Patent Application
20250161714
The present invention relates to the planning of ion-based radiotherapy treatment and in particular planning of treatment involving ion arcs.
In particle-based radiotherapy treatment, patients are irradiated with charged particles such as protons, helium or carbon ions. The particles are controlled in such a way that they will deposit most of their energy at specific depths in the patient so that the whole target will be 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 the delivery of highly localized doses at well-controlled positions in the patient. A certain combination of kinetic energy and lateral deflection of the beam is referred to as a spot. The relative number of particles delivered to a spot is commonly referred to as the spot weight. The use of spots in many different locations in a three-dimensional space, enables fully covering the target volume with the desired dose distribution. This procedure is called active scanning ion beam therapy, also known as pencil beam scanning.
The kinetic energies of the spots are often, but not necessarily, distributed over a number of discrete energies. A group of spots with the same kinetic energy, but different lateral deflection is often referred to as an energy layer. All spots within one energy layer thus have the same energy level. To cover a desired volume in a patient, different energy layers, with different energy levels, are defined such that particles of a particular energy layer will deposit their energy at a certain (water equivalent) depth in the patient. The energy layers are selected in such a way that the Bragg peaks will be distributed over the volume to be treated.
The spot weights of each energy layer are determined in the treatment planning system through optimization, and the spot weights are iteratively varied to achieve desired objectives or constraints related to dose levels or other relevant quantities. The case where the spot weights are allowed to vary freely over the beams is referred to as intensity modulated ion therapy. In the common case of protons, it is referred to as intensity-modulated proton therapy (IMPT).
Ion arc therapy involves radiation in a sequence of a large number of principal irradiation directions, for example 10 or more, 50 or more, or 100 or more irradiation directions, each having a number of energy layers, for example up to 20 energy layers. The adjustment between each energy layer, and between each irradiation direction, takes time. Typically, only one energy layer is delivered per direction. The arc can be delivered either through a continuous moving arc where the radiation is delivered during movement, or controlled by a series of static beams describing a trajectory with stops where the beam is turned on. The arc is defined by control points, each pair of control points defining an initial and final energy level and a start and stop angle for the irradiation. Two adjacent control points may vary in irradiation angle, energy level or both. The start and stop angles are typically close to each other to ensure that the irradiation is delivered approximately from the principal irradiation direction. The control points are selected to achieve a short delivery time, while still maintaining a high-quality plan which will ensure effective treatment of the patient.
The present disclosure aims to provide ion arc treatment plans that will allow time-efficient delivery to a patient while ensuring a suitable dose distribution.
Hence, an aspect of the disclosure relates to a computer-implemented method of creating an ion-based radiotherapy treatment plan for treating a patient, the method including a spot-weight optimization procedure arranged to create the plan so that it involves an arc with a first part which is a first sub-arc, said 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 irradiation angles shifting the beam in a first direction, and so that the plan further involves a second part 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, wherein,
By arranging the radiation in an arc having a first and a second part, where at least the first part is a sub-arc, a suitable dose distribution can be ensured, while the plan may be setup such that the delivery time is reduced by a suitable arrangement of the energy layers. The energy levels are selected together for the whole plan, so that they can complement each other across the treatment area. This enables a grouping of energy levels into the first and second sets in a way that will minimize the time needed for energy level changes during delivery. The first and second parts may be delivered in any suitable order, that is, the second part may be delivered before the first part. Where the first and the second part involve sub-arcs moving in the same direction, at least one of the first or the second sub-arc may describe a full revolution and the other sub-arc may describe a full or a partial revolution around the patient. Alternatively, both sub-arcs may describe partial revolutions which together describe more than a full revolution.
In some embodiments, the second part involves a static beam containing at least two different energy levels irradiated from the same direction. The static beam enables a higher number of energy levels delivered from one irradiation angle, compared to the energy layers included in the sub-arc, where typically one energy level is used for each principal irradiation direction.
In other embodiments, the second part involves a second sub-arc in a different direction from the first sub-arc, and the second set of energy levels is distributed over a second trajectory. The direction of the second sub-arc may be selected freely. In some cases, the direction may be opposite of the first direction. Having the beam turned on during gantry movement in both directions will save time in cases where the gantry is moving back and forth. Selecting the first and second directions independently will be feasible, for example, where translation and rotation are combined, for optimal coverage of the target.
In yet other embodiments, the second part involves a second sub-arc, at least partly overlapping the first sub-arc trajectory, the second direction being the same as the first direction. This is feasible, for example, if the relative movement between the gantry and the patient describes a full revolution around the patient. In such cases, each of the first and the second sub-arc may describe a full revolution or part of a revolution. In addition, in an embodiment where the irradiation angles are changed using a gantry, the patient may be moved during the treatment in a direction different from the movement of the irradiation device. This can be achieved by moving the support on which the patient is positioned. This may involve raising or lowering the chair, or by moving the couch horizontally. In this case the first and/or the second sub-arc will describe a spiral rather than a circle around the patient. Overlapping sub-arcs in the same direction may also be achieved by moving the gantry back and forth so it can move in the same direction more than once.
If the second sub-arc and the first sub-arc have overlapping portions, either in the same or in opposite directions, the irradiation angles of the sub-arcs may be the same, or may be selected to complement each other. For example, the irradiation angles of the second sub-arc can be shifted in order to achieve different principal irradiation directions in the second sub-arc than in the first sub-arc. Additionally, the energy levels in the second sub-arc may be mirrored with respect to the first sub-arc. This means that an irradiation angle that involves a high energy level for the first sub-arc will have a low energy level in the second arc, and vice versa.
As will 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 may be combined. For example, a first sub-arc may be combined with several second parts of different types, for example, 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 a second sub-arc.
The method may include grouping the energy layers of each part into at least a first and a second sector wherein the energy levels within each sector are arranged in order to reduce delivery time. This typically involves grouping the energy layers into sectors in such a way that the energy levels decrease within each sector, to reduce the number of increases of energy levels in the sub-arc, since increases in many systems take longer time than decreases. In the case of mirroring, the sectors from the first arc may be used for the second arc as well, and the energy levels be mirrored within each sector.
The selection of energy layers is made for all sub-arcs and static beams simultaneously. In some embodiments, the step of selecting the first and second, and possibly further, sets of energy layers together includes a pre-selection step, wherein the energy layers are selected prior to the spot-weight optimization procedure. The pre-selection of energy layers can be performed in order to use the same sectors in the first and second sub-arc. The sectors in the first and second sub-arcs can also be shifted with respect to each other in order to achieve large flexibility in the optimization while maintaining a short delivery time. The pre-selection may be performed by treating the first and second sub-arc as one single arc. Alternatively, the energy level selection is performed as part of a spot-weight optimization procedure based on dose-based optimization objectives.
Pre-selection could be based on any suitable criterion, for example, one of the following
The methods according to the present disclosure may be combined with further techniques for improving the resulting plan. For example, robust optimization may be applied. A particularly favorable addition would be applying an energy level reduction technique on the 1st and 2nd set of energy levels together to reduce the total number of energy levels further. Examples of energy level reduction techniques are discussed, for example, in EP18165472.4 by the same applicant.
Aspects of the disclosure also relate 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 preceding claims. The computer program product may be stored in any suitable way but is preferably stored on a non-transitory storage medium. Aspects of the disclosure also relate to a computer having a processor and a program memory, wherein the program memory includes such a computer program product, stored in such a way that it can be executed in the processor.
The methods according to the disclosure enable the creation of time-efficient treatment plans by minimizing the need for time-consuming energy layer changes without sacrificing the flexibility needed to ensure a suitable dose distribution. Such changes, typically when changing to a higher energy, are known to be time-consuming, to the degree that scanning the patient over several revolutions, using one energy layer per irradiation direction may be faster than changing energy layers multiple times from the same or close directions. The methods will also allow to be combined with robust optimization so that the generated plans will be robust to uncertainties in, e.g., patient setup, patient anatomy and interpretation of density in different voxels of the patient. This is an important feature of any particle treatment plan.
The invention will be described in more detail in the following, by way of examples and with reference to the appended drawings.
The present invention is suitable for planning any type of ion-based radiotherapy arc plans. In some examples below, protons are mentioned by way of example but it should be understood that the method is not limited to protons.
An arc may be defined as a beam that defines a trajectory on a patient. As explained above, the arc is typically defined by a sequence of control points, each consecutive pair of which defines a start and stop angle and an initial and a final 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 the set of control points always has at least two consecutive control points that have different angles of irradiation relative to the patient. This means that the beam will enter the patient in at least two different points from at least two different directions because of relative movement between the beam and the patient. The movement may describe 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.
An arc may be continuous in the sense that the beam is on during movement and thus between control points. The control points can be grouped in pairs. A pair of control points defines a gantry angle window over which the irradiation is delivered. In other words, if the current and the next control point are contained in the same control point pair, the irradiation is on between the control points. If the current and the next control point belong to different control point pairs, the irradiation may be turned off between these control points to provide the prescribed radiation to the patient before moving on to the next control point pair. Control points belonging to the same pair typically have the same energy level and the energy level is typically changed between control point pairs. It is desirable to reduce the number of energy layers for the arc, since both irradiation of an energy layer and changing between energy layers, and thus energy levels, takes time. For many machines, the time for switching the energy levels in one direction is substantially higher than switching in the other direction, e.g., changing from a high energy to a low energy is faster than switching from a low to a high energy. As an alternative or in addition to energy layer reduction, the sequence of energy layers may be selected in such a way that the changes and total delivery take as little time as possible.
The arc is achieved by a relative movement between the beam and the patient. This may be achieved by rotating the gantry, and/or 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 moving support such as a rotating chair or couch. Such moving patient supports are known in the art.
According to the present disclosure, an arc may include one or more sub-arcs, where the sub-arcs differ in direction, and/or the energy layers involved. According to an embodiment of the present disclosure, a first part of the delivery is in the form of a first sub-arc, having a first set of energy layers. A second part of the delivery involves at least a second part having a second set of energy layers that is different from the first set.
The second part may be in the form of the following:
In the first and second alternative above, the result may be seen as a multi-arc, comprising the first and second sub-arcs. In the third alternative, the result may be seen as a hybrid arc, comprising the 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.
As will be understood, any combination of the above, in any order, is possible. For example, the treatment could consist in 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 different trajectories altogether. An arc may also comprise two or more sub-arcs describing the same full revolution with a static beam between.
In the second option, the number of revolutions/changes of direction could be set by the user (e.g., 2 or 3) or be chosen by the algorithm based on goodness measures such as target coverage and delivery time. It could be combined with a maximum number of revolutions to have an upper limit, or with a combined goodness measure taking number of revolutions into account. The resulting arc could also include fractions of full revolutions, i.e., the resulting arc could have, for example, 2⅓ revolutions, if this is beneficial.
In the third option, the directions for the static beams in the hybrid arc could be specified by the user or determined automatically by the algorithm based on goodness measures, which typically involve a combination of dosimetric measures and time measures.
Different methods for selecting static beam directions could include:
Static beams can be combined with several arc revolutions/rotation directions. The stops should then preferably be made to achieve the best delivery time, e.g.:
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, selection of numbers and/or beam angles may be left to the optimization procedure. In a third, optional step S33, the energy levels to be used in the sub-arc or sub-arcs, and in the static beams, are pre-selected. Methods of performing this pre-selection will be discussed below. The energy levels may also be left to the optimization procedure instead.
An optimization problem S34 is provided, which is arranged to optimize goodness measures such as target coverage and delivery time. In step S35 the optimization is performed based on the optimization problem. If the predetermining and pre-selection steps S31, S32, S33 have been performed, the results from these steps are also used as input to the optimization. The result of the optimization is a treatment plan defining an arc comprising one or more sub-arcs and optionally one or more static beams, in terms of control points including irradiation angles and energy levels.
Steps S31, S32, and S33 may be included or omitted independently of each other, and may be performed in any suitable order.
The multiple energy layers are selected by analyzing the target and the patient geometry for all revolutions simultaneously, or based on objectives such as dose or LET. This could be done by a pre-selection method or as part of the spot-weight optimization.
Pre-selection methods include, for example:
Selecting energy layers as part of the spot-weight optimization based on optimization objectives involves, for example:
As a final step after these methods for selecting energy layers, the total number of energy layers can be further reduced by the use of energy layer reduction techniques. This will reduce the delivery time, which is beneficial in the clinical workflow.
The program memory 45 holds a computer program arranged to control the processor to perform the optimization procedure according to the invention. Like the data memory 44, the program memory may also be implemented as one or several units as is seen fit. The data memory 44 holds input data that may be used in the treatment planning, and output data resulting from the planning. Input data includes patient data and information om clinical goals for the patient. Output data includes control point information such as energy levels, angles, spot weights and MU.
| Number | Date | Country | Kind |
|---|---|---|---|
| 22159913.7 | Mar 2022 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/086900 | 12/20/2022 | WO |
