A collimation system for spatial fractionated radiotherapy and a method for controlling multi-slit collimators

Abstract

The disclosure regards a collimation system for a radiotherapy system, the collimation system comprising: a first multi-slit collimator having multiple first parallel slits, the first multi-slit collimator being adapted to be placed between a radiation source and an object, a second multi-slit collimator having multiple second parallel slits, the second multi-slit collimator being adapted to be placed between the first multi-slit collimator and the object, and a controller for holding and adjusting a relative slit orientation between the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator by rotating at least one of the first multi- slit collimator and the second multi-slit collimator around a beam axis between the radiation source and the object. The disclosure further relates to a radiotherapy system and a method of controlling multi-slit collimators in a radiotherapy system.

Description

[0001] A collimation system for spatial fractionated radiotherapy and a method for controlling multi-slit collimators

[0002] The present disclosure relates to a novel collimator setup for spatial fractionated radiation therapy and a method for controlling the width and position of the dose peaks.

[0003] Background

[0004] The state of the art in radiation therapy typically involves using an accelerator, which can accelerate particles and produce beams of particles or X-rays that are capable of damaging the DNA of cancerous tissue, as well as healthy tissue. To minimize the damage on the normal tissue, spatially fractionated radiotherapy is proposed. This method produces a series of dose-peaks and dose-valleys of radiation intensity, effectively creating a lateral pattern of dose gradients, which can reduce the damage on the healthy tissue before the planning target volume (PTV). However, current solutions for spatially fractionated radiotherapy methods using a metal collimator have various limitations, as the parameters are not easily customable and it can be costly and time consuming to produce different configurations for each patient.

[0005] Therefore, a novel system is desirable, which can assist in creating a customable spatially fractionated radiotherapy system tailored for the needs of each patient, with an affordable and fast method.

[0006] Summary

[0007] The present disclosure relates to, according to a first embodiment, a collimation system for a radiotherapy system, the collimation system comprising: a first multi-slit collimator having multiple first parallel slits, the first multi-slit collimator being adapted to be placed between a radiation source and an object, a second multi-slit collimator having multiple second parallel slits, the second multi-slit collimator being adapted to be placed between the first multi-slit collimator and the object, and a controller for holding and adjusting a relative slit orientation between the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis between the radiation source and the object. The main idea of the presently disclosed system is based on the spatially fractionated radiotherapy method, which involves exposing a patient with a radiation of spatially alternating intensity of dose. That can be done if for example a grid of a material that can absorb radiation is placed in front of the radiation source, and it can lead to an inhomogeneous dose pattern. That would lead to an exposed pattern on the patient where some areas would not be affected by radiation, while other areas would be exposed, albeit much smaller volumes. The latter is associated (among others) with the dose-volume effect, which is well known in radiotherapy, as smaller irradiated volumes are associated with larger dose tolerance. Thus adopting this spatial pattern of high and low dose, may lead to a much less damaged healthy tissue on the patient. For example, one can imagine a chess pattern, where the white boxes would be exposed, and the black ones would not. Another example can be to imagine a square lattice, where the centers of the squares are hollow, allowing radiation to pass though, and the lines of the squares are made of a material capable of absorbing radiation, effectively creating a heterogeneous radiation pattern. Interestingly, this has been shown to lead to a recovery of the areas exposed by radiation. As a result, spatially fractionated radiotherapy may offer significant advantages over traditional radiotherapy techniques, as it can minimize the side effects of radiation on the healthy tissue. To achieve such grid patterns, blocks of metal such as brass or lead can be manufactured, having a specific grid pattern tailored for each tumor case. However, this can be a relatively time consuming process. This disclosure provides a solution which involves the employment of two set of multi-slit collimators, positioned one behind the other. By rotating at least one of the two multi-slit collimators around the axis of the source beam, it is possible to create such grid patterns, also known as moire patterns. Moire patterns are large-scale interference patterns that can be produced when an opaque ruled pattern with transparent gaps is overlaid on another similar pattern. Such ruled patterns can be the multi-slit collimators of the present disclosure. Depending on the angle, the pattern characteristics can change, making this collimation system suitable for a variety of tumor types and sizes, without the need for producing a different set of collimators for each patient.

[0008] Furthermore, in order to modify the radiotherapy beam, the collimation system can be configured such that the multiple first and second slits of the first multi-slit collimator and the second multi-slit collimator are arranged substantially perpendicular to the beam axis between the radiation source and the object. This would allow the creation of a grid pattern of the radiation beam from the beam source.

[0009] Moreover, the collimation system can be configured to comprise a processing unit configured to compute a radiation pattern at one or more radiation depths for at least one given relative slit orientation between the multiple first and second slits of the first multi-slit collimator and slits of the second multi-slit collimator. In addition, the collimation system can be configured such that the processing unit is configured to compute a radiation pattern in a planning target volume related to the object. These features can be beneficial for the design of a customized system for spatially fractionated radiotherapy, as by simply moving one multi-slit collimator with respect to the other multi-slit collimator, it is possible to change the angle and therefore change the resulting beam pattern. The system may comprise a spot scanning system, wherein the system is configured to vary a center to center distance of the first multi-slit collimator and the second multi-slit collimator to cover irregular tumours located at different depths during beam delivery.

[0010] The disclosure also relates to a radiotherapy system comprising at least one radiation source configured to generate a radiation beam, and a collimation system according to any of the features described.

[0011] The disclosure further relates to a method of controlling multi-slit collimators in a radiotherapy system, comprising the steps of a) generating a radiation beam from a beam source to an object, and b) controlling a relative slit orientation between multiple first parallel slits of a first multi-slit collimator and multiple first parallel slits of a second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis of the radiation beam.

[0012] In summary, the present disclosure provides an efficient novel tool for custom spatially fractionated radiotherapy solutions, employing a moire pattern resulting from the interference of the source beam through a set of multi-slit collimators. This solution can be highly beneficial in contrast to conventional ones, as by simply changing the angle of one collimator with respect to the other, or the slit spacing of a collimator, it is possible to affordably and efficiently customize and tailor the system for the needs of each patient. Description of Drawings

[0013] Various embodiments are described hereinafter with reference to the drawings. The drawings are examples of embodiments and are intended to illustrate some of the features of the presently disclosed collimation system, and are not limiting to the presently disclosed system and method.

[0014] Fig. 1 shows a schematic of a multi-slit collimator.

[0015] Fig. 2 shows an example of a beam source generating a beam passing through two multi-slit collimators before it interacts with an object.

[0016] Fig. 3 shows an example of a moire pattern created by two multi-slit collimators.

[0017] Fig. 4 shows the combined center-to-center distance of the moire pattern created by two multi-slit collimators.

[0018] Fig. 5 shows simulations of beam intensity for different angles of the two multi-slit collimators.

[0019] Fig. 6 shows simulations of beam intensity at the entrance and the center of the target volume for different angles.

[0020] Fig. 7 shows a schematic describing a method for generating a radiation beam through two multi-slit collimators.

[0021] Fig. 8 shows simulations of beam intensity at the entrance and the center of the target volume for different center to center distances.

[0022] Fig. 9 shows simulations of beam intensity at the entrance and the center of the target volume for different throughput values.

[0023] Detailed description

[0024] The present disclosure relates to a collimation system for a radiotherapy system, wherein the collimation system comprises: a) a first multi-slit collimator having multiple first parallel slits, the first multi-slit collimator being adapted to be placed between a radiation source and an object. An example of a multi-slit collimator 100 can be seen in Fig. 1. The radiation may be applied perpendicular to the collimator, such that it can pass through the slits of the collimator. As the radiation source can be particles or electromagnetic radiation in the X-ray spectrum, the collimator can act as a filter which can allow the radiation to penetrate only through the slits of the collimator. As demonstrated in Fig. 1, a multi slit-collimator can be defined by a plurality of slits 101 and a plurality of collimator leaves 102. The slits 101 correspond to distances between two collimator leaves 102. Each collimator leaf has a width. A center to center distance 104 describes the distance between two slits . These parameters along with more parameters such as the thickness of the collimator leaves, are further described on the following paragraphs.

[0025] The collimation system can also comprise b) a second multi-slit collimator, having multiple second parallel slits, the second multi-slit collimator being adapted to be placed between the first multi-slit collimator and the object. An example of such an arrangement can be seen in Fig. 2 where a second multi-slit collimator 202 is placed between the first multi-slit collimator and the object. Fig. 2 shows a side view of the radiotherapy system, where a beam source 200 emits one or more beams which can flow through the two collimators 201, 202 before it hits the object 203. The second multi-slit collimator can have the same pattern as the first collimator, meaning that the slits have the same width and distance from one to the other, or the second multi-slit collimator can be configured to have different parameters.

[0026] Additionally, the collimation system may also comprise c) a controller for holding and adjusting a relative slit orientation between the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multislit collimator around a beam axis between the radiation source and the object. As a result, by adding an additional multi-slit collimator and by rotating one with respect to the other allows the modification of the spatial radiation dose distribution of the radiation field. This effect occurs due to the interference of the beam with the grid pattern created from the two multi-slit collimators. Such a pattern is also known as the moire effect. A special case, which is included as a possibility in the presently disclosed collimation system, is when the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator are oriented with an angle of 90° relative to each other. The system then forms a cartesian grid. The importance of forming a grid pattern is high, as it is known that an alternating intensity of a radiation beam can result into better healing of the irradiated healthy tissue. This is exploited by the current disclosure. For example, in Fig. 5 a simulation of a radiation beam is shown as a function of transverse position (X) and lateral position (Y). The left column corresponds to the radiation at an entrance of a target volume, i.e. at a position closer to the beam source than the center of the target object, passing through a collimation system as described in this disclosure. It can be seen that the radiation follows a grid pattern, which as described above, can lead to less damage on the tissue. If on the other hand, the radiation was homogeneous, the damage on the healthy tissue is anticipated to be more significant, and possible unable to be healed in some cases. In addition, a heterogeneous radiation on the tumor itself may also prove beneficial and advantageous in comparison to a normal homogeneous dose for specific tumor types, such as bulky tumors or tumors with hypoxic cores. For example, targeting endothelial cells or occlusion of small capillaries inside a tumor could lead to an avalanche of death of tumor cells. This can be an advantageous feature of the present disclosure, as by controlling the angle between the two multi-slit collimators, it can be possible to shift from a homogeneous to a heterogeneous grid pattern, depending on the characteristics of a tumor. The simulations as the ones shown in Fig. 5 can be generated by using software programs such as Geant4, which allows the simulation of particles through matter. Other radiation transport simulations tools such as Fluka, can be used to study dose profile.

[0027] The controller can be managed by a user who can utilize a processing unit to set and / or tune the relative slit orientation between the two multi-slit collimators. The controller may be located in the same room as the collimation system, or at an adjacent room, and the processing unit may assist the user by creating simulations of the resulting grid pattern, depending on the parameters of the two multi-slit collimators, the type of the object, or any other variable settings. Fig. 2 shows an example of a beam source 200 generating a beam passing through two multi-slit collimators 201, 202 before it interacts with an object 203. In the example of Fig. 2 a controller 207 for controlling the relative slit orientation between the two multi-slit collimators 210, 202 comprises a processing unit 208.

[0028] The collimation system can be further configured, such that the first multi-slit collimator and the second multi-slit collimator are fixed multi-slit collimators. This would mean that the collimators have pre-built parameters such as fixed center to center period, or throughput. By throughput we refer to the area of a collimator that is transparent. For example, the wider the slits of the collimators, the thinner the hollow space, allowing less beam to pass through the collimators, which effectively reduces the throughput.

[0029] In one embodiment, the collimation system can be configured such that the multiple first and second slits of the first multi-slit collimator and the second multi-slit collimator are arranged substantially perpendicular to the beam axis between the radiation source and the object. For example, the radiation source can create a beam that would be perpendicular to the collimators, as seen in Fig. 2. In case that the beam is not perpendicular to the collimators, then the angle formed between the beam and the collimators needs to be taken into account when simulating the resulting grid pattern. Therefore, it can be advantageous to have the beam perpendicular to the collimators, as that can simplify the calculations of the incident beam to the object. If for example the beam has a certain non-perpendicular angle to the collimators, reflections of the beam may complicate the resulting beam on the object.

[0030] Moreover, the collimation system can be configured such that the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator are configured to provide a grid pattern of a radiation beam from the beam source. . This can be achieved by rotating one of the collimators with respect to the other, creating a grid pattern of the resulting beam after exiting the two collimators and before entering the object. That pattern is also known as a moire pattern. An example of two multi-slit collimators which are rotated in respect to one another can be seen in Fig. 3. As seen in Fig. 4, depending on the angle of rotation a 401 , or the center to center distance of each of the two multi-slit collimators 7i, ?2 402,403, a different grid pattern would be created. As a result, the collimation system can be further configured, such that the first multi-slit collimator and the second multi-slit collimator produce a combined center to center distance Tm= .T1T2where

[0031] IT^ -2T1T2cosa+T2

[0032] Ti is the center to center distance of the first multi-slit collimator and ?2 is the center to center distance of the second multi-slit collimator. As seen in Fig. 4, the grid pattern would result into a combined center to center distance Tm404 which would modify the effect of the incident beam. A number of parameters can be configured to modify Tmand eventually modify the properties of the beam that will hit the object. As a result, it is possible by combining two multi-slit collimators to realize a plurality of grid patterns with different parameters.

[0033] Furthermore, the collimation system can be further configured such that it can comprise a processing unit configured to compute a radiation pattern at one or more radiation depths for at least one given relative slit orientation between the first multi-slit collimator and the second multi-slit collimator. This can be beneficial as it can assist a user of the radiation therapy with choosing the specific parameters of the collimation system in order to get the desired beam pattern for a given patient. For example, the user could take initial measurements of a tumor on a patient such as shape, position, depth or type, and then the user could compute the optimal radiation pattern based on the measurements, and then adjust accordingly the parameters of the two collimators in order to create an optimal beam result on the tumor. This can be a method which can save a lot of time in radiation therapy sessions, as it would not be required for a user to order a collimator with specific grid parameters for each patient and tumor, as the user can simply tune the angles of the two multi-slit collimators to acquire the desired result.

[0034] The collimation can be configured such that the processing unit is configured to compute a radiation pattern in a planning target volume related to the object. By target volume we refer to an area of interest enclosing the object. For example, it can be beneficial to study the radiation pattern at various positions of the target volume 206, as this can provide a better idea of how the pattern changes as a function of distance. Specifically, the collimation system can be further configured such that the processing unit is configured to compute a radiation pattern in a center of the planning target volume and at an entrance of the planning target volume. For example, it can be possible to compute the radiation pattern at the center of the target volume 205 and at the entrance of the target volume 204, as illustrated in the example of Fig. 2. The center of the target volume may coincide with the core of the object, which can be for example a tumor that is wished to be damaged by the radiation. The entrance of the target volume can be for example the healthy tissue which surrounds the tumor. It can be useful to monitor the radiation at the entrance, as it can be an indication of the radiation that will be spread to the healthy tissues of the patient, therefore one can choose the parameters in such a way to minimize the damage on the healthy tissue. At the same time, it can be useful to monitor the radiation at the center of the target volume, as this could be for example a tumor that is wished to be damaged. An embodiment of such computation can be seen in Fig. 5 where the angle a is modified from 20, to 30 and to 40 degrees, while the beam intensity is measured at the entrance and at the center of the object. In this example, one desirable result would be to have an periodic beam intensity at the entrance of the target volume, and a more uniform beam intensity at the center of the target volume, as shown for the 40 degrees case. This result can also be highlighted in Fig. 6 where a line-cut is taken at the lateral position Y=0 of the graphs in Fig.5, and the beam intensity is plotted as a function of transverse position (X) for varying angles for the entrance of the target volume and at the center of the target volume. Apart from changing the angle of the multi-slit collimators, it may also be possible to have multi-slit collimators of different center to center distance. The center to center distance is another parameter that can affect the result of the grid pattern at the entrance and at the center of the target volume, as seen in Fig. 8. By modifying the center to center distance from 1.2 mm to 2 mm and to 2.8 mm the intensity of the beam increases significantly, and the grid pattern at the center of the target volume can become more homogeneous, while keeping an oscillating grid pattern at the entrance of the target volume. In addition, it may also be possible to modify the throughput of the multi-slit collimators, as the throughput is another factor that can impact the resulting grid pattern. This effect can be seen in Fig. 9. By increasing the throughput from 35% to 50% and to 65% it is possible to increase the intensity of the beam and to also produce a more homogeneous grid pattern at the center of the target volume, while keeping an oscillating grid pattern at the entrance of the target volume. The above results of an oscillating beam intensity can be beneficial for patients, as they effectively create a dose gradient, which can reduce the damage on the healthy tissue surrounding the targeted tumour. On the other hand, as the beam intensity can be tuned to be homogeneous on the center of the target area, which can be for example a tumour, the effect of the radiation can be as effective as conventional radiation therapies that do not employ a collimation system. As a result, the collimation system can produce the same effective results on damaging cancerous tissue while at the same time it can reduce the damage on the healthy tissue of a patient.

[0035] Moreover, the collimation system can be configured such that the processing unit is configured to compute radiation patterns for a number of relative slit orientations. This feature can be useful as the processing unit is not limited to specific slit orientations, such as specific angles between the two collimators, or specific center to center distances, but it can be capable of computing radiation patterns for any number of relative slit orientations. In addition, the collimation system can be configured such that the processing unit is further configured to communicate a preferred relative slit orientation to the controller based on the computed radiation patterns. For example, the processing unit can have as input the specifications of the tumor such as size, shape, position or type, and it can recommend to the controller an optimal slit orientation of the two collimators, in order to have as efficient as possible irradiation of the tumor, while at the same time minimizing the damage on the healthy tissue.

[0036] To be able to create a grid pattern from the incident beam, the collimation system can be configured such that the first multi-slit collimator and the second multi-slit collimator are made of a metal, such as tungsten, or a metal alloy. It can be useful if the collimators are made of such specific materials such as tungsten, which can absorb radiation effectively while allowing only a small percentage of radiation to penetrate the material. As a person skilled in the art would know, many other materials can be used to absorb X-ray or gamma-ray radiation, such as lead, brass or any other materials with a large atomic number. A large atomic number means that there is a large number of protons in the nucleus of such materials, which can be ideal for absorbing photon radiation. For the purpose of this disclosure, such materials are beneficial since they can allow the creation of any grid pattern, since a minimum amount of radiation can pass through the metallic pieces of the collimators.

[0037] The collimation system can be configured such that the center to center distance of the first multi-slit collimator and the second multi-slit collimator is between 0.5 mm and 10 mm, preferably between 1 mm and 3 mm, . The optimal center to center distance can vary depending on the location of the target and the desired dose profile. The dose profile can be homogeneous or heterogeneous, depending on the type of the tumor. Therefore, it can be possible to tune the collimation system depending on the needs of each case, by changing the center to center distance using collimators with slitadjustability.

[0038] The collimation can be further configured, such that the thickness of the collimator leaves on a collimator is between 5 mm and 50 mm, preferably between 15 mm and 45 mm, more preferably between 30 mm and 40 mm. The thickness of the collimators depends on the energy of the beam, and the type of the material used for the collimator leaves. Naturally, the thickness to stop a charged particle is energy dependent. For example, for a proton beam of 100 MeV then a tungsten collimator can have a thickness of 8.2 mm to effectively absorb all protons. In practice, leaves may have to be thicker than this to stop non-parallel protons hitting the tungsten leaves at oblique angles.

[0039] The collimation system can be configured, such that the distance between the first multi-slit collimator and the second multi-slit collimator is less than 20 mm, preferably less than 10 mm, more preferably less than 2 mm, most preferably no distance, by abutting each other. The distance between the two collimators can be important for the production of the desired beam pattern Therefore, it can be useful for the collimation system if the distance between the two collimators is small and adjustable.

[0040] Moreover, the collimation system can be further configured, such that the distance between the second multi-slit collimator and the object should be as small as possible. In one embodiment the distance between the second multi-slit collimator and the object is between 200 mm and 50 mm, preferably between 75 mm and 125 mm. The distance between the second multi-slit collimator and the object can affect the resulting grid pattern due to multiple Coulomb scattering with air particles prior to the target.

[0041] The collimation system can be further configured to be used for proton, electron, and photon based spatially fractionated radiation therapy. Depending on the case and the object type, it might be beneficial to use proton beam, electron beam, or other types of radiation therapies such as proton minibeam radiation. A conventional X-ray radiation may also be used in combination with the collimation system. A conventional X-ray radiation can be generated by using an accelerator, which accelerates electrons. These electrons can collide to an atom within the accelerator, removing one electron from it. Then, another electron may fill that vacancy, and by doing so it releases energy, which is in the x-ray or gamma-ray spectrum. That energy can be used for radiation therapies.

[0042] A cyclotron can deliver high energy beam of proton. The energy determines the range of proton beam inside body, providing a radiation dose to the tumor. Protons have the unique advantage of minimizing or even eliminating the dose in normal healthy tissue beyond the tumor, and they also scatter less in healthy tissue.

[0043] A proton minibeam radiation can be generated by segmenting a uniform broad bream into arrays of parallel slatted beamlets that can be spaced between 0.5-3.5 mm apart. The advantage of a minibeam is that the toxicity on the healthy tissue can be less. Combining the minibeam therapy with the collimation system of the present disclosure can introduce flexibility in beam generation for further reduce the damage on the healthy tissue , while at the same time successfully damaging the cancerous cells.

[0044] The collimation system has the versatility to be applicable on various radiation therapy methods, as the thickness of the collimator leaves of the collimators can be thick enough and made of the required materials, to absorb radiation and allow the creation of spatially fractionated dose patterns. For example, as the object type can be any type of cancerous tissue, such as tumors on any part of the body, it can be possible to apply various kinds of radiation therapies through the multi-slit collimators. Examples of cancerous tumors can be related to lung cancer, breast cancer, prostate cancer, esophagus cancer, rectum cancer, uterus cancer, cervix cancer, skin cancer, or any other type of cancer that can affect the human body. This disclosure further relates to a radiotherapy system comprising at least one radiation source configured to generate a radiation beam, and a collimation system according to any of the features described above.

[0045] The radiotherapy system can be further configured, such that the radiotherapy system is a proton radiotherapy system, wherein the at least one radiation source comprises a proton accelerator. The proton accelerator can be used for the creation of proton beam radiation therapies.

[0046] This disclosure further relates to a method of controlling multi-slit collimators in a radiotherapy system, comprising the steps of a) generating a radiation beam from a beam source to an object, b) controlling a relative slit orientation between multiple first parallel slits of a first multi-slit collimator and multiple first parallel slits of a second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis of the radiation beam. Fig. 7 illustrates the steps of the method described above. A generator generates a beam from a beam source 700, which can then interact with two multi-slit collimators that are placed in front of the beam source 701. Finally the relative slit orientation between the two multislit collimators is controlled by rotating at least one of the multi-slit collimators around the beam axis 702.

[0047] This disclosure further relates to a computer program having instructions which, when executed by a computing device or computing system, cause the computing device or computing system to carry out the method of controlling multi-slit collimators in a radiotherapy system according to the information described above.

[0048] Further details

[0049] 1 . A collimation system for a radiotherapy system, the collimation system comprising: a first multi-slit collimator having multiple first parallel slits, the first multi-slit collimator being adapted to be placed between a radiation source and an object; a second multi-slit collimator having multiple second parallel slits, the second multi-slit collimator being adapted to be placed between the first multislit collimator and the object; and a controller for holding and adjusting a relative slit orientation between the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis between the radiation source and the object.

[0050] 2. The collimation system according to item 1 , wherein the first multi-slit collimator and the second multi-slit collimator are fixed multi-slit collimators.

[0051] 3. The collimation system according to any one of the preceding items, wherein the multiple first and second slits of the first multi-slit collimator and the second multi-slit collimator are arranged substantially perpendicular to the beam axis between the radiation source and the object.

[0052] 4. The collimation system according to any one of the preceding items, wherein the multiple first and second parallel slits of the first multi-slit collimator and the second multi-slit collimator are configured to provide a grid pattern of a radiation beam from the beam source.

[0053] 5. The collimation system according to any one of the preceding items, wherein the first multi-slit collimator and the second multi-slit collimator produce a combined center to center distance Tm= .T1T2where Ti is the center

[0054] IT^ -2T1T2cosa+T2 to center distance of the first multi-slit collimator and T2 is the center to center distance of the second multi-slit collimator.

[0055] 6. The collimation system according to any one of the preceding items, comprising a processing unit configured to compute a radiation pattern at one or more radiation depths for at least one given relative slit orientation between the multiple first and second slits of the first multi-slit collimator and slits of the second multi-slit collimator.

[0056] 7. The collimation system according to item 6, wherein the processing unit is configured to compute a radiation pattern in a target volume related to the object. 8. The collimation system according to item 7, wherein the processing unit is configured to compute a radiation pattern in a center of the target volume and at an entrance of the object.

[0057] 9. The collimation system according to any one of items 7-8, wherein the processing unit is configured to compute radiation patterns for a number of relative slit orientations.

[0058] 10. The collimation system according to item 9, wherein the processing unit is further configured to communicate a preferred relative slit orientation to the controller based on the computed radiation patterns.

[0059] 11 . The collimation system according to any one of the preceding items, wherein the first multi-slit collimator and the second multi-slit collimator are made of a metal, such as tungsten, or a metal alloy.

[0060] 12. The collimation system according to any one of the preceding items, wherein the center to center distance of the first multi-slit collimator and the second multi-slit collimator is between 0.5 mm and 10 mm, preferably between 0.5 mm and 3 mm, , most preferably between 0.5 mm and 1.0 mm.

[0061] 13. The collimation system according to any one of the preceding items, wherein the first multi-slit collimator and the second multi-slit collimator comprises collimator leaves having a thickness between 5 mm and 100 mm, preferably between 20 mm and 70 mm, more preferably between 30 mm and 50 mm.

[0062] 14. The collimation system according to any one of the preceding items, wherein the distance between the first multi-slit collimator and the second multi-slit collimator is less than 20 mm, preferably less than 10 mm, more preferably less than 2 mm, most preferably no distance, by abutting each other.

[0063] 15. The collimation system according to any one of the preceding items, wherein the distance between the second multi-slit collimator and the object is between 10 mm and 70 mm, preferably between 20 mm and 40 mm.

[0064] 16. The collimation system according to any one of the preceding items, wherein the collimation system is configured to be used for proton, electron, and photon based spatially fractionated radiation therapy.

[0065] 17. A radiotherapy system comprising: at least one radiation source configured to generate a radiation beam; and a collimation system according to any one of the preceding items.

[0066] 18. The radiotherapy system according to item 17, wherein the radiotherapy system is a proton radiotherapy system, wherein the at least one radiation source comprises a proton and / or particle accelerator.

[0067] 19. A method of controlling multi-slit collimators in a radiotherapy system, comprising the steps of: generating a radiation beam from a beam source to an object; controlling a relative slit orientation between multiple first parallel slits of a first multi-slit collimator and multiple first parallel slits of a second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis of the radiation beam.

[0068] 20. A computer program having instructions which, when executed by a computing device or computing system, cause the computing device or computing system to carry out the method of controlling multi-slit collimators in a radiotherapy system according to item 19.

Claims

Claims1. A collimation system for a radiotherapy system, the collimation system comprising: a first multi-slit collimator having multiple first parallel slits, the first multi-slit collimator being adapted to be placed between a radiation source and an object; a second multi-slit collimator having multiple second parallel slits, the second multi-slit collimator being adapted to be placed between the first multislit collimator and the object; and a controller for holding and adjusting a relative slit orientation between the multiple first parallel slits of the first multi-slit collimator and the multiple second parallel slits of the second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis between the radiation source and the object.

2. The collimation system according to claim 1 , wherein the first multi-slit collimator and the second multi-slit collimator are fixed multi-slit collimators.

3. The collimation system according to any one of the preceding claims, wherein the multiple first and second slits of the first multi-slit collimator and the second multi-slit collimator are arranged substantially perpendicular to the beam axis between the radiation source and the object.

4. The collimation system according to any one of the preceding claims, wherein the multiple first and second parallel slits of the first multi-slit collimator and the second multi-slit collimator are configured to provide a grid pattern of a radiation beam from the beam source.

5. The collimation system according to any one of the preceding claims, wherein the first multi-slit collimator and the second multi-slit collimator produce a combined center to center distance Tm= .T1T2where Ti is the centerIT^ -2T1T2cosa+T2 to center distance of the first multi-slit collimator and T2 is the center to center distance of the second multi-slit collimator.

6. The collimation system according to any one of the preceding claims, comprising a processing unit configured to compute a radiation pattern at one or more radiation depths for at least one given relative slit orientation between the multiple first and second slits of the first multi-slit collimator and slits of the second multi-slit collimator.

7. The collimation system according to claim 6, wherein the processing unit is configured to compute a radiation pattern in a target volume related to the object.

8. The collimation system according to claim 7, wherein the processing unit is configured to compute a radiation pattern in a center of the target volume and at an entrance of the object.

9. The collimation system according to any one of claims 7-8, wherein the processing unit is configured to compute radiation patterns for a number of relative slit orientations.

10. The collimation system according to claim 9, wherein the processing unit is further configured to communicate a preferred relative slit orientation to the controller based on the computed radiation patterns.

11. The collimation system according to any one of the preceding claims, wherein the first multi-slit collimator and the second multi-slit collimator are made of a metal, such as tungsten, or a metal alloy.

12. A radiotherapy system comprising: at least one radiation source configured to generate a radiation beam; and a collimation system according to any one of the preceding claims.

13. The radiotherapy system according to claim 12, wherein the radiotherapy system is a proton radiotherapy system, wherein the at least one radiation source comprises a proton and / or particle accelerator.

14. A method of controlling multi-slit collimators in a radiotherapy system, comprising the steps of: generating a radiation beam from a beam source to an object; controlling a relative slit orientation between multiple first parallel slits of a first multi-slit collimator and multiple first parallel slits of a second multi-slit collimator by rotating at least one of the first multi-slit collimator and the second multi-slit collimator around a beam axis of the radiation beam.

15. A computer program having instructions which, when executed by a computing device or computing system, cause the computing device or computing system to carry out the method of controlling multi-slit collimators in a radiotherapy system according to claim 14.

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