ROTATING ENERGY DEGRADER

Abstract

Embodiments disclose an energy degrader for attenuating the energy of a charged particle beam, comprising a first energy attenuation member presenting a beam entry face having the shape of a part of a first helical surface, a second energy attenuation member presenting a beam exit face having the shape of a part of a second helical surface, the beam exit face being positioned downstream of said beam entry face with respect to the beam direction, and a drive assembly for rotating the first and/or the second energy attenuation members about respectively a first and/or a second rotation axis while crossed by the particle beam. The first and second helical surfaces are continuous surfaces and have the same handedness, to enable a more compact degrader with a smaller moment of inertia.

Claims

1. An energy degrader for attenuating the energy of a charged particle beam extracted from a particle accelerator, the energy degrader comprising: a first energy attenuation member including a first beam entry face having a shape of part of a first helical surface, the first energy attenuation member having a first axis and a first beam exit face; a second energy attenuation member, separate from the first energy attenuation member, including a second beam exit face having a shape of a part of a second helical surface, the second energy attenuation member having a second axis and a second beam entry face; and a drive assembly operably connected to the first energy attenuation member, the second energy attenuation member, or both the first and the second energy attenuation members, the drive assembly configured to rotate the first energy attenuation member, the second energy attenuation member, or both the first and the second energy attenuation members around respectively the first axis, the second axis, or both the first and the second axis, wherein: the first axis is parallel to or coincident with the second axis; the first beam exit face and the second beam entry face are facing each other; the first and second helical surfaces are continuous surfaces; and the first and second helical surfaces have the same handedness.

2. An energy degrader according to claim 1, wherein the drive assembly is operably connected to the first and the second energy attenuation members, the drive assembly configured to rotate the first and the second energy attenuation members around respectively the first axis and the second axis.

3. An energy degrader according to claim 2, wherein the drive assembly comprises: a first motor operably connected to the first energy attenuation member, the first motor configured to rotate the first energy attenuation member around the first axis; and a second motor operably connected to the second energy attenuation member, the second motor configured to rotate the second energy attenuation member around the second axis.

4. An energy degrader according to claim 1, wherein: the first beam exit face has the shape of an annulus or a portion thereof; the second beam entry face has the shape of an annulus or a portion thereof; the first beam exit face is parallel to the second beam entry face; and the first beam exit face and the second beam entry face are perpendicular to the first and second rotation axes.

5. An energy degrader according to claim 4, comprising: a gap between the first beam exit face and the beam second entry face, wherein the gap is smaller than 10 mm.

6. An energy degrader according to claim 5, wherein the gap is smaller than 5 mm.

7. An energy degrader according to claim 5, wherein the gap is smaller than 1 mm.

8. An energy degrader according to claim 1, wherein the first and second energy attenuation members are identical in shape and size.

9. An energy degrader according to claim 1, wherein the first and the second helical surfaces are cylindrical helical surfaces.

10. An energy degrader according to claim 9, wherein: the first and the second helical surfaces have the same radius and the same pitch; and the first rotation axis is coincident with the second rotation axis.

11. An energy degrader according to claim 9, wherein: the radius of the first helical surface is smaller than the radius of the second helical surface; the pitch of the first helical surface is smaller than the pitch of the second helical surface; and the first rotation axis is different from the second rotation axis.

12. An energy degrader according to claim 1, wherein: the first and the second helical surfaces are conical helical surfaces; the first and second energy attenuation members are right circular truncated cones, the truncated cones having truncated faces facing each other; and the first axis of the first helical surface is coincident with the second axis of the second helical surface.

13. An energy degrader according to claim 12, wherein: the truncated cones of the first and second energy attenuation members have the same aperture α; the first and second helical surfaces each have a slope which is equal to the aperture α; and the first and the second helical surfaces have the same pitch.

14. A particle therapy system comprising: a particle accelerator configured to extract a charged particle beam; and an energy degrader configured to attenuate the energy of the particle beam, the energy degrader comprising: a first energy attenuation member including a first beam entry face having a shape of part of a first helical surface, the first energy attenuation member having a first axis and a first beam exit face; a second energy attenuation member, separate from the first energy attenuation member, including a second beam exit face having a shape of a part of a second helical surface, the second energy attenuation member having a second axis and a second beam entry face; and a drive assembly operably connected to the first energy attenuation member, the second energy attenuation member, or both the first and the second energy attenuation members, the drive assembly configured to rotate the first energy attenuation member, the second energy attenuation member, or both the first and the second energy attenuation members around respectively the first axis, the second axis, or both the first and the second axis, wherein: the first axis is parallel to or coincident with the second axis; the first beam exit face and the second beam entry face are facing each other; the first and second helical surfaces are continuous surfaces; and the energy degrader is positioned and oriented with respect to the particle beam such that the particle beam enters the energy degrader at the first beam entry face and exits the energy degrader at the second beam exit face.

15. A particle therapy system according to claim 14, wherein: the first and the second helical surfaces are cylindrical helical surfaces; and the energy degrader is positioned and oriented with respect to a path of the particle beam such that the path of the particle beam is parallel to the first axis at the first beam entry face of the energy degrader.

16. A particle therapy system according to claim 15, wherein: the first and the second helical surfaces have the same radius and the same pitch; and the first rotation axis is coincident with the second rotation axis.

17. A particle therapy system according to claim 15, wherein: the radius of the first helical surface is smaller than the radius of the second helical surface; the pitch of the first helical surface is smaller than the pitch of the second helical surface; and the first rotation axis is different from the second rotation axis.

18. A particle therapy system according to claim 14, wherein: the first and the second helical surfaces are conical helical surfaces; the first and second energy attenuation members are right circular truncated cones, the truncated cones having truncated faces facing each other; the first axis of the first helical surface is coincident with the second axis of the second helical surface; and the energy degrader is positioned and oriented with respect to a path of the particle beam such that the path of the particle beam is parallel to a normal vector to the first helical surface at the first beam entry face of the energy degrader.

19. A particle therapy system according to claim 18, wherein: the truncated cones of the first and second energy attenuation members have the same aperture α; the first and second helical surfaces each have a slope which is equal to the aperture α; and the first and the second helical surfaces have the same pitch.

20. A particle therapy system according to claim 15, wherein the particle accelerator is a fixed-energy accelerator.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] These and further aspects of the present disclosure will be explained in greater detail by way of example and with reference to the accompanying drawings in which:

[0038] FIG. 1 schematically shows a front view of an exemplary energy degrader according to the present disclosure;

[0039] FIG. 2 schematically shows a top view of the energy degrader of FIG. 1;

[0040] FIG. 3 schematically shows a partial sectional view of the energy degrader of FIG. 1 at a high energy attenuation level;

[0041] FIG. 4 schematically shows a partial sectional view of the energy degrader of FIG. 1 at a low energy attenuation level;

[0042] FIG. 5 schematically shows a front view of another exemplary energy degrader according to the present disclosure;

[0043] FIG. 6 schematically shows a top view of the energy degrader of FIG. 5;

[0044] FIG. 7 schematically shows a front view of another exemplary energy degrader according to the present disclosure;

[0045] FIG. 8 schematically shows a top view of the energy degrader of FIG. 7;

[0046] FIG. 9 schematically shows a perspective view of the energy degrader of

[0047] FIG. 7;

[0048] FIG. 10 schematically shows a partial sectional view of the energy degrader of FIG. 7 at a high energy attenuation level;

[0049] FIG. 11 schematically shows a partial sectional view of the energy degrader of FIG. 7 at a low energy attenuation level;

[0050] FIG. 12 schematically shows a particle therapy system comprising a particle accelerator and an energy degrader according to the present disclosure;

[0051] FIG. 13 schematically shows another particle therapy system comprising a particle accelerator and an energy degrader according to the present disclosure.

[0052] The drawings of the figures are neither drawn to scale nor proportioned. Generally, similar or identical components are denoted by the same reference numerals in the figures.

DETAILED DESCRIPTION

[0053] FIG. 1 schematically shows a front view of an exemplary energy degrader (1) according to the present disclosure, in an XYZ referential.

[0054] The energy degrader (1) comprises two disjoint energy attenuation members: a first energy attenuation member (10) and a second energy attenuation member (20).

[0055] The first energy attenuation member (10) presents a first beam entry face (11) having the shape of a part of a first continuous helical surface having a first axis (A1) and an opposed first beam exit face (12).

[0056] The second energy attenuation member (20) presents a second beam entry face (21), and an opposed second beam exit face (22) having the shape of part of a second continuous helical surface having a second axis (A2). The second axis (A2) is parallel to or coincident with the first axis (A1). The first and the second helical surfaces have the same handedness.

[0057] The first and second helical surfaces each make a turn of less than or equal to 360° so that there is no overlap of their respective entry and exit faces in the axial direction. In other words, each of the first and second helical surfaces have a height which is less than or equal to their respective pitch.

[0058] It is to be noted that a helical surface may have a close-up appearance of a helical staircase with very small steps, for example in case an energy attenuation member is made with a 3D printer, but that it is still to be considered as a continuous helical surface in case a minimum run (tread depth) of its steps is smaller than a minimum average beam diameter at a level where the beam crosses the helical surface (for example a minimum run of its steps which is smaller than 8 mm in case of an average beam diameter ranging between 8 mm and 30 mm when crossing the helical surface).

[0059] As can be seen on FIG. 1, the first and second energy attenuation members (10, 20) are positioned with respect to each other in such a way that the first beam exit face (12) and the second beam entry face (21) are facing each other.

[0060] The energy degrader (1) further comprises a drive assembly which is operably connected to the first and/or the second energy attenuation members (10, 20). This drive assembly is configured for driving the first energy attenuation member (10) and/or the second energy attenuation member (20) into rotation about respectively the first axis (A1) and/or the second axis (A2).

[0061] The drive assembly may for example comprise a single motor (M1) as well as an optional transmission linking said single motor to the first energy attenuation member (10) so as to rotate the first energy attenuation member (10) about the first axis (A1), the second energy attenuation member (20) being fixed (not rotating).

[0062] Alternatively, the drive assembly may for example comprise a single motor as well as a transmission linking said single motor to respectively the first and the second energy attenuation members so as to rotate respectively the first and the second energy attenuation members, for example in opposite directions (i.e. when the first energy attenuation member (10) is driven to rotate clockwise, the second energy attenuation member (20) will be driven to rotate anticlockwise and vice-versa).

[0063] As shown on FIG. 1, the drive assembly comprises a first motor (M1) operably connected to the first energy attenuation member (10) for rotating the first energy attenuation member about the first axis (A1), and a second motor (M2) operably connected to the second energy attenuation member (20) for rotating the second energy attenuation member about the second axis (A2). The first and second motors may be stepper motors for example. Though not shown on FIG. 1, the energy degrader (1) may further comprise (an) intermediary transmission(s) between the first and/or the second motors on the one hand and respectively the first and second energy attenuation members on the other hand, in order to adapt the speed and/or the torque applied by the motors to their corresponding energy attenuation members, and/or to improve the accuracy of the movements.

[0064] On FIG. 1 is further shown a particle beam (2) when crossing the first and second energy attenuation members (10, 20). Given the geometry of these two attenuation members, it will be clear that an energy of an incoming particle beam will be more or less attenuated in function of the angular position(s) of the first and the second energy attenuation members with respect to the particle beam (2). A control unit (60), operably connected to the drive assembly (M1, M2), may be used to modify said angular positions, for example in function of energy attenuation settings received from a system using the energy degrader (1).

[0065] FIG. 2 schematically shows a top view of the energy degrader (1) of FIG. 1.

[0066] According to the present disclosure, the first beam exit face (12) and the second beam entry face (21) may have various shapes, provided the first and second energy attenuation members (10, 20) are sufficiently spaced apart, so that one energy attenuation member is not hindered by the other energy attenuation member in the course of its rotation.

[0067] The first beam exit face (12) has the shape of an annulus or a disk or a portion thereof, and the second beam entry face (21) has the shape of an annulus or a disk or a portion thereof. The first beam exit face (12) may be parallel to the second beam entry face (21). The first beam exit face (12) and the second beam entry face (21) may be perpendicular to the first and second rotation axes (A1, A2). With such a configuration, the gap (30) between the first beam exit face (12) and the second beam entry face (21) can be made small, which is desirable to reduce beam dispersion, particularly at high energy attenuation levels.

[0068] In such a case, the first and second energy attenuation members are arranged in such a way that the gap (30) between the first beam exit face (12) and the second beam entry face (21) is smaller than 5 cm, preferably smaller than 1 cm, preferably smaller than 5 mm, preferably smaller than 1 mm. The first beam exit face and the second beam entry face may, for example, not touch each other in order to avoid wear.

[0069] According to the present disclosure, the first energy attenuation member (10) and/or the second energy attenuation member (20) may be made of beryllium or carbon graphite. The first energy attenuation member (10) may be made of the same material as the second energy attenuation member (20).

[0070] The first and the second helical surfaces are cylindrical helical surfaces, as can be seen on the example of FIGS. 1 and 2. The first axis (A1) may be the same as (coincident with) the second axis (A2). The radius (R1) of the first helical surface may be the same as the radius (R2) of the second helical surface. The first and the second helical surfaces may have the same pitch. The first and second energy attenuation members (10, 20) may be identical in shape and in size.

[0071] FIG. 3 schematically shows a partial sectional and developed view of the energy degrader (1) of FIG. 1 at a high energy attenuation level. In this exemplary representation, the first and second energy attenuation members (10, 20) have the same size and the same shape, which means that the first and second helical surfaces have the same radius, the same handedness and the same pitch.

[0072] The particle beam (2) is here shown enlarged in order to more clearly see its sectional size. As can be seen on FIG. 3, a particle of the leftmost part of the beam (2) will travel through thicknesses E1a and E2a of the energy attenuation members via a gap (30). A particle of the rightmost part of the beam (2) will travel through thicknesses E1b and E2b of the energy attenuation members via the same gap (30). The gap (30) may for example be an air gap or a vacuum gap. A total attenuation of the energy of a particle may be estimated as the sum of the energy attenuations provided by the first and the second energy attenuation members along the path of the particle. In this exemplary configuration, we have that E1a+E2a=E1b+E2b, so that it will be understood that the energy of these two particles will be attenuated by the same amount. The same holds for the other particles of the beam (2). Such situation is desirable in order to limit the energy spread of the particles of the particle beam at the output of the degrader.

[0073] FIG. 4 schematically shows a partial sectional and developed view of the energy degrader (1) of FIG. 1 at a low energy attenuation level. This configuration may be obtained by rotating the first energy attenuation member (10) by a certain angle in the appropriate direction (in order to reduce the thicknesses E1a and E1b) and/or by rotating the second energy attenuation member (20) by a certain angle in the opposite direction (in order to reduce the thicknesses E2a and E2b). As can be seen on FIG. 4, a particle of the leftmost part of the beam (2) will travel through thicknesses E3a and E4a of the energy attenuation members via the gap (30). A particle of the rightmost part of the beam (2) will travel through thicknesses E3b and E4b of the energy attenuation members via the same gap (30). It will therefore be understood that the energy of these two particles will be attenuated by the same amount. The same holds for the other particles of the beam (2). Such situation is desirable in order to limit the energy spread of the particles of the particle beam at the output of the degrader. Since E3a+E4a is smaller than E1a+E2a, the energy of the beam will be less attenuated than with the arrangement of FIG. 3.

[0074] FIG. 5 schematically shows a front view of another exemplary energy degrader (1) according to the present disclosure, in an XYZ referential. It is similar to the degrader of FIG. 1, except that, in this case, the radius (R1) of the first helical surface is smaller than the radius (R2) of the second helical surface, and that the first axis (A1) is different from and parallel to the second axis (A2). Preferably, R1<0.5.R2, more preferably, R1<0.2.R2, even more preferably R1<0.1.R2.

[0075] In this case, in order to have the same slope on both helical surfaces, the pitch of the first helical surface is smaller than the pitch of the second helical surface.

[0076] FIG. 6 schematically shows a top view of the energy degrader (1) of FIG. 5, whereon one can also see that the first and second helical surfaces each make a turn of less than or equal to 360° so that there is no overlap in the axial direction. In other words, each of the first and second helical surfaces have a height which is less than or equal to their respective pitch.

[0077] FIG. 7 schematically shows a front view of another exemplary energy degrader (1) according to the present disclosure in an XYZ referential. It is similar to the degrader of FIG. 1, except that, in this case, the first and second helical surfaces are conical helical surfaces, and the first and second energy attenuation members are right circular truncated cones (10, 20) whose truncated faces (12, 21) are the same and are facing each other. The first axis (A1) of the first helical surface is coincident with the second axis (A1) of the second helical surface. Hence the two cones also have the same axis (A1). It is known in geometry that the aperture of a right circular cone is the maximum angle between two generatrix lines of the cone and that, if a generatrix makes an angle α/2 to the axis of the cone, the aperture of the cone is equal to α. The first energy attenuation member (10) is designed in such a way that the aperture α of its truncated cone is equal to the slope of the first helical surface, so that a normal vector (v1) to the first helical surface makes the same angle α with the axis (A1) of the cone. In this case, the second energy attenuation member (20) is designed in the same way, thus with the same angles α, as shown on FIG. 7. The height of the truncated cone of the first energy attenuation member may be equal or different from the height of the truncated cone of the second energy attenuation member. The first and second energy attenuation members (10, 20) are identical in shape and in size. The first and second helical surfaces each make a turn of less than or equal to 360° so that there is no overlap in the axial direction. In other words, each of the first and second helical surfaces have a height which is less than or equal to their respective pitch.

[0078] With such a geometry, as shown on FIG. 7, a particle beam (2) whose path makes an angle α with the axis (A1) will enter into the degrader perpendicularly to the first beam entry face (11), will further pass through the matter of the two truncated cones (10, 20), and will thereafter exit the degrader perpendicularly to the second beam exit face (22), and this whatever the angular position of the first and second energy attenuation members. Having a particle beam entering and exiting the degrader perpendicularly to its entry and exit faces advantageously reduces dispersion of the beam.

[0079] FIG. 8 schematically shows a top view of the energy degrader of FIG. 7. The truncated cones (10, 20) may or may not be hollow. In order to reduce their moment of inertia, they may be hollow, as better seen shown on FIG. 8 and FIG. 9.

[0080] FIG. 9 schematically shows a perspective view of the energy degrader of FIG. 7.

[0081] For the sake of clarity, the drive assembly and its control unit are not shown on FIGS. 8 and 9.

[0082] FIG. 10 schematically shows a partial and developed sectional view of the energy degrader of FIG. 7 at a high energy attenuation level, when crossed by particles of a particle beam (2) entering the first energy attenuation member (10) perpendicular to the first beam entry face (11). In this exemplary representation, the first and second energy attenuation members have the same size and the same shape. By analogy with the description of FIG. 3, it will be understood that E1a+E2a=E1b+E2b, so that the energy of the corresponding two particles will be attenuated by the same amount. The same holds for the other particles of the beam (2).

[0083] FIG. 11 schematically shows a partial and developed sectional view of the energy degrader of FIG. 7 at a low energy attenuation level. This configuration may be obtained by rotating the first energy attenuation member (10) by a certain angle in the appropriate direction (in order to reduce the thicknesses E1a and E1b) and/or by rotating the second energy attenuation member (20) by a certain angle in the opposite direction (in order to reduce the thicknesses E2a and E2b). As for the case shown on FIG. 10, the energy of the particles of the beam (2) will be attenuated by approximately the same amount.

[0084] As schematically shown on FIG. 12, the present disclosure also concerns a particle therapy system configured for irradiating a target (200) with a charged particle beam (2). Said particle therapy system comprises a particle accelerator (100) configured for generating and extracting a beam (2) of charged particles, such as a beam of protons or carbon ions for example, and an energy degrader (1) as described hereinabove for attenuating the energy of said charged particle beam (2) before it reaches the target (200).

[0085] In this example, the energy degrader is positioned and oriented with respect to a path of the extracted particle beam (2) in such a way that the path of the extracted particle beam is parallel to the first axis (A1) at the first beam entry face (11) of the energy degrader.

[0086] For the sake of clarity, FIG. 12 does not necessarily show all components of a particle therapy system, which are well known from the prior art, but only those components which are necessary to understand the present disclosure.

[0087] FIG. 13 schematically shows another particle therapy system comprising a particle accelerator (100) and an energy degrader (1) according to the present disclosure, and more specifically a degrader as shown in FIG. 7. It is similar to the system of FIG. 12, except that in this case the energy degrader is positioned and oriented with respect to a path of the extracted particle beam (2) in such a way that the path of the extracted particle beam is parallel to a normal vector (v1) to the first helical surface at the first beam entry face (11) and/or parallel to a normal vector (v2) to the second helical surface (22) at the second beam exit face (22) of the energy degrader.

[0088] The particle accelerator (100) may be a fixed-energy accelerator, for example, a cyclotron or a synchrocyclotron.

[0089] The particle accelerator (100) may be configured for delivering at its output (110) a particle beam (2) whose maximal energy is comprised between 1 MeV and 500 MeV, preferably between 100 MeV and 300 MeV, more preferably between 200 MeV and 250 MeV.

[0090] In such a case, a typical desired beam energy at an output (22) of an energy degrader (1) according to the present disclosure is also in the MeV range, such as in the range of 50 MeV to 230 MeV for an upstream energy of 230 MeV for example.

[0091] With these Exemplary Energies:

[0092] a minimal thickness (taken along the path of the particle beam) of the first energy attenuation member (10) lies in the interval [1 mm, 100 mm], more preferably [1 mm, 50 mm], even more preferably [1 mm, 10 mm]. The same holds for the second energy attenuation member (20),

[0093] a maximal thickness (taken along the path of the particle beam) of the first energy attenuation member (10) lies in the interval [10 mm, 300 mm], more preferably [10 mm, 200 mm], even more preferably [10 mm, 100 mm]. The same holds for the second energy attenuation member (20), and

[0094] a maximum diameter of the first energy attenuation member (10) lies in the interval [10 mm, 300 mm], more preferably [10 mm, 200 mm], even more preferably [10 mm, 150 mm]. The same holds for the second energy attenuation member (20).

[0095] The present disclosure may also be described as follows: an energy degrader (1) for attenuating the energy of a charged particle beam (2) and comprising: a first energy attenuation member (10) presenting a beam entry face (11) having the shape of a part of a first helical surface, a second energy attenuation member (20) presenting a beam exit face (22) having the shape of a part of a second helical surface, said beam exit face being positioned downstream of said beam entry face with respect to the beam direction, and a drive assembly (M1, M2) for rotating the first and/or the second energy attenuation members about respectively a first and/or a second rotation axis (A1, A2). The first and second helical surfaces are continuous surfaces and have the same handedness, thereby allowing to build a more compact degrader with a smaller moment of inertia. More accurate and faster variation of the energy of the beam can hence be achieved.

[0096] While the present disclosure is illustrated and described in detail according to the above embodiments, the present disclosure is not limited to these embodiments and additional embodiments may be implemented. Further, other embodiments and various modifications will be apparent to those skilled in the art from consideration of the specification and practice of one or more embodiments disclosed herein, without departing from the scope of the present disclosure.

[0097] Reference numerals in the claims do not limit their protective scope.

[0098] Use of the verbs “to comprise”, “to include”, “to be composed of”, or any other variant, as well as their respective conjugations, does not exclude the presence of elements other than those stated.

[0099] Use of the article “a”, “an” or “the” preceding an element does not exclude the presence of a plurality of such elements.