Radiation therapy device

Abstract

A particle accelerator includes a waveguide comprising a series of accelerating units. The series of accelerating units includes an input accelerating unit configured to accelerate an electron beam along a central axis of the unit. An electron source is configured to input the electron beam into the input accelerating unit, and a magnet arrangement is configured to prevent electrons that have deviated from the electron beam from impacting the electron source.

Description

Technical Field

[0001] This disclosure relates to the field of particle accelerators, and more specifically to linear accelerators for generating electron beams or other charged particles. Background Technology

[0002] Radiation therapy devices are essential tools in modern cancer treatment. They are large and complex machines with numerous moving parts and interoperable mechanisms. Despite sophisticated engineering and rigorous testing, certain components of a radiation therapy machine may begin to degrade during the machine's lifespan. One example of a radiation source used to generate an electron beam is a linear accelerator (LINAC). Clinical LINAC devices are configured to deliver high-energy radiation to patients.

[0003] Linear accelerators (especially those used in medicine) accelerate electrons or other charged particles to relativistic velocities along an acceleration path using waveguides. An electron source, such as an electron gun, is configured to inject electrons into the waveguide. The electrons are injected by the electron gun and accelerated through the waveguide. Radio frequency (RF) electromagnetic waves are applied to the waveguide, providing an oscillating electric field within it to accelerate the electrons. The accelerated electrons strike a target and produce X-rays used in medicine, such as for radiotherapy.

[0004] Due to the complexity of the mechanics and many operating mechanisms, linear accelerators can sometimes malfunction. Specifically, the electron gun may break down. This results in machine downtime for repairs and gun replacement. Such events are inconvenient because they increase treatment time and, in some cases, mean that the treatment must be ended prematurely. Unplanned equipment downtime can disrupt scheduled treatments and can be costly for the owner, whether due to lost revenue, service and repair costs, or both.

[0005] In some cases, the electron gun can be damaged when electrons move backward rather than being accelerated along the electron beam. This is a phenomenon known as back bombardment.

[0006] The present invention aims to address these and other drawbacks encountered due to electron backbombardment by providing an improved waveguide for radiotherapy. Summary of the Invention

[0007] The invention is set forth in the independent claims. Optional features are set forth in the dependent claims. Attached Figure Description

[0008] The following describes specific embodiments by way of example only and with reference to the accompanying drawings, wherein:

[0009] Figure 1A schematic diagram of the LINAC device is shown.

[0010] Figure 2 An electron gun is shown.

[0011] Figure 3 The waveguide is shown.

[0012] Figures 4a to 4c A series of simulations of electrons in a waveguide are shown, demonstrating the back-boom.

[0013] Figure 5 The electron gun, linear accelerator, and magnet arrangement are shown.

[0014] Figure 6a and Figure 6b The arrangement of magnets in a linear accelerator is shown. Figure 6c and Figure 6d The use of an α magnet in a magnet arrangement is shown.

[0015] Figure 7 A linear accelerator including a flow channel is shown. Detailed Implementation

[0016] This disclosure relates to waveguides for use in particle accelerators, such as linear accelerators. Linear accelerators can be used in radiotherapy devices. Radiotherapy devices can be used to deliver radiation beams to patients to treat tumors.

[0017] Specifically, this application relates to protecting an electron gun used in a particle accelerator and protecting the cathode of the electron gun. Such techniques are advantageous because they allow for an increase in the lifespan of the electron gun. This allows manufacturers or maintenance service providers to reduce the need for regular machine maintenance, thereby saving time and avoiding costly repairs. The disclosed techniques allow for protection of the electron gun from backfire, thus extending the lifespan of the electron gun cathode filament. The disclosed techniques help reduce machine downtime, thereby minimizing disruption to normal machine operation. The disclosed techniques can also be used to generate electron beams with greater flow, thereby delivering higher doses to patients. This, in turn, reduces treatment time and allows for the treatment of more patients within a given time period.

[0018] Figure 1 A LINAC (Radiation Injection Assisted Transmission) device, suitable for delivery to a patient during radiotherapy treatment and configured to deliver a radiation beam to the patient, is described. In operation, the LINAC device generates and shapes the radiation beam and directs it to a target area within the patient's body according to the radiotherapy treatment plan.

[0019] Medical LINAC machines are inherently complex, with many interoperable components. This will be addressed... Figure 1The LINAC device depicted in the figure provides a brief overview of typical LINAC operation, which includes a radio frequency source 102, a waveguide 104, an electron source 106, a heavy metal target 116, and a treatment head, wherein the heavy metal target 116 generates X-rays 120 when struck by an electron beam 118, and the treatment head houses various devices configured, for example, to collimate and shape the generated X-ray beam.

[0020] A radio frequency (RF) source 102, such as a magnetron, generates RF waves. The RF source 102 is coupled to a waveguide 104 and configured to pulse the RF waves into the waveguide 104. An electron source 106, such as an electron gun, is coupled to the waveguide 104 and configured to inject electrons into the waveguide 104. In the electron source 106, electrons are emitted from the cathode filament in a thermionic manner when the filament is heated. The temperature of the filament controls the number of electrons injected. The injection of electrons into the waveguide 104 is synchronized with the pumping of RF waves into the waveguide 104. The design and operation of the RF source 102, the electron source 106, and the waveguide 104 enable the RF waves to accelerate the electrons to very high energies as they travel through the waveguide 104. The design of the waveguide 104 depends on whether the LINAC uses standing waves or traveling waves to accelerate the electrons, although the waveguide typically comprises a series of units or cavities, each connected by apertures or "iris" through which the electron beam 118 can pass. The accelerating unit is coupled to generate a suitable electric field mode, thereby accelerating the electrons transmitted through waveguide 104.

[0021] As electrons are accelerated in waveguide 104, the electron beam 118 is controlled by a suitable arrangement of steering magnets or steering coils surrounding waveguide 104. The arrangement of steering magnets may include, for example, two sets of quadrupole magnets.

[0022] To ensure that electron transmission is unimpeded as the electron beam 118 travels toward the target, the waveguide 104 is evacuated using a vacuum.

[0023] When high-energy electrons strike a target, X-rays are generated in multiple directions. A collimator then blocks the X-rays traveling in specific directions, allowing only the forward-moving X-rays to pass through, creating a cone-shaped beam. Before entering the patient as part of a radiotherapy treatment, this beam can be shaped in various ways using beamforming devices, such as by using a multi-leaf collimator.

[0024] In some embodiments, the LINAC is configured to emit an X-ray beam 120 or an electron particle beam (not shown). Such an embodiment allows the device to provide electron beam therapy, i.e., an external beam therapy, in which electrons, rather than X-rays, are directed to the target area. By adjusting the components of the LINAC, a "switch" can be made between a first mode of emitting X-rays and a second mode of emitting electrons.

[0025] The LINAC device also includes several other components and systems. As those skilled in the art will understand, a LINAC device for radiotherapy will have additional devices such as a gantry for supporting and rotating the LINAC, a patient support surface, and a controller or processor configured to control the LINAC device.

[0026] Figure 2 An electron gun 200 (i.e., an electron source) suitable for generating and inputting electrons into a waveguide is shown. The electron gun 200 injects electrons into the waveguide to generate an electron beam. The electron gun 200 includes a metal plate 204 (also called a cathode) heated by a filament 202 connected to a low voltage 210. Some of the conductive electrons move freely in the metal because they do not bind to ions in the crystal lattice. As the metal plate 204 is heated, the electrons gain kinetic energy. Some of them gain enough kinetic energy to escape from the surface of the metal plate 204. The entire electron gun 200 is placed in a vacuum because electrons evaporating in a vacuum can move freely without being rapidly absorbed as would happen in air. By placing an anode 206 (positive electrode) nearby, the electrons are pulled away from the hot surface of the metal plate 204. The anode 206 is created by connecting an electrode to the positive terminal of the power supply 210, and the metal plate 204 (or cathode) is connected to the negative terminal of the power supply 210. Due to electrostatic attraction, the electrons are drawn toward the anode 206. There is a small hole on the anode 206, through which some electrons will pass to form an electron beam. The anode includes a hole through which electrons can exit the electron gun 200. Figure 2 The anode shown includes a nozzle 208 through which electrons exit the electron gun 200. The nozzle can be formed in various shapes and sizes, and is not limited to these. Figure 2 As shown in the description. The nozzle is not a necessary feature of the electron gun.

[0027] The electron gun 200 may also have a control gate (not shown). The control gate is an electrode used to control the flow of electrons from the metal plate 204 to the anode 206 electrode. The control gate is located between the metal plate 204 and the anode 206. The control gate between the metal plate 204 and the anode 206 acts as a gate to control the electron current reaching the anode 206. A negative voltage on the gate repels electrons back to the cathode, thus reducing the number of electrons entering the anode. A "less" negative voltage or a positive voltage on the gate allows more electrons to pass through, increasing the current in the anode 206 and thus increasing the electron current emitted from the electron gun 200.

[0028] A radio frequency (RF) field exists within the waveguide. Due to the statistical output of the electron gun 200, electrons entering the waveguide can be accelerated or decelerated. As electrons enter the waveguide, those entering at the RF peaks are accelerated, a phenomenon known as "in-phase." Those entering at the RF troughs are decelerated, a phenomenon known as "out-of-phase." Electrons entering between these time points experience some acceleration or deceleration. This forms a bundle. Particles that significantly deviate from or cross the axis may not become part of the bundle and, due to the RF, may eventually return to the electron gun and thus to the cathode.

[0029] Figure 3 A portion of a known waveguide 300 is shown. Four acceleration units 302 in a series of connected acceleration units are shown. Each acceleration unit is connected along the central axis 304 via a diaphragm 306. Figure 3 Only four accelerating units 302 are shown in the diagram, but typical waveguides will have more. The exact number will vary depending on the accelerator's design specifications. Each unit is defined by a recess within a surrounding shell of a conductive material (typically copper).

[0030] A radio frequency (RF) source (not shown) is coupled to waveguide 300 and configured to pulse RF waves into waveguide 300. The RF wave travels from the RF source through an RF input window. The design and operation of the RF source, electron source, and waveguide 300 enable the RF wave to accelerate electrons to very high energies as they travel through waveguide 300. The design of waveguide 104 depends on whether the LINAC uses standing waves or traveling waves to accelerate the electrons. Acceleration unit 302 is coupled to generate a suitable electric field mode, thereby accelerating the electrons traveling through waveguide 300. The electric field mode accelerates the electrons along the acceleration path. The acceleration path is along the central axis 304 of acceleration unit 302.

[0031] Electrons enter the input acceleration unit 308 at its first end 312. An electron source is located at and connected to the first end 312 to input electrons into the input acceleration unit 308. When an electron enters the input acceleration unit 308 in the waveguide 300, it is accelerated by an electric field. The electron, traveling forward along the central axis 304 of the waveguide 300, gains energy and is accelerated forward toward the second end 314 of the input acceleration unit 308, eventually entering the second acceleration unit 310. (See also...) Figure 4a Some electrons emitted in a phase-out manner relative to the radio frequency do not gain enough energy to leave the input acceleration unit 308 before the oscillating electric field reverses. The reversed oscillating electric field accelerates the electrons in a backward direction toward the first end 312 of the input acceleration unit 318, see [link to relevant documentation]. Figure 4b and 4cThis phenomenon is called backbombardment. The effect is most pronounced when electrons are emitted into the input acceleration unit with a phase difference of approximately 180 degrees relative to the radio frequency phase. Backbombardment can occur in any acceleration unit, but it is most damaging to the electron source when it occurs in the input acceleration unit 308.

[0032] Backflushing has adverse effects on machine performance, including damage to the electron source. For example, the electron gun 200, and more specifically, its cathode, can be damaged by the rebounding electrons. The energy gained from the radio frequency waves causes the backward-moving electrons to accelerate, increasing their velocity and thus exacerbating the damage they cause. These backward-moving electrons may collide with the cathode, depositing their kinetic energy as heat, thus raising the cathode's temperature. As the cathode heats up, more electrons are emitted. This can cause the electron gun 200 to malfunction or even fail completely, reducing its lifespan. For grid-controlled electron guns, the rebounding electrons can damage the grid. Furthermore, this can lead to a runaway state, where backflushing causes the cathode to heat up further, resulting in the emission of more electrons, which in turn leads to more backflushing, creating a feedback loop. Damage to the electron gun 200 results in machine downtime because maintenance and replacement of the electron gun must be performed regularly. This reduces the time available for patient treatment.

[0033] Linear accelerators may also include a target (typically made of tungsten) to generate X-rays when the target (not shown) is bombarded by an electron beam. To treat patients more quickly, it is desirable to deliver a higher dose rate of X-rays to them. To achieve this, a higher incident electron beam power must be generated on the target by increasing the radio frequency to accelerate the electrons to a higher speed. However, a larger radio frequency simultaneously accelerates the electrons' movement in both the forward and backward directions, increasing the speed at which the electrons return to the electron gun. In practice, this results in a maximum limitation on the electron current the machine can generate, as electrons traveling at a faster backward speed generate more heat and cause more damage to the electron gun. This leads to a limitation on the X-ray dose rate, and therefore also limits the rate of patient treatment.

[0034] Therefore, it is desirable to provide a medical linear accelerator that reduces backlash, thereby extending the lifespan of the electron gun and allowing the linear accelerator to treat patients more quickly.

[0035] One solution to mitigate the backbombing problem presented in this paper is to place a magnet arrangement between the electron source (i.e., electron gun) and the waveguide to prevent backbombing electrons from reaching the electron source.

[0036] Figure 5A waveguide for use in a particle accelerator (e.g., a linear accelerator) is shown. Waveguide 300 includes a series of acceleration units 302. A first acceleration unit is an input acceleration unit 308 through which electrons enter waveguide 300. Waveguide 300 also includes an electron source 200, such as an electron gun. The electron source guides an electron beam 207 into the input acceleration unit 308. When the electron beam 207 enters the input acceleration unit 308 in waveguide 300, it is accelerated by an electric field. The electron beam 207 is guided to an output acceleration unit (not shown). The electron beam 207 is guided along the central axis 304 of the acceleration unit. The output acceleration unit is located at the opposite end of the waveguide compared to the first acceleration unit. Both the output acceleration unit and the input acceleration unit 308 are located at opposite ends along the central axis 304 of the waveguide. A target may be located near the output unit and the end of the waveguide. Electrons strike the target and produce X-rays for medical purposes (e.g., radiotherapy). Alternatively, a target may be omitted, and the electron beam itself may be used to treat a patient.

[0037] The waveguide includes a magnet arrangement 500. The magnet arrangement 500 can be positioned near the acceleration unit. The magnet arrangement 500 can be located in the input acceleration unit 308 or in any of a series of acceleration units. Figure 5 In this configuration, a magnet arrangement 500 is located at the first end 312 of the input acceleration unit 308. The magnet arrangement is situated at the intersection between the electron source 200 and the input acceleration unit 308. The magnet arrangement 500 is located at the nozzle 208 of the electron source. In the case where the electron source is an electron gun, the nozzle 208 is an orifice within the electron gun. Electrons exit the electron source through the nozzle 208. The nozzle 208 is connected to the first end 312 of the input acceleration unit 308. The nozzle 208 allows electrons to exit the electron gun 200 and enter the input acceleration unit 308. The nozzle 208 can form the boundary between the electron gun 200 and the waveguide. The nozzle 208 is maintained under vacuum conditions.

[0038] If the electron gun is not positioned on the axis (not shown) and thus not along the central axis of the acceleration unit, the position of the magnet arrangement 500 will change accordingly. The magnet arrangement 500 is located near the electron source 200 to prevent backfire electrons from damaging the electron source. The magnet arrangement 500 is located at the intersection between the electron source 200 and the input acceleration unit 308.

[0039] Figure 6a and Figure 6b One embodiment is shown in which a magnet arrangement 500 is formed in a ring 602 surrounding the central axis of an acceleration unit 601, as shown in the figure. Figure 6a and 6b As shown. Figure 6a The arrangement of the ring 602 magnets formed around the central axis of the acceleration unit is shown. Figure 6b This shows the effect when viewed along the central axis of the acceleration unit 601. Figure 6aThe same embodiment is shown. The central axis of the acceleration unit 601 corresponds to the electron beam 612 emitted from the electron source. The magnet arrangement of the ring 602 can have a cylindrical shape, wherein the inner portion 604 is removed to allow the waveguide to fit within the inner portion 604. The ring can have a radius equal to the radius of the waveguide. The ring 602 is formed around the electron beam 612. The ring 602 is located at the intersection between the electron source and the input acceleration unit 608. The ring can be formed around the nozzle 606. The nozzle 606 injects electrons into the acceleration unit.

[0040] The magnet arrangement 500 can be formed by a single magnet or a series of magnets. The magnet arrangement 500 includes at least one conductor through which current flows to generate a magnetic field. The magnet arrangement 500 is formed by magnets used for focusing and manipulating an electron beam. The magnet arrangement 500 is formed by current flowing through the conductor to generate a magnetic field. The magnetic field is used to move negatively charged electrons.

[0041] The magnet arrangement 500 may include one or more alpha magnets. Figure 6c An example of an alpha magnet is shown. An alpha magnet is a type of magnet that can be used to deflect an electron beam by 270 degrees, such as... Figure 6c As shown. Alpha magnets are used in radiotherapy machines to bend the electron beam, guiding the electron beam generated by a linear accelerator towards a target. Alpha magnets are suitable for use in radiotherapy systems and can provide focusing to diffuse the energy in the electron beam to a small focal point. For example, high-energy medical electron LINACs are typically mounted horizontally, such as... Figure 1 As shown, the emitted electron beam from the accelerating tube is magnetically deflected by 90° or 270° into a vertical plane to impact an X-ray target or electron scatterer. This invention utilizes alpha magnet technology to mitigate backfire.

[0042] Figure 6c A square alpha magnet 620 with chamfered edges 622 is shown. The square alpha magnet 620 has an electron beam channel 624 etched therefrom. The alpha magnet can be formed in any shape. The electron beam channel 624 is where the electron beam is guided, and the electron beam bends around this channel. Electrons enter and exit the alpha magnet at the same entry / exit point 262. The magnetic field strength of the alpha magnet increases with increasing distance from the entry / exit point 262. The magnetic field gradient is as follows... Figure 6c The magnetic field acting on an electron is minimal when it first enters the alpha magnet, and maximal when it is furthest from the entry / exit point. Figure 6c Regions with high and low magnetic fields are marked. An alpha magnet is an electromagnet, and its magnetic field can be adjusted, for example, by changing the current within the electromagnet.

[0043] Figure 6cThe alpha magnet shown can bend an electron beam by 270 degrees. A single alpha magnet can be used to redirect electrons away from the electron source. Alpha magnets are achromatic, meaning that electrons of different energies will focus at a single point. This can be seen from... Figure 6c As can be seen from the different electron beam paths shown, electrons of different energies are accelerated and decelerated at different rates, but all of these electrons leave the alpha magnet at the same location.

[0044] Figure 6d A magnet arrangement 630 including a first α magnet and a second α magnet is shown. In the example shown, the first α magnet (magnet A) and the second α magnet (magnet B) are identical and... Figure 6c The individual magnets shown are identical. A first α magnet (magnet A) and a second α magnet (magnet B) are positioned adjacent to each other. The first α magnet (magnet A) and the second α magnet (magnet B) form a 90-degree angle. The magnets are arranged such that return electrons traveling toward the electron gun are first redirected by the first α magnet at a 270-degree angle, and then redirected by the second α magnet at a 270-degree angle. Figure 6d As shown, this combination of alpha magnet arrangements means that the backflush electrons are redirected at an angle of approximately 180 degrees. This means that the backflush electrons can join the electron beam that is accelerated along the central axis 304 of the acceleration unit.

[0045] Using two alpha magnets is advantageous because the magnetic field can be adjusted to change the angle of the redirected electrons (not shown). For example, backfiring electrons can travel in multiple directions upon reaching the alpha magnets. Therefore, it is desirable to ensure that the redirected electrons are redirected at the required precise angle to allow them to join the electron beam accelerated along the central axis 304 of the acceleration unit. The angle of the redirected electrons can be changed by adjusting the angle between the alpha magnets or by changing the magnetic field within the alpha magnets.

[0046] Figure 6c and 6d The α magnet arrangement shown can be arranged in Figure 6a and 6b In the ring-shaped configuration shown. These types of magnet arrangements are suitable for standing waveguides or traveling waveguides. α magnets may require a cooling mechanism (not shown) to prevent overheating.

[0047] In order to use such Figure 5Similar to the α-magnet arrangement shown in Figure 6, it is also desirable to move the electron gun off-axis (not shown) so that it is not along the central axis of the acceleration unit. This ensures that the magnetic field of the magnet arrangement does not affect the electrons when they first enter the input acceleration unit 308. To achieve this, the electron beam entering the input acceleration unit from the "off-axis" electron gun will be bent by using the electron gun magnet arrangement. When some of these electrons experience backfire, they will be redirected by the magnet arrangement in the same manner as previously discussed.

[0048] The magnet arrangement 500 prevents backbomb electrons from reaching the electron source 200. The magnet arrangement 500 can prevent backbomb electrons from reaching the electron source 200 by slowing them down and, in some cases, bringing them to a standstill. The magnet arrangement can also repel backbomb electrons that have already deviated from the electron beam 118 away from the electron source. Electrons are repelled by the magnet arrangement towards the output acceleration unit. The repelled electrons can then rejoin the electron beam.

[0049] Alternatively, the magnet arrangement is formed as a magnetic trap. A magnetic trap holds electrons at a single point, preventing them from moving. This trap works because most charged particles interact with the magnetic field through their magnetic dipole moments. If a charged particle moves in a magnetic field, it gains and loses energy as the strength of the magnetic field near the charged particle changes. The generation of a magnetic field that increases in all directions from the central minimum means that if a charged particle moves away from the minimum, it will gain potential energy and lose kinetic energy. Charged particles with sufficiently low total energy will convert all their kinetic energy into potential energy and be reflected from the higher magnetic field and trapped. When the magnet arrangement is formed as a magnetic trap, electrons are prevented from reaching the electron source because the magnets slow them down and trap them within the waveguide, preventing them from reaching the source.

[0050] Alternatively, a magnet arrangement can be used to completely redirect electrons away from waveguide 300. For example, a magnet arrangement 500 can be used to redirect back-bombardment electrons through a hole in electron gun 200. This hole can be formed in the metal plate 204 (also called the cathode) and filament wire 202 of electron gun 200. The advantage of this is that an off-axis gun is not required. Once the electrons leave the gun, they are quickly absorbed without damaging the electron gun.

[0051] Repelled electrons can be rejoined to the electron beam 118. As electrons rejoin the electron beam 118, this increases the electron beam current. This, in turn, increases the efficiency of the waveguide 300 and allows for the use of stronger currents to treat patients. Increased dose rate means patients can be treated more quickly and damage to healthy tissue can be prevented. In conventional waveguide systems, more electrons are typically generated to increase the current passing through the electron gun. However, when electrons “bombard back” in the wrong direction, many of the generated electrons are wasted and do not contribute to the overall output of the electron beam 118. This means that by using the magnet arrangement 500 to prevent backbombarded electrons from reaching the electron source 200 and redirecting the electrons to rejoin the electron beam, the number of electrons output through the waveguide 300 can be increased without adjusting the current of the electron source 200.

[0052] As previously mentioned, the backflush process has adverse effects on machine performance, including damage to the electron source. For example, the electron gun 200, and more specifically, its cathode, can be damaged by the bounced electrons. When backward-moving electrons collide with the cathode, they store their kinetic energy as heat, causing the cathode temperature to rise. This effect can be eliminated by using a magnet to trap the electrons. Therefore, this allows for better control of electron emission because the cathode temperature can be regulated. Furthermore, since the electron gun 200 overheats less, damage to the electron gun 200 can be limited. This prevents machine downtime and allows for continuous waveguide operation while reducing the risk of failure.

[0053] The previously described method of expecting to treat patients more quickly can be achieved by delivering a higher dose rate of X-rays to the patient. To do this, a higher incident electron beam power must be generated on the target by creating a larger electron beam current. This actually limits the maximum electron current the machine can produce, as electrons traveling at a faster speed in the backward direction generate more heat and cause more damage to the electron gun. This limitation on the X-ray dose rate can be overcome when using a magnet arrangement of 500. Intentional heating of the cathode can be increased to generate more electrons and a higher electron current without worrying about the cathode overheating due to the back-bombardment of electrons.

[0054] Another solution to mitigate the backbombing problem presented in this paper is to use a flow channel to remove backbombing electrons from waveguide 300 and prevent backbombing electrons from reaching electron source 200.

[0055] The flow channel can be configured to remove electrons from the waveguide or redirect electrons within a series of accelerating cells, for example by spraying electrons onto the walls of the cells to reduce the effects of backbombardment.

[0056] Figure 7An embodiment of a waveguide is shown, comprising a guide channel 700 for removing electrons from the waveguide. This waveguide is used in particle accelerators, such as linear accelerators. Waveguide 300 is designed to work with... Figure 3 and Figure 5 The waveguide operates in a similar manner. That is, the waveguide includes a series of accelerating units. The first accelerating unit is the input accelerating unit 308 through which electrons enter the waveguide 300. The waveguide 300 also includes an electron source 200, such as an electron gun. The electron source guides an electron beam 118 into the input accelerating unit 308. When the electron beam 118 enters the input accelerating unit 308 in the waveguide 300, it is accelerated by an electric field. The electron beam is then guided to an output accelerating unit (not shown). The electron beam is guided along the central axis of the accelerating unit. The output accelerating unit is located at the opposite end of the waveguide compared to the first accelerating unit. Both the output accelerating unit and the input accelerating unit are located at opposite ends along the central axis 304 of the waveguide 300. Figure 1 In one embodiment, the waveguide includes a current-guiding channel 700. The current-guiding channel 700 is configured to remove electrons traveling toward the electron source 200 from the waveguide 300. The current-guiding channel 700 is also configured to remove electrons from the input acceleration unit 308.

[0057] The current channel 700 has an opening located at the intersection between the electron source 200 and the input acceleration unit 308. The current channel 700 is located at the first end 312 of the input acceleration unit 318. There may be one or more current channels 700. Multiple current channels 700 can be present within the input acceleration unit 318, and these current channels 700 can all lead to a single output. The multiple current channels 700 can be arranged at regular intervals around the acceleration unit, for example, at multiple intervals around the first end of the input acceleration unit. There may also be current channels located on some or all of a series of acceleration units. The current channels of each acceleration unit in a series of acceleration units can lead to the same single output. Maximum electron yield can be achieved by having current channels 700 in the input acceleration unit 318 because back-boosting electrons are most prevalent in this unit. The yield of the current channel 700 decreases the further away it is from the electron source 200, and the current channel 700 is placed within the acceleration unit.

[0058] In one embodiment, a flow channel 700 is formed in a ring around the circumference of waveguide 300. This ring is located at the intersection between the electron source 200 and the input acceleration unit 308. The ring flow channel may be cylindrical, with its inner portion removed to allow the waveguide or nozzle to fit within the inner portion 603. The ring may be formed around the circumference of nozzle 208.

[0059] The current channel 700 is configured to direct electrons away from the waveguide. In one embodiment, the current channel 700 may be connected to a cavity (not shown) to store electrons. This removes electrons from the waveguide 300 and prevents them from damaging the electron source 200. The cavity is formed by a hollow space surrounded by a panel. The panel is made of an electron-absorbing surface. The panel is constructed to allow for quick and easy replacement.

[0060] In another embodiment, the flow channel 700 is configured to accelerate the secondary electron beam. For example... Figure 7 As shown, the flow channel 700 can be connected to a second particle accelerator 710. The second particle accelerator 710 is positioned along an axis parallel to the central axis of the acceleration unit 601. The flow channel 700 includes a 180-degree bend to guide electrons into the second particle accelerator 710, which is positioned along an axis parallel to the central axis of the acceleration unit. Figure 6c and Figure 6d The α-magnet configuration shown can be used to direct electrons into the second particle accelerator 710. This works in the same manner as described above for redirecting electrons within the main particle accelerator. Figure 6d As shown, two alpha magnets can be used to bend the electron path by 180 degrees.

[0061] The second particle accelerator 710 also requires a second radio frequency (RF) radiation source to accelerate electrons along its path. The second RF radiation source is coupled to the second particle accelerator, for example, a solenoid or magnetron. The second particle accelerator 710 has waveguides and acceleration units similar to the main particle accelerator. That is, the second particle accelerator 710 operates in a similar manner to the main particle accelerator, but electrons enter the second particle accelerator 710 from the guide channel 700 instead of from the electron gun 200. Furthermore, the guide channel 700 itself may also require an RF radiation source to ensure that the electrons have sufficient energy to be guided to the second particle accelerator 710 and to bend the electrons by 180 degrees. The second RF radiation source can be the same RF radiation source used in the main particle accelerator. Alternatively, the second radiation source can use power reflected from an RF radiation source used in the main particle accelerator or reflected from elsewhere. The second radiation source can use power extracted from higher-order modes.

[0062] A second particle accelerator 710 and a secondary electron beam are used for patient imaging. The second particle accelerator 710 is directed to a second tungsten target 720. The target 720 is located near the second particle accelerator. The target 720 is typically made of tungsten. This produces an X-ray source that can be used for imaging, while the main accelerator unit is used for its usual therapeutic purposes.

[0063] In an alternative embodiment, the second particle accelerator 710 can be configured to guide electrons such that they strike the same target (e.g., tungsten) (not shown) guided by a series of acceleration units. The resulting radiation beam can be used for patient treatment or imaging. This embodiment has the advantages of recovering back-bombarded electrons and improving waveguide efficiency. The second particle accelerator 710 is positioned along an axis parallel to the central axis of the acceleration unit 601 to allow the second particle accelerator to guide electrons to the target.

[0064] Waveguides can also be switched between the different uses described above. Electrons from the second particle accelerator can be used for individual imaging or guided to collide with the same target directed by a series of accelerator units. This reduces the number of devices required to perform different tasks. The switching mechanism can be assisted by detuning units. For example, since the same accelerator channel is used for both imaging and treatment, the energy beam required for imaging will be lower than that required for treatment. Therefore, it is desirable to detune the unit to allow for reduced beam power when using the accelerator channel for imaging. Similarly, detuning can then be turned off again to allow for acceleration for treatment.

[0065] The features of the above aspects can be combined in any suitable manner. It should be understood that the above description is only as specific embodiments of the aspects, and many modifications and changes will be within the capabilities of those skilled in the art and are intended to be covered by the scope of the appended claims.

Claims

1. A particle accelerator comprising: a waveguide (300) comprising a series of acceleration cells (302), wherein the series of acceleration cells comprises an input acceleration cell, the series of acceleration cells being configured to accelerate an electron beam along a central axis of the acceleration cells; an electron source (200) configured to input an electron beam (207) into the input acceleration cell; and a magnet arrangement (500) configured to prevent electrons that have strayed from the electron beam from hitting the electron source and to redirect the electrons that have strayed back into the electron beam at an angle of substantially 180 degrees.

2. The particle accelerator of claim 1, wherein a nozzle (208) of the electron source is configured to output electrons into the input acceleration cell, and the magnet arrangement is located at the nozzle.

3. The particle accelerator of claim 1 or 2, wherein the magnet arrangement is located at an intersection between the electron source and the input acceleration cell.

4. The particle accelerator of claim 1 or 2, wherein the magnet arrangement is a ring around a first end of the input acceleration cell.

5. The particle accelerator of claim 1, wherein the magnet arrangement comprises an alpha magnet comprising: an entry point configured to receive electrons travelling in a first direction; and a magnetic field that increases in strength in a direction away from the entry point, such that the received electrons travel along an electron beam path and exit the magnet at the entry point travelling in a second direction.

6. The particle accelerator of claim 5, wherein the second direction is at a 270 degree angle to the first direction.

7. The particle accelerator of claim 5 or 6, wherein the magnet arrangement comprises a first alpha magnet and a second alpha magnet, wherein the second alpha magnet is positioned to receive electrons from the first alpha magnet, and the first alpha magnet is at a 90 degree angle to the second alpha magnet.

8. The particle accelerator of claim 1 or 2, wherein the electron source is located at a position that is not along the central axis of the acceleration cells.

9. A method for a particle accelerator, the method comprising: generating an electron beam from an electron source; inputting the electron beam into an input acceleration cell of a waveguide; applying a radio frequency field to the waveguide to generate an oscillating electric field along a central axis of the waveguide, thereby accelerating the electron beam along the central axis; trapping electrons that have strayed from the electron beam using a magnet arrangement; and turning off the magnet arrangement to allow the trapped electrons to join the electron beam.

10. The method of claim 9, wherein the step of turning off the magnet arrangement is timed to coincide with a phase change of the radio frequency field applied to the waveguide.

11. A radiotherapy device comprising the particle accelerator of any one of claims 1 to 8. ​ ​ ​

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