PARTICLE BEAM GUIDING SYSTEM AND RELATED RADIOTHERAPY SYSTEM

Abstract

A particle beam guiding system (1a, 1b, 1c) for receiving an incoming particle beam (6a, 6b, 6c) along an incoming trajectory (T1) and controlling an exit energy level and an exit trajectory (T3) of the particle beam, wherein the particle beam guiding system comprises an attenuator (22) for adjusting the energy level of the particle beam; a first beam guide (26) positioned downstream of the attenuator, comprising first and second guiding dipoles, each comprising two magnets for creating magnetic fields for deflecting the particle beam from the incoming trajectory into an intermediate trajectory (T2), wherein the first dipole of the first beam guide is arranged to deflect the particle beam in a first plane, and the second dipole of the first beam guide is arranged to deflect the particle beam in a second plane which is orthogonal to the first plane; and a second beam guide (28) positioned downstream of the first beam guide, comprising first and second guiding dipoles, each comprising two magnets for creating magnetic fields for deflecting the particle beam from the intermediate trajectory into the exit trajectory, wherein the first dipole of the second beam guide is arranged to deflect the particle beam in a first plane and the second dipole of the second beam guide is arranged to deflect the particle beam in a second plane which is orthogonal to the first plane. A radiotherapy system comprising such particle beam guiding systems is also disclosed.

Claims

1. A particle beam guiding system (1a, 1b, 1c) for receiving an incoming particle beam (6a, 6b, 6c) along an incoming trajectory (T1) and controlling an exit energy level and an exit trajectory (T3) of the particle beam (6a, 6b, 6c), wherein the particle beam guiding system (1a, 1b, 1c) comprises: an attenuator (22) for adjusting the energy level of the particle beam (6a, 6b, 6c); a first beam guide (26) positioned downstream of the attenuator (22), comprising first and second guiding dipoles (26a, 26b), each comprising two magnets for creating magnetic fields for deflecting the particle beam (6a, 6b, 6c) from the incoming trajectory (T1) into an intermediate trajectory (T2), wherein the first dipole (26a) of the first beam guide (26) is arranged to deflect the particle beam (6a, 6b, 6c) in a first plane, and the second dipole (26b) of the first beam guide (26) is arranged to deflect the particle beam (6a, 6b, 6c) in a second plane which is orthogonal to the first plane; a second beam guide (28) positioned downstream of the first beam guide (26), comprising first and second guiding dipoles (28a, 28b), each comprising two magnets for creating magnetic fields for deflecting the particle beam (6a, 6b, 6c) from the intermediate trajectory (T2) into the exit trajectory (T3), wherein the first dipole (28a) of the second beam guide (28) is arranged to deflect the particle beam (6a, 6b, 6c) in a third plane and the second dipole (28b) of the second beam guide (28) is arranged to deflect the particle beam (6a, 6b, 6c) in a fourth plane which is orthogonal to the third plane; and a beam trajectory monitoring and control unit (30) positioned downstream of the second beam guide (28) and arranged for controlling the intended exit trajectory (T3), wherein the beam trajectory monitoring and control unit (30) comprises first and second beam trajectory control disks (30a, 30b) of a particle beam attenuating material, each being individually movable in individual, parallel planes which are orthogonal to the incoming trajectory (T1), and each displaying an opening (31a, 31b), the alignment of which openings (31a, 31b) defines the intended exit trajectory (T3).

2. The particle beam guiding system (1a, 1b, 1c) according to claim 1, wherein the gap between the first and second beam guides (26, 28) is within the range of 30 to 150 cm.

3. The particle beam guiding system (1a, 1b, 1c) according to any one of the preceding claims, wherein the particle beam guiding system (1a, 1b, 1c) comprises: a focusing unit (24) positioned downstream of the attenuator (22) and upstream of the first beam guide (26), comprising a set of magnets (24a, 24b) forming focusing quadrupoles for focusing the particle beam (6a, 6b, 6c).

4. The particle beam guiding system (1a, 1b, 1c) according to any one of the preceding claims, wherein the attenuator (22) comprises: a pair of sliding wedges (22a, 22b) which can be moved towards or away from each other in order to increase or decrease the amount of attenuating material in the path of the particle beam (6a, 6b, 6c).

5. The particle beam guiding system (1a, 1b, 1c) according to any one of the preceding claims, wherein the magnets of the first and second beam guides (26, 28) are superconductive magnets.

6. A radiotherapy system comprising: a plurality of particle beam guiding systems (1a, 1b, 1c) according to any one of the preceding claims, each particle beam guiding system (1a, 1b, 1c) being arranged for receiving an incoming particle beam (6a, 6b, 6c) along an incoming trajectory (T1) and controlling an exit energy level and an exit trajectory (T3) of the particle beam (6a, 6b, 6c) towards a three-dimensional radiation target (3) located inside the body of a radiotherapy patient (4); an imaging system (2) arranged to monitor the position and orientation in space of the three-dimensional radiation target (3), including direction and speed of any movement of the radiation target, and also to monitor tissue characteristics of body tissue (5) surrounding the radiation target (3) located in the radiation paths of the particle beams (6a, 6b, 6c); a particle beam control system (7) which, during a radiation treatment session: receives information on the position and orientation of the radiation target (3) and on said tissue characteristics from the imaging system (2); based on the received information on said tissue characteristics, identifies body tissue (5) which shall not be exposed to the particle beams (6a, 6b, 6c); and in response to movement of the radiation target (3) and/or of body tissue (5) surrounding the radiation target (3), controls the particle beam guiding systems (1a, 1b, 1c) so that: (i) Bragg peaks of the particle beams (6a, 6b, 6c) are brought to intersect in a predetermined beam intersect region (8) inside the radiation target (3); and (ii) the radiation paths of the particle beams (6a, 6b, 6c) do not travel through said body tissue identified as not to be exposed to the particle beams (6a, 6b, 6c).

7. The radiotherapy system according to claim 6, wherein the particle beam control system (7) is arranged to update setpoint values for the exit energy level and the exit trajectory (T3), and to send control signals to said plurality of particle beam guiding systems (1a, 1b, 1c) to effectuate the setpoint values, at an interval within the range of 0.1 to 0.05 seconds.

8. The radiotherapy system according to any one of claims 6 and 7, characterised in that the imaging system comprises any one of an X-ray computed tomography imaging system, a magnetic resonance imaging system, an ultrasound imaging system, a proton computed tomography imaging system and a positron emission tomography imaging system.

9. The radiotherapy system according to any one of claims 6-8, characterised in that the particle beam control system (7), during a radiation treatment session, is arranged to lock the beam intersect region (8) to a predetermined position within the radiation target (3).

10. The radiotherapy system according to any one of claims 6-8, characterised in that the particle beam control system (7), during a radiation treatment session, is arranged to sweep the beam intersect region (8) across the radiation target (3) along a predetermined path.

11. The radiotherapy system according to any one of claims 6-8, characterised in that the particle beam control system (7), during a radiation treatment session, is arranged to stepwise reposition the beam intersect region (8) to predetermined position within the radiation target (3).

12. The radiotherapy system according to any one of claims 6-11, characterised in that the particle beams are proton beams.

13. A method of controlling, in a particle beam guiding system (1a, 1b, 1c), an exit energy level and an exit trajectory (T3) of a particle beam (6a, 6b, 6c), the method comprising the steps of: receiving, in the particle beam guiding system (1a, 1b, 1c), an incoming particle beam (6a, 6b, 6c) along an incoming trajectory (T1); adjusting the energy level of the particle beam (6a, 6b, 6c) in an attenuator (22) of the particle beam guiding system (1a, 1b, 1c); deflecting the particle beam (6a, 6b, 6c) from the incoming trajectory (T1) into an intermediate trajectory (T2) using a first beam guide (26) of the particle beam guiding system (1a, 1b, 1c) positioned downstream of the attenuator (22), the first beam guide (26) comprising first and second guiding dipoles (26a, 26b), each comprising two magnets for creating magnetic fields for deflecting the particle beam (6a, 6b, 6c) from the incoming trajectory (T1) into the intermediate trajectory (T2), wherein the first dipole (26a) of the first beam guide (26) is arranged for deflecting the particle beam (6a, 6b, 6c) in a first plane, and the second dipole (26b) of the first beam guide (26) is arranged for deflecting the particle beam (6a, 6b, 6c) in a second plane which is orthogonal to the first plane; deflecting the particle beam (6a, 6b, 6c) from the intermediate trajectory (T2) into the exit trajectory (T3) using a second beam guide (28) of the particle beam guiding system (1a, 1b, 1c) positioned downstream of the first beam guide (26), the second beam guide (28) comprising first and second guiding dipoles (28a, 28b), each comprising two magnets for creating magnetic fields for deflecting the particle beam (6a, 6b, 6c) from the intermediate trajectory (T2) into the exit trajectory (T3), wherein the first dipole (28a) of the second beam guide (28) is arranged for deflecting the particle beam (6a, 6b, 6c) in a third plane and the second dipole (28b) of the second beam guide (28) is arranged for deflecting the particle beam (6a, 6b, 6c) in a fourth plane which is orthogonal to the third plane; and controlling the intended exit trajectory (T3) using a beam trajectory monitoring and control unit (30) of the particle beam guiding system (1a, 1b, 1c) positioned downstream of the second beam guide (28), wherein the beam trajectory monitoring and control unit (30) comprises first and second beam trajectory control disks (30a, 30b) of a particle beam attenuating material, each being individually movable in individual, parallel planes which are orthogonal to the incoming trajectory (T1), and each displaying an opening (31a, 31b), the alignment of which openings (31a, 31b) defines the intended exit trajectory (T3).

14. The method according to claim 13, comprising the step of: focusing the particle beam (6a, 6b, 6c) using a focusing unit (24) of the particle beam guiding system (1a, 1b, 1c) positioned downstream of the attenuator (22) and upstream of the first beam guide (26), wherein the focusing unit (24) comprises a set of magnets (24a, 24b) forming focusing quadrupoles for focusing the particle beam (6a, 6b, 6c).

15. The method according to any one of claims 13 and 14, wherein the step of adjusting the energy level of the particle beam (6a, 6b, 6c) in the attenuator (22) comprises: moving a pair of sliding wedges (22a, 22b) in the attenuator (22) towards or away from each other in order to increase or decrease the amount of attenuating material in the path of the particle beam (6a, 6b, 6c).

Description

DESCRIPTION OF THE DRAWINGS

[0073] FIG. 1 illustrates Bragg peaks of three different particle beams.

[0074] FIGS. 2 and 3 show an embodiment of a radiotherapy system according to the invention.

[0075] FIGS. 4 and 5 shows schematically a particle beam guiding system according to the invention.

[0076] FIG. 6 illustrates particle beam bending.

[0077] FIGS. 7a and 7b show angle of bending as a function of applied magnetic field in a particle beam guiding sub-system.

DETAILED DESCRIPTION

[0078] When a charged particle moves through matter, it ionizes atoms of the material and deposits a dose along its path. As the velocity of the charged particle decreases, the deposited energy increases. For protons, a-rays, and other ion rays, the deposited energy peaks immediately before the particles come to rest and, consequently, if the energy loss of such ionizing radiation is plotted as a function of distance travelled through matter, the resulting curve will display a pronounced peak, as so-called Bragg peak, immediately before the deposited energy becomes zero.

[0079] This is illustrated in FIG. 1 which discloses Bragg peaks from three different particle beams.

[0080] FIGS. 2 and 3 disclose an embodiment of a radiotherapy system according to the invention. The radiotherapy system comprises a plurality of particle beam guiding systems 1a-1c which are arranged to radiate particle beams 6a-6c on a three-dimensional radiation target 3 located inside the body of a radiotherapy patient 4.

[0081] The radiotherapy system also comprises a particle beam control system 7 which is arranged to individually control and adjust the energy levels and the trajectories of the particle beams 6a-6c exiting the particle beam guiding systems 1a-1c so that the Bragg peaks of the particle beams 6a-6c are brought to intersect in a predetermined beam intersect region 8 inside the radiation target 3 during a radiation treatment session.

[0082] The exit trajectory control comprises controlling three variables defining the position of each particle beam source, e.g. represented by Cartesian coordinates x, y, y, and two variables defining the pith and yaw of the particle beam originating from the beam source, e.g. as represented by angles of rotation measured about orthogonal pitch and yaw axes.

[0083] Adjusting the exit energy level of the particle beams 6a-6c may comprise dynamically inserting and removing one or a plurality of attenuator elements (see FIG. 4) in the path of the particle beam 6a-6c.

[0084] The radiotherapy system further comprises an imaging system 2 which is arranged to monitor the position and orientation in space of the three-dimensional radiation target 3, and also to monitor tissue characteristics of body tissue 5 surrounding the radiation target 3 located in the radiation paths of the particle beams 6a-6c. Based on the monitored data, the imaging system is arranged to dynamically map the target 3 and the surrounding tissue 5 and construct a mathematical model representing the relevant part of the patient's body, i.e. the target 3 and the surrounding tissue 5 lying between the target 3 and the particle beam sources 1a-1c. In this mapping, different types of surrounding tissue (bone, flesh, organs, etc.) are mapped and known information on how the different types of tissue interact with the particle beams is used to produce the mathematical model, in particular information on how much different types of tissue attenuate the particle beams.

[0085] In operation, the imaging system 2 monitors the position and orientation in space of the target 3 and surrounding tissue 5, and continuously updates the map of the target 3 and the surrounding tissue 5 and as well as the mathematical model representing the relevant part of the body of the patient 4. The updated map and/or the updated mathematical model is forwarded to the particle beam control system 7.

[0086] The particle beam control system 7 processes the information received from the imaging system 2 and, based on this information, produces control signals which are sent to the particle beam guiding systems 1a-1c to adjusts the exit energy levels and the exit trajectories of the particle beams 6a-6c so that the Bragg peaks of the particle beams 6a-6c are maintained within the intended beam intersect region 8, taking into account any change of position and/or attitude of the target 3.

[0087] This is illustrated in FIG. 3, where a change in position and/or orientation in space of the target 3, e.g. due to the patient or internal organs of the patient moving, prompts the particle beam control system 7 to adjust the exit energy levels and the exit trajectories of the particle beams 6a-6c.

[0088] From the information received from the imaging system 2, the particle beam control system 7 also identifies body tissue which, according to the treatment plan, shall not be exposed to the particle beams 6a-6c. When adjusting the exit energy levels and the exit trajectories of the particle beams 6a-6c, the particle beam control system 7 ensures that such body tissue is not exposed to the particle beams 6a-6c.

[0089] Adjustment of the exit energy levels and the exit trajectories of the particle beams 6a-6c may not necessarily be triggered by a movement of the radiation target but may be triggered by a movement causing body tissue not to be exposed to the particle beam 1a-1c to be brought into the radiation paths of the particle beams 6a-6c. For example, a rotation of the patient's body leaving the radiation target essentially in the same location in space, may nevertheless require the exit energy level and the exit trajectory of one or a plurality of the particle beams 6a-6c to be adjusted if the rotation brings body tissue not to be irradiated into the radiation path of a particle beam 6a-6c.

[0090] If the particle beam control system 7 cannot find a safe radiation path for a particle beam 6a-6c, i.e. a radiation path avoiding body tissue not to be exposed to the particle beams, the particle beam control system 7 may have to shut down the particle beam until such a radiation path is found, e.g. until the radiation target and surrounding tissue are shifted so that such a radiation path becomes available again.

[0091] The intended beam intersect region 8 may be locked to a given position in the target 3, as is disclosed in FIGS. 2 and 3. Alternatively, the beam intersect region 8 may be arranged to sweep over the target 3, continuously or stepwise, in which case the beam control system 7 must also take into account the new position of the beam intersect region when adjusting the exit energy levels and an exit trajectories of the particle beams 6a-6c in addition to compensating for any change in position and/or orientation in space of the target and for any change in the composition of the tissue lying in the paths of the particle beams 6a-6c.

[0092] FIGS. 4 and 5 show an embodiment of a particle beam guiding system 1a, 1b, 1c for repositioning and realigning the particle beams 6a, 6b, 6c of the radiotherapy system, wherein the particle beam guiding system 1a-1c is arranged for receiving an incoming particle beam 6a-6c along an incoming trajectory T1 and controlling an exit energy level and an exit trajectory T3 of the particle beam 6a-6c.

[0093] The particle beam guiding system 1a-1c comprises, at the end of the system 1a-1c facing away from the radiation target 3, an attenuator 22, which is arranged for adjusting the particle beam energy level so that the Bragg peak occur at the determined point in the radiation target 3. In the disclosed embodiment, the attenuator 22 comprises a pair of sliding wedges 22a, 22b which can be moved towards or away from each other in order to increase or decrease the amount of attenuating material that is in the path of the particle beam 6.

[0094] The particle beam guiding system 1a-1c also comprises a focusing unit 24 is arranged downstream of the attenuator 22, i.e. on the radiation target side of the attenuator 22. The focusing unit 24 comprises a set of magnets 24a, 24b forming focusing quadrupoles for focusing the particle beam 6a-6c after it has passed the attenuator 22.

[0095] The particle beam guiding system 1a-1c further comprises a first beam guide 26 positioned downstream of the attenuator 22. The first beam guide 26 comprises first and second guiding dipoles 26a, 26b, and each guiding dipoles 26a, 26b comprises two superconductive magnets for creating magnetic fields for deflecting the particle beam 6a-6c from the incoming trajectory T1 into an intermediate trajectory T2, wherein the first dipole 26a is arranged to deflect the particle beam 6a-6c in a first plane, e.g. in the horizontal plane, and the second dipole 26b is arranged to deflect the particle beam 6a-6c in a second plane which is orthogonal to the first plane, e.g. in the vertical plane.

[0096] The particle beam guiding system 1a-1c further comprises a second beam guide 28 positioned downstream of the first beam guide 26. The second beam guide 28 comprises first and second guiding dipoles 28a, 28b, each comprising two superconductive magnets. The guiding dipoles 28a, 28b are arranged to deflect the particle beam 6a-6c from the intermediate trajectory T2 into the exit trajectory T3. As in the first beam guide 26, one dipole 28a is arranged deflect the particle beam 6a-6c in a first plane, and the other dipole 28b is arranged to deflect the particle beam 6a-6c in a second plane which is orthogonal to the first plane.

[0097] The first beam guide 26 is able to deflect the incoming beam 6a-6c so that it enters the second beam guide 28 of-centre, i.e. along a trajectory which is non-parallel to the incoming trajectory T1. This will enable the particle beam 6a-6c to exit the second beam source 28 from anywhere within a planar circular area 29 being orthogonal to the incoming trajectory T1 and having a centre which is coaxial with the incoming trajectory T1 (see FIG. 5). The maximum deflection possible, i.e. defining the radius of circular area 29, will be determined by the strength and extent of the magnets of the first beam guide as well as by how energetic the particle beam is.

[0098] The second beam guide 28 controls the alignment by which the particle beam 6a-6c exits the second beam guide 28. In other words, the second beam guide 28 controls the pitch and yaw of the exit trajectory T3.

[0099] Consequently, the first beam guide 26 controls the starting position of the exit trajectory T3 (within the circle 29), and the second beam guide 28 controls the pitch and yaw of the exit trajectory T3, thus allowing the particle beam guiding system 1a-1c to adopt the exit trajectory T3 to the position of the radiation target and surrounding tissue.

[0100] FIG. 6 shows the general principle of how a charged particle, e.g. a proton, obtains a new direction when passing through a magnetic field, and FIGS. 7a and 7b show the angle of bending achieved in the first beam guide 26 as a function of applied magnetic field strength for different lengths of the magnetic field, l, in particular for l=200 mm (curves Da, Db), l=300 mm (curves Ea, Eb), l=400 mm (curves Fa, Fb) and l=500 mm (curves Ga, Gb). FIG. 7a shows the angle of bending achieved for a particle beam having an energy of 150 MeV and FIG. 7b shows the angle of bending achieved for a particle beam having an energy of 250 MeV.

[0101] Downstream of the second beam guide 28, the particle beam guiding system 1a-1c comprises a beam trajectory monitoring and control unit 30. This unit 30 comprises two parallel beam trajectory control disks 30a, 30b which are individually movable in individual planes which are orthogonal to the incoming trajectory. The distance between the control disks 30a, 30b is within the range of 40 to 150 mm. Each control disk 30a, 30b, displays a circular opening 31a, 31b for the particle beam to pass through, the openings 31a, 31b each having a diameter which is slightly larger than the diameter of the particle beam 6a-6c. The diameter of the openings 31a, 31 may for example be within the range of 3 to 10 mm.

[0102] In operation, the first and second beam trajectory control disks 30a, 30b are positioned so that the openings 31a, 31b define a desired exit trajectory of the particle beam guiding system. If the first and second beam guides 26, 28 have succeeded in achieving the exit trajectory set by the particle beam control system 7, the particle beam will pass through the aligned openings 31a, 31b. However, if the beam guides 26, 28 have misaligned the particle beam, the particle beam will hit the first or second control disk.

[0103] Consequently, the openings 31a, 31b will at all times be kept in a position which allows a particle beam having the desired exit trajectory to pass through the openings 31a, 31b, thus acting as a safety measure to ascertain that the particle beam does not hit any other position than the specified target area. Each of the beam trajectory control disks 30a, 30b has a surface which absorbs any stray protons, plus sensors for registration of the amount of stray protons, thus allowing information on the misalignment to be fed back to the particle beam guiding system allowing it to adjust, in real time or in near real time, the attenuator and/or the beam guides to reduced deviation between desired and detected exit trajectory.

[0104] This functionality may be improved over time through computed learning. This functionality is obtained without interfering with the main particle beam.

[0105] The particle beam guiding system 1a-1c comprises a chamber (not shown) in which the components of the particle beam guiding system is enclosed. The chamber provides atmospheric control, e.g. a vacuum enclosure and/or temperature control, to ensure cryogenic cooling. The chamber also provides magnetic shielding, preventing the magnetic fields from one particle beam guiding system from interfering with the operation of another particle beam guiding system.

[0106] In the preceding description, various aspects of the apparatus according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the apparatus and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the apparatus, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention a defined by the following claims.