Patent Description:
Radiation therapy is commonly applied to the cancerous tumor due to its ability to control cell growth. Ionizing radiation works by damaging the DNA of cancerous tissue leading to cellular death. To reduce exposure of healthy tissues (e.g. tissues which radiation must pass through to treat the tumor), radiation beams can be aimed from different angles to intersect at the tumor.

Electron beam radiation therapy is currently used to direct radiation to a target region (e.g. a region containing the tumor) to destroy cells within the target region. Typical electron systems are limited in the depth that a target region can be successfully treated. In addition, typical systems do not provide dynamic control of the radiation depth and can direct unwanted radiation to healthy tissues surrounding the target region.

For example, with existing systems the beam energy is manually selected to control the depth of radiation penetration up to a peak dose depth of approximately <NUM> (determined by currently commercially available maximum clinical electron beams energy of <NUM> MeV). In such systems the beam energy is increased in order to increase the depth of radiation penetration. This provides for higher radiation levels for tissue at or near the surface, and can lead to unwanted excessive radiation exposure to surrounding healthy tissue.

Further, document <CIT> discloses an electron beam radiotherapy device wherein a broad beam can be weakly converged; the focus depth being adjustable with help of the converging magnets. Document <CIT> describes a radiotherapy device emitting narrow, steerable electron beams. The beams are diverging.

Accordingly, a need exists for new radiation therapy apparatus and methods that provide greater control of radiation dosage levels at varying depths and minimize radiation exposure to surrounding healthy tissues.

As explained in more detail below, exemplary embodiments of the present disclosure enable improvements in many aspects of electron beam radiation therapy as compared to current apparatus and methods.

The invention is defined in the following claims. Other embodiments, examples and methods are not a part of the invention.

The invention encompasses the following devices:
An apparatus for controlling a radiotherapy electron beam, the apparatus comprising: an electron beam generator configured to generate an electron beam; a plurality of magnets producing a plurality of magnetic fields configured to focus the electron beam to a focal point at a convergence angle of between <NUM> and <NUM> mrad, wherein the plurality of magnets comprise electromagnets; and a control system configured to alter one or more parameters of the plurality of magnets to dynamically move the focal point from a first location to a second location, wherein the first location is located at a first depth within a target region and the second location is located at a second depth within the target region, wherein the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and wherein the control system is configured to alter the electrical current through the electromagnets, and wherein the alteration of the magnet parameters changes the depth of focal point by allowing the focal point to be moved closer to and farther from the magnets in an axial direction.

An apparatus for controlling a radiotherapy electron beam, the apparatus comprising:an electron beam generator configured to generate an electron beam with a power between <NUM> megaelectron volts and <NUM> megaelectron volts;a plurality of magnets comprising electromagnets configured to focus the electron beam ata focal spot; anda control system configured dynamically move the focal spot from a first location at a firstdepth to a second location at a second depth, wherein the power of the electron beam is maintained at a consistent level when the focal spot is moved from the first location to the second location, wherein the control system is configured to alter one or more parameters of the plurality of magnets to move the focal spot from the first location to the second location; and wherein the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and wherein the control system is configured to alter the electrical current through the electromagnets,and wherein the alteration of the magnet parameters changes the depth of focal spot by allowing the focal spot to be moved closer to and farther from the magnets in an axial direction.

Exemplary embodiments of the present disclosure include an electron beam delivery and control system using very high energy electrons (VHEE) to produce a localized focal spot of high radiation dosage within the target volume. Exemplary embodiments are able to control the location of the focal spot through a technique referred to herein as magnetically optimized very high energy electron treatment (MOVHEET).

Apparatus incorporating MOVHEET techniques can be dynamically controlled to produce a distribution of radiation dosage within a target region (e.g. a tumor volume) that is higher than surrounding normal tissue. This ability can result in greater normal tissue sparing and a larger degree of radiation control around the tumor volume. Exemplary embodiments include the ability to dynamically focus an electron beam of <NUM> - <NUM> megaelectron volts (MeV) to a focal spot at a desired target depth. As used herein, the term "depth" when used in reference to the focal spot refers to a dimension measured parallel to the electron beam (e.g. parallel to the primary axis of the beam prior to entering the magnetic control apparatus). The desired target depth can be determined by a radiation treatment plan dose distribution, where the output of the focusing system is a beam with optimized symmetry and a focusing angle that results in a low beam density at the target surface producing low entrance dose.

Unclaimed methods for dynamically controlling the focal spot depth of the electron focusing system can include the use of magnetic fields outside the target volume to alter the electron trajectories to produce the desired beam behavior.

One embodiment of the focusing system utilizes quadrupole magnetic fields which are produced by a magnet having four inwardly directed poles such that each adjacent pole carries a magnetic field of opposite polarity. Current-carrying coils can be arranged in such a way to produce a magnetic field inside the ferromagnetic magnet material, where the strength of the magnetic quadrupole field may be adjusted by varying the coil current. This type of magnet design is referred to as iron-dominated.

Another embodiment of a quadrupole magnet is based on a coil-dominated design where the current-carrying coils are designed in such a way such that the magnetic multipole field experienced by the charged particle beam is produced directly by the coils themselves without the use of a ferromagnetic core. Varying the current in the coils adjust strength of the magnetic field.

A quadrupole magnetic field has the effect of defocusing a charged particle beam in one plane while focusing the beam in the orthogonal plane. This can allow for overall focusing in both planes being accomplished with a combination of quadrupole magnets whose currents, positions, and other magnet parameters have been chosen to produce the desired beam. A variety of exit beam shapes may be used, and certain configurations of quadrupoles may be used to generate symmetric beams.

In one such configuration, a combination of three collinear quadrupole magnets can produce symmetrically focused beams for parallel incoming electron beams. Such systems can also provide for stigmatic focusing of a diverging beam where the beam focal spot may be adjusted by varying the quadrupole magnet strengths (alone or in conjunction with other parameter alterations).

In another such configuration, a combination of two collinear quadrupole magnets can be use to produce output beams with an oblong shape that may be ideal for certain dose distributions that have strict spatial tolerances due to surrounding critical structures. The use of quadrupole systems with two or three quadrupoles allows for the user to choose the appropriate focusing distribution based on the target area.

For example, in order to attain the desired depth dose distribution for the range of depths typically used for clinical treatment (e.g. <NUM> - <NUM> centimeters), the quadrupole separation distances and triplet position can be varied to achieve the optimal treatment beam. During operation, a quadrupole magnet system can produce a focused beam when the quadrupoles are operated under a specific set of conditions determined by the solution to a system of differential equations that govern the trajectories of the electrons within the field regions.

In exemplary embodiments, a control system for the magnet parameters takes the dose distribution from the treatment planning software and uses an algorithm to calculate the necessary focusing system parameters to produce the desired beam trajectories.

The beam can also be scanned laterally by means of orthogonal dipole fields which produce a uniform offset to the beam in their respective directions to produce a three-dimensional dose distribution. Other embodiments may mechanically move the focusing system to produce a three-dimensional dose distribution. The lateral scanning parameters can be included in the beam control system and determined by the treatment planning software.

For focusing systems using diverging input beams, the beam divergence and origination point are also variables that can be determined by the control system algorithm. As an example, a pencil beam may be made divergent by the use of a scattering foil designed to produce a unique divergence pattern, where the divergent beam is then passed through a collimator in order to restrict the divergence angle for input into the quadrupole focusing system. The relative locations between the scattering foil, collimator, and quadrupole entrance are unique for a particular exit beam and can be determined along with the quadrupole settings.

It should be noted that magnetic fields can have inherent inconsistencies or errors that can translate into nonuniformities in the focused electron beam. Careful consideration for such inconsistencies may be taken into account with the use of sextupole and octupole configurations, for example, to compensate for various geometrical and chromatic inconsistencies. One embodiment of the focusing system may use a quadruplet of quadrupole magnets coincident with three interspersed octupole magnets to produce a focused beam with geometrical aberration correction.

In certain embodiments, an algorithm may be used to solve for the magnet parameters that produce a symmetrically focused beam where inconsistencies introduced by the quadrupoles have been compensated for by the octupole magents producing a higher quality dose distribution in the target volume. The control system can dynamically adjust the parameters to optimize the beam determined by the treatment planning system. It is understood that the magnet configurations disclosed herein are merely exemplary, and that other combinations of magnets may be used to correct for other magnet-induced inconsistencies.

Certain embodiments may dynamically control beam depth by utilizing a posterior solenoidal magnet to produce a magnetic field gradient within the target volume such that the electrons reverse direction at a depth determined by the magnetic field strength. An anterior solenoidal magnet may be used in conjuction with the posterior magnet to modify the magnetic field in the target volume and enhance the dose deposition. The localized high dose region depth may be controlled with a control system designed to adjust the solenoid currents based on the desired dose distribution.

Exemplary embodiments include an apparatus for controlling a radiotherapy electron beam, where the apparatus comprises: an electron beam generator configured to generate an electron beam; a plurality of magnets producing a plurality of magnetic fields configured to focus the electron beam to a focal spot; and a control system configured to alter one or more parameters of the plurality of magnets to move the focal spot from a first location to a second location, where the first location is located at a first depth within a target region and the second location is located at a second depth within the target region.

In certain embodiments, the target region is below an epidermal surface of a subject; the first location or the second location is at a depth between <NUM> and <NUM> centimeters from the epidermal surface. In particular embodiments, the electron beam has a energy of between <NUM> and <NUM> megaelectron volts (MeV). In some embodiments, the energy of the beam is not modulated when the focal spot is moved from the first location to the second location. In specific embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In certain embodiments, the plurality of collinear multipole magnets comprises at least two collinear quadrupole magnets.

In particular embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets. In some embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In specific embodiments, the plurality of magnets comprise electromagnets; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets. In certain embodiments, the electromagnets are iron-dominated or coil dominated superconducting electromagnets.

In particular embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In some embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In certain embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In particular embodiments, the focal spot comprises a maximum electron dose concentration.

In certain embodiments, the target region is below an epidermal surface of a subject; and the first location or the second location is at a depth between <NUM> and <NUM> centimeters from the epidermal surface. In particular embodiments, the electron beam has a power of between <NUM> megaelectron volts and <NUM> megaelectron volts. In some embodiments, the power of the beam is not modulated when the focal spot is moved from the first location to the second location. In specific embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In certain embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets.

In particular embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets. In some embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In specific embodiments, the plurality of magnets comprise electromagnets; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets.

In certain embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In particular embodiments, the plurality of magnetic fields are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In some embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In specific embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In certain embodiments, the focal spot comprises a maximum electron dose concentration.

Exemplary embodiments include an apparatus for controlling a radiotherapy electron beam, where the apparatus comprises: an electron beam generator configured to generate an electron beam with a power between <NUM> megaelectron volts and <NUM> megaelectron volts; a plurality of magnets configured to focus the electron beam at a focal spot; and a control system configured move the focal spot from a first location at a first depth to a second location at a second depth, wherein the power of the electron beam is maintained at a consistent level when the focal spot is moved from the first location to the second location.

In certain embodiments, the first location and the second location are located within a target region. In particular embodiments, the target region is below an epidermal surface of a subject; and the first location or the second location is at a depth between <NUM> and <NUM> centimeters from the epidermal surface. In some embodiments, the control system is configured to alter one or more parameters of the plurality of magnets to move the focal spot from the first location to the second location. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets.

In certain embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In particular embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In some embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets. In specific embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and the control system is configured to alter the separation distance between the plurality of collinear multipole magnets.

In certain embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In particular embodiments, the plurality of magnets comprise electromagnets; the control system is configured to alter one or more parameters of the plurality of magnets to move the focal spot from the first location to the second location; the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and the control system is configured to alter the electrical current through the electromagnets.

In particular embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In some embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In specific embodiments, the focal spot comprises a maximum electron dose concentration.

Certain embodiments include a method of controlling a radiotherapy electron beam, where the method comprises: generating an electron beam having a power between <NUM> megaelectron volts and <NUM> megaelectron volts; focusing the electron beam to a focal spot with a plurality of magnets; and moving the focal spot from a first location at a first depth to a second location at a second depth while maintaining the power of the electron beam at a consistent level.

In particular embodiments, the first location and the second location are located within a target region. In certain embodiments, the target region is below an epidermal surface of a subject; the first location or the second location is at a depth between <NUM> and <NUM> centimeters from the epidermal surface. In some embodiments, moving the focal spot from a first location at a first depth to a second location at a second depth comprises altering one or more parameters of the plurality of magnets. In specific embodiments, the control system comprises an algorithm to calculate the one or more parameters of the plurality of magnets. In particular embodiments, the control system receives input from a treatment planning software program configured to calculate a dose distribution. In certain embodiments, the plurality of magnets comprise a plurality of collinear multipole magnets. In some embodiments, the plurality of collinear multipole magnets comprises at least three collinear quadrupole magnets.

In specific embodiments, the one or more parameters of the plurality of magnets comprises a separation distance between the plurality of collinear multipole magnets; and altering one or more parameters of the plurality of magnets comprises altering the separation distance between the plurality of collinear multipole magnets. In certain embodiments, the plurality of magnets comprise an anterior lens magnet, a posterior reflective magnet, and a plurality of radial focal magnets. In particular embodiments, the plurality of magnets comprise electromagnets; and moving the focal spot from a first location at a first depth to a second location at a second depth comprises altering an electrical current through the electromagnets.

In certain embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In particular embodiments, the plurality of magnets are configured to focus the electron beam at a convergence angle of between <NUM> and <NUM> mrad. In some embodiments, the focal spot comprises a maximum electron dose concentration.

In the following, the term "coupled" is defined as connected, although not necessarily directly, and not necessarily mechanically.

The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more" or "at least one. " The terms "about", "substantially" and "approximately" mean, in general, the stated value plus or minus <NUM>%. The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternative are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or.

The terms "comprise" (and any form of comprise, such as "comprises" and "comprising"), "have" (and any form of have, such as "has" and "having"), "include" (and any form of include, such as "includes" and "including") and "contain" (and any form of contain, such as "contains" and "containing") are open-ended linking verbs. As a result, a method or device that "comprises," "has," "includes" or "contains" one or more steps or elements, possesses those one or more steps or elements, but is not limited to possessing only those one or more elements. Likewise, a step of a method or an element of a device that "comprises," "has," "includes" or "contains" one or more features, possesses those one or more features, but is not limited to possessing only those one or more features. Furthermore, a device or structure that is configured in a certain way is configured in at least that way, but may also be configured in ways that are not listed.

Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the scope of the invention will be apparent to those skilled in the art from this detailed description.

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The present disclosure may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

Referring initially to <FIG>, an apparatus <NUM> for controlling a radiotherapy electron beam is shown. In this embodiment, apparatus <NUM> comprises an electron beam generator <NUM> configured to generate an electron beam <NUM>. Apparatus <NUM> further comprises a plurality of magnets <NUM> that includes collinear multipole magnets.

In this embodiment, magnets <NUM> include a first quadrupole magnet <NUM>, a second quadrupole magnet <NUM> and a third quadrupole magnet <NUM>. First quadrupole magnet <NUM> comprises first pole <NUM>, second pole <NUM>, third pole <NUM> and fourth pole <NUM>. It is understood that second quadrupole magnet <NUM> and third quadrupole magnet <NUM> also comprise four poles (not labeled in the figures for purposes of clarity). A top perspective view of magnets <NUM> is shown in <FIG>.

During operation of apparatus <NUM>, magnets <NUM> produce a plurality of magnetic fields configured to focus electron beam <NUM> and provide a maximum electron dose concentration at a focal spot in a target region. Referring specifically to <FIG> and <FIG>, simulated dose distribution plots are shown for apparatus <NUM> in the X-Z plane (<FIG>) and Y-Z plane (<FIG>). Dose distributions where calculated using the Monte Carlo calculation code FLUKA© which is a general purpose code for simulating the interactions of energetic particles in matter. See "<NPL>); see also "<NPL>), INFN/TC_05/<NUM>, SLAC-R-<NUM>. <FIG> and <FIG> were produced by tracking <NUM>. 5x10<NUM> with a minimum step size of <NUM>, charged particle cutoff energy of <NUM> keV, and dose binning grid size of <NUM>. In this example, electron beam <NUM> is a <NUM> megaelectron volt (MeV), <NUM> centimeter radius electron beam. Electron beam <NUM> is shown passing through <NUM> centimeters of air and incident on a water phantom (at Z dimension <NUM> centimeters, corresponding to an epidermal surface of a subject). In the illustrated embodiment, magnets <NUM> are configured as a quadrupole triplet and function as a symmetric uniform focusing lens.

As shown in <FIG>, first quadrupole magnet <NUM> focuses electron beam <NUM> in the X-Z plane, while second quadrupole magnet <NUM> defocuses electron beam <NUM>, and third quadrupole magnet <NUM> focuses electron beam <NUM>. As shown in <FIG>, magnets <NUM>, <NUM> and <NUM> perform the inverse operations on electron beam <NUM> in the Y-Z plane. In particular, first quadrupole magnet <NUM> defocuses beam <NUM> in the Y-Z plane, while second quadrupole magnet <NUM> focuses electron beam <NUM>, and third quadrupole magnet <NUM> defocuses electron beam <NUM>.

As shown in <FIG> and <FIG>, magnets <NUM> may be configured to focus electron beam <NUM> and provide a maximum electron dose concentration at a focal point <NUM>. As explained further below, during operation control system <NUM> (shown in <FIG>) can alter one or more parameters of magnets <NUM> to move focal spot <NUM> to different depths within a target region in the Z-plane. In exemplary embodiments, the power of electron beam <NUM> is not modulated when focal spot <NUM> is moved to different depths within a target region.

For example, control system <NUM> may control the position of individual magnets in the group of magnets <NUM> in order to alter the separation distance between the magnets. In particular, control system <NUM> may alter the separation distance between first quadrupole magnet <NUM> and second quadrupole magnet <NUM>. Control system <NUM> may also alter the separation distance between second quadrupole magnet <NUM> and third quadrupole magnet <NUM>.

The separation distance between magnets <NUM>, <NUM> and <NUM> may be altered by any one of suitable mechanisms, including for example, one or more linear actuators. For example, as shown in <FIG>, control system <NUM> can control the position of magnets <NUM>, <NUM> and <NUM> via linear actuators <NUM>, <NUM> and <NUM> respectively. By adjusting the position of each magnet <NUM>, <NUM> and <NUM>, the separation distances between the magnets can be altered. The alteration of the separation distances between magnets in the group of magnets <NUM> affects the focusing of electron beam <NUM> and convergence angle A, shown in <FIG>.

As convergence angle A is increased, focal spot <NUM> is moved closer to magnets <NUM>. Conversely, as the separation distance between magnets <NUM> is controlled to decrease convergence angle A, focal spot <NUM> is moved farther from magnets <NUM>. In certain embodiments, apparatus <NUM> can increase convergence angle A up to values of approximately <NUM> milliradians. This can allow focal spot <NUM> to be moved within the target region, which is typically between <NUM> and <NUM> centimeters from the surface. It is understood that a similar convergence angle is present in the X-Z plane of <FIG>. The convergence angle present in <FIG> is not labeled for purposes of clarity.

In other embodiments, control system <NUM> may control different parameters in order to control electron beam <NUM> and focal spot <NUM>. For example, in certain embodiments magnets <NUM> may comprise electromagnets and control system <NUM> can be configured to alter the electrical current through the electromagnets. Similar to the magnet separation distance, altering the electrical current through each of magnets <NUM>, <NUM> and <NUM> can also affect convergence angle A and the position of focal spot <NUM>. Accordingly, the alteration of magnet parameters (e.g. magnet separation distance or electrical current) can change the depth of focal spot <NUM> by allowing focal spot <NUM> to be moved closer to and farther from magnets <NUM> in an axial direction (e.g. collinear with electron beam <NUM>).

The ability to control convergence angle A and the location of focal spot <NUM> via magnetic parameters can provide numerous advantages. For example, the radiation dose can be reduced in regions outside of the target region. In particular, the ability to create a higher convergence angle can provide a larger cross section of beam <NUM> at the skin surface as compared to the cross section at focal spot <NUM>. Particular embodiments may be capable of producing surface entrance doses as low as fifteen percent of the maximum dose at the focal spot <NUM>, as opposed to typical current technologies that provide surface doses of approximately eighty or ninety percent of the maximum dosage. The ability to control the axial depth location of the focal spot and minimize radiation dosage levels to healthy tissues outside the target region can improve patient outcomes and reduce recovery times.

Furthermore, exemplary embodiments also provide the ability to control the depth of the radiation dose peak at focal point <NUM> within a target region without modulating the energy of beam <NUM>. Current electron therapy technology typically varies the energy of the electron beam to adjust the depth of penetration, which is done manually and is not suited for dynamic control of the dosage level. For example, changing the energy of the beam to adjust the depth of penetration does not allow for independent control of focal spot depth and radiation levels.

In contrast, exemplary embodiments of the present disclosure are configured to penetrate the full clinical range of patient thicknesses and then use the magnetic system parameters to produce a high dose focal region in the target which may be moved throughout the target depth. The target depth can be controlled by parameters (e.g. magnet current and/or positions) other than electron beam energy levels.

As a result of dose peak depth control as disclosed herein, beams of varying dose peak depths may be superimposed to produce a region of constant dose over a region of depth within the patient corresponding to a tumor or treatment site.

<FIG> illustrates a graph of a simulated percent dose distributions for <NUM> MeV electron beams on water for a <NUM> centimeter radius circular beam. In one plot of <FIG>, the electron beam is not focused, while in the other plot the same beam is focused with a collinear quadrupole magnet configuration as shown in <FIG> and <FIG>. As shown in <FIG>, the percent dose at the surface (e.g. depth of <NUM>) is substantially reduced for the focused beam as compared to the unfocused beam. The focused beam provides a dose at the surface of between <NUM> and <NUM> percent of the maximum dose, while the unfocused beam provides a surface dose of between <NUM> and <NUM> percent of the maximum. <FIG> also illustrates the focused beam provided a maximum dose at slightly less than <NUM> depth.

Other embodiments may comprise a different configuration of magnets than those previously shown and described. For example, referring now to <FIG>, an apparatus <NUM> comprises a plurality of magnets <NUM> that are not collinear and are configured to control an electron beam <NUM>. In this embodiment, magnets <NUM> are configured as solenoidal electromagnets and comprise an anterior lens magnet <NUM>, a posterior reflective magnet <NUM>, and a plurality of radial focal magnets <NUM>, <NUM>, <NUM> and <NUM>.

During operation of apparatus <NUM>, a control system <NUM> can control parameters of magnets <NUM> to focus beam <NUM> at different depths, in a manner similar to the previously-described embodiments. For example, control system <NUM> can control an electrical current through each of magnets <NUM>-<NUM> and <NUM>-<NUM>. Control system may also be configured to control the position of magnets <NUM>-<NUM> and <NUM>-<NUM> so that the separation distance between each of the magnets is altered to change the focal spot (not shown in <FIG> for purposes of clarity) of beam <NUM>.

In the configuration shown in <FIG>, anterior lens magnet <NUM> is the primary source of focusing. Radial focal magnets <NUM>, <NUM>, <NUM> and <NUM> produce a magnetic field within the target that modifies the anterior lens magnet <NUM> field and provides additional focusing. The plane of radial focal magnets <NUM>, <NUM>, <NUM> and <NUM> can be adjusted based on the treatment depth. Posterior reflective magnet <NUM> produces a magnetic field gradient such that electrons are reflected at a depth dependent on the magnetic field strength of magnet <NUM>, resulting in a radiation dose confined to a desired depth.

<FIG> illustrates a graph of simulated percent depth dose curves for <NUM> MeV, <NUM> radius electron beams incident on a water phantom, where the beam has been focused using the <FIG> configuration with different depths of the magnetic plane as defined by the in-plane magnets <NUM>, <NUM>, <NUM>, and <NUM>. As shown in <FIG>, the different depths magnetic planes corresponds to a shift in the dose peak to different depths. The <NUM> magnetic plane has a maximum dose peak at approximately <NUM>, the <NUM> magnetic plane has a maximum dose peak at approximately <NUM>, the <NUM> magnetic plane has a maximum dose peak at approximately <NUM>, and the <NUM> magnetic plane has a maximum dose peak at approximately <NUM>. For comparison, the percent depth dose curve for a <NUM> radius circular beam of <NUM> MeV electrons without any focusing magnetic fields is shown. As shown in <FIG>, the surface dose of the unfocused <NUM> MeV beam is between <NUM> and <NUM> percent, while the focused beams have a surface dose between <NUM> and <NUM> percent.

<FIG> illustrates a Monte Carlo calculation of a composite dose distribution from five focused electron beams of varying energies on a prostate CT (computed tomography) image using the magnet configuration shown in <FIG>. <FIG> illustrates a Monte Carlo calculation of a composite dose distribution from <NUM> focused electron beams of varying energies utilizing a form of "dose painting" (e.g. altering the depth of a focal spot for each of the beams). This technique can be been used to increase the high dose coverage throughout the prostate using the magnet configuration shown in <FIG>.

<FIG> illustrates a graph of the percent dose versus depth for different configurations of the embodiment shown in <FIG> utilizing radial focal magnets with an anterior lens magnet and a posterior reflective magnet. The graphs include a <NUM> centimeter magnetic plane configuration, a <NUM> centimeter magnetic plane configuration with the intensities of each distribution optimized to prodcue a simulated spread out Bragg peak ("pseudo SOBP") configuration. The graphs illustrated in <FIG> included simulated data for a <NUM> MeV electron beam with a <NUM> centimeter radius.

Claim 1:
An apparatus for controlling a radiotherapy electron beam, the apparatus comprising:
an electron beam generator (<NUM>) configured to generate an electron beam;
a plurality of magnets (<NUM>, <NUM>, <NUM>) producing a plurality of magnetic fields configured to focus the electron beam to a focal point at a convergence angle of between <NUM> and <NUM> mrad, wherein the plurality of magnets comprise electromagnets; and
a control system configured to alter one or more parameters of the plurality of magnets to dynamically move the focal point from a first location to a second location,
wherein the first location is located at a first depth within a target region and the second location is located at a second depth within the target region, wherein the one or more parameters of the plurality of magnets comprises an electrical current through the electromagnets; and wherein the control system is configured to alter the electrical current through the electromagnets,
and wherein the alteration of the magnet parameters changes the depth of focal point by allowing the focal point to be moved closer to and farther from the magnets in an axial direction.