Particle therapy device and method of tuning the position of a charged particle beam in the device

Abstract

A particle therapy device and a method of tuning a position of a charged particle beam in the device. The device is configured to scan a charged particle beam over a target according to a predefined treatment field covering a treatment surface in an isocenter plane of the device. The device is capable of scanning the beam over an accessible surface covering and larger than the treatment surface. A beam stopper is arranged downstream of a scanning magnet of the device at a position preventing the beam from reaching at least a portion of the accessible surface and allowing the beam to reach any portion of the treatment surface. A control system is configured to control the device to direct the beam to the beam stopper and simultaneously measure a position of the beam, calculate a difference between a desired position and a measured position of the beam when the beam is directed to the beam stopper, and scan the beam over the target according to the predefined treatment field by taking into account the calculated difference.

Description

TECHNICAL FIELD

[0001] The present invention relates to an apparatus and method for tuning the position of a charged particle beam, and more in particular to an apparatus and method for tuning the position of a charged particle beam in a charged particle beam therapy device. BACKGROUND

[0002] Charged particle beam therapy devices for treating a target such as a tumor in a patient's body using such a charged particle beam are known for many years. It is also known that the position of the charged particle beam has to be tuned so that it corresponds to the desired position when irradiating the target using the beam.

[0003] This tuning is even more relevant when the particle beam is scanned over the target.

[0004] Pencil beam scanning (hereinafter PBS) for example uses a tuning point to ensure the correct alignment of the pencil beam for each layer of the target to be irradiated. To do this, a "tuning" cycle is used. The tuning cycle checks the position of the un-scanned beam on the ionization chamber (IC) and calculates the offset to apply to the scanning magnet in order to achieve the correct absolute point positioning at the isocenter.

[0005] The method described in EP2552545B1 uses a PBS scanning algorithm that selects the tuning point on each target layer by finding the highest dose point within the layer and irradiates this point with as low dose as possible while checking the position of the beam on the ionization chamber. From the position measured on the ionization chamber, it is possible to geometrically determine / calculate where the point falls within the target volume. A correction is then made to the scanning magnet, the point is irradiated again and the position of the beam on the ionization chamber is checked again. This process is called a tuning cycle. All the dose delivered for this tuning point during the tuning cycle is measured and subtracted from the dose of the point to ensure that the desired dose determination of the point is adhered to. As stated in EP2252545B1 paragraph 57, "by using the irradiation apparatus and method of the invention, it is not necessary to insert a beam stop between the irradiation unit and the target during the tuning phase." This is a real advantage because there is a time gain in controlling the beam position and because the therapy machine also remains simple. However, this method is not applicable when a high dose rate of dose is delivered to the target in a single scan, for example using FLASH irradiation techniques.

[0006] With FLASH treatment, a single scan of the beam at very high dose rate is performed on a ridge filter to irradiate the target volume in one shot. If the conventional PBS tuning cycle described above is to be deployed, this would proportionally mean that the tuning point dose will be much higher, as the higher dose rate will deliver proportionally more dose in a given time. This higher dose tuning point will further reduce the dose rate of the PBS field and risk negating the FLASH effect. Reducing the dose rate during the tuning point is suboptimal as the tuning will be performed at beamline conditions different from those used during treatment beam delivery and the outcome of the tuning can not transfer from one beamline state to the other.

[0007] In the prior art, alternative methods for beam position control have been proposed.

[0008] EP2833970B1 describes for example a method in which beam position correction data can be introduced into the beam steering data set or automatically after running a test irradiation data set independent of the treatment. This method proposes a beam position correction model which is developed after testing the treatment machine before the treatment of a patient, thus requiring time which cannot be used for the treatment of a patient.

[0009] US10195465B2 relates to a system for providing real-time correction of the position of a charged particle beam. This system can be used when a patient is in a treatment position at the isocenter, for example during a medical treatment. In this case, a movable beam stop is provided between a detector device and a scanning magnet. The beam stop can block the beam from reaching the patient during retuning / correction / setup without having to move the patient and allow the beam to pass and reach the patient when the retuning / correction / setup is completed, for example to provide treatment to the patient. For example, the beam stop can be a solid object that moves perpendicular to the beam in the X or Y direction, like a swing or a guillotine. The measurement of the beam position and the correction of the deflector are done before the scanning magnet. However, this solution is not adapted to take into account the position errors that can be introduced by the scanning magnet. It is also complex and expensive due to the need to move the beam stop, the movement of which can also be affected by malfunctions, in which case an incorrect dose can be delivered to the patient. SUMMARY

[0010] It is an object of the present invention to solve the problems of the prior art devices and methods to tune the position of a charged particle beam in a particle therapy device.

[0011] The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

[0012] According to the invention, there is provided a particle therapy device comprising:

[0013] - a particle accelerator for delivering a charged particle beam;

[0014] - a beam transport system for delivering the charged particle beam according to a main beam axis (Z) to a target in an isocenter plane perpendicular to the main beam axis (Z);

[0015] - a scanning magnet for scanning the charged particle beam over the target;

[0016] - a beam position detector arranged downstream of the scanning magnet and adapted to detect an X position and a Y position of the charged particle beam when the charged particle beam passes through the detector;

[0017] - a beam stopper arranged downstream of the beam position detector, the beam stopper being adapted to stop the charged particle beam when the charged particle beam hits the beam stopper;

[0018] - a control system configured to drive the scanning magnet to scan the charged particle beam over the target according to a predefined treatment field covering a treatment surface in the isocenter plane, the control system further being able to drive the scanning magnet to scan the charged particle beam according to an accessible field covering an accessible surface in the isocenter plane, the accessible surface covering and being larger than the treatment surface.

[0019] The beam stopper is arranged at a position preventing the charged particle beam from reaching at least a part of the accessible surface and allowing the charged particle beam to reach any part of the treatment surface.

[0020] The control system is configured to control the particle therapy device:

[0021] - to direct the charged particle beam to the beam stopper and, simultaneously, to measure the X position and the Y position of the charged particle beam by using the beam position detector,

[0022] - to calculate a difference between a desired X position and a desired Y position of the charged particle beam and a measured X position and a measured Y position of the charged particle beam when the charged particle beam is directed to the beam stopper, respectively, and

[0023] - to scan the charged particle beam over the target according to the predefined treatment field by taking into account the calculated difference.

[0024] In fact, since the beam stopper is located downstream of the scanning magnet, the device according to the invention is adapted to take into account beam position errors that can be introduced by the scanning magnet.

[0025] Moreover, since the beam stopper is arranged at a position preventing the charged particle beam from reaching at least a part of the accessible surface and allowing the charged particle beam to reach any part of the treatment surface, it is not necessary to remove the beam stopper in order to irradiate the target using the treatment field, thereby saving treatment time.

[0026] Furthermore, the device according to the invention is well suited for FLASH treatment, because the beam position tuning step has no or little impact on the dose delivered to the target during treatment.

[0027] In some examples, the control system is configured to control the particle therapy device to scan the charged particle beam over the target according to the predefined treatment field by correcting the beam position according to a difference between the desired X position and Y position of the charged particle beam and the measured X position and Y position of the charged particle beam when directed to the beam stopper.

[0028] In some examples, the beam stopper remains in place while the charged particle beam is scanned over the target according to the predefined treatment field.

[0029] Hence, the time of the patient treatment is saved and the device is also more reliable since the beam stopper is not moved. The beam stopper not being moved makes the device also safer since it eliminates or mitigates the risk of the beam stopper being positioned incorrectly after having been moved.

[0030] In some examples, the beam stopper is arranged as close as possible to the main beam axis (Z), which allows for a more accurate tuning of the beam position.

[0031] In some examples, the particle accelerator is a cyclotron or a synchrotron.

[0032] In some examples, the charged particle beam is a proton beam or a carbon ion beam.

[0033] It is noted that, as with conventional particle therapy devices, the X and Y axes form an orthogonal reference with the Z axis.

[0034] The invention also relates to a method for tuning the position of a charged particle beam in a particle therapy device. BRIEF DESCRIPTION OF DRAWINGS

[0035] These and other aspects of the invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings, in which:

[0036] Figure 1 An exemplary device according to the invention is schematically illustrated;

[0037] Figure 2 A cross-section of an exemplary beam shaping apparatus comprising a beam stopper according to the invention is schematically illustrated.

[0038] The drawings are not drawn to scale nor are they in proportion. Generally, like or similar parts are indicated by the same reference numbers throughout the drawings. DETAILED DESCRIPTION

[0039] Figure 1An exemplary particle therapy device according to the present application is schematically shown. The device comprises a particle accelerator, for example a cyclotron or a synchrotron, to deliver a charged particle beam, for example a proton beam or a carbon ion beam.

[0040] The device further comprises a beam transport system for delivering the charged particle beam to a target in an isocenter plane perpendicular to a main beam axis (Z) according to the main beam axis (Z). The target is for example a tumor of a patient to be treated.

[0041] The device further comprises a scanning magnet for scanning the charged particle beam over the target, a beam position detector arranged downstream of the scanning magnet and adapted to detect an X position and a Y position of the charged particle beam when the charged particle beam passes the beam position detector, a beam stop arranged downstream of the beam position detector and adapted to stop the charged particle beam when the charged particle beam hits the beam stop, and a control system configured to drive the scanning magnet to scan the charged particle beam over the target according to a predefined treatment field covering a treatment surface in the isocenter plane. The control system is further capable of driving the scanning magnet to scan the charged particle beam according to an accessible field covering an accessible surface in the isocenter plane, the accessible surface covering and being larger than the treatment surface.

[0042] The accessible surface is a surface in the isocenter plane to which the device is capable of directing the particle beam by driving its scanning magnet according to the X direction and the Y direction. The accessible surface is for example a largest surface in the isocenter plane to which the device is capable of directing the particle beam by driving its scanning magnet according to the X direction and the Y direction.

[0043] For example, if we consider a conventional proton therapy device using a pencil beam scanning (PBS) irradiation method, the scanning magnet within the nozzle of such a device has the ability to deliver a pencil beam spot at any position within an accessible surface of up to 400 mm by 300 mm when projected at the isocenter in the treatment room. However, the largest treatment surface for flash therapy using such a device can be smaller, for example 80 mm by 80 mm.

[0044] Such a device is known per se in the art and will therefore not be described further. The particularity of the present application lies in the position of the beam stop and the way in which the beam position tuning is performed, which will be explained in detail hereinafter.

[0045] As Figure 1 shown, the position of the beam stop prevents the charged particle beam from reaching at least a part of the accessible surface and allows the charged particle beam to reach any part of the treatment surface. To understand this expression, Figure 1A projection of the reachable surface (22') and a projection of the treatment surface are shown, both projections being on a plane perpendicular to the main beam axis (Z), i.e. the plane in which the beam stop is located (hereinafter referred to as the blocking plane), the projections being according to different beam directions when the beam is scanned in the X- and Y-directions. Further as Figure 1 shown, the beam stop is arranged at a position in the projection of the reachable surface in the blocking plane, but not in the projection of the treatment surface. Thus, when the particle beam is directed to the beam stop, it will stop the beam and the beam will not reach the target. However, when the particle beam is directed to any point of the treatment surface, it will not be stopped by the beam stop and the beam will reach the target to perform the treatment.

[0046] The beam stop can be a piece of metal, e.g. brass.

[0047] The control system is configured to control the particle therapy device to direct the charged particle beam to the beam stop and at the same time to measure the X- and Y-positions of the charged particle beam by using the beam position probe, to calculate a difference (or deviation) between the desired (or planned) X- and Y-positions of the charged particle beam and the measured X- and Y-positions of the charged particle beam when directed to the beam stop, and to scan the charged particle beam on the target according to the predefined treatment field by taking into account the calculated difference (or deviation).

[0048] In some examples, the control system is configured to control the particle therapy device to scan the charged particle beam on the target according to the predefined treatment field by correcting the beam position according to the difference between the desired X- and Y-positions of the charged particle beam and the measured X- and Y-positions of the charged particle beam when directed to the beam stop, respectively.

[0049] If the desired or planned X-position of the beam is e.g. 125 (virtual value) and the measured X-position of the beam when directed to the beam stop is e.g. 130 (virtual value), the control system can correct the magnetic settings of the X-scan magnet to compensate for this difference, in particular to eliminate or reduce the difference between the two values. The same applies to the Y-position of the beam and the Y-scan magnet.

[0050] Once the difference or deviation between the desired X- and Y-positions of the charged particle beam and the measured X- and Y-positions of the charged particle beam from the reference point (here the position of the beam stop), respectively, is known, the correction to be applied to the X- and Y-scan magnets is generally known in the art, e.g. from EP 2552545 B1, which is incorporated herein by reference.

[0051] In some examples, the beam stop remains in place while the charged particle beam is scanned on the target according to the predefined treatment field when the device is in operation.

[0052] In some examples, the beam stopper is arranged as close as possible to the main beam axis (Z), of course without overlapping with the projection (21 ') of the treatment surface on the blocking plane. Typically, the main beam axis (Z) is the axis of the unscanned particle beam, i.e. when the beam passes through the isocenter, for example as shown in Figure 1

[0053] The beam stopper can be arranged at any position in the longitudinal direction (along the beam path) between the detector and the target. Preferably, the beam stopper is part of or mounted on the device.

[0054] In some examples, the treatment device comprises a beam shaping device arranged downstream of the beam position detector. The beam shaping device can for example be a ridge filter, and / or a range shifter, and / or a compensator, and / or a collimator, which are generally known in the art and used to shape and / or modulate the particle beam before it reaches the target.

[0055] In some examples, the beam stopper is an integral part of or attached to the beam shaping device or to one of the beam shaping devices, preferably removably attached to the beam shaping device or to one of the beam shaping devices.

[0056] In some examples, the beam stopper is placed in a fitting holder which is fixed to a part of the particle therapy device, preferably to the nozzle of the particle therapy device.

[0057] In some examples, the beam shaping device comprises a ridge filter and a collimator, the collimator being preferably arranged downstream of the ridge filter. In this case, the beam stopper is for example an integral part of or attached to the collimator, preferably removably attached to the collimator.

[0058] In some examples, the collimator has a ring shape, for example as disclosed in EP2532385B1. In this case, the beam stopper can for example be part of this collimator or placed near the outer lateral surface of the collimator. Figure 2 ​A cross-section of an exemplary collimator (40) comprising a beam stop according to the present application is schematically shown. The collimator has an annular shape with a central opening (aperture) whose shape depends on the shape of the target and which defines the passage of the particle beam to the target during treatment. In the present example, the beam stop has the shape of a "bump" of the collimator ring. The bump preferably has a diameter of at least 10*sigma, so that when the particle beam hits the center of the bump, the particle beam will be stopped by the bump. In general, to account for possible errors on the beam position before tuning position, the size of the beam stop should preferably have a sufficient margin compared to the size of the beam spot at the position of the beam stop. Thus, the size of the beam stop is preferably chosen according to the size of the beam spot foreseen by the treatment plan.

[0059] In some examples, the control system is configured to control the particle device to deliver a predefined treatment field to the target by scanning the charged particle beam over the target in a single scan.

[0060] The present application also relates to a method for tuning the position of a charged particle beam in a particle therapy device, the particle device (1) comprising:

[0061] - a particle accelerator (2) for delivering a charged particle beam;

[0062] - a beam transport system (4) for delivering the charged particle beam according to a main beam axis (Z) to a target (50) in an isocenter plane (11) perpendicular to the main beam axis (Z);

[0063] - a scanning magnet (5) for scanning the charged particle beam over the target;

[0064] - a beam position detector (6) arranged downstream of the scanning magnet and adapted to detect an X position and a Y position of the charged particle beam when the charged particle beam passes through the detector;

[0065] - a beam stop (10) arranged downstream of the beam position detector, the beam stop being adapted to stop the charged particle beam when the charged particle beam hits the beam stop;

[0066] - a control system (20) configured to drive the scanning magnet to scan the charged particle beam over the target according to a predefined treatment field covering a treatment surface (21) in the isocenter plane (11), the control system further being able to drive the scanning magnet to scan the charged particle beam according to an accessible field covering an accessible surface (22) in the isocenter plane (11), the accessible surface (22) covering and being larger than the treatment surface (21),

[0067] The method comprises the following steps:

[0068] - placing a beam stopper (10) at a position preventing the charged particle beam from reaching at least a part of the accessible surface (22) and allowing the charged particle beam to reach any part of the treatment surface (21),

[0069] - directing the charged particle beam to the beam stopper and simultaneously measuring the X position and the Y position of the charged particle beam by using a beam position probe,

[0070] - calculating a difference between a desired X position and a desired Y position of the charged particle beam and a measured X position and a measured Y position of the charged particle beam when the charged particle beam is directed to the beam stopper,

[0071] - applying a correction to the magnetic settings of the X scan magnet and the Y scan magnet by taking into account the calculated difference between the desired X position and the desired Y position of the charged particle beam and the measured X position and the measured Y position of the charged particle beam when directed to the beam stopper.

[0072] The application has been described in terms of specific embodiments which are illustrative only and not to be construed as limiting the application. More generally, those skilled in the art will appreciate the application is not limited to what has been particularly shown and / or described above.

[0073] The use of the verb "comprise" "comprise" "comprise" or any other variant thereof, and their respective conjugations, does not exclude the presence of elements other than those mentioned in the claim.

[0074] The use of the words "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0075] The use of the words "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

[0076] The application can also be described as follows: a particle therapy device configured to scan a charged particle beam over a target according to a predefined treatment field covering a treatment surface in the isocenter plane of the device. The device is capable of scanning the beam over an accessible surface covering and larger than the treatment surface. A beam stopper is arranged downstream of the scanning magnets of the device at a position preventing the beam from reaching at least a part of the accessible surface and allowing the beam to reach any part of the treatment surface. A control system is configured to control the device to direct the beam to the beam stopper and simultaneously measure the position of the beam, calculate a difference between a desired position and a measured position of the beam when directed to the beam stopper, and scan the beam over the target according to the predefined treatment field by taking into account the calculated difference.

Claims

1. A particle therapy device, comprising - a particle accelerator (2) for delivering a charged particle beam; - a beam transport system (4) for delivering the charged particle beam according to a main beam axis (Z) to a target (50) in an isocenter plane (11) perpendicular to the main beam axis (Z); - a scanning magnet (5) for scanning the charged particle beam over the target; - a beam position detector (6) arranged downstream of the scanning magnet and adapted to detect an X position and a Y position of the charged particle beam when the charged particle beam passes through the beam position detector (6); - a beam stopper (10) arranged downstream of the beam position detector, the beam stopper being adapted to stop the charged particle beam when the charged particle beam hits the beam stopper; - a control system (20) configured to drive the scanning magnet to scan the charged particle beam over the target according to a predefined treatment field covering a treatment surface (21) in the iso-center plane (11), the control system further being able to drive the scanning magnet to scan the charged particle beam according to an accessible field covering an accessible surface (22) in the iso-center plane (11), the accessible surface (22) covering and being larger than the treatment surface (21), wherein, the beam stopper (10) being arranged at a position that prevents the charged particle beam from reaching at least a part of the reachable surface (22) and that allows the charged particle beam to reach any part of the treatment surface (21), and wherein the control system is configured to control the particle therapy device: - to direct the charged particle beam to the beam stopper and simultaneously to measure the X position and the Y position of the charged particle beam by using the beam position detector, - to calculate a difference between a desired X position and a desired Y position of the charged particle beam and a measured X position and a measured Y position of the charged particle beam when directed to the beam stopper, respectively, - to scan the charged particle beam over the target according to the predefined treatment field by taking into account the calculated difference.

2. The particle therapy device of claim 1, wherein, The control system is configured to control the particle therapy device to scan the charged particle beam over the target according to the predefined treatment field by correcting the beam position according to the difference between the desired X position and the desired Y position of the charged particle beam and the measured X position and the measured Y position of the charged particle beam when directed to the beam stopper.

3. The particle therapy device of claim 1, wherein, When in operation, the beam stopper remains in place while the charged particle beam is scanned over the target according to the predefined treatment field.

4. The particle therapy device of any one of claims 1 to 3, wherein, The beam stopper is arranged as close as possible to the main beam axis (Z).

5. The particle therapy device of claim 1, further comprising a beam shaping device arranged downstream of the beam position detector.

6. The particle therapy device of claim 5, wherein, The beam shaping device comprises a ridge filter, and / or a range shifter, and / or a compensator, and / or a collimator.

7. The particle therapy device of claim 5, wherein, The beam stopper is an integral part of the beam shaping device or of one of the beam shaping devices, or is attached to the beam shaping device or to one of the beam shaping devices.

8. The particle therapy device of claim 1, wherein, The beam stopper is placed in a fitting holder that is fixed to a part of the particle therapy device, preferably to a nozzle of the particle therapy device.

9. The particle therapy device of claim 5, wherein, The beam shaping device comprises a ridge filter and a collimator, the collimator being preferably arranged downstream of the ridge filter.

10. The particle therapy device of claim 9, wherein, The beam stopper is an integral part of the collimator or is attached to the collimator.

11. The particle therapy device of claim 10, wherein, The collimator has a ring shape.

12. The particle therapy device of claim 1, wherein, The control system is configured to control the particle therapy device to deliver the predefined treatment field to the target by scanning the charged particle beam over the target in a single scan.

13. The particle therapy device of claim 1, wherein, The particle accelerator is a cyclotron or a synchrotron.

14. The particle therapy device of claim 1, wherein, The charged particle beam is a proton beam or a carbon ion beam.

15. A method for tuning the position of a charged particle beam in a particle therapy device, the particle therapy device comprising: - a particle accelerator (2) for delivering the charged particle beam; - a beam transport system (4) for delivering the charged particle beam to a target (50) in an isocenter plane (11) perpendicular to a main beam axis (Z) according to the main beam axis (Z); - a scanning magnet (5) for scanning the charged particle beam over the target; - a beam position detector (6) arranged downstream of the scanning magnet and adapted to detect the X and Y positions of the charged particle beam when the charged particle beam passes through the beam position detector (6); - a beam stopper (10) arranged downstream of the beam position detector, the beam stopper being adapted to stop the charged particle beam when the charged particle beam hits the beam stopper; - a control system (20) configured to drive the scanning magnet to scan the charged particle beam over the target according to a predefined treatment field covering a treatment surface (21) in the isocenter plane (11), the control system further being able to drive the scanning magnet to scan the charged particle beam according to an accessible field covering an accessible surface (22) in the isocenter plane (11), the accessible surface (22) covering and being larger than the treatment surface (21), wherein the method comprises the steps of: - placing the beam stopper (10) at a position preventing the charged particle beam from reaching at least a part of the accessible surface (22) and allowing the charged particle beam to reach any part of the treatment surface (21), - directing the charged particle beam to the beam stopper and simultaneously measuring the X and Y positions of the charged particle beam by using the beam position detector, - calculating the difference between the desired X and Y positions of the charged particle beam and the measured X and Y positions of the charged particle beam when directed to the beam stopper, respectively, - applying a correction to the magnetic settings of the X and Y scanning magnets by taking into account the calculated difference between the desired X and Y positions of the charged particle beam and the measured X and Y positions of the charged particle beam when directed to the beam stopper.

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