direction, and the relative movement between the gantry and the patient through the arc represents more than a full revolution around the patient; or d. the second portion is involved in a second sub-arc that at least partially overlaps the first sub-arc; The method includes jointly selecting the first and second sets of energy levels. Computer-implemented method.

2. The computer-implemented method of claim 1 , wherein the second direction of the second sub-arc is opposite to the first direction.

3. The computer-implemented method of claim 1 , wherein the second portion is a second sub-arc and the second set of control points defines a second trajectory along the first direction.

4. The computer-implemented method of claim 1 , wherein a second sub-arc and the first sub-arc at least partially overlap, and the entrance angles are selected to complement each other.

5. 5. The computer-implemented method of claim 1, wherein a second sub-arc and the first sub-arc at least partially overlap, and at least some of the irradiation angles are selected to be the same for the first and second sub-arcs.

6. 6. The computer-implemented method of claim 1, wherein the energy levels of each portion are grouped into at least first and second sectors, and the energy levels within each sector are adjusted to reduce delivery time.

7. The computer-implemented method of claim 5 , wherein the energy levels are grouped into sectors in a manner such that the energy levels decrease within each sector.

8. 8. The computer-implemented method of claim 1, wherein both the steps of selecting the first and second sets of energy levels comprise a pre-selection step, the energy levels being selected prior to the spot weight optimization procedure.

9. The computer-implemented method of claim 7 , wherein the energy level sector is the same for the first and second sub-arcs.

10. The computer-implemented method of claim 8 , wherein the pre-selection is performed by treating multi-arcs as a large single arc.

11. The computer-implemented method of claim 1 , wherein the selection of the energy level is performed as part of a spot weights optimization procedure based on a dose-based optimization goal.

12. 12. The computer-implemented method of claim 1, wherein the total number of energy levels is further reduced by applying an energy level reduction technique to the first and second sets of energy levels.

13. A computer program product comprising computer readable code means which, when executed on a computer, causes the computer to carry out the method according to any one of claims 1 to 12.

14. 15. A computer (41) having a processor (43) and a program memory (45), the program memory (45) including the computer program product of claim 14 stored in such a manner that it can be executed within the processor.

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