CONFIGURABLE COLLIMATOR CONTROLLED

USING LINEAR MOTORS

TECHNICAL FIELD

[0001] This disclosure relates generally to a configurable collimator that is controlled using linear motors.

BACKGROUND

[0002] Particle therapy systems use an accelerator to generate a particle beam for treating afflictions, such as tumors. In operation, particles are accelerated in orbits inside a cavity in the presence of a magnetic field, and are removed from the cavity through an extraction channel. A magnetic field regenerator generates a magnetic field bump near the outside of the cavity to distort the pitch and angle of some orbits so that they precess towards, and eventually into, the extraction channel. A beam, comprised of the particles, exits the extraction channel.

[0003] A scanning system is down-beam of the extraction channel. In this context, "down-beam" means closer to an irradiation target (here, relative to the extraction channel). The scanning system moves the particle beam across at least part of the irradiation target to expose various parts of the irradiation target to the particle beam. For example, to treat a tumor, the particle beam may be "scanned" over different cross-sectional layers of the tumor.

[0004] The particle beam can damage healthy tissue adjacent to the irradiation target. A structure defining an edge may be used to limit exposure of the healthy tissue to the particle beam. For example, the structure, or a portion thereof, may be placed in between the particle beam and the healthy tissue, thereby preventing exposure of the healthy tissue to the particle beam.

SUMMARY

[0005] An example device for trimming a particle beam comprises: structures comprised of material that blocks passage of the particle beam, with the structures being configurable to define an edge that is movable into a path of the particle beam such that a first part of the particle beam on a first side of the edge is blocked by the structures and such that a second part of the particle beam on a second side of the edge is not blocked by the structures; and linear motors that are controllable to configure the structures to define the edge. Each of the linear motors comprises a movable component and a stationary component, with the stationary component comprising a magnetic field generator to generate a first magnetic field, and with the movable component comprising one or more coils to conduct current to produce a second magnetic field that interacts with the first magnetic field to cause the moveable component to move relative to the stationary component. The movable component of each linear motor is connected to, or part of, a corresponding one of the structures such that the corresponding structure moves along with movement with the movable component. The example device may also include one or more of the following features, either alone or in combination.

[0006] The magnetic field generator may comprise magnets having like poles that are aligned, with the one or more coils being at least partly between the magnets. The example device may comprise one or more processing devices to control the linear motors to configure the structures. The one or more processing devices may be controllable to output one or more control signals to control one or more of the linear motors to extend or to retract one or more of the structures to define the edge. The one or more processing devices may be at least partly shielded from exposure to environmental neutron radiation impacting the structures and the linear motors during operation of the device. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices remotely from the structures and the linear motors. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices in a different room from the structures and the linear motors.

[0007] The example device may comprise encoders that are configured to track movement of the structures and to provide information to the one or more processing devices about the movement of the structures. The encoders may comprise electronic devices that are connected to a same assembly as the structures and the linear motors. The encoders may comprise one or more of laser sensors, optic sensors, or diode sensors.

[0008] The structures may comprise leaves and each magnetic field generator may comprise a pair of magnets, with each leaf being between a corresponding pair of magnets. The example device may comprise a first carriage configured to move in a first dimension, with the first carriage holding the structures and the linear motors; and a second carriage configured to move in a second dimension that is different from the first dimension, with the first carriage being coupled to the second carriage. The structures may be movable also in the first dimension relative to, and separate from movement of, the first carriage. The structures may define a first edge, and the device may further comprise: second structures that are configurable to define a second edge that is movable into a path of the particle beam such that a third part of the particle beam on a first side of the second edge is blocked by the second structures and such that a fourth part of the particle beam on a second side of the second edge is not blocked by the second structures; and second linear motors that are controllable to configure the second structures to define the second edge. The device further may further comprise a third carriage that is movable in the first dimension and that is coupled to the second carriage, with the third carriage holding the second structures and the second linear motors. The second structures may be movable also in the first dimension relative to, and separate from movement of, the third carriage. The first carriage and the third carriage may be controllable to trim a single spot of the particle beam, with the single spot corresponding to a cross- sectional area of the particle beam. The first carriage and the third carriage may be controllable to trim an area having a size that covers multiple spots of the particle beam, with a spot corresponding to a cross-sectional area of the particle beam. The first carriage and the third carriage may be configured to move independently.

[0009] An example device to trim a particle beam comprises: a first carriage that is movable in a first dimension; second carriages that are coupled to the first carriage and therefore movable in the first dimension along with the first carriage, with each of the second carriages also being movable in a second dimension that is different from the first dimension. A second carriage among the second carriages comprises: structures comprised of material that blocks passage of the particle beam, with the structures being configurable to define an edge that is movable into a path of the particle beam such that a first part of the particle beam on a first side of the edge is blocked by the structures and such that a second part of the particle beam on a second side of the edge is not blocked by the structures; and linear motors to configure the structures to define the edge, with each of the linear motors being controllable to drive a corresponding one of the structures linearly in the second dimension towards, or away from, the second carriage. The example device may comprise one of more of the following features, either alone or in combination.

[0010] A linear motor among the linear motors may comprise a movable component and a stationary component, with the stationary component comprising a magnetic field generator to generate a first magnetic field, and with the movable component comprising one or more coils to conduct current to produce a second magnetic field that interacts with the first magnetic field to cause the moveable component to move relative to the stationary component. The movable component of the linear motor may be connected to, or part of, a corresponding one of the structures such that the corresponding structure moves along with movement with the movable component. The magnetic field generator may comprise magnets having like poles that are aligned, with the one or more coils being at least partly between the magnets.

[0011] The example device may comprise one or more processing devices to control the linear motors to configure the structures. The one or more processing devices may be controllable to output one or more control signals to control one or more of the linear motors to extend or to retract one or more of the structures in the second dimension to define the edge, with the one or more processing devices being shielded from exposure to environmental neutron radiation impacting the structures and the linear motors during operation of the device. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices remotely from the structures and the linear motors. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices in a different room from the structures and the linear motors.

[0012] The example device may comprise encoders that are configured to track movement of the structures and to provide information to the one or more processing devices about the movement of the structures. The encoders may comprise electronic devices that are more tolerant than the one or more processing devices to exposure to the neutron radiation impacting the structures and the linear motors during operation of the device. The encoders may comprise one or more of laser sensors, optic sensors, or diode sensors.

[0013] An example particle therapy system comprises: a particle accelerator to output a particle beam, with the particle accelerator generating neutron radiation in an enclosed treatment space during operation; one or more scanning magnets to move the particle beam relative to an irradiation target in a patient; and a device to trim the particle beam, with the device being between the one or more scanning magnets and the patient. The device comprises structures comprised of material that blocks passage of the particle beam, with the structures being configurable to define an edge that is movable into a path of the particle beam such that a first part of the particle beam on a first side of the edge is blocked by the structures and such that a second part of the particle beam on a second side of the edge is not blocked by the structures; and linear motors that are controllable to configure the structures by driving the structures linearly to define the edge. One or more processing devices are configured to control operation of the device to trim the particle beam, with the one or more processing devices being located in an area that is exposed to less than a specified amount of the neutron radiation. The example particle therapy system may comprise one or more of the following features, either alone or in combination.

[0014] The area may be a room that is external to the enclosed treatment space. The enclosed treatment space may be at least partly shielded to reduce exposure of the room to the neutron radiation. A linear motor among the linear motors may comprise a movable component and a stationary component, with the stationary component comprising a magnetic field generator to generate a first magnetic field, and with the movable component comprising one or more coils to conduct current to produce a second magnetic field that interacts with the first magnetic field to cause the moveable component to move relative to the stationary component. The movable component of the linear motor may be connected to, or part of, a corresponding one of the structures such that the corresponding structure moves along with movement with the movable component to drive the

corresponding structure linearly. The magnetic field generator may comprise magnets having like poles that are aligned, with the one or more coils being at least partly between the magnets.

[0015] The device may comprise encoders that are configured to track movement of the structures and to provide information to the one or more

processing devices about the movement of the structures, with the encoders being within the enclosed treatment space and subjected to the neutron radiation. The encoders may comprise one or more of laser sensors, optic sensors, or diode sensors. The structures may comprise leaves and each magnetic field generator may comprise a pair of magnets, with each leaf being between a corresponding pair of magnets.

[0016] The particle accelerator may be, or include, a synchrocyclotron. The particle therapy system may comprise a gantry on which at least the

synchrocyclotron is mounted, with the gantry being movable relative to the patient to move the synchrocyclotron relative to the patient.

[0017] The synchrocyclotron may comprise: a voltage source to provide a radio frequency (RF) voltage to a cavity to accelerate particles from a particle source, with the voltage source being controlled to sweep the RF voltage over a frequency range in a cycle; a coil to receive electrical current having one of multiple values and to generate a magnetic field corresponding to the electrical current, with the magnetic field for causing the particles to move orbitally within the cavity at an energy that corresponds to the electrical current, the magnetic field being at least 4 Tesla; and an extraction channel to receive the particles from the cavity and to output the particles received from the cavity to the scanning system, with the particles that are output from the cavity having an energy that is based on the electrical current. The synchrocyclotron may be configured to enable setting of the electrical current to one of the multiple values, with each of the multiple values corresponding to a different energy at which particles are output from the cavity. The voltage source may be controllable to sweep the RF voltage over a different frequency ranges, with each different frequency range corresponding to each different energy at which the particles are output from the cavity.

[0018] The synchrocyclotron may comprise: a particle source for holding ionized plasma, with the particle source being in a cavity and comprising two parts that are separated at an acceleration region; a voltage source to provide a radio frequency (RF) voltage to the cavity to accelerate particles from the ionized plasma at a separation region of the particle source, with the voltage source being

controllable to sweep the RF voltage over a frequency range in a cycle; a coil to receive electrical current to generate a magnetic field based on the electrical current, with the magnetic field for causing the particles to move orbitally within the cavity, with the magnetic field in the cavity being a maximum of 4 Tesla or more; at least one magnetic pole piece, with the at least one magnetic pole piece comprising ferromagnetic material that borders the cavity; and an extraction channel to receive the particles from the cavity and to output the particles received towards the one or more scanning magnets.

[0019] An example device for trimming a particle beam comprises: structures comprised of material that blocks passage of the particle beam, with the structures being configurable to define an edge that is movable into a path of the particle beam; and linear motors that are controllable to configure the structures to define the edge. The example device may comprise one or more of the following features, either alone or in combination.

[0020] The example device may comprise one or more processing devices to control the linear motors to configure the structures. The one or more processing devices may be controllable to output one or more control signals to control one or more of the linear motors to extend or to retract one or more of the structures to define the edge. The one or more processing devices may be at least partly shielded from exposure to environmental neutron radiation impacting the structures and the linear motors during operation of the device. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices remotely from the structures and the linear motors. The one or more processing devices may be shielded from exposure to the environmental neutron radiation by locating the one more processing devices in a different room from the structures and the linear motors.

[0021] The example device may comprise encoders that are configured to track movement of the structures and to provide information to the one or more processing devices about the movement of the structures. The encoders may comprise electronic devices that are connected to a same assembly as the structures and the linear motors. The encoders may comprise one or more of laser sensors, optic sensors, or diode sensors.

[0022] Two or more of the features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein.

[0023] Control of the various systems described herein, or portions thereof, may be implemented via a computer program product that includes instructions that are stored on one or more non-transitory machine-readable storage media, and that are executable on one or more processing devices (e.g., microprocessor(s), application-specific integrated circuit(s), programmed logic such as field

programmable gate array(s), or the like). The systems described herein, or portions thereof, may be implemented as an apparatus, method, or electronic system that may include one or more processing devices and computer memory to store executable instructions to implement control of the stated functions.

[0024] The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 is a perspective view of an example configurable collimator leaf that is usable with the example configurable collimators described herein. [0026] Fig. 2 is a top view of configurable collimator leaves positioned relative to a treatment area of an irradiation target.

[0027] Fig. 3 is a top view of configurable collimator leaves positioned relative to a treatment area of an irradiation target.

[0028] Fig. 4 is a perspective view of an example configurable collimator.

[0029] Fig. 5 is a side view of an example configurable collimator.

[0030] Fig. 6 is a perspective, view of an example configurable collimator having components portrayed in see-through to show the interiors thereof.

[0031] Fig. 7 is a block diagram of an example linear motor and example configurable collimator leaves controlled thereby.

[0032] Fig. 8 is a block diagram of an example set of leaves for a carriage that are controllable by the linear motors described herein.

[0033] Fig. 9 shows a cut-away, back view of example implementation of part of a configurable collimator.

[0034] Fig. 10 is a top view of configurable collimator leaves on carriages mounted on a track that is curved relative to the direction of a particle beam.

[0035] Fig. 1 1 is a perspective view of a configurable collimator positioned relative to a patient during particle therapy treatment.

[0036] Fig. 12 is a cut-away view of part of an example particle accelerator that is usable in the particle therapy system described herein.

[0037] Fig. 13 is a perspective view of components of an example scanning system.

[0038] Fig. 14 is a perspective view of components of an example scanning system.

[0039] Fig. 15 is a front view of an example magnet for use in a scanning system of the type shown in Figs. 13 and 14.

[0040] Fig. 16 is a perspective view of an example magnet for use in a scanning system of the type shown in Figs. 13 and 14.

[0041] Fig. 17 is a perspective view of an example energy degrader (range modulator) for use in a scanning system of the type shown in Figs. 13 and 14. [0042] Fig. 18 is a perspective view of a process for moving a leaf of an energy degrader in the path of a particle beam.

[0043] Figs. 19 and 20 are front and perspective views, respectively, of an example particle therapy system.

[0044] Fig. 21 is a perspective view of an example particle therapy system.

[0045] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0046] Described herein are example implementations of a configurable collimator that may be used to control the extent of radiation, such as a proton or ion beam, applied to a patient. In this regard, a configurable collimator includes a structure that is controllable to allow some radiation to pass to a patient and to block some radiation from passing to the patient. Typically, the radiation that passes is directed to an irradiation target to be treated, and the radiation that is blocked would otherwise hit, and potentially damage, healthy tissue. In operation, the configurable collimator is placed in the radiation path between a radiation source and an irradiation target and is controlled to produce an opening of an appropriate size and shape to allow some radiation to pass through the opening to the irradiation target, while a remainder of the structure blocks some radiation from reaching adjacent tissue. The configurable collimator may be used in any appropriate radiation therapy system, and is not limited to use with any particular type of system.

[0047] In some implementations, the configurable collimator contains generally flat structures, which are referred to as "plates" or "leaves", and which are controllable to move into the "beam" or "treatment" area to block passage of some radiation and allow passage of other radiation. In some implementations, there are two sets of leaves that face each other. The sets of leaves are controllable to produce an opening of size and shape that is appropriate for treatment. For example, each set of leaves is configurable to define an edge that is movable into a path of the particle beam so that a first part of the particle beam on a first side of the edge is blocked by the leaves, and so that a second part of the particle beam on a second side of the edge is not blocked by the leaves and is allowed to pass to the treatment area. In some implementations the leaves are connected to, are part of, or include, linear motors - one per leaf - that are controllable to control movement of the leaves towards or away from the treatment area to define the edge.

[0048] In some implementations, the linear motors are controllable to configure a set of leaves to define a first edge, and to configure another set of leaves to define a second edge that faces the first edge. As described herein, each of the linear motors may include a movable component and a stationary component. The stationary component includes a magnetic field generator to generate a first magnetic field. An example of a magnetic field generator includes two stationary magnets that are adjacent and spaced apart, and that have their poles aligned. The movable component includes one or more coils to conduct current to produce a second magnetic field that interacts with the first magnetic field to cause the moveable component to move relative to the stationary component. For example, the movable component may be a coil-carrying plate between the two magnets that make up the stationary component. When current passes through the coil, that current produces a magnetic field that interacts with the magnetic field produced by the two magnets, and that causes the movable component (e.g., the current-carrying plate) to move relative to the two magnets. Because a leaf is attached to the movable component, the leaf moves along with the movable component. The linear motors of different leaves may be controlled to control movement of the leaves, and thus to define the edges of the configurable collimator described above.

[0049] As noted, in some implementations, a linear motor includes two magnets that are adjacent and spaced apart and that have their poles aligned, and a coil-carrying plate that is sandwiched between the two magnets and that moves relative to the two magnets. This configuration allows multiple linear motors to be arranged in a row, each in close proximity to the next, as may be required to control leaves of the configurable collimator. For example, in some implementations, the leaves are on the order of millimeters thick (e.g., five millimeters or less). Leaves of this thickness enable relatively high precision edges; however, leaves of this thickness may make implementation using other types of motors impractical in some cases. However, the linear motors described herein enable use of leaves having thicknesses of this magnitude. For example, the two stationary magnets shield the coil-carrying plate that moves between them, thereby controlling movement of the leaves. By shielding the coil-carrying plate from stray magnetic fields, it is possible to control movement of the plates even when multiple coil-carryings and

corresponding stationary magnets are close proximity to each other.

[0050] In some implementations, a computing system, which may be comprised of one or more processing devices, is programmed to control the linear motors to thereby control positioning of leaves to define an edge. For example, the computing system may be controllable to output one or more control signals to control one or more of the linear motors to extend or to retract one or more of the leaves to define the edge. The computing system is at least partly shielded from exposure to environmental neutron radiation impacting leaves and the linear motors during particle therapy. More specifically, application of particle therapy causes stray neutrons to be present in the treatment room (e.g., a proton center). Stray neutrons can have a deleterious effect on electronics and, therefore, it is beneficial to shield those electronics from the neutrons. For example, processing devices, such as microprocessors, microcontrollers, field-programmable gate arrays

(FPGAs), applications-specific circuits (ASICs), and so forth can be susceptible to environmental neutron radiation. Accordingly, in some implementations, the computing system is shielded by locating the computing system remotely from the source of the neutron radiation. For example, the computing system may be shielded by locating the computing system remotely from the collimation device, including the linear motors, that are controlled by the computing system. In some examples, the computing system may be located in a different room from where treatment occurs. The room may be appropriately shielded to reduce, or to prevent, the effects of neutron radiation on the computing system.

In some implementations, motion of the linear motors may be tracked using encoders. In some examples, encoders include electronic devices that are connected to a same assembly as the leaves and the linear motors. The encoders may include or more of laser sensors, optic sensors, or diode sensors. The encoders detect movement of the leaves, e.g., by detecting where markings or other indicia on the leaves, or on structures that are connected to and that move with the leaves, are located relative to the encoders. Information about locations of the leaves is fed back to the computing system, and is used by the computing system to confirm the position of the leaves during operation and, in some implementations, to change their position. The encoders may be, or include, simple electronic sensors that are not as sensitive to neutron radiation as the processing devices above and that, therefore, may be located in the treatment room.

[0051] Fig. 1 shows an example of a leaf 140 that may be used in the configurable collimator, although the configurable collimator is not limited to use with this type of leaf. The height 150 of the leaf is along the beamline (e.g., the direction of the particle beam). The length 152 of the leaf is along its direction of actuation into and out of the treatment area, and is based on the field size, or portion thereof, that the system can treat. The field size corresponds to the treatment area that the beam can impact. The width 153 of the leaf is the direction along which multiple leaves stack when actuated. Generally, the more leaves that are used, the higher the resolution of the aperture that can be produced, including for curved boundaries.

[0052] In Fig. 1 , leaf 140 includes a tongue and groove feature 155 along its side, which is configured to reduce inter-leaf leakage when multiple such leaves stack. In this example, the curved end 156 of leaf 140 is configured to maintain a surface tangent to the beam at all locations in the treatment area. However, as also described herein, the end of each leaf may be flat, not curved.

[0053] In some implementations, the configurable collimator leaves have a height that is sufficient to block at least the maximum beam energy (e.g., the maximum energy of the particle beam output by the system). In some

implementations, the configurable collimator leaves have a height that blocks less than the maximum beam energy. In some implementations, the configurable collimator leaves have lengths that are dictated not by the area of an entire treatment area, but rather by the area of a single beam spot or multiple beam spots. In this context, a "beam spot" is the cross-sectional area of a particle beam.

[0054] In some implementations, the particle therapy system may be configured to treat a tumor having a cross-section that can fit into a 20cm x 20cm square area. In this example, each leaf in the configurable collimator may have a length of about 2cm, which is about enough to block particles in half of one beam spot. As noted, the configurable collimator includes sets of leaves that face each other. So, leaves from each set may be controlled to cover the whole, single beam spot, if necessary, thereby preventing passage of radiation. The leaves may also be controllable to create an opening through which some, or all, of the radiation from the single beam spot can pass.

[0055] In operation, the configurable collimator is configured to move as the beam scans across the radiation target, and to track the beam's movement during scanning. In this example, the configurable collimator may be configured to move about 20cm so as to enable coverage over the entirety of the 20cm x 20cm area. As described above, the configurable collimator may be configured to use enough leaves to cover (or "trim") one beam spot and, in some case, a small amount of extra area (e.g., 5% extra area, 10% extra area, 15% extra area, or 20% extra area).

[0056] Fig. 2 shows an example implementation of a configurable collimator 200. Configurable collimator 200 includes leaves 201 having a height and made of a material, such as nickel, brass, tungsten, or other metal, sufficient to inhibit or prevent passage of radiation at a given energy. For example in some systems, a particle accelerator is configured to generate a particle beam having a maximum energy of 100 MeV to 300 MeV. Accordingly, in such systems, the leaves may be constructed to prevent passage of a beam having an energy of 100 MeV, 150 MeV, 200 MeV, 250 Mev, 300 MeV, and so forth.

[0057] Leaves 201 are mounted on carriages to control their movement relative to a treatment area of an irradiation target, such as a cross-sectional layer of a tumor in a patient. The movement is controlled to cause leaves 201 to cover some parts of treatment area 204, thereby preventing radiation from impacting those parts during treatment, while leaving other parts of treatment area exposed to the radiation. In the example implementation of Fig. 2, there are fourteen leaves in total, seven on the left and seven on the right. In some implementations, there may be a different number of leaves, e.g., ten in total, five on the left and five on the right, twelve in total, six on the left and six on the right, and so forth. [0058] The configurable collimator may be used with any appropriate type of radiation therapy system. In an example implementation, the radiation therapy system is a proton therapy system. As described herein, an example proton therapy system scans a proton beam across a treatment area of an irradiation target in order to destroy malignant tissue. During scanning, the particle beam moves across the treatment area to cover the treatment area with radiation. In an example

implementation, the particle beam is pulsed. Because the particle beam is pulsed, the affected parts of the treatment area constitute a series of spots, one for each pulse that hits the treatment area. Depending upon the size of the beam, the result may leave some areas untreated. As a result, it may be beneficial to scan the same treatment area more than once in order to ensure that the entire area is treated. Each successive scan may be offset from the other(s) in order to hit all areas. An example of this type of scanning is called pencil-beam scanning, and the repetitive scans are referred to as painting or repainting the treatment area.

[0059] The irradiation target is typically three-dimensional in structure.

Accordingly, as described herein, the irradiation target is treated cross-sectional layer (or simply "layer") by layer. That is, a layer of the irradiation target is treated, followed by another treatment of another layer, and so forth until the entire target is treated. Different layers of an irradiation target are treated by varying an energy level of the particle beam. That is, different energy levels of the particle beam impact different layers of the irradiation target, with higher energy levels affecting layers deeper inside the irradiation target relative to the particle beam source.

Accordingly, during treatment, the energy level of the particle beam is changed in order to reach, and thus treat, different layers of the irradiation target.

[0060] Fig. 2 shows leaves 201 configured allow radiation to impact part of a layer (e.g., the treatment area) and to prevent radiation from impacting other parts of the layer (e.g., healthy tissue). In Fig. 2, locations 202 represent centers of beam spots to be delivered during a scan of a proton beam across treatment area 204. Circle 208 represents a treatment boundary beyond which no radiation is intended to be delivered. Beam spots that are close to this boundary (e.g., within one standard deviation of the particle beam's profile) border healthy tissue. These are spots that are trimmed (that is, blocked) by appropriate configuration and placement of leaves on the configurable collimator. An example of a beam spot to be trimmed is beam spot 21 1 , having its center at location 206. As shown, leaves 201 are configured to block the portion of beam spot 21 1 that extends beyond circle 208 and into healthy tissue (or at least tissue not designated for treatment).

[0061] In an example implementation, on each of two separate carriages, there are five leaves that are about 5mm in width and two leaves that are about 20mm in width. In some implementations, on each of two separate carriages, there are seven leaves, two of which each have widths that are three times or more the widths of each of five other leaves. Other implementations may contain different numbers, sizes, and configurations of leaves, and different numbers and

configurations of carriages. For example, some implementations may include any number between five and fifty leaves per carriage, e.g., 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29, 30, 31 , 32, 33, 34, 35, 36, 37, 38, 39, 40, 41 , 42, 43, 44, 45, 46, 47, 48, 49, or 50 leaves (or more) per carriage.

[0062] The carriages can move both horizontally and vertically, as described herein. The leaves are also movable horizontally relative to each carriage into, and out of, the treatment area. In this way, the leaves are configurable to approximate the shape of the treatment boundary in the region near the area being treated (e.g., circle 21 1 or a portion thereof in this example).

[0063] The leaves may be moved vertically and/or horizontally between different scans of the particle beam so that the leaves are in appropriate positions when the beam is delivered to a particular area. The leaves need not necessarily be moved for every scan pass, but instead may be moved to a location appropriate for an area. In some cases, e.g., for spots interior to the treatment area, radiation treatment may proceed without the trimming provided by the configurable collimator.

[0064] Fig. 3 shows another example of leaves 300 that are part of a configurable collimator configured to trim a radiation spot 301 centered at location 302. In this example, there are seven leaves on each of two sides of the

configurable collimator (supported by corresponding carriages). The leaves on each side include two leaves that are wider than the other five; however, the configurable collimator is not limited to this configuration. In this case, spot 301 has a radius of 2.5 sigma defining an 8mm Gaussian radiation spot.

[0065] Figs. 4, 5, and 6 show an example implementation of a configurable collimator, including carriages 413, 414, 415 configured to hold, and to move, the leaves described above both vertically and horizontally relative to the treatment target. As shown, vertical movement includes movement in the Cartesian Z- direction 417, and horizontal movement includes movement in the Cartesian X direction 418 (with the Cartesian Y direction being into, or out of, the page in Fig. 5). Figs. 5 and 6 show parts of carriage housings as transparent in order to show components inside the housings; however, the housings are not actually

transparent.

[0066] Carriage 413 is referred to herein as the primary carriage, and carriages 414 and 415 are referred to herein as secondary carriages. Secondary carriages 414, 415 are coupled to primary carriage 413, as shown in Figs. 4 to 6. In this example, secondary carriages 414, 415 each include a housing that is fixed to primary carriage 415 via a corresponding member 418, 419. In this example, primary carriage 413 is movable vertically relative to the irradiation target and relative to particle accelerator along tracks 420. The vertical movement of primary carriage 413 also causes the secondary carriages to move vertically. In some implementations, the secondary carriages move vertically in concert. In some implementations, vertical movement of each secondary carriage is independent of vertical movement of the other secondary carriage.

[0067] As shown in Figs. 4 to 6, each secondary carriage 414, 415 is connected to a corresponding rod or rail 422, 423, along which the secondary carriage moves. More specifically, in this example, motor 425 drives secondary carriage 414 to move along rod 422 towards or away from secondary carriage 415. Likewise, in this example, motor 426 drives secondary carriage 415 to move along rod 423 towards or away from secondary carriage 414. Control over movement of the primary and secondary carriages is implemented to position the leaves relative to the irradiation target, as described herein. In addition, the leaves themselves are also configured to move in and out of the carriages, as also described herein.

[0068] As shown in Fig. 6, a motor 430 drives the vertical movement of primary carriage 413. For example, as shown in Fig. 6, lead screw 431 is coupled to housing 432, which holds motors 425, 426 that drive corresponding secondary carriages 414, 415, and which is mounted on tracks 420. Lead screw 431 is coupled to, and driven vertically by, motor 430. That is, motor 430 drives lead screw 431 vertically, either towards or away from the irradiation target. Because lead screw 431 is fixed to housing 432, this movement also causes housing 432, and thus secondary carriages 414, 415, to move along tracks 420, either towards or away from the irradiation target.

[0069] In this example implementation, as noted, seven leaves 435, 436 are mounted on each secondary carriage 414, 415. Each secondary carriage may be configured to move its leaves horizontally into, or out of, the treatment area. The individual leaves on each secondary carriage may be independently and linearly movable, using linear motors, in the X dimension relative to other leaves on the same secondary carriage. In some implementations, the leaves may also be configured to move in the Y dimension. Furthermore, the leaves on one secondary carriage 414 may be movable independently of the leaves on the other secondary carriage 415. These independent movements of leaves on the secondary carriages, together with the vertical movements enabled by the primary carriage, allow the leaves to be moved into various configurations. As a result, the leaves can conform, both horizontally and vertically, to treatment areas that are randomly shaped both in horizontal and vertical dimensions. The sizes and shapes of the leaves may be varied to create different conformations.

[0070] The leaves may be made of any appropriate material that prevents or inhibits transmission of radiation. The type of radiation used may dictate what material(s) are used in the leaves. For example, if the radiation is X-ray, the leaves may be made of lead. In the examples described herein, the radiation is a proton or ion beam. Accordingly, different types of metals or other materials may be used for the leaves. For example, the leaves may be made of nickel, tungsten, lead, brass, steel, iron, or any appropriate combinations thereof. The height of each leaf may determine how well that leaf inhibits transmission of radiation.

[0071] In some implementations, the leaves may have the same height, whereas in other implementations, some of the leaves may have heights that are different from heights of others of the leaves. For example, in Figs. 2 to 6, a set of leaves are each 5mm in height. However, any appropriate heights may be used. For example, leaves 435, 436 may have any of the following (or other heights): 1 mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm, 1 1 mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, 20mm, 21 mm, 22mm, 23mm, 24mm, 25mm, 26mm, 27mm, 28mm, 29mm, and so forth. The leaves may have any combination of the foregoing heights. In addition, each of the leaves may have a different height than one or more others of the leaves.

[0072] In some implementations, shorter leaves (e.g., leaves of lesser height) may be used in connection with longer leaves. In some implementations, the leaves have enough height to completely block the particle beam at the maximum beam energy. In some implementations, the leaves have enough height to block the particle beam at less than the maximum beam energy (and not to block the particle beam at maximum energy). For example, while a proton therapy system may have the capability to deliver a beam of energy 230 MeV that can treat to a depth in the patient of 32cm, in some implementations, the configurable collimator can only block protons of at most 175 MeV that can treat to a depth of no more than 20cm. In doing so, less beam-stopping material may be used, e.g., 2.1 cm of Tungsten instead of 3.3cm, or 3.3cm of Nickel instead of 5.2cm. In this example, the proton therapy system would still be capable of treating at depths exceeding 20cm, but the configurable collimator would not be used for such treatments. This may be deemed acceptable because, in some circumstances, deeper treatments benefit less from the example particle beam collimation that the configurable collimator provides. That is, in some treatment scenarios, shallow, low-energy treatments are where the configurable collimator will be most effective, and there may be engineering advantages to reducing the amount of material in the leaves. Thus, in some example implementations, the configurable collimator may be restricted to use with shallow, lower-than-maximum energy treatments.

[0073] In the implementations of Figs. 2 to 6, the leaves are semi-rectangular in shape and have about the same surface area when viewed from the side. In some implementations, this need not be the case. For example, the leaves may have different shapes than those shown. Example shapes include, but are not limited to, circular shapes, curvilinear shapes, oval shapes, square shapes, and triangular shapes. Furthermore, individual leaves may have different shapes than others of the leaves contained in the same carriage or in a different carriage. For example, one carriage may contain both rectangular and curvilinear shaped leaves.

[0074] In some implementations, the leaves have heights that are enough not only to fully stop a particle beam at the maximum expected proton energy (e.g., 3.3cm of Tungsten at 230 MeV or, e.g., 5.2cm of nickel), but also to have enough extra material to prevent proton transmission between the leaves. This material may have a tongue and groove structure as shown in Fig. 1 , or a similar configuration. The leaf ends may be configured to include curved or tapered surfaces to enhance delivered penumbra for proton beams of various divergence.

[0075] In some implementations, there may be more than one primary carriage and corresponding motors and rails. For example, a first primary carriage may control vertical movement of a first secondary carriage, and a second primary carriage may control vertical movement of a second secondary carriage. Therefore, in such implementations, the two secondary carriages can be moved independently in the vertical dimension, if desired. In any case, the primary carriage may be computer controlled. For example, executable instructions are stored in computer memory (e.g., one or more non-transitory machine-readable storage media), and executed by one or more processing devices to control the movement. Control may be performed with, or without, user input during treatment.

[0076] As explained, each secondary carriage 414, 415 includes a

corresponding motor to control horizontal carriage movement, as described above. In some implementations, all leaves on a single carriage are independently movable using linear motors - with one linear motor controlling each leaf. Fig. 7 shows an example implementation of a linear motors for use in controlling operations of leaves

701 , 702, and 703, which may be the type of leaves shown in Figs. 1 to 6. Although only three leaves are shown in Fig. 6, any appropriate number of leaves may be included, as illustrated by ellipses 706. Furthermore, any appropriate number of linear motors may be configured to control the leaves to move out of a carriage into a treatment area, and from the treatment area back into the carriage.

[0077] Taking leaf 702 as an example, an example linear motor that controls operation of leaf 702 includes a movable component and stationary component comprised of two parts - in this example, magnets 710a and 710b. The two magnets are arranged side-by-side, with their poles aligned. That is, as shown, the positive pole (+) of magnet 710a is aligned to the positive pole (+) of magnet 701 b, and the negative pole (-) of magnet 701 a is aligned to the negative pole (-) of magnet 710b. The movable component comprises a coil-carrying plate 709 between magnets 710a and 710b. Coil-carrying plate 709 is connected, physically, to leaf

702, and controls movement of leaf 702 along the directions of arrow 71 1 , e.g., into and out of a treatment area, to form part of an edge of the configurable collimator.

[0078] As explained, coil-carrying plate 709 includes one or more conductive traces or other conductive structures, that pass current in order to generate a magnetic field. The magnetic field is controlled by controlling the current through the coil-carrying plate in order to control movement of the coil carrying plate, and thus of the leaf 702. That is, current through the coils generates a magnetic field that interacts with the magnetic field produced by magnets 710a and 710b. This interaction causes movement of coil carrying plate 709 and of leaf 702 along a direction of arrow 71 1 , either into, or out of, the treatment area. For example, larger magnetic fields generated by the coil-carrying plate 709 may cause the leaf to move into the treatment area, and smaller magnetic fields generated by the coil-carrying plate may cause the leaf to retract away from the treatment area.

[0079] In some implementations, the conductive traces or other conductive structures on the coil-carrying plate may include three windings embedded in aluminum. In some implementations, the leaf may be made of nickel, and be physically attached to the coil-carrying plate. In some implementations, the number of windings and the materials used may be different than those described herein. In some implementations, the coil-carrying plate may be an integral part of the leaf. That is, the leaf itself may include the conductive structures or traces.

[0080] In some implementations, the linear motors may include a bearing rod for each leaf. In some implementations, the bearing rod may be between the coil- carrying-plate and the leaf to guide movement of the leaf.

[0081] As shown in Fig. 7, in some implementations, the current through the coil-carrying plates may be controlled by signals received from a computing system 714. As explained, the computing system may be susceptible to neutron radiation and, therefore, is located in a remote room 716. In some implementations, remote room 716 may be shielded from neutron radiation produced by the particle

accelerator. In some implementations, the remote room may be located far enough away from the treatment room 717 so as not to be affected by neutron radiation from the particle accelerator. In some implementations, the computing system may be located in the treatment room, but be shielded from neutron radiation emitted by the particle accelerator. In some implementations, all computing functionality is shielded from neutron radiation, and the electronics that are not shielded can still operate in the presence of neutron radiation. Encoders are examples of such electronics.

[0082] In this regard, encoders (not shown) may include or more of laser sensors, optic sensors, or diode sensors. The encoders detect movement of the leaves, e.g., by detecting where markings or other indicia on the leaves or on structures connected to, and that move with, the leaves are located relative to the encoders. This information about where the leaves are is fed back to the computing system, and is used by the computing system to confirm the position of the leaves during operation. The encoders may be located at any appropriate location. In some implementations, the encoders are located on a housing that includes the leaves. As the leaves move, markings or other indicia that move with the leaves move past the encoders. The encoders then relay that information to computing system 714. Computing system 714 may use that information to control operation of the configurable collimator, including positioning the leaves. [0083] Fig. 8 shows an example of components of a carriage 801 , which may be of the same type as carriage 414 or 415 of Fig. 4. Carriage 801 includes leaves 802 that are controlled by linear motors of the type described herein. Each leaf 802 may be controlled by a linear motor of the type described in Fig. 7 to create an edge to block at least some radiation from reaching the patient, e.g., to trim one or more spots produced by the particle beam. That is, each linear motor drives its corresponding leaf linearly to reach its position in a configured edge.

[0084] Adding rotational degrees of freedom can improve the ability of the configurable collimator to conform to radiation targets. For example, the entirety of the assembly of Figs. 4 to 6 may be configured to be rotated in a plane

perpendicular to the beam direction, in a plane parallel to the beam direction, or in a combination thereof. In some implementations, each individual secondary carriage 414, 415 may be configured to rotate independently in a same plane. In this way, the configurable collimator may provide more flexibility to conform to complex shapes that are not ideally oriented. In some implementations, both the primary carriage and each secondary carriage may be rotatable.

[0085] In the example implementations described above, each leaf is independently actuatable using a separate, and independently-controllable, linear motor such that any appropriate shape can be traced with a leaf configuration. It may be, however, that such flexibility is not required to achieve acceptable edge conformality. The leaves could be mechanically constrained with the ability to achieve only a finite number of configurations. For example, the leaves could be restricted to arrangements that put them in a vertical line, forward diagonal shape, backward diagonal shape, concave shape, convex shape, or any other achievable shape. In this way, flexibility could be traded for mechanical simplicity.

[0086] Fig. 9 shows a cut-away, back view of example implementation of a configurable collimator containing carriages 901 and 902, which may be of the same type as carriage 414 or 415 of Fig. 4. As shown, carriages 901 and 902 are configured to travel along rail 903, either into, or out of, the treatment area 905. Leaves, such as leaves 907 and 908, are controlled by the linear motors described herein to move into, or out of, treatment area 905 independently of the movement of carriages 901 and 902, respectively, to form edges for trimming the particle beam.

[0087] The configurable collimator may be used to collimate edges that are completely internal to the treatment/beam field. If a treatment plan calls for a volume to be treated that completely surrounds a volume to be protected - for example, a tumor that completely surrounds a spinal cord - a single, machined structure will typically be unable to block radiation to the protected volume without blocking some of treated volume as well. The configurable collimator can treat such a field using a sequence of leaf positions. For example, the configurable collimator can be reconfigured dynamically, and during treatment, to protect the areas that require protection, while allowing treatment on areas that require treatment.

[0088] In some cases, better beam performance (penumbra or edge sharpness) results when the particle beam is tangent to the surface of a leaf edge. However, since the beam effectively originates from a single point source, the angle with which it passes through the plane of the configurable collimator changes as the beam is moved away from the center of the field. For this reason, leaves may have curved edges, as shown in Fig. 1 , so that the edges can always be placed a location that makes them tangent to the particle beam. In an example implementation of the configurable collimator, the tracks on which both primary and secondary carriages move are curved so that flat leaf edges can be used in lieu of curved leaf edges, and so that the flat but remain tangent to the particle beam.

[0089] Fig. 10 shows an example implementation of a configurable collimator having curved track 1020, along which carriages move. In the example of Fig. 10, the particle beam 1021 originates from source 1022, which may be a particle accelerator like the synchrocyclotron described herein. Particle beam 1022 may scan through field 1023 and, at one extent, may be at location 1025 and, at another extent, may be at location 1026. Carriages holding leaves 1028 and 1029 are mounted on curved track 1020 so that leaves 1028 and 1028 can move towards or away from each other. In this example, the leaves have straight ends (or "fronts") 1031 , 1031 in contrast to curved end 156 of Fig. 1 . By employing a curved track, the particle beam can remain tangent, or substantially tangent, to the straight ends throughout the scan field 1023. Keeping the particle beam tangent to the ends can be advantageous in that it enables the trimming provided by the configurable collimator to be consistent throughout the range of the beam field.

[0090] To summarize, in some implementations, the configurable collimator may have a relatively small size, at least in part due to the linear motors described herein. Thus, in contrast to standard multi-leaf collimators, an example configurable collimator may therefore be used to trim a fraction of a treatment area at one time, e.g., an area that is less than the entire treatment area and that is about equal to one spot size, two spot sizes, three spots sizes, four spot sizes, five spot sizes, and so forth. Thus, in some implementations, the configurable collimator may be small enough to trim a single spot at once and may be large enough to trim several spots in one position, but not the entire field without moving. Thus, the configurable collimator may be configured to move around and within the field as the beam scans. That is, in some implementations, the configurable collimator tracks the beam as it scans, and its configuration and reconfiguration may be synchronized to the scanning and to the pulses provided by the beam (e.g., different reconfigurations for different beam pulses and/or locations). By not using leaves large enough to trim an entire treatment area, the configurable collimator can be made smaller and therefore the configurable collimator can be placed closer to the patient with little or no interference from other devices. In some implementations, no leaf of the configurable collimator even has one dimension that spans an entire maximum treatment area. In some implementations, each individual leaf is movable in two dimensions within the treatment area, and the device is mounted on a gantry (e.g., in the context of a particle therapy system such as that described herein) to be rotated on one or more axes and made extendable towards and away from isocenter.

[0091] Furthermore, as described herein, use of linear motors to control the leaves enables further reductions in collimator size. In particular, linear motors having stationary magnets and a movable coil-carrying plate enables the leaves to be stacked relatively close together, which enables individual spot trimming, e.g., trimming in the millimeter range. Heretofore, in known linear motors, current- carrying plates were stationary. However, in some cases, that configuration may not be amenable to stacking leaves of the sizes described herein at least because magnetic fields from the stationary current-carrying plates affect adjacent linear motors, thereby leading to less accurate operation or more system complexity to address these adjacent fields. In any case, the known configurations were not conducive to stacking and controlling leaves of the sizes used in the configurable collimator described herein.

[0092] A scanning system includes the configurable collimator describe herein, which is placeable relative to the irradiation target to limit the extent of the particle beam and thereby limit the extent of the particle beam. For example, the configurable collimator may be placed in the beam path down-beam of the energy degrader and before the particle beam hits the treatment area of the irradiation target. The configurable collimator is controllable to allow the particle beam to pass therethrough and then hit certain parts of the treatment area, while preventing the particle beam from hitting other parts of the patient. As noted, the configurable collimator may be controlled to prevent the particle beam from hitting healthy tissue or to prevent the particle beam from hitting other parts of the irradiation target (e.g., if certain parts of the target are to receive more radiation than other parts). Fig. 1 1 depicts placement of an implementation of the configurable collimator 1 170 relative to a patient 1 171. The direction of beam 1 171 a is also shown.

[0093] As noted, the configurable collimator may be part of, or used with, a scanning system in a particle therapy system. Fig. 12 shows a cross-section of components 1210 of an example superconducting synchrocyclotron that may be used to provide a particle (e.g., proton) beam in the particle therapy system. In this example, components 1210 include a superconducting magnet 121 1 . The

superconducting magnet includes superconducting coils 1212 and 1213. The superconducting coils are formed, e.g., of multiple superconducting strands (e.g., four strands or six strands) wound around a center strand which may itself be superconducting or non-superconducting (e.g., copper). Each of the

superconducting coils 1212, 1213 is for conducting a current that generates a magnetic field (B). The resulting magnetic field is shaped by magnetic yokes 1214, 1215. In an example, a cryostat (not shown) uses liquid helium (He) to maintain each coil at superconducting temperatures, e.g., around 4° Kelvin (K). The magnetic yokes 1214, 1215 (or smaller magnetic pole pieces) are located inside the cryostat, and define the shape of a cavity 1216 in which particles are accelerated.

[0094] In some implementations, the particle accelerator includes a particle source 1217 (e.g., a Penning Ion Gauge - PIG source) to provide an ionized plasma column to the cavity 1216. Hydrogen gas, or a combination of hydrogen gas and a noble gas, is ionized to produce the plasma column. A voltage source provides a varying radio frequency (RF) voltage to cavity 16 to accelerate pulses of particles from the plasma column within the cavity. The magnetic field in the cavity is shaped to cause particles to move orbitally within the cavity. In some implementations, the maximum magnetic field produced by the superconducting coils may be within the range of 4 Tesla (T) to 20T, as explained herein. The example synchrocyclotron employs a magnetic field that is uniform in rotation angle and falls off in strength with increasing radius. In some implementations, such a field shape can be achieved regardless of the magnitude of the magnetic field.

[0095] As noted, in an example, the particle accelerator is a synchrocyclotron. Accordingly, the RF voltage is swept across a range of frequencies to account for relativistic effects on the particles (e.g., increasing particle mass) when accelerating particles within the acceleration cavity. The magnetic field produced by running current through the superconducting coils, together with the shape of the cavity, causes particles accelerated from the plasma column to accelerate orbitally within the cavity and to increase in energy with an increasing number of turns.

[0096] As noted, the superconducting coils (called the main coils) can produce relatively high magnetic fields. In an example implementation, the maximum magnetic field generated by a main coil (e.g., at the center of the acceleration cavity) may be within a range of 4T to 20T or more. For example, the superconducting coils may be used in generating magnetic fields at, or that exceed, one or more of the following magnitudes: 4.0T, 4.1T, 4.2T, 4.3T, 4.4T, 4.5T, 4.6T, 4.7T, 4.8T, 4.9T, 5.0T, 5.1T, 5.2T, 5.3T, 5.4T, 5.5T, 5.6T, 5.7T, 5.8T, 5.9T, 6.0T, 6.1 T, 6.2T, 6.3T, 6.4T, 6.5T, 6.6T, 6.7T, 6.8T, 6.9T, 7.0T, 7.1 T, 7.2T, 7.3T, 7.4T, 7.5T, 7.6T, 7.7T, 7.8T, 7.9T, 8.0T, 8.1T, 8.2T, 8.3T, 8.4T, 8.5T, 8.6T, 8.7T, 8.8T, 8.9T, 9.0T, 9.1T, 9.2T, 9.3T, 9.4T, 9.5T, 9.6T, 9.7T, 9.8T, 9.9T, 10.0T, 10.1 T, 10.2T, 10.3T, 10.4T, 10.5T, 10.6T, 10.7T, 10.8T, 10.9T, HOT, 1 1 .1 T, 1 1 .2T, 1 1 .3T, 1 1 .4T, 1 1 .5T, 1 1.6T, 1 1 .7T, 1 1 .8T, 1 1 .9T, 12.0T, 12.1T, 12.2T, 12.3T, 12.4T, 12.5T, 12.6T, 12.7T, 12.8T, 12.9T, 13.0T, 13.1T, 13.2T, 13.3T, 13.4T, 13.5T, 13.6T, 13.7T, 13.8T, 13.9T, 14.0T, 14.1 T, 14.2T, 14.3T, 14.4T, 14.5T, 14.6T, 14.7T, 14.8T, 14.9T, 15.0T, 15.1T, 15.2T, 15.3T, 15.4T, 15.5T, 15.6T, 15.7T, 15.8T, 15.9T, 16.0T, 16.1 T, 16.2T, 16.3T, 16.4T, 16.5T, 16.6T, 16.7T, 16.8T, 16.9T, 17.0T, 17.1 T, 17.2T, 17.3T, 17.4T, 17.5T, 17.6T, 17.7T, 17.8T, 17.9T, 18.0T, 18.1T, 18.2T, 18.3T, 18.4T, 18.5T, 18.6T, 18.7T, 18.8T, 18.9T, 19.0T, 19.1T, 19.2T, 19.3T, 19.4T, 19.5T, 19.6T, 19.7T, 19.8T, 19.9T, 20.0T, 20.1 T, 20.2T, 20.3T, 20.4T, 20.5T, 20.6T, 20.7T, 20.8T, 20.9T, or more. Furthermore, the superconducting coils may be used in generating magnetic fields that are outside the range of 4T to 20T or that are within the range of 4T to 20T but that are not specifically listed herein.

[0097] In some implementations, such as the implementations shown in Fig. 12, the relatively large ferromagnetic magnetic yokes 1214, 1215 act as returns for stray magnetic fields produced by the superconducting coils. In some systems, a magnetic shield (not shown) surrounds the yokes. The return yokes and the shield together act to reduce stray magnetic fields, thereby reducing the possibility that stray magnetic fields will adversely affect the operation of the particle accelerator.

[0098] In some implementations, the return yokes and shield may be replaced by, or augmented by, an active return system. An example active return system includes one or more active return coils that conduct current in a direction opposite to current through the main superconducting coils. In some example

implementations, there is an active return coil for each superconducting main coil, e.g., two active return coils - one for each main superconducting coil. Each active return coil may also be a superconducting coil that surrounds the outside of a corresponding main superconducting coil concentrically.

[0099] By using an active return system, the relatively large ferromagnetic magnetic yokes 1214, 1215 can be replaced with magnetic pole pieces that are smaller and lighter. Accordingly, the size and weight of the synchrocyclotron can be reduced further without sacrificing performance. An example of an active return system that may be used is described in U.S. Patent No. 8,791 ,656 entitled "Active Return System", the contents of which are incorporated herein by reference.

[00100] At or near the output of the extraction channel of the particle

accelerator, there may be one or more beam shaping elements, such as a scanning system and/or a scattering system. Components of these systems may be mounted on, or otherwise attached to, the nozzle for positioning relatively close to the patient during treatment. In some implementations, however, beam spreader(s) may be mounted closer to (e.g., on) the accelerator or the outer gantry itself (e.g., mounted to the outer gantry in the absence of an accelerator mounted there).

[00101] Referring to Fig. 13, in an example implementation, at the output of extraction channel 1320 of synchrocyclotron 1321 (which may have the configuration of Fig. 12) are example scanning components 1322 that may be used to scan the particle beam across all or part of an irradiation target. Fig. 14 also shows examples of the components of Fig. 13. These include, but are not limited to, a scanning magnet(s) 1324, an ion chamber 1325, an energy degrader 1326, and a

configurable collimator 1328 of the type described herein. Other components that may be down-beam of the extraction channel are not shown in Figs. 13 or 14, including, e.g., one or more scatterers for changing beam spot size.

[00102] In an example operation, scanning magnet 1324 is an example beam spreader, and is controllable in two dimensions (e.g., Cartesian XY dimensions) to position the particle beam in those two dimensions, and to move the particle beam across at least a part (e.g., a cross-section) of an irradiation target. Ion chamber 1325 detects the dosage of the beam and feeds-back that information to a control system to adjust beam movement. Energy degrader 1326 is controllable to move material (e.g., one or more individual plates) into, and out of, the path of the particle beam to change the energy of the particle beam and therefore the depth to which the particle beam will penetrate the irradiation target. In this way, the energy degrader can position the particle beam at a depth-wise layer of an irradiation target, e.g., to the layer. In some implementations, the energy degrader uses wedges or other types of structures instead of, or in addition to, plates. For example, energy degrader 1326 may be controllable to move material (e.g., one or more individual wedges) into, and out of, the path of the particle beam to change the energy of the particle beam and therefore the depth to which the particle beam will penetrate the irradiation target.

[00103] Figs. 15 and 16 show views of an example scanning magnet 1324. In this example implementation, scanning magnet 1324 includes two coils 1341 , which control particle beam movement in the X direction, and two coils 1342, which control particle beam movement in the Y direction. Control is achieved, in some

implementations, by varying current through one or both sets of coils to thereby vary the magnetic field(s) produced thereby. By varying the magnetic field(s)

appropriately, the particle beam can be moved in the X and/or Y direction across the irradiation target.

[00104] Referring back to Fig. 13, a current sensor 1327 may be connected to, or be otherwise associated with, scanning magnet 1324. For example, the current sensor may be in communication with, but not connected to, the scanning magnet. In some implementations, the current sensor samples current applied to the magnet, which may include current to the coil(s) for controlling beam scanning in the X direction and/or current to the coil(s) for controlling beam scanning in the Y direction. The current sensor may sample current through the magnet at times that correspond to the occurrence of pulses in the particle beam or at a rate that exceeds the rate that the pulses occur in the particle beam. In the latter case, the samples, which identify the magnet current, are correlated to detection of the pulses by the ion chamber described below. For example, the times at which pulses are detected using the ion chamber may be correlated in time to samples from the current sensor, thereby identifying the current in the magnet coil(s) at the times of the pulses. Using the magnet current, it thus may be possible to determine the location on the irradiation target (e.g., on a depth-wise layer of the irradiation target) where each pulse, and thus dose of particles, was delivered. The location of the depth-wise layer may be determined based on the configuration of the energy degrader (e.g., the number of plates) in the beam path.

[00105] During operation, the magnitude(s) (e.g., value(s)) of the magnet current(s)) may be stored for each location at which a dose is delivered, along with the amount (e.g., intensity) of the dose. A computer system, which may be either on the accelerator or remote from the accelerator and which may include memory and one or more processing devices, may correlate the magnet current to coordinates within the radiation target, and those coordinates may be stored along with the amount of the dose. For example, the location may be identified by depth-wise layer number and Cartesian XY coordinates or by Cartesian XYZ coordinates (with the depth-wise layer corresponding to the Z coordinate). In some implementations, both the magnitude of the magnet current and the coordinate locations may be stored along with the dose at each location. The foregoing information may be stored in memory either on, or remote from, the accelerator. This information may be used during scanning to apply multiple doses of the same or of different amounts to the same locations to achieve target cumulative doses, including at areas of overlap between adjacent/sequential beam fields, as described herein.

[00106] In some implementations, ion chamber 1325 detects dosage (e.g., one or more individual doses) applied by the particle beam to positions on an irradiation target by detecting the numbers of ion pairs created within a gas caused by incident radiation. The numbers of ion pairs correspond to the dose provided by the particle beam. That information is fed-back to the computer system and stored in memory along with the time that the dose is provided. This information may be correlated to, and stored in association with, the location at which the dose was provided and/or the magnitude of the magnet current at that time, as described above.

[00107] Configurable collimator 1328 may be located down-beam of the scanning magnets and down-beam of the energy degrader, as shown in Figs. 13 and 14. The configurable collimator may trim the particle beam on a spot-by-spot basis during movement of the particle beam during scanning. For example, the configurable collimator may include sets of leaves that face each other, and that are movable into and out of carriages to create an aperture shape. Parts of the particle beam that exceed the aperture shape are blocked, and do not pass to the patient. The parts of the beam that pass to the patient are at least partly collimated, thereby providing a beam with a relatively precise edge. In some implementations, each leaf in a set of leaves (e.g., on a carriage) in the configurable collimator is controllable using a single linear motor to define an edge that is movable into a path of the particle beam such that a first part of the particle beam on a first side of the edge is blocked by the multiple leaves and such that a second part of the particle beam on a second side of the edge is not blocked by the multiple leaves. The leaves in each set are individually controllable during scanning to trim an area as small as a single spot, and can also be used to trim larger multi-spot areas.

[00108] Fig. 17 shows a range modulator 1360, which is an example

implementation of energy degrader 1326. In some implementations, range modulator 1360 may be located down-beam of the scanning magnets between the configurable collimator and the patient. In some implementations, such as that shown in Fig. 17, the range modulator includes a series of plates 1361 . The plates may be made of one or more of the following example materials: polycarbonate, carbon, beryllium or other material of low atomic number. Other materials, however, may be used in place of, or in addition to, these example materials.

[00109] One or more of the plates is movable into, or out of, the beam path to thereby affect the energy of the particle beam and, thus, the depth of penetration of the particle beam within the irradiation target. Plates are moved physically into, and out of, the path of the particle beam. For example, as shown in Fig. 18, a plate 1370 moves along the direction of arrow 1372 between positions in the path of the particle beam 1373 and outside the path of the particle beam. The plates are computer- controlled. Generally, the number of plates that are moved into the path of the particle beam corresponds to the depth at which scanning of an irradiation target is to take place. Thus, the particle beam can be positioned into the interior of a target by appropriate control of the plates.

[00110] Some components of the scanning system, including the configurable collimator, may be mounted on, or coupled to, a nozzle 1981 of the particle therapy system's inner gantry 1980 (see Fig. 19), and may be controlled by a control system, such as one or more computing devices that also controls operation of other components of the particle therapy system. Fig. 21 shows another implementation of a particle therapy system having an inner gantry 2190 with a nozzle 2191 on which some components of the scanning system, including the configurable collimator may be mounted. In both examples, the nozzle is movable along a track of the inner gantry (1980 or 2190) relative to the patient and the particle accelerator, and is extensible towards, and retractable away from, the patient, thereby also extending and retracting the components mounted thereon.

[00111] As noted, the particle beam passes from the range modulator, through the configurable collimator, to the patient. Passage through air can cause the beam spot size to increase. The longer that the beam passes through air, the greater this spot size increase may be. Accordingly, in some implementations, it is

advantageous to reduce the maximum distance that the beam can pass through the air. As explained above, in some examples, the components mounted on the nozzle closest to the patient (e.g., a collimator and energy degrader) may reduce the amount that the beam passes through the air. However, in some examples, because of their proximity to the patient, those components may be made relatively small. The size of those components is related to the treatable field size. That is, these smaller components may result in a relatively smaller beam field size.

[00112] Figs. 19 and 20 show parts an example of a particle therapy system 1982 containing a particle accelerator mounted on a gantry - in this example, a superconducting synchrocyclotron having a configuration described herein is used. In some implementations, the gantry is steel and has two legs (not shown) mounted for rotation on two respective bearings that lie on opposite sides of a patient. The gantry may include a steel truss, connected to each of its legs, that is long enough to span a treatment area in which the patient lies and that is attached at both ends to the rotating legs of the gantry. The particle accelerator may be supported by the steel truss. An example of a gantry configuration that may be used is described in U.S. Patent No. 7,728,31 1 entitled "Charged Particle Radiation Therapy", the contents of which are incorporated herein by reference.

[00113] In the example of Figs. 19 and 20, the patient is located on a treatment couch 1984. In this example, treatment couch 1984 includes a platform that supports the patient. The platform also may include one or more restraints (not shown) for holding the patient in place and for keeping the patient substantially immobile during movement of the couch and during treatment. The platform may, or may not, be padded and/or have a shape (e.g., an indentation) that corresponds to the shape of part of the patient. The couch may be moved via arm 1985.

[00114] Fig. 21 shows an example of the gantry configuration described in U.S. Patent No. 7,728,31 1 , and includes components of an alternative implementation of a particle therapy system that usable with the configurable collimator described herein. The example particle therapy system of Fig 21 includes an inner gantry 2190 having a nozzle 2191 , a treatment couch 2192, and a particle accelerator 2193 (e.g., a synchrocyclotron of the type described herein) mounted on an outer gantry 2194 for rotation at least part-way around the patient to deliver radiation to target(s) in the patient. Treatment couch 2192 is controllable and configured to rotate and to translate the patient in the manner described herein.

[00115] In the example of Fig. 21 , particle accelerator is also mounted to outer gantry 2194 also to enable linear movement (e.g., translational movement) of the particle accelerator in the directions of arrow 2195 along arms 2196. As shown in Fig. 21 , the particle accelerator 2193 may be connected to a gimbal 2199 for pivoting motion relative to the gantry. This pivoting motion may be used to position the accelerator, and thus the beam, for treatment.

[00116] Operation of the example particle therapy systems described herein, and operation of all or some component thereof, can be controlled (as appropriate), at least in part, using one or more computer program products, e.g., one or more computer programs tangibly embodied in one or more non-transitory machine- readable media, for execution by, or to control the operation of, one or more data processing apparatus, e.g., a programmable processor, a computer, multiple computers, and/or programmable logic components.

[00117] A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a network. [00118] Actions associated with implementing all or part of the operations of the example particle therapy systems described herein can be performed by one or more programmable processors executing one or more computer programs to perform the functions described herein. All or part of the operations can be implemented using special purpose logic circuitry, e.g., an FPGA (field

programmable gate array) and/or an ASIC (application-specific integrated circuit).

[00119] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only storage area or a random access storage area or both. Elements of a computer (including a server) include one or more processors for executing instructions and one or more storage area devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from, or transfer data to, or both, one or more machine-readable storage media, such as mass PCBs for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Non-transitory machine-readable storage media suitable for embodying computer program instructions and data include all forms of non-volatile storage area, including by way of example, semiconductor storage area devices, e.g., EPROM, EEPROM, and flash storage area devices; magnetic disks, e.g., internal hard disks or removable disks; magneto- optical disks; and CD-ROM and DVD-ROM disks.

[00120] Any "electrical connection" as used herein may imply a direct physical connection or a wired or wireless connection that includes intervening components but that nevertheless allows electrical signals to flow between connected

components. Any "connection" involving electrical circuitry that allows signals to flow, unless stated otherwise, is an electrical connection and not necessarily a direct physical connection regardless of whether the word "electrical" is used to modify "connection".

[00121] Any two more of the foregoing implementations may be used in an appropriate combination with an appropriate particle accelerator (e.g., a

synchrocyclotron). Likewise, individual features of any two more of the foregoing implementations may be used in an appropriate combination. Elements may be left out of the processes, systems, apparatus, etc., described herein without adversely affecting their operation. Various separate elements may be combined into one or more individual elements to perform the functions described herein.

[00122] In some implementations, the synchrocyclotron used in the particle therapy system described herein may be a variable-energy synchrocyclotron. In some implementations, a variable-energy synchrocyclotron is configured to vary the energy of the output particle beam by varying the magnetic field in which the particle beam is accelerated. For example, the current may be set to any one of multiple values to produce a corresponding magnetic field. In an example implementation, one or more sets of superconducting coils receives variable electrical current to produce a variable magnetic field in the cavity. In some examples, one set of coils receives a fixed electrical current, while one or more other sets of coils receives a variable current so that the total current received by the coil sets varies. In some implementations, all sets of coils are superconducting. In some implementations, some sets of coils, such as the set for the fixed electrical current, are

superconducting, while other sets of coils, such as the one or more sets for the variable current, are non-superconducting (e.g., copper) coils.

[00123] Generally, in a variable-energy synchrocyclotron, the magnitude of the magnetic field is scalable with the magnitude of the electrical current. Adjusting the total electric current of the coils in a predetermined range can generate a magnetic field that varies in a corresponding, predetermined range. In some examples, a continuous adjustment of the electrical current can lead to a continuous variation of the magnetic field and a continuous variation of the output beam energy.

Alternatively, when the electrical current applied to the coils is adjusted in a non- continuous, step-wise manner, the magnetic field and the output beam energy also varies accordingly in a non-continuous (step-wise) manner. The scaling of the magnetic field to the current can allow the variation of the beam energy to be carried out relatively precisely, thus reducing the need for an energy degrader. In a variable-energy synchrocyclotron, the voltage source is controllable to sweep RF voltage over a different frequency ranges, with each different frequency range corresponding to each different energy at which the particles are output from the cavity. An example of a variable-energy synchrocyclotron that may be used in the particle therapy system is described in U.S. Patent Publication No. 2014/037151 1 entitled "Particle Accelerator That Produces Charged Particles Having Variable Energies", the contents of which are incorporated herein by reference. Linear motor- driven collimators may be used in a variable-energy synchrocyclotron system of the type described in U.S. Patent Publication No. 2014/037151.

[00124] In some implementations, a particle accelerator other than a

synchrocyclotron may be used in the particle therapy system described herein. For example, a cyclotron, a synchrotron, a linear accelerator, or the like may be substituted for the synchrocyclotron described herein. Although a rotational gantry has been described (e.g., the outer gantry), the example particle therapy systems described herein are not limited to use with rotational gantries. Rather, a particle accelerator may be mounted, as appropriate, on any type of robotic or other controllable mechanism(s) - characterized herein also as types of gantries - to implement movement of the particle accelerator. For example, the particle

accelerator may be mounted on or more robotic arms to implement rotational, pivotal, and/or translational movement of the accelerator relative to the patient. In some implementations, the particle accelerator may be mounted on a track, and movement along the track may be computer-controlled. In this configuration, rotational and/or translational and/or pivotal movement of the accelerator relative to the patient can also be achieved through appropriate computer control.

[00125] The example linear motors described may be used in conjunction with any appropriate features and systems described in U.S. Patent Publication No.

2017/0128746 (Application No. 14/937,048) entitled "Adaptive Aperture", which is incorporated herein by reference.

[00126] What is claimed is: