A variable collimator for spatially fractionated radiotherapy

Abstract

The disclosure regards a variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator, and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves to adjust the leaf width of the variable slit collimator. The disclosure further relates to a radiotherapy system and to a method of controlling a slit collimator in a radiotherapy system, such as a spatially fractionated radiotherapy system.

Description

[0001] A variable collimator for spatially fractionated radiotherapy

[0002] The present disclosure relates to a collimator setup for radiation therapy and a method for controlling the collimator slits.

[0003] Background

[0004] The state of the art in radiation therapy typically involves using a linear accelerator, which can accelerate electrons and produce beams of particles or X-rays that are capable of damaging the DNA of cancerous tissue, as well as healthy tissue. As the radiation dose which can be delivered to the tumour target may be limited by normal tissue complications, a different method has been developed which involves spatially fractionated radiotherapy. This method produces a series of peaks and valleys of radiation intensity, effectively creating a dose gradient, which can reduce the damage on the healthy tissue at the entrance of the targeted tumour. 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 time consuming to produce different components for each patient.

[0005] Therefore, the need for a novel system is required, 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 variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator, and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves to adjust the leaf width of the variable slit collimator.

[0008] One idea of the present disclosure is based on the spatially fractionated radiotherapy method, which involves exposing a patient with a radiation of alternating intensity. 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 radiation pattern on the healthy tissue surrounding the target tumor. That would lead to an exposed pattern on the patient where some areas would not be affected by radiation, while other would, leading to a much less damaged healthy tissue on the patient. For example, one can 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 have significant advantages over traditional radiotherapy techniques, as it can minimize the side effects of radiation on the healthy tissue, thus increasing the radiation dose tolerance. 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 an expensive and time consuming process, as the most optimal configuration is patientspecific. The present disclosure provides a solution by employing a collimator with a plurality of leaf pairs, wherein the leaf pairs can be controlled by a leaf adjustment mechanism allowing the leafs to move towards or away from each other in a longitudinal direction, effectively changing the width of the leaf pair, and the beam that can pass through the collimator. Further variable slit collimators may be stacked behind the first variable slit collimator rotated with an angle, with the purpose of achieving a 2- D pattern of apertures, or even hexagonal shaped apertures. This effect can be useful as it can cause the radiation pattern to change, making this variable collimator suitable for a variety of tumor types and sizes, without the need for producing individual patientspecific collimators for each patient or tumor site.

[0009] Furthermore, to control the leaf pairs, the variable slit collimator can be configured such that the two tapered collimator leaves comprise a lower leaf having a lower base side and a tapered upper side; and an upper leaf having an upper base side and a tapered lower side. This design allows the two leaves to be moved and slid. When the two leaves are moving away from one another in the longitudinal direction, the width of the leaf pair decreases, eventually increasing the slit from which the beam can pass. On the other hand, when the two leaves are moving towards each other in the longitudinal direction, the width of the leaf pair increases, and that causes a decrease in the slit from which the beam can pass. To achieve the control of the collimator leaves, the variable slit collimator can be further configured, such that the leaf adjustment mechanism comprises a first structure connected to or attached to the tapered collimator leaves, wherein the first structure comprises one or more transversal width adjusting bars attached to the tapered collimator leaves, wherein the transversal width adjusting bars can be moved along the longitudinal direction of the two tapered collimator leaves to move the two tapered collimator leaves towards and away from each other.

[0010] Moreover, the variable slit collimator can be configured such that a plurality of spacing wedge pairs are arranged between the collimator leaf pairs, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element, and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaf pairs of the variable slit collimator. That can be an alternative method to change the resulting beam pattern that would be realized after the source beam passes through the variable slit collimator.

[0011] Similar to the design of the two tapered collimator leaves, the variable slit collimator can be further configured such that the two tapered wedges comprise a lower wedge having a lower base side and a tapered upper side; and an upper wedge having an upper base side and a tapered lower side.

[0012] The disclosure also relates to a variable slit collimator for a spatially fractionated radiotherapy system, comprising a plurality of spaced collimator leaves, a plurality of spacing wedge pairs arranged between the spaced collimator leaves, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element, and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaves of the variable slit collimator.

[0013] Any of the plurality of collimator leaf pairs and the plurality of spacing wedge pairs may be operated continuously and / or seamlessly as part of a radiotherapy system. As demonstrated in the present disclosure, the plurality of collimator leaf pairs and the plurality of spacing wedge pairs of the variable slit collimator may have control mechanisms and / or elements that enable such control. The radiotherapy system may comprise a control unit, such as a processing unit, configured to control the variable slit collimator. The disclosure further relates to a method of controlling a slit collimator in a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising the steps of providing a variable slit collimator comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator, and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves, and using the leaf adjustment mechanism to move the two tapered collimator leaves towards and away from each other to adjust at least the leaf width of the variable slit collimator.

[0014] In summary, the present disclosure provides an efficient novel tool for custom spatially fractionated radiotherapy solutions, employing a radiation pattern resulting from the interference of the source beam through a variable slit collimator. This solution can be highly beneficial in contrast to conventional ones, as by simply adjusting the leaf mechanisms it is possible to alter the passing beam. Thus, using the present disclosure it is possible to affordably and efficiently customize and tailor a spatially fractionated radiotherapy for the needs of each patient.

[0015] Description of Drawings

[0016] 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 variable collimator, and are not limiting to the presently disclosed system and method.

[0017] Fig. 1 A, B shows a schematic of collimator leaf pairs and a schematic of a variable slit collimator having a number of the collimator leaf pairs.

[0018] Fig. 2 shows an example of two tapered collimator leaves.

[0019] Fig. 3 shows an example of a variable slit collimator demonstrating the width adjusting bars attached to the tapered collimator leaves.

[0020] Fig. 4 shows a schematic illustrating the change of width in the slits of the variable collimator when moving the leaf pairs towards or away of each other.

[0021] Fig. 5 shows a schematic showing the principle of the wedge configuration in the variable slit collimator.

[0022] Fig. 6 shows an example of a variable slit collimator demonstrating the space adjusting transversal bars, which tune the spacing of the leaf pairs. Fig. 7 shows schematics highlighting the result of the tuning the wedges.

[0023] Fig. 8 describes a method for tuning a variable slit collimator.

[0024] Detailed description

[0025] The present disclosure relates to a variable slit collimator for a spatially fractionated radiotherapy system, comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator. The leaves can be positioned towards or away from each other, effectively altering the width of the collimator leaf pair, and changing the slit width of the collimator. This process can allow a modification of the amount of radiation that can pass through the variable slit collimator.

[0026] The variable slit collimator may further comprise a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves to adjust the leaf width of the variable slit collimator. An example showing such a variable slit collimator can be seen in Fig. 1. Fig 1A shows three different settings of a collimator leaf pair 100, wherein the collimator leaf pair comprises a first collimator leaf 101 and a second collimator leaf 102. The leaf pairs can be positioned closer to each other as seen in the upper schematic of Fig. 1 A, or they can be positioned further away from each other as seen in the middle and the lower schematic of Fig. 1 A. This modification of the collimator leaves would affect the width of the collimator leaf pair, effectively changing the slit width of the collimator, allowing more or less radiation to pass through. An example of a variable slit collimator 103 is shown in Fig. 1B, where the transversal axis (Y) and the longitudinal axis (X) are shown. In this illustration, the variable slit collimator 103 is rotated counter-clockwise by 90 degrees. In this example, a plurality of collimator leaf pairs are positioned one on top of the other, creating a series of slits. The slit width, can be altered by the mechanism described above, by moving the collimator leaves towards or away from each other. An additional mechanism of controlling the amount of radiation passing through is described on the paragraphs below. In this embodiment, a frame 104 encapsulates the variable slit collimator, which can be equipped with two rails 105 that can host bars 106, which can simultaneously control multiple collimator leaf pairs and their spacings. More information and detailed description about these mechanisms is disclosed in the following paragraphs. The variable slit collimator can be further configured, such that the two tapered collimator leaves comprise a lower leaf having a lower base side and a tapered upper side; and an upper leaf having an upper base side and a tapered lower side. This geometry can be useful, as it can allow to easily tune the total width of the collimator leaf pair by moving the two collimator leaves with respect to each other. An embodiment of the two tapered collimator leaves can be seen in Fig. 2. In this example, a first collimator leaf 204 and a second collimator leaf 205 are abutting each other forming a collimator leaf pair 206. The first collimator leaf can be named as upper leaf and the second collimator leaf can be named as lower leaf. The lower leaf has a lower base side 200 and a tapered upper side 201. The upper leaf has an upper base side 202 and a tapered lower side 203. As a person skilled in the art would know, the leaves of the variable slit collimator may have any other type of geometry, as long as the geometry would allow an incident beam to partially pass through the collimator. For example, the collimator leaves can have an isosceles triangle shape, a right angle shape, a scalene triangle shape, or they could even have a polygon shape, such as a diamond shape.

[0027] ‘Tapered collimator leaves’ within the context of the present disclosure shall be construed broadly. ‘Tapered’ may be seen as shape that diminishes or reduces towards one end. An example is seen in Fig. 2, in which two tapered collimator leaves abut each. The two tapered collimator leaves may, for example, be wedge-shaped and / or have a triangular shape, as described above. As demonstrated in fig. 1A, when the two tapered collimator leaves are moved in a longitudinal direction of the two tapered collimator leaves towards and away from each other, the thickness of the leaf pair changes.

[0028] The variable slit collimator can be further configured, such that the tapered upper side of the lower leaf and the tapered lower side of the upper leaf abut each other. It can be useful for the two leaf pairs to abut each other, since that can allow the sliding mechanism to operate. In addition, it might also be possible to create leaf pairs that do not abut each other, but instead they have a finite distance between the tapered upper side of the lower leaf and the tapered lower side of the upper leaf. If the leafs did not abut each other, then it would be difficult to define a change in the width of the leaf pair as there would be a gap between the two collimator leaves. Even if the width would be well defined, the gap between the collimator leaves would influence the beam passing through the variable slit collimator. The tapered upper side of the lower leaf 201 and the tapered lower side of the upper leaf 203 can abut each other as shown in Fig. 2. This way of having the two collimator leaves abut each other can be optimal, as it allows to gradually change the width of the leaf pair. It is also a convenient way, as when the two collimator leaves as moved fully towards one another, then a rectangular can be formed. An embodiment of that case where the two collimator leaves are moved fully towards one another be seen in Fig. 1.

[0029] The variable slit collimator can be further configured, such that the lower base side of the lower leaf and the upper base side of the upper leaf are parallel. This can be one way of defining the two collimator leaves, as it can allow a smooth movement of a plurality of leaves. If the two sides were not parallel, then that may lead to complications such as blockings in the variable slit collimator. It is also possible to consider the two collimator leaves as two identical triangles which are mirrored on the X and the Y direction.

[0030] Moreover, the variable slit collimator can be further configured, such that the leaf adjustment mechanism comprises a first structure connected to or attached to the tapered collimator leaves. Such a structure can be beneficial, as it can simultaneously control all the leaf pairs of the variable slit collimator, producing a uniform slit pattern. A number of different mechanisms could be employed, which could have the desired effect of uniformly controlling the width of the leaf pairs. Specifically, the variable slit collimator can be further configured, such that the first structure comprises one or more transversal width adjusting bars attached to the tapered collimator leaves, wherein the transversal width adjusting bars can be moved along the longitudinal direction of the two tapered collimator leaves to move the two tapered collimator leaves towards and away from each other. An embodiment of the width adjusting bars can be seen in Fig. 3. Here, an example is shown where the width adjusting bars are positioned in such a way, such that the left bar 300 is attached on all the upper collimator leaves, while the right bar 301 is attached on all the lower collimator leaves. By controlling the width adjusting bars, it is possible to move them along the longitudinal direction (X) and effectively change the width of the leaf pairs. The lower image of Fig. 3 shows an example where the width adjusting bars 302 have moved closer to one another, simultaneously bringing the upper collimator leaves and the lower collimator leaves closer to the center, which increases the width of the leaf pairs. In the embodiment shown in Fig. 3, the left width adjusting bar 300 and the right width adjusting bar 301 initially have a distance of 250 mm, while at the lower schematic of Fig. 3, their distance has decreases to 140 mm. This results to a change in leaf pair width, for example, from 1.03 mm to 2.05 mm, as seen in Fig. 4. Choosing an optimal combination of parameters can be beneficial, as it can create a system with high resolution, since by changing the width adjusting bar distance by 1 mm, it would result into changing the leaf pair width by approximately 0.01 mm. This can be an important feature, since small width changes can result into significant changes in the spatial radiation pattern the patient treated will be exposed to. Therefore, it is important to be able to tune the variable slit collimator with such high resolution.

[0031] The present disclosure may comprise an additional way of controlling the slit characteristics of the collimator. Specifically, the variable slit collimator can be configured to comprise a plurality of spacing wedge pairs arranged between the collimator leaf pairs, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element, and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaf pairs of the variable slit collimator.

[0032] One aspect of the present disclosure therefore relates to a variable slit collimator for a spatially fractionated radiotherapy system, comprising: a plurality of parallel collimator leafs; and a leaf spacing adjustment mechanism for adjusting the distance between the leafs comprising: a plurality of spacing wedge pairs arranged between the collimator leafs, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element; and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leafs of the variable slit collimator.

[0033] ‘Wedge pairs’ and the wedge pairs comprising ‘two tapered wedges’ shall be construed broadly to comprise any suitable tapered shape for adjusting the distance between the leafs. A ‘tapered wedge’ in this context may generally be interpreted is any suitable tapered shape, preferably a triangular shape, for achieving the described functionality. By having the spacing wedge pairs arranged between the collimator leafs, moving the two tapered wedges towards each other in a longitudinal direction may increase the space between the plurality of parallel collimator leafs. Similarly, when the two tapered wedges are moved away from each other in a longitudinal direction, the thickness and thus the space between the plurality of parallel collimator leafs is reduced.

[0034] In one embodiment, the spacing wedge pairs can have the same geometry as the leaf pairs, but mirrored with respect to the X axis. An example of wedge pairs 500 can be seen in Fig. 5. In this example, the wedge pairs are scaled down to smaller objects with comparison to the collimator leaves, and they can be positioned above or below 501 a collimator leaf 505. By changing the relative position of the two wedges, it is possible to change the width of the wedge pair, in a similar fashion as changing the width of the leaf pair as described in the previous paragraphs. Therefore, by changing the wedge pair width, the spacing between adjacent leaf pairs is also modified. By approaching the wedges closer to each other as shown in configuration 502 in the longitudinal direction, the spacing 504 between adjacent leaf pairs would increase, while by moving the wedges one away from each other 503 in the longitudinal direction, the spacing 504 of adjacent leaf pairs would decrease.

[0035] The variable slit collimator can be further configured, such that the two tapered wedges comprise a lower wedge having a lower base side and a tapered upper side, and an upper wedge having an upper base side and a tapered lower side. An example of the two wedges 500 can be seen in Fig. 5, where a lower wedge has a lower base side and a tapered upper side, while the upper wedge has an upper base side and a tapered lower side. In one embodiment, the lower wedge can be more elongated than the upper wedge, a feature that can allow a smoother operation of the leaf collimators. In addition, the variable slit collimator can be further configured, such that the lower base side of the lower wedge and the upper base side of the upper wedge are oriented towards and abut the collimator leaf pairs. Such an example can be seen in Fig. 5, showing a set of wedges which abut each other. Similarly to the arguments given for the design of the leaf collimators, the wedge pairs also have an advantage for having this shape, since it can be possible to estimate the relation between the width change of the wedge and the effective change in the spacing between adjacent leaf collimators.

[0036] The variable slit collimator can be further configured, such that space adjustment mechanism comprises a second structure connected to or attached to the tapered wedges. For example, that structure can be any kind of mechanism that can allow multiple sets of wedges to be controlled at the same time, with the purpose of uniformly changing the spacing between leaf pairs in a variable slit collimator. Specifically, the variable slit collimator can be further configured, such that the second structure comprises one or more space adjusting transversal bars attached to the tapered wedges, wherein the space adjusting transversal bars can be moved along the longitudinal direction of the two tapered collimator wedges to move the two tapered wedges towards and away from each other. An embodiment illustrating a set of transversal bars attached to the tapered wedges can be seen in Fig. 6. An inner left bar 600 can be attached to the wedges controlling the upper collimator leaves, and an inner right bar 601 can be attached to the wedges controlling the lower collimator leaves. Since all the wedge sets are attached on the same left or right bar, by moving the bar it is possible to change the shape of each wedge, effectively pushing away or closer the adjacent leaf pairs, and modifying the spacing between them. For example, by changing the distance 602 of the inner bars 600 and 601 from 57 mm to 77 mm, it is possible to change spacing between leaf pairs, for example, from 2.15 mm to 2.68 mm, as seen in Fig. 7. Such a spacing difference is capable of influencing the resulting spatial radiation pattern that can be directed towards a patient after interfering with the variable slit collimator. The relation between the distance of the inner bars and the spacing of the leaf pairs can be linear. For a linear correlation, the resolution of this mechanism can be 0.025 mm. This could lead the wedge mechanism to be used for coarser changes in the slits of the collimator, while the mechanism that can change the width of the leaf pairs could be used for finer adjustments on the slits. Furthermore, depending on the choice of the slope of the tapered sides of the wedges and the collimators, the resolution can either increase or decrease. If the slope is faint, then a change of a collimator leaf or a wedge in the longitudinal direction would result into a fainter change in the width. On the other hand, if the slope is more steep, that could result into a much more abrupt change in the width. Therefore, depending on the needs, it can be possible to manufacture different variable slit collimators that have leaves of different tapered side slope.

[0037] The variable slit collimator can be further configured to comprise an upper rail and / or a lower rail in which the one or more transversal width adjusting bars and / or the one or more space adjusting transversal bars can slide to adjust the leaf width and / or the space between the collimator leaf pairs. For example, as seen in Fig. 3 and Fig. 6, the variable slit collimator can comprise two rail mechanisms 303, 304 which can host the width adjusting bars and the space adjusting transversal bars, allowing them to slide in the longitudinal direction. The width adjusting and space adjusting transversal bars can be attached to the rail using a fitting part 305. The person skilled in the art would know, that any other mechanism that would allow the collimator leaves or the wedges to move simultaneously could also be applied. For example, the transversal width adjusting bars and the space adjusting transversal bars could be equipped with wheels in order to roll in a rail mechanism. In addition, the transversal width adjusting bars and the space adjusting transversal bars could be equipped with a sliding mechanism, allowing them to slide in the longitudinal direction.

[0038] The variable slit collimator can be further configured to comprise a first width adjusting bar connected to the all of the lower leaves of the leaf pairs, a second width adjusting bar connected to the all of the upper leaves of the leaf pairs, a first space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on the first collimator leaves, and a second space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on either the first or the second collimator leaves. The width adjusting and space adjusting transversal bars may also be connected in different pairings to the leaf pairs and the wedge pairs. For example, the first width adjusting bar could be connected to all of the upper leaves of the leaf pairs, while the second width adjusting bar could be connected to all of the lower leaves of the leaf pairs. Accordingly, a person skilled in the art would know that regarding the space adjusting transversal bars, they can be connected to the wedge pairs in any possible way that can allow to simultaneously tune the spacing between multiple collimator leaf pairs.

[0039] An embodiment of the way the width adjusting bars and the spacing adjusting transversal bars are connected to the leaf pairs and the wedge pairs can be seen in Fig. 3 and Fig. 6, where a first width adjusting bar 300 can be connected to all the upper leaves of the leaf pairs, and a second width adjusting bar 301 can be connected to all of the lower leaves of the leaf pairs. Regarding the wedge pairs, a first space adjusting transversal bar 600 can be connected to the all of the upper wedges of the wedge pairs which are positioned on the upper leaves of the leaf pairs, and a second space adjusting transversal bar 601 can be connected to all of the upper wedges of an additional set of wedge pairs which are positioned on the upper leaves of the leaf pairs. Other combinations of connecting the width adjusting and space adjusting transversal bars can also be applied, such as connecting the first width adjusting bar to all of the upper leaves of the leaf pair and the second width adjusting bar to all of the upper lower leaves of the leaf pair. This feature can be important, as it can allow the user to tune with high resolution the change in width and spacing of the collimator leaves, by simultaneously controlling a plurality of leaf pairs. It is important that all the leaf pairs and wedge pairs are connected via the same width adjusting or space adjusting transversal bar, since that can allow to create a uniform pattern.

[0040] The variable slit collimator can be further configured, such that the system is configured to adjust a center to center distance of the leaves of the variable slit collimator. In one embodiment, the space adjusting transversal bar which can be connected to the wedges can move in the longitudinal direction and cause the wedge pairs to either decrease or increase their width. That will lead to the center to center distance of the leaves of the variable slit collimator to decrease or increase respectively. An example of this effect can be seen in Fig. 7, where the center to center distance has increased 700. Fig. 7A, B show a plurality of collimator leaves in a variable slit collimator. By moving the space adjusting transversal bars which are connected to the collimator leaves, it can be possible to modify the spacing between adjacent collimator leaves. Moreover, an algorithm could be applied to the system, allowing to calculate the change in the width or the spacing of the leaf pairs, depending on the change in the distance between the width adjusting or space adjusting transversal bars. That feature could be useful for a user of the variable slit collimator, since depending on the size, type or location of the tumor, slight changes on the grid pattern may need to be made. Therefore, a good resolution and prediction system of the final width and spacing of the collimator leaves can be useful.

[0041] The width of the collimator leaves can be approximately 2 mm, and their length could be between 10 and 50 cm. A larger length can be beneficial, as it can allow a larger range of tuning of the width of the leaf pair. In addition, a small width may also be useful, as it can allow the system to have a larger resolution in tuning of the parameters (width of leaf pairs and spacing between adjacent leaf pairs). The wedges can have a width of 2 mm and a length of 5 to 10 cm. Using the same reasoning, it can be beneficial if the wedges have small width and larger length, as this can provide a wider range of tuning of the spacing of the leaf pairs, and it can also increase the resolution.

[0042] The variable slit collimator can be further configured, such that the first collimator leaves and the second collimator leaves are made of a metal, such as tungsten, or a metal alloy. As a person skilled in the art would know, any kind of material that is capable of absorbing or reducing at a high percentage radiation can be used for manufacturing the variable slit collimator. Specifically, many materials can be used to absorb X-ray or gamma-ray radiation, such as lead, brass or any other materials with a high density (high-Z number). For charged particle beams, such as protons, materials with low-atomic number has the advantage of low radioactive activation and low secondary neutron production at the expense of thicker collimator leaves, compared to materials with high atomic number. As a compromise the collimator material may comprise a combination of high density (high-Z) and low density (low-Z) materials, exposing the most energetic part of the incoming beam to the latter. 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 collimator leaves and obtain high contrast between the dose peaks and dose valleys. If the wedges were not manufactured of sufficiently absorbing materials, then the resulting grid pattern would show inferior contrast as the radiation from non-parallel beams could pass through parts of the wedges.

[0043] The variable slit collimator may further comprise a secondary variable slit collimator, wherein the variable slit collimator and the secondary variable slit collimator are cascaded and wherein the secondary variable slit collimator has a slit orientation rotated 90° with respect to the slit orientation of the slit collimator. A person skilled in the art will realize that the slit orientation does not have to be exactly 90° but within a reasonable margin. The variable slit collimator and the secondary variable slit collimator being cascaded means that there are arranged in a parallel configuration wherein a beam from a beam source will have to pass both of them.

[0044] The present disclosure further relates to a variable slit collimator for a spatially fractionated radiotherapy system, comprising a plurality of spaced collimator leaves, a plurality of spacing wedge pairs arranged between the spaced collimator leaves, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element, and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaves of the variable slit collimator.

[0045] The present disclosure further relates to a radiotherapy system comprising at least one radiation source configured to generate a radiation beam, and a variable slit collimator according to any one of the preceding claims. A variety of radiation beams can be used, depending on the characteristics of the tumor and the status of the patient. For example, it might be beneficial to use ion beams, electron beams, or other types of radiation therapies, when a variable spatial geometry is requested. The present disclosure is particularly applicable for proton minibeam radiation therapy, where careful tuning of the collimator parameters is needed in order to maximize contrast outside the planning target volume while having homogenous coverage of the latter. For X-ray radiation, a variable collimator is desirable for e.g. biological research to identify the most optimal geometrical pattern for various tissues. Thus, a conventional gamma-ray or X-ray irradiation system may also be used in combination with the present collimation system, in case certain spatially fractionated patterns should mitigate radiation damage to specific tissues of various organs at risk. Conventional therapy X-ray radiation can be generated by using a linear accelerator, which accelerates electrons. These electrons can collide on a production target within the accelerator, generating bremsstrahlung X-rays. That energy spectrum is used for conventional radiation therapies.

[0046] A proton beam can be generated typically using a cyclotron or a synchrotron, which accelerates protons. The high speed of the protons means high kinetic energy, and this energy makes the protons traverse to the desired depth in the body, where the protons eventually stop. Protons, and any charged particle in general, have the property that the energy loss per distance traversed in any medium, increases as their speed become comparable to that of electrons orbiting the target medium nuclei, which results in a distinct peak in the energy loss per distance traveled. This peak can be utilized to cover a tumour, and offers, a unique advantage of minimizing or even eliminating the dose in normal healthy tissue beyond the tumor.

[0047] One advantage of a spatially fractionated beam is that the detriment on the healthy tissue can be reduced. Proton minibeam radiation is a variant of spatial fractionated therapy which can be generated by segmenting a uniform broad beam into arrays of parallel slatted beamlets that can be spaced less than 0.5-3.5 mm apart. This variant of spatial fragmentation is limited to the healthy tissue, as proton beams gradually scatter throughout the medium due to Coulomb interactions, and at a certain depth, eventually become a homogenous beam. Combining the minibeam therapy with the collimation system of the present disclosure can seamlessly select the most optimal depth by selecting by case to case a specific center-to-center distance, thereby minimizing the damage on the healthy tissue surrounding the tumor, while at the same time obtaining homogenous tumour dose needed for successfully ablating the tumour target. The presently disclosed variable slit collimator may be used as part of a system or method comprising a scanned pencil beam. In such a system the configuration of the variable slit collimator may by adapted as the beam is scanned, actively taking any shape of the planned target volume (i.e. the tumour) into account.

[0048] The present disclosure further relates to a method of controlling a slit collimator in a spatially fractionated radiotherapy system slit, comprising the steps of providing a variable slit collimator comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator; and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves, and using the leaf adjustment mechanism to move the two tapered collimator leaves towards and away from each other to adjust at least the leaf width of the variable slit collimator. The steps of the method described above are sketched in Fig. 8.

[0049] The present disclosure describes one unit of a variable slit collimator used for spatially fractionated radiotherapy. It can be beneficial to include further variable slit collimators, which can be positioned beneath the first one, and they may be rotated at any angle, in order to create a grid pattern. For example, a second variable slit collimator can be positioned beneath the first variable slit collimator, and it can be rotated by 90 degrees around the axis perpendicular to the collimator leaves. That effect could form a square lattice grid pattern, which can be then used for spatially fractionated radiotherapy.

[0050] The variable slit collimator can be further configured, such that the thickness of the collimator leaves on a variable slit 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 collimator leaves depends on the energy of the beam, and the type of the material used for the collimator leaves. For example, for a proton beam of 100 MeV then a brass collimator can have a thickness of 30 mm to 40 mm to effectively stop the primary proton beam. Thick enough collimator leaves can be important, for shaping practical beams, as these are not perfectly parallel, leading to inferior contrast in the normal tissue, since parts of the primary beam could pass through parts of the collimator leaves at oblique angles. For ion beams, multi-material collimator may be an advantage. Such material may comprise initial low-Z material to slow down the ions with little induced radioactivity and secondary neutrons, and then a subsequent high-Z material to shape the remaining low energy part of the charged particles.

[0051] The entire system can be positionally shifted along the lateral direction by one center- to-center distance or more for accurate positioning taking a possible phase shift of the periodic structure into account.

[0052] Further details

[0053] 1. A variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising: a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator; and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves to adjust the leaf width of the variable slit collimator.

[0054] 2. The variable slit collimator according to item 1 , wherein the two tapered collimator leaves comprise a lower leaf having a lower base side and a tapered upper side; and an upper leaf having an upper base side and a tapered lower side.

[0055] 3. The variable slit collimator according to item 2, wherein the tapered upper side of the lower leaf and the tapered lower side of the upper leaf abut each other.

[0056] 4. The variable slit collimator according to any one of items 2-3, wherein the lower base side of the lower leaf and the upper base side of the upper leaf are parallel.

[0057] 5. The variable slit collimator according to any one of the preceding items, wherein the leaf adjustment mechanism comprises a first structure connected to or attached to the tapered collimator leaves.

[0058] 6. The variable slit collimator according to item 5, wherein the first structure comprises one or more transversal width adjusting bars attached to the tapered collimator leaves, wherein the transversal width adjusting bars can be moved along the longitudinal direction of the two tapered collimator leaves to move the two tapered collimator leaves towards and away from each other.

[0059] 7. The variable slit collimator according to any one of the preceding items, further comprising: a plurality of spacing wedge pairs arranged between the collimator leaf pairs, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element; and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaf pairs of the variable slit collimator.

[0060] 8. The variable slit collimator according to item 7, wherein the two tapered wedges comprise a lower wedge having a lower base side and a tapered upper side; and an upper wedge having an upper base side and a tapered lower side.

[0061] 9. The variable slit collimator according to item 8, wherein the lower base side of the lower wedge and the upper base side of the upper wedge are oriented towards and abut the collimator leaf pairs.

[0062] 10. The variable slit collimator according to any one of items 7-9, wherein space adjustment mechanism comprises a second structure connected to or attached to the tapered wedges.

[0063] 11. The variable slit collimator according to item 10, wherein the second structure comprises one or more space adjusting transversal bars attached to the tapered wedges, wherein the space adjusting transversal bars can be moved along the longitudinal direction of the two tapered collimator wedges to move the two tapered wedges towards and away from each other.

[0064] 12. The variable slit collimator according to item 6 or 11 , further comprising an upper rail and / or a lower rail in which the one or more transversal width adjusting bars and / or the one or more space adjusting transversal bars can slide to adjust the leaf width and / or the space between the collimator leaf pairs. 13. The variable slit collimator according to item 12, comprising a first width adjusting bar connected to the all of the lower leaves of the leaf pairs; a second width adjusting bar connected to the all of the upper leaves of the leaf pairs; a first space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on the first collimator leaves; and a second space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on either the first or the second collimator leaves.

[0065] 14. The variable slit collimator according to any one of the preceding items, wherein the system is configured to adjust a center to center distance of the leaves of the variable slit collimator.

[0066] 15. The variable slit collimator according to any one of the preceding items, wherein the system is configured to adjust the leaf width of the plurality of collimator leaf pairs.

[0067] 16. The variable slit collimator according to any one of the preceding items, wherein the first collimator leaves and the second collimator leaves are made of a metal, such as tungsten, or a metal allow.

[0068] 17. The variable slit collimator according to any one of the preceding items, further comprising a secondary variable slit collimator, wherein the variable slit collimator and the secondary variable slit collimator are cascaded and wherein the secondary variable slit collimator has a slit orientation rotated 90° with respect to the slit orientation of the slit collimator.

[0069] 18. A variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising: a plurality of spaced collimator leaves; a plurality of spacing wedge pairs arranged between the spaced collimator leaves, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element; and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaves of the variable slit collimator.

[0070] 19. A radiotherapy system comprising: at least one radiation source configured to generate a radiation beam; and a variable slit collimator according to any one of the preceding items.

[0071] 20. A method of controlling a slit collimator in a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising the steps of: providing a variable slit collimator comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator; and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves; and using the leaf adjustment mechanism to move the two tapered collimator leaves towards and away from each other to adjust at least the leaf width of the variable slit collimator.

Claims

Claims1. A variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising: a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator; and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves to adjust the leaf width of the variable slit collimator.

2. The variable slit collimator according to claim 1 , wherein the two tapered collimator leaves comprise a lower leaf having a lower base side and a tapered upper side; and an upper leaf having an upper base side and a tapered lower side.

3. The variable slit collimator according to claim 2, wherein the tapered upper side of the lower leaf and the tapered lower side of the upper leaf abut each other.

4. The variable slit collimator according to any one of claims 2-3, wherein the lower base side of the lower leaf and the upper base side of the upper leaf are parallel.

5. The variable slit collimator according to any one of the preceding claims, wherein the leaf adjustment mechanism comprises a first structure connected to or attached to the tapered collimator leaves.

6. The variable slit collimator according to claim 5, wherein the first structure comprises one or more transversal width adjusting bars attached to the tapered collimator leaves, wherein the transversal width adjusting bars can be moved along the longitudinal direction of the two tapered collimator leaves to move the two tapered collimator leaves towards and away from each other.

7. The variable slit collimator according to any one of the preceding claims, further comprising:a plurality of spacing wedge pairs arranged between the collimator leaf pairs, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element; and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaf pairs of the variable slit collimator.

8. The variable slit collimator according to claim 7, wherein the two tapered wedges comprise a lower wedge having a lower base side and a tapered upper side; and an upper wedge having an upper base side and a tapered lower side.

9. The variable slit collimator according to claim 8, wherein the lower base side of the lower wedge and the upper base side of the upper wedge are oriented towards and abut the collimator leaf pairs.

10. The variable slit collimator according to any one of claims 7-9, wherein space adjustment mechanism comprises a second structure connected to or attached to the tapered wedges.

11. The variable slit collimator according to claim 10, wherein the second structure comprises one or more space adjusting transversal bars attached to the tapered wedges, wherein the space adjusting transversal bars can be moved along the longitudinal direction of the two tapered collimator wedges to move the two tapered wedges towards and away from each other.

12. The variable slit collimator according to claim 6 or 11 , further comprising an upper rail and / or a lower rail in which the one or more transversal width adjusting bars and / or the one or more space adjusting transversal bars can slide to adjust the leaf width and / or the space between the collimator leaf pairs.

13. The variable slit collimator according to claim 12, comprising a first width adjusting bar connected to the all of the lower leaves of the leaf pairs; a second width adjusting bar connected to the all of the upper leaves of the leaf pairs; a first space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on the first collimator leaves; and asecond space adjusting transversal bar connected to all of the either upper or lower wedges of the wedge pairs positioned on either the first or the second collimator leaves.

14. A variable slit collimator for a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising: a plurality of spaced collimator leaves; a plurality of spacing wedge pairs arranged between the spaced collimator leaves, each spacing wedge pair comprising two tapered wedges abutting each other to form a spacing element; and a space adjustment mechanism for moving the two tapered wedges towards and away from each other to adjust the space between the collimator leaves of the variable slit collimator.

15. A method of controlling a slit collimator in a radiotherapy system, such as a spatially fractionated radiotherapy system, comprising the steps of: providing a variable slit collimator comprising a plurality of collimator leaf pairs, each collimator leaf pair comprising two tapered collimator leaves abutting each other to form a leaf of the variable slit collimator; and a leaf adjustment mechanism for moving the two tapered collimator leaves towards and away from each other in a longitudinal direction of the two tapered collimator leaves; and using the leaf adjustment mechanism to move the two tapered collimator leaves towards and away from each other to adjust at least the leaf width of the variable slit collimator.

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