Systems and methods to create electron minibeams

Abstract

A magnetic system capable of creating electron minibeams includes a first dipole, a second dipole, a third dipole, a fourth dipole, and a quadrupole. The first dipole defines a first central aperture, the second dipole defines a second central aperture, the third dipole defines a third central aperture, the fourth dipole defines a fourth central aperture, and the quadrupole defines a quadrupole aperture. The first central aperture, the second central aperture, the third central aperture, and the fourth central aperture are coaxially aligned to define a dipole axis. The first dipole, the second dipole, the third dipole, and the fourth dipole are rotatable about the dipole axis and translatable along the dipole axis relative to each other. The quadrupole is selectively spinnable about a quadrupole axis defined by the quadrupole aperture.

Description

SYSTEMS AND METHODS TO CREATE ELECTRON MINIBEAMSCross-Reference to Related Applications

[0001] This claims priority to, and benefit of, U.S. Provisional Patent Application Serial No. 63 / 558,610 filed February 27, 2024. The entire contents of the above application are hereby incorporated by reference.Background1. Technical Field

[0002] The present disclosure relates to electron beam therapy systems and, more specifically, to electron beam therapy systems capable of forming electron minibeams.2. Discussion of Related Art

[0003] In general, radiation therapy is commonly applied to cancerous tumors due to its ability to control cell growth. Electron beam radiation therapy (EBRT) utilizes ionizing radiation, typically as part of cancer treatment to destroy malignant cells. Electron beam therapy may be used to treat a number of types of cancer. In particular, electron beam therapy may be used to treat cancers that are localized to one area of the body (e.g., localized electron beam radiation therapy (LEBT)). It may also be used to deliver a dose distribution over a large treatment field (e.g., total skin electron beam therapy (TSEBT)). Electron beam therapy may also be used as part of adjuvant therapy to prevent tumor recurrence after surgical removal of a primary malignant tumor (e.g., intraoperative radiation therapy (IORT)). For example, electron beam therapy may be used as part of adjuvant therapy in the initial stages of certain types of cancer such as breast cancer. In such a case, a patient may undergo a complete or a partial mastectomy. Once the cancerous tissue is removed, then electron beam therapy may be used to kill any remaining cancer cells that surgical removal may have left behind to reduce the chance of the cancer returning.

[0004] Electron beam radiation therapy is used to direct radiation to a target region, e.g., a region containing the tumor, to destroy cells within the target region. However, as with all types of external beam radiation, dose is deposited in the normal tissue that a beam must pass through to reach the tumor. Spatially fractionated radiation therapy is a paradigm of dose delivery where the dose is intentionally delivered in a heterogeneous pattern, where there are narrow high dose peaks separated from low dose valleys. It has been found experimentally that normal tissue is able to toleratesurprisingly high dose peaks whereas tumor tissue lethality is the same or increased. It is widely understood that DNA damage is the primary cause of the cellular death that results in tissue lethality in conventional ionizing radiation treatments. However, radiobiological mechanisms beyond DNA damage appear to be responsible for the effects following spatial fractionated dose deposits, with candidate mechanisms including dose-volume, bystander, vascular and immune mediated sequelae. A better understanding of these mechanisms along with the development of practical technology to deliver suitable spatially fractionated proton minibeams is essential for safe and effective clinical treatments.

[0005] Therapeutic electron beams are typically spread out by scattering foils to cover radiation fields with dimensions of a few to tens of centimeters (e g., 10 cm x 10 cm). However, the use of electron beams with dimensions of a few millimeters is desirable to create spatially fractionated electron radiation distributions. Additionally, if such small diameter beams could be scanned to create an array of such beams, such a system could allow spatially fractionated electron minibeam radiation treatments as well as provide an accessible platform to perform preclinical research to investigate the radiobiological mechanisms underlying spatially fractionated dose deposits. The potential use of spatially fractionated dose distributions in electron therapy using beams with small diameters has been termed electron minibeam therapy (eMBRT).Summary

[0006] Accordingly, a need exists for new radiation therapy apparatuses and methods that provide greater control of the level and spatial distribution of radiation dosage and minimize radiation exposure to surrounding healthy tissues. In particular, the creation and delivery of small diameter electron minibeams for both clinical and preclinical applications is a challenging problem of keen interest. This disclosure relates generally to a magnetic system for electron beam scanning capable of creating electron minibeams.

[0007] In an aspect of the present disclosure, a magnetic system for electron beam scanning, capable of creating electron minibeams, includes a first dipole, a second dipole, a third dipole, a fourth dipole, and a quadrupole. The first dipole defines a first central aperture, the second dipole defines a second central aperture, the third dipole defines a third central aperture, the fourth dipole defines a fourth central aperture, and the quadrupole defines a quadrupole aperture. The first central aperture, the second central aperture, the third central aperture, and the fourth central aperture are coaxially aligned to define a dipole axis. The first dipole, the second dipole, the third dipole, and the fourthdipole are rotatable about the dipole axis and translatable along the dipole axis relative to each other. The quadrupole is selectively spinnable about a quadrupole axis defined by the quadrupole aperture.

[0008] In aspects, the first dipole, the second dipole, the third dipole, and the fourth dipole each include an outer cylinder and inner cylinder. The inner cylinder may define a respective central aperture of the first dipole, the second dipole, the third dipole, and the fourth dipole. The inner cylinder may be nested within the outer cylinder. The inner cylinder may be rotatable with respect to the outer cylinder. Rotating the inner cylinder of a respective dipole with respect to the outer cylinder may change a magnitude of a magnetic field of the respective dipole. The magnetic field of each dipole may be substantially confined within the central aperture of the respective dipole.

[0009] In some aspects, the first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole each comprise a plurality of magnetic segments. Each magnetic segment of the plurality of magnetic segments may be a permanent magnet. The first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole may be Halbach cylinders.

[0010] In certain aspects, the magnetic system has a first end and a second end opposite the first end. The first dipole may be positioned adjacent to the first end and the quadrupole may be positioned adjacent to the second end. The second dipole may be positioned adjacent to the first dipole between the first dipole and the quadrupole. The third dipole may be positioned adjacent to the second dipole between the second dipole and the quadrupole. The fourth dipole may be positioned adjacent to the third dipole between the third dipole and the quadrupole. The second dipole may be spaced apart from the first dipole a first separation. The third dipole may be spaced apart from the second dipole a second separation, and the fourth dipole may be spaced apart from the third dipole a third separation. The quadrupole may be spaced apart from the fourth dipole a fourth separation. Translating the first dipole, the second dipole, the third dipole, or the fourth dipole along the dipole axis may increase or decrease the first separation, the second separation, the third separation, or the fourth separation. The first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole may be spaced apart from one another such that the first separation, the second separation, the third separation, and the fourth separation are equal.

[0011] In particular aspects, the quadrupole is capable of spinning at a rate in a range of 50 RPM to 7,500 RPM. The quadrupole may have a magnetic field gradient in a range of 5 T / m to 200 T / m.

[0012] In aspects, the first dipole and the second dipole each have a magnetic field. The magnitude of the magnetic field of the first dipole and the magnitude of the second dipole may be equal to each other. The direction of the magnetic field of the first dipole and the direction of the magnetic field of the second dipole may be antiparallel to each other. The third dipole and the fourth dipole may each have a magnetic field. The magnitude of the magnetic field of the third dipole and the magnitude of the magnetic field of the fourth dipole may be equal to each other. The direction of the magnetic field of the third dipole and the direction of the magnetic field of the fourth dipole may be antiparallel to each other.

[0013] In some aspects, the first dipole, the second dipole, the third dipole, and the fourth dipole each have a magnetic field in a range of 20 mT to 2 T. The first dipole, the second dipole, the third dipole, and the fourth dipole may each have a length in a range of 20 mm to 100 mm.

[0014] In another aspect of the present disclosure, a magnetic system for electron beam scanning, capable of creating electron minibeams, includes a first dipole, a second dipole, the third dipole, a fourth dipole, and a quadrupole. The first dipole and the second dipole are configured to steer an electron beam horizontally. The third dipole and the fourth dipole are configured to steer the electron beam vertically. The quadrupole is configured to selectively spin about the electron beam and magnetically focus the electron beam into an electron minibeam.

[0015] In aspects, spinning the quadrupole about the electron beam magnetically focuses the electron beam from a first diameter to a second diameter, that is smaller than the first diameter, to form the electron minibeam. The electron minibeam may have a circular cross section. The quadrupole may be configured to magnetically focus the electron beam such that the electron minibeam has a planar profile when the quadrupole is stationary with respect to the electron beam.

[0016] In some aspects, the first dipole, the second dipole, the third dipole, and the fourth dipole each define a central aperture therethrough. Each central aperture defines a dipole axis. The dipole axes of the first dipole and the second dipole may be coaxially aligned and the dipole axes of the third dipole and the fourth dipole may be coaxially aligned. The first dipole may be configured to steer the electron beam by deflecting the electron beam in a horizontal direction by a first horizontal angle with respect to the dipole axis and the second dipole may be configured to steer the electron beam by deflecting the electron beam in a horizontal direction a second horizontal angle with respect to the dipole axis. The second horizontal angle may be equal to and opposite of the first horizontal angle.The third dipole may be configured to steer the electron beam by deflecting the electron beam in a vertical direction by a first vertical angle with respect to the dipole axis and the fourth dipole is configured to steer the electron beam by deflecting the electron beam in a vertical direction by a second vertical angle with respect to the dipole axis. The second vertical angle may be equal to and opposite of the first vertical angle. The first dipole and the second dipole may be configured to steer the electron beam by displacing the electron beam a horizontal deflection with respect to the dipole axis and the third dipole and the fourth dipole are configured to steer the electron beam by displacing the electron beam a vertical deflection with respect the dipole axis. The horizontal deflection may be defined by the first horizontal angle and the second horizontal angle and a longitudinal distance traveled by the electron beam between exiting the first dipole and entering the second dipole and the vertical deflection defined by the first vertical angle and the second vertical angle and a longitudinal distance traveled by the electron beam between exiting the third dipole and entering the fourth dipole. The second dipole may be spaced apart from the first dipole a first separation, the third dipole may be spaced apart from the second dipole a second separation, the fourth dipole may be spaced apart from the third dipole a third separation, and the quadrupole is spaced apart from the fourth dipole a fourth separation. Increasing or decreasing the first separation increases or decreases the horizontal deflection of the electron beam when the first dipole and the second dipole are configured to deflect the electron beam at the first horizontal angle and the second horizontal angle, respectively. Increasing or decreasing the third separation increases or decreases the vertical deflection of the electron beam when the third dipole and the fourth dipole are configured to deflect the electron beam at the first vertical angel and the second vertical angle, respectively.

[0017] In certain aspects, a system includes an electron beam source and the magnetic system operably coupled to the electron beam source.

[0018] In another aspect of the present disclosure, a method of shaping an electron beam includes selecting an operational status of a magnetic system configured to shape the electron beam and passing the electron beam through the magnetic system to shape the electron beam.

[0019] In aspects, selecting the operational status includes positioning a first dipole and a second dipole such that the electron beam passes therethrough when the electron beam is passed through the magnetic system. The first dipole and the second dipole may be configured to steer the electron beam to a horizontal position with respect to a target tissue. Positioning the first dipole and the second dipole may include rotating the first dipole or the second dipole about a respective dipole axis suchthat a magnetic field of the first dipole or the second dipole is equal in magnitude and antiparallel to the magnetic field of the other of the first dipole or the second dipole. Positioning the first dipole and the second dipole may include rotating an inner cylinder or an outer cylinder of the first dipole or an inner cylinder or an outer cylinder of the second dipole such that the magnetic field of the first dipole or the second dipole is equal in magnitude and antiparallel to the magnetic field of the other of the first dipole or the second dipole. Rotating the inner cylinder or the outer cylinder of the first dipole or the inner cylinder or the outer cylinder of the second dipole may change the magnitude or the direction of the magnetic field of the respective dipole. Positioning the first dipole and the second dipole may include translating the first dipole or the second dipole with respect to other of the first dipole or the second dipole such that the first dipole and the second dipole are spaced apart a first separation.

[0020] In certain aspects, selecting the operational status includes positioning a quadrupole with respect to the electron beam. The quadrupole may be configured to magnetically focus the electron beam into an electron minibeam. Positioning the quadrupole may include spinning the quadrupole about the electron beam to form the electron minibeam such that the electron minibeam has a circular cross-section. Selecting the operational status may include positioning a third dipole and a fourth dipole such that the electron beam passes therethrough when the electron beam passes therethrough the magnetic system. The third dipole and the fourth dipole may be configured to steer the electron beam to a vertical position with respect the target tissue. Positioning the quadrupole may include coaxially aligning a quadrupole aperture defined by the quadrupole with the electron beam such that the electron beam passes therethrough after being steered by the first dipole and the second dipole. Positioning the third dipole and the fourth dipole may include rotating an inner cylinder or an outer cylinder of the third dipole or the fourth dipole such that a magnetic field of the third dipole or the fourth dipole may be equal in magnitude and antiparallel to the magnetic field of the other of the third dipole or the fourth dipole. Positioning the third dipole and the fourth dipole may include translating the third dipole or the second dipole with respect to the other of third dipole or second dipole such that the second dipole and the third dipole are spaced apart a second separation. Positioning the third dipole and the fourth dipole may include translating the third dipole or the fourth dipole with respect to the other of third dipole or the fourth dipole such that the third dipole and the fourth dipole are spaced apart third separation.

[0021] Further, to the extent consistent, any of the embodiments or aspects described herein may be used in conjunction with any or all of the other embodiments or aspects described herein.Brief Description of the Drawings

[0022] Various aspects of the present disclosure are described hereinbelow with reference to the drawings, which are not necessarily drawn to scale, which are incorporated in and constitute a part of this specification, wherein:

[0023] FIG. 1 is a schematic illustration of a magnetic system in accordance with embodiments of the present disclosure;

[0024] FIG. 2 is a schematic illustration of a dipole in accordance with embodiments of the present disclosure;

[0025] FIG. 3 is a schematic illustration of the magnetic system of FIG. 1 showing deflection of an electron beam in the horizontal plane in accordance with embodiments of the present disclosure;

[0026] FIG. 4 is a schematic illustration of the magnetic system of FIG. 1 showing deflection of an electron beam in the vertical plane in accordance with embodiments of the present disclosure;

[0027] FIG. 5 is a perspective view of a quadrupole in accordance with embodiments of the present disclosure;

[0028] FIG. 6 is a schematic illustration representing a magnetic field of the quadrupole of FIG. 5;

[0029] FIG. 7 is an illustration representing a dose map of an example electron beam having beamlets of circular profile;

[0030] FIG. 8 is an illustration representing a dose map of an example electron beam having beamlets of planar profile;

[0031] FIG. 9 is a table illustrating a plurality of electron beam arrays the magnetic system is capable of producing in accordance with embodiments of the present disclosure;

[0032] FIG. 10 is a front view of a positioning system in accordance with embodiments of the present disclosure;

[0033] FIG. 11 is a side view of the positioning system of FIG. 10;

[0034] FIG. 12 is a flowchart illustrating a method of shaping electron beams in accordance with embodiments of the present disclosure;

[0035] FIG. 13 is an illustration representing the three-dimensional 50% dose contour of an example planar electron beam passed through a magnetic system in accordance with embodiments of the present disclosure;

[0036] FIG. 14 represents a dose map of the example electron beam of FIG. 13 at the entrance of a water phantom;

[0037] FIG. 15 is a dose map of the example electron beam of FIG. 13 at a target depth within the water phantom;

[0038] FIG. 16 is a one-dimensional transverse dose profile taken along the horizontal axis of the dose maps of FIGS. 14 and 15; and

[0039] FIG. 17 shows the Peak Depth Dose Profile (PDDP) and the Valley Depth Dose Profile (VDDP) of the example electron beam of FIG. 13 taken along the beam axis and in a dose valley adjacent to the beam axis.Detailed Description

[0040] The present disclosure will now be described more fully hereinafter with reference to example embodiments thereof with reference to the drawings in which like reference numerals designate identical or corresponding elements in each of the several views. These example embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Features from one embodiment or aspect can be combined with features from any other embodiment or aspect in any appropriate combination. For example, any individual or collective features of method aspects or embodiments can be applied to apparatus, product, or component aspects or embodiments and vice versa. The disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification and the appended claims, the singular forms “a,” “an,” “the,” and the like include plural referents unless the context clearly dictates otherwise. Inaddition, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to manufacturing or engineering tolerances or optimizations or the like.

[0041] Referring now to FIG. 1, an example magnetic system 100 for electron minibeam scanning is schematically shown. The magnetic system 100 includes a first dipole 110, a second dipole 120, a third dipole 130, a fourth dipole 140, and a quadrupole 150. The magnetic system 100 can be operatively coupled to an electron source 10 (e.g., a therapeutic LINAC operating in electron mode) to form electron minibeams from an electron beam 12 emitted from the electron source 10. The magnetic system 100 directs the electron beam 12 toward a target tissue 20, e g., a cancerous tumor, for treatment. The magnetic system 100 may shape the electron beam 12 to produce electron minibeams without the use of direct mechanical collimation, e.g., a physical barrier to form or shape the electron beam 12. More specifically, the magnetic system 100 can produce electron minibeams by steering the electron beam 12 to a particular location in a plane transverse to the source beam axis (e.g., 5 mm along the x-axis and -2 mm along the y-axis) using the dipoles 110, 120, 130, 140, and then focusing the electron beam 12 with the quadrupole 150 to reduce the cross-section, e.g., beam diameter, as measured by the full width at half maximum (FWHM) (i.e., the distance between two points on the beam’s dose or fluence profile where the value is half the maximum value).

[0042] The magnetic system 100 has a first end or a breech 102 and a second end or a muzzle 104. The electron beam 12 may enter the magnetic system 100 through the breech 102 and may exit through the muzzle 104. The breech 102 may be configured to mount the magnetic system 100 to the electron source 10, e.g., inside a linear accelerator (LINAC), such that the magnetic system 100 is operably coupled to the electron source 10. The first dipole 110 may be positioned at or adjacent to the breech 102 and the quadrupole 150 may be positioned at or adjacent to the muzzle 104. The second dipole 120, the third dipole 130, and the fourth dipole 140 may be disposed between the first dipole 110 and the quadrupole 150. The dipoles 110, 120, 130, and 140, and the quadrupole 150 may be constructed as Halbach cylinders. The dipoles 110 and 120 may be generally coaxially aligned with one another, and the dipoles 130 and 140 may be generally coaxially aligned with one another. In some embodiments, each of the dipoles 110, 120, 130 and 140 may be generally coaxially aligned with one another. The dipoles 110, 120, 130, and 140, and the quadrupole 150 may be positioned sothat, as the electron beam 12 travels downstream through the magnetic system 100, the electron beam 12 passes through the dipoles 110, 120, 130, 140 and the quadrupole 150.

[0043] The muzzle 104 of the magnetic system 100 may be positioned near a target body 24, e.g., a patient or a test phantom. The muzzle 104 of the magnetic system 100 may be a distance D from an entrance 22 of the target body 24. The target tissue 20 may be a target depth T from the entrance 22 within the target body 24.

[0044] Continuing to refer to FIG. 1, the dipoles 110, 120, 130, 140 steer or aim the electron beam 12 and deliver a dose of radiation to the target tissue 20 or portion of the target tissue 20. The dipoles 110, 120, 130, 140 steer the electron beam 12 by deflecting the electron beam 12 with their respective magnetic fields. Two of the dipoles 110, 120, 130, 140 are X-dipoles and two of the dipoles 110, 120, 130, 140 are Y-dipoles. The X-dipoles may be configured to deflect the electron beam 12 in the horizontal plane. The Y-dipoles may be configured to deflect the electron beam 12 in the vertical plane. The dipoles 110, 120, 130, 140 may be positioned in any order with respect to each other. For example, as illustrated in FIG. 1, the first dipole 110 and the second dipole 120 may be the X-dipoles and the third dipole 130 and the fourth dipole 140 may be the Y-dipoles. In some embodiments, the first dipole 110 and the second dipole 120 may be the Y-dipole and the third dipole 130 and the fourth dipole 140 may be the X-dipoles. In certain embodiments, the position of the X-dipoles and the Y- dipoles alternate so that the X-dipoles are separated by a Y-dipole and the Y-dipoles are separated by a X-dipole. For example, the first dipole 110 may be an X-dipole, the second dipole 120 may be a Y-dipole, the third dipole 130 may be a X-dipole, and the fourth dipole 140 may be a Y-dipole. In other embodiments, the first dipole 110 may be a Y-dipole, the second dipole 120 may be a X-dipole, the third dipole 130 may be a Y-dipole, and the fourth dipole 140 may be a X-dipole.

[0045] In particular embodiments, the magnetic system 100 includes only two dipoles, e.g., the first dipole 110 and the second dipole 120, and may deflect the electron beam 12 in one plane. For example, the magnetic system 100 may include only X-dipoles or only Y-dipoles. In some embodiments, the two dipoles may rotate about their central axes and with respect to the axis of the electron beam 12. Rotating the two dipoles may allow for deflecting the electron beam 12 to a position that has components in both the horizontal plane and the vertical plane. For example, when the first dipole 110 and the second dipole 120 are in a first radial orientation the dipoles 110, 120 may function as X-dipoles and deflect the electron beam 12 in the horizontal plane. Rotating both the first dipole 110 and the second dipole 120 to a second radial orientation may allow the dipoles 110, 120to function as Y-dipoles and deflect the electron beam 12 in the vertical plane. Additionally, rotating both the first dipole 110 and the second dipole 120 to a third radial orientation between the first radial orientation and the second radial orientation may allow the dipoles 110, 120 to deflect the electron beam 12 with one component in the horizontal plane and one component in the vertical plane.

[0046] Referring to FIG. 2, the dipoles 110, 120, 130, 140 are Halbach cylinders. More particularly, the dipoles 110, 120, 130, 140 may be constructed as nested Halbach cylinders with each of the dipoles 110, 120, 130, 140 including an inner cylinder 112 and outer cylinder 114. The inner cylinder 112 is nested within the outer cylinder 114. In certain embodiments, one or more of the dipoles 110, 120, 130, 140 may be non-nested Halbach cylinders, without an inner and outer cylinder. The inner cylinder 112 may define a central aperture 116. The cylinders 112, 114 may each include a plurality of magnet segments arranged in an array to create a magnetic field with two poles. The magnetic segments may be a permanently magnetic material. The magnetic segments may be arranged such that the magnetic field of the respective dipole 110, 120, 130, 140 is substantially confined within the respective central aperture 116. The central aperture 116 of each dipole 110, 120, 130, 140 may define a respective central axis of each of the dipoles 110, 120, 130, 140. The dipoles 110, 120, 130, 140 may be coaxially aligned with each other, as shown in FIG. 1, to define a dipole central axis. Each dipole 110, 120, 130, 140 may have a length Li, L2, L3, L4, respectively, in the range of 20 mm to 100 mm, e g., 35 or 75 mm. The dipoles 110, 120, 130, 140 may have the same lengths Li, L2, L3, L4. In some embodiments, the dipoles 110, 120, 130, 140 may have different lengths Li, L2, L3, L4. The dipoles 110, 120, 130, 140 may have magnetic field strengths in the range of 20 mT to 2 T, e.g., 40 mT, 100 mT, 500 mT, 750 mT, IT, or 1.5 T.

[0047] In particular embodiments, the dipoles 110, 120, 130, 140 may include more than one Halbach cylinder coaxially aligned with one another. Forming the dipoles 110, 120, 130, 140 with more than one Halbach cylinder can increase the lengths Li, L2, L3, L4 of the respective dipoles 110, 120, 130, 140 and, thus, increase the deflection of the electron beam 12 by the dipoles 110, 120, 130, 140. In embodiments where the dipoles 110, 120, 130, 140 are formed of more than one Halbach cylinder, each Halbach cylinder may have the same magnetic field strength. In certain embodiments where the dipoles 110, 120, 130, 140 are formed of more than one Halbach cylinder, each Halbach cylinder forming each respective dipole 110, 120, 130, 140 may have a different magnetic field. In certain embodiments, the dipole 110, 120, 130, 140 may be modular. In such an embodiment, one or more dipole Halbach cylinder may be inserted into or removed from a respective dipole 110, 120,130, 140 to increase or decrease the amount of deflection by any or all of the dipoles 110, 120, 130,140.

[0048] The inner cylinder 112 and the outer cylinder 114 each have an array of magnets to create a magnetic field with two poles, e.g., a dipole. The inner cylinder 112 and the outer cylinder 114 are rotatable with respect to each other. For example, the inner cylinder 112 and the outer cylinder 114 may be independently rotatable with respect to each other or the inner cylinder 112 and the outer cylinder 114 may be rotated in concert with each other. Rotating the nested cylinders 112, 114 radially offsets the magnetic fields of the nested cylinders 112, 114 and can alter the total magnetic field of the respective dipole 110, 120, 130, 140. More particularly, rotating the inner cylinder 112 and the outer cylinder 114 with respect to each other can alter the magnitude of the total magnetic field within the central aperture 116 by the superposition of the magnetic field of the inner cylinder 112 and the magnetic field of the outer cylinder 114. For example, as shown in FIG. 2, rotating the inner cylinder 112 and the outer cylinder 114 to a first radial position Ri may superimpose the magnetic fields of the cylinders 112, 114 to result in a magnetic field having a maximum magnitude and a first field direction. Rotating the inner cylinder 112 and the outer cylinder 114 to a second radial position R2 may superimpose the magnetic fields of the cylinders 112, 114 to result in a zero magnetic field, e.g., where the fields of the cylinders 112, 114 cancel. Rotating the inner cylinder 112 and the outer cylinder 114 to a third radial position R3 may superimpose the magnetic fields of the cylinders 112, 114 to result in a magnetic field having a maximum magnitude and a second field direction opposite the field direction when the cylinders 112, 114 are in the first radial position Ri. The cylinders 112, 114 may be rotated to any radial position between Ri and Rsto achieve the desired magnitude of the resultant magnetic field of each respective dipole 110, 120, 130, 140. In some embodiments, the entire dipole 110, 120, 130, 140 may be rotated, e.g., rotating the inner cylinder 112 and the outer cylinder 114 the same amount.

[0049] Referring to FIGS. 3 and 4, the dipoles 110, 120, 130, and 140 may be translatable with respect to each other along or parallel to the central axis of the magnetic system 100. The quadrupole 150 may be translatable with respect to the dipoles 110, 120, 130, and 140 along or parallel to the central axis of the magnetic system 100. Translating the dipoles 110, 120, 130, 140 and the quadrupole 150 may space the dipoles 110, 120, 130, 140 and the quadrupole 150 apart from each other along the central axis of the magnetic system 100. Increasing or decreasing the space between the dipoles 110, 120, 130, 140 and the quadrupole 150 may increase or decrease the deflection of theelectron beam 12 by the magnetic system 100. Specifically, the first dipole 110 and the second dipole 120 may be spaced apart a first separation Si, the second dipole 120 and the third dipole 130 may be spaced apart a second separation S2, the third dipole 130 and the fourth dipole 140 may be spaced apart a third separation S3, and the fourth dipole 140 and the quadrupole 150 may be spaced apart a fourth separation S4. The dipoles 110, 120, 130, 140 and the quadrupole 150 may be independently translatable. Translating one or more of the dipoles 110, 120, 130, 140, or the quadrupole 150 may adjust one or more of the separations Si, S2, S3, S4. The separations Si, S2, S3, S4inay be in the range of 5 mm to 100 mm, e.g., 10 mm or 15 mm. In some embodiments, the separations Si, S2, S3, S4 may be equal to each other. For example, each of the separations Si, S2, S3, S4may be equal to 10 mm. In certain embodiments, each of the separations Si, S2, S3, S4 may be different from each other. For example, the first separation Si may be 10 mm, the second separation S2 may be 20 mm, the third separation S3 may be 15 mm, and the fourth separation S4 may be 25 mm. In some embodiments, one or more of the separations Si, S2, S3, S4 may be constant or variable. For example, the separation52 and the separation S4 may be held constant while the separation Si and the separation S3 are increased or decreased.

[0050] In some embodiments, one or more of the dipoles 110, 120, 130, 140 are positionally fixed and not translatable along the central axis of the magnetic system 100 to increase or decrease the respective separations Si, S2, S3, S4. Positionally fixing the dipoles 110, 120, 130, 140 keep the separation Si, S2, S3, S4 between respective dipoles 110, 120, 130, 140 constant. For example, the first dipole 110 and the third dipole 130 may be translatable and the second dipole 120 and the fourth dipole 140 may fixed. In such an embodiment, translating the first dipole 110 may increase or decrease separation Si, translating the third dipole 130 may increase or decrease separation S2 and / or the separation S3, and fixation of the fourth dipole 140 may hold the separation S4 between the fourth dipole 140 and the quadrupole 150 constant. In some embodiments, the second dipole 120 and the fourth dipole 140 may be translatable and the first dipole 110 and the third dipole 130 may fixed. In such an embodiment, translating the second dipole 120 may increase or decrease the separation Si and / or the separation S2 and translating the fourth dipole 140 may increase or decrease the separation53 and / or the separation S4. In certain embodiments, the second dipole 120 and the third dipole 130 are translatable and the first dipole 110 and the fourth dipole 140 are positionally fixed. In such an embodiment, translating the second dipole 120 may increase or decrease the first separation Si and / or the second separation S2 and translating the third dipole 130 may increase or decrease the second separation S2 and / or the third separation S3.

[0051] In general, the total deflection of the electron beam 12 by the magnetic system 100 is defined by the magnetic field of the dipoles 110, 120, 130, 140 and the longitudinal distance traveled equal to the sum of the lengths Li, L2, L3, L4 of the dipoles 110, 120, 130, 140 and the respective separations Si, S3 between dipoles 110 and 120, and dipoles 130 and 140. As such, translating the dipoles 110, 120, 130, 140 may alter the amount of the deflection of the electron beam 12. For example, spacing the dipoles 110, 120, 130, and 140 further apart may provide for more deflection and spacing the dipoles 110, 120, 130, and 140 closer together may provide less deflection. Additionally, the energy of the electron beam 12 may contribute to the amount of deflection of the electron beam 12 by the magnetic system 100. Specifically, the higher the energy of the electron beam 12, the less the deflection the electron beam 12 may be deflected by the magnetic system 100 for a given magnetic field strength and longitudinal distance traveled by the electron beam 12. For example, the magnetic system 100 may deflect an electron beam 12 having an energy of 5 MeV more than an electron beam 12 having an energy of 10 MeV with the same operational parameters.

[0052] In some embodiments, a plurality of electron beamlets passed through the magnetic system 100 may be scanned to form a spatially fractionated dose distribution. Translating the dipoles 110, 120, 130, and 140 may arrange the electron beamlets into an array, e.g., a rectangular or square grid, with a center-to-center gap between each of the beamlets. As described above, the total deflection of the electron beam 12 is defined by the magnetic field of the dipoles 110, 120, 130, 140, the separation Si between the dipoles 110 and 120, and the separation S3 between the dipoles 130 and 140. Therefore, where a spatially fractionated dose distribution is used, the array of beamlets is constructed by choosing a suitable set of magnetic field values for the dipoles 110, 120, 130, 140 and the dipole separations Stand S3.

[0053] Particularly referring to FIG. 3, when the dipoles 110, 120, 130, 140 steer the electron beam 12 the total magnetic fields of the two X-dipoles are equal in magnitude and antiparallel to each other and the total magnetic fields of the two Y-dipoles are equal in magnitude and antiparallel to each other. For example, in an embodiment where the first dipole 110 and the second dipole 120 are the X-dipoles and the first dipole 110 and the second dipole 120 deflect the electron beam 12 in the horizontal plane, the electron beam 12 may enter the first dipole 110 with an entry trajectory and leave the first dipole 110 having been deflected away from the axis of the magnetic system 100 by a first horizontal angle Oxi in the horizontal plane. The electron beam 12 continues to travel downstream with this first horizontal angle Oxi until the electron beam 12 enters the second dipole 120. The seconddipole 120, having a total magnetic field that is equal in magnitude and antiparallel to the magnetic field of the first dipole 110, will deflect the electron beam 12 back towards the axis of the magnetic system 100 at a second horizontal angle 0X2that is equal to the first horizontal angle Oxi. Accordingly, the electron beam 12 is displaced a horizontal deflection dxand has a resulting exit trajectory that is parallel to that of the entry trajectory but shifted in the horizontal plane. For example, if the entry trajectory is parallel to the central axis of magnetic system 100, the exit trajectory will also be parallel but shifted in the horizontal plane, as seen in FIG. 3.

[0054] Referring to FIG. 4, deflection of the electron beam 12 by the dipoles 110, 120, 130, 140 in the vertical plane occurs similarly. For example, in an embodiment where the third dipole 130 and the fourth dipole 140 are the Y-dipoles, the electron beam 12 may enter the third dipole 130 with an entry trajectory and leave the third dipole 130 having been deflected away from the axis of the magnetic system 100 by a first vertical angle 0yiin the vertical plane. The electron beam 12 continues to travel downstream with this vertical angle 0yiuntil the electron beam 12 enters the fourth dipole 140. The fourth dipole 140, having a total magnetic field that is equal in magnitude and antiparallel to the magnetic field of the third dipole 130, will deflect the electron beam 12 back towards the axis of the magnetic system 100 at a second vertical angle 0y2 equal to the first vertical angle 0yi. Accordingly, the electron beam 12 is displaced a vertical deflection dyand has a resulting exit trajectory that is parallel to that of the entry trajectory but shifted in the vertical plane. For example, if the entry trajectory is parallel to the central axis of the magnetic system 100, the exit trajectory will also be parallel but shifted in the vertical plane, as seen in FIG. 4.

[0055] Referring to FIGS. 1, 5, and 6, the quadrupole 150 magnetically focuses the electron beam 12 as the electron beam 12 passes therethrough. The magnetic focusing of the electron beam 12 may decrease the diameter of the electron beam 12 at delivery to the target tissue 20 and may form electron minibeams. In some embodiments, the quadrupole 150 may focus the electron beam 12 into a planar electron minibeam having an elongated or planar profile. In such an embodiment, the quadrupole 150 may focus the electron beam 12 to decrease the diameter along only one axis, resulting in planar electron minibeam with a very narrow minor axis. The quadrupole 150 may form electron minibeams having a diameter, or half diameter, less than or equal to 5 mm e.g., 0.5, 1, 2, 3, or 4 mm. In embodiments, compared to mechanical collimation, magnetic focusing with the quadrupole 150 may reduce secondary particle production, e.g., photons, and associated extraneous dose of radiation. Directly intercepting the electron beam 12 with direct mechanical collimation (e.g., passing theelectron beam 12 through relatively narrow apertures) leads to secondary particle production because of physical interactions between electrons and collimator materials. However, because direct interception of the electron beam 12 with the walls of the quadrupole 150 is relatively minimal, fewer secondary particles are produced.

[0056] The quadrupole 150 may be a Halbach cylinder. The quadrupole 150 may include a plurality of magnet segments 151 arranged in an array to create a magnetic field with four poles, as shown in FIG. 6. The magnetic segments 151 may be a permanently magnetic material. The quadrupole 150 may define a quadrupole aperture 152. The quadrupole aperture 152 may define a central quadrupole axis. The magnetic segments 151 may be arranged such that the magnetic field of the quadrupole 150 is substantially confined within the quadrupole aperture 152. The quadrupole 150 may have a magnetic field gradient in the range of 5 T / m to 200 T / m, e.g., 40 or 100 T / m. The quadrupole 150 may have a quadrupole length LQ in the range of 20 mm to 100 mm, e.g., 30 mm, 50 mm, or 75 mm, etc. In particular embodiments, the quadrupole 150 may include more than one Halbach cylinder coaxially aligned with one another. Forming the quadrupole 150 with more than one Halbach cylinder may increase the effective quadrupole length LQ and, thus, also increase the amount that the electron beam 12 is magnetically focused. In embodiments where the quadrupole 150 are formed of more than one Halbach cylinder, each Halbach cylinder may have the same magnetic field gradient. In certain embodiments where the quadrupole 150 is formed of more than one Halbach cylinder, each Halbach cylinder may have a different magnetic field gradient.

[0057] In embodiments, quadrupoles 150 of different lengths or magnetic gradients may be swapped into or out of the magnetic system 100 to increase or decrease the length or magnetic gradient of the quadrupole 150. Changing the quadruple 150 for a different quadrupole 150 may increase or decrease the amount the electron beam 12 is focused. In certain embodiments, the quadrupole 150 may be modular. In such an embodiment, more than one quadrupole may be inserted into the magnetic system 100 in series with each other, or removed from the magnetic system 100, to increase or decrease length of the quadrupole 150. In embodiments, the quadrupole 150 may be adjustable to increase or decrease the magnetic field gradient of the quadrupole 150 and, thus, the amount the electron beam 12 is magnetically focused by quadrupole 150. In particular embodiments, the quadrupole 150 may be a quadrupole Halbach cylinder nested in a magnetic mangle that can be adjusted to alter the magnetic field gradient of inside the nested Halbach cylinder 150 to increase or decrease the amount the electron beam 12 is focused by the quadrupole 150.

[0058] The quadrupole 150 is configured to selectively spin about the central quadrupole axis and the electron beam 12 or to remain stationary when the electron beam 12 is passed through the quadrupole aperture 152. Spinning the quadrupole 150 about the electron beam 12 may shape the electron beam 12 into an electron minibeam with a circularly symmetric electron fluence e.g., at the target tissue 20, as depicted in FIG. 7. Spinning the quadrupole 150 may create minibeams with a circular profile where a single electron beam 12 is passed through the magnetic system 100. In embodiments, spinning the quadrupole 150 creates a statistically identical beam phase space in both transverse planes, e.g., the horizonal plane and the vertical plane. For example, spinning the quadrupole 150 about the electron beam 12 may result in essentially identical average particle displacement, average particle divergence, particle displacement-divergence correlations and emittance of the electron beam 12 in the vertical and the horizontal planes. Depending on dose rate (e g., conventional or ultra-high dose rates), the quadrupole 150 may spin at a rate in the range of 50 RPM to 7,500 RPM, e.g., 300 RPM for a conventional dose rate and 6,000 RPM for ultra-high dose rates. The quadrupole 150 may spin clockwise or counterclockwise about the electron beam 12.

[0059] In embodiments that produce a spatially fractionated dose distribution, spinning the quadrupole 150 may shape the electron beam 12 such that each beamlet of spatially fractionated dose distribution has a circular profile. Adjusting the magnitude of the magnetic fields of the dipoles 110, 120, 130, and 140, and / or translating the dipoles 110, 120, 130, and 140 may arrange the electron beamlets into an array, e.g., a rectangular or square grid, with a center-to-center gap between each of the beamlets.

[0060] In embodiments where the quadrupole 150 is held stationary, not spinning, with respect to the electron beam 12, the magnetic system 100 may produce electron minibeams having an elongated or planar cross-sectional profile, as shown in FIG. 8. Holding the quadrupole 150 stationary may create minibeams with a planar profile where a single electron beam 12 is passed through the magnetic system 100. In some embodiments, an array of a plurality of electron beamlets each with an elongated or planar profile may be created by holding the quadrupole 150 stationary and passing the electron beam 12 through the magnetic system 100 to form a planar spatially fractionated dose distribution. Adjusting the magnitude of the magnetic fields of the dipoles 110, 120, 130, and 140, and / or translating the dipoles 110, 120, 130, and 140 may arrange the electron beamlets into an array, e.g., a linear grid, with a center-to-center gap between each of the beamlets. In embodiments that produce planar electron minibeams, the electron minibeams may have a minor axis diameterdimension near the beam waist, e.g., the region of minimum minor diameter of the planar electron beam 12, less than or equal to 5 mm, e.g., 1.5 mm. The orientation of the planar minibeams may be controlled by rotating the quadrupole 150 to a different fixed position with respect to the electron beam 12. More particularly, rotating the quadrupole 150 to a different fixed position repositions the magnetic poles of the quadrupole 150 with respect the electron beam 12. As such, the elongated profile of the planar minibeam may be on the horizontal plane, the vertical plane, or at an angle between horizontal and vertical, e.g., at a 45-degree angle to the horizontal or the vertical planes. For example, rotating the quadrupole 150 to a first fixed position may position the magnetic poles of the quadrupole 150 such that the electron beam 12 is focused into a vertical planar minibeam and rotating the quadrupole 150 to a second fixed position may position the magnetic poles of the quadrupole 150 such that the electron beam 12 is focused into a horizontal planar minibeam. In embodiments, the second fixed position of the quadrupole 150 may be radially offset 90 degrees from the first fixed position. In some embodiments, rotating the quadrupole 150 to a third fixed position may position the magnetic poles of the quadrupole 150 such that the electron beam 12 is focused into an angular planar minibeam. The third fixed position may be between the first fixed position and the second fixed position.

[0061] Additionally referring to FIG. 9, a plurality of beam arrays that the magnetic system 100 is capable of producing are shown. The magnetic system 100 can operate in different configurations. First, the magnetic system 100 has a two-dimensional (2D) scanning configuration. In the 2D scanning configuration, the magnetic system 100 utilizes the four dipoles 110, 120, 130, 140 and the quadrupole 150 which allows for steering the electron beam 12 in both the horizontal and the vertical planes. Second, the magnetic system 100 has a linear or ID scanning configuration. In the linear scanning configuration, the magnetic system 100 utilizes two dipoles, e.g., the first dipole 110 and the second dipole 120, and the quadrupole 150 which allows for steering the electron beam 12 in a single plane, e.g., the horizontal plane or the vertical plane. In certain embodiments, when the magnetic system 100 is in the linear configuration, the magnetic system 100 may operate in a pseudo- 2D scanning configuration. In the pseudo-2D configuration the two dipoles may be successively rotated by any chosen angle about the central axis, and steer the electron beam 12 to form a linear array of beams in the plane inclined by the chosen angle. For example, the dipoles may be rotated by 45 degrees where a linear array of beams is formed, rotated by another 45 degrees where another linear array is formed, and so on, until the array formed by all the beams falls on a cross sectional pattern of concentric circles. Finally, the magnetic system 100 has a single beam configuration wherea single electron beam 12 is passed through the magnetic system 100 (i.e., the electron beam 12 is not scanned at all).

[0062] Additionally, the magnetic system 100 can operation in different modes when in the different configurations. First, the magnetic system 100 may operate in a planar beam mode in which the magnetic system 100 can produce planar minibeams having an elongate profile. In the planar mode the quadrupole 150 is held fixed with respect to the electron beam 12. Second, the magnetic system 100 may operate in a symmetric beam mode in which the magnetic system 100 can produce minibeams having a circular profile. In the symmetric beam mode, the quadrupole 150 spins, continuously, about the electron beam 12 as it passes therethrough. Third, the magnetic system 100 may also operate in a scan only or unfocused mode where the quadrupole 150 is positioned such that the electron beam 12 does not pass therethrough, and the unmodified electron beam 12 is delivered by the magnetic system 100. More particularly, when the magnetic system 100 is in the unfocused mode the electron beam 12 is not focused by the quadrupole 150 and is only deflected by the dipoles 110, 120, 130, 140.

[0063] The magnetic system 100 may operate in one of the 2D scanning configuration, the linear or ID scanning configuration, the pseudo-2D scanning configuration, or the single beam configuration, and one of the planar beam mode, the symmetric beam mode, or unfocused beam mode. For example, the magnetic system 100 may be in the 2D scanning configuration and the symmetric beam mode. In embodiments, the magnetic system 100 may be in the 2D scanning configuration and the planar mode. In some embodiments, the magnetic system 100 may be in the linear scanning configuration and the symmetric beam mode. In particular embodiments, the magnetic system 100 may be in the linear scanning configuration and the planar beam mode. In some embodiments, the magnetic system 100 may be in the single beam configuration and the unfocused beam mode.

[0064] Referring to FIGS. 10 and 11, the magnetic system 100 may include a positioning system 160 that positions the quadrupole 150 with respect to the electron beam 12. Specifically, the positioning system 160 coaxially aligns the quadrupole aperture 152 of the quadrupole 150 with the electron beam 12 after the electron beam 12 is deflected by the dipoles 110, 120, 130, 140. The quadrupole 150 is mounted on the positioning system 160. The quadrupole 150 may be moved by the positioning system 160 based on the deflection of the electron beam 12 by the dipoles 110, 120, 130, 140. The positioning system 160 is a six-axis robotic arm, as shown in FIGS. 10 and 11. In such an embodiment, the positioning system 160 includes a head 162 defining a passage 164 throughthe head 162. The quadrupole 150 is mounted to the positioning system 160 such that the quadrupole aperture 152 coaxially aligns with the passage 164. In some embodiments, the positioning system 160 may have three degrees of freedom, to manipulate and position the quadrupole 150. In such an embodiment, the positioning system 160 may include a plurality of linear actuators, e.g., ball screws, to position the quadrupole 150. In such an embodiment, the positioning system 160 may translate the quadrupole 150 in the horizontal plane and the vertical plane to align the quadrupole aperture 152 with the deflected electron beam 12, and translate along or parallel to the central axis of the magnetic system 100 to increase or decrease the fourth separation S4 between the quadrupole 150 and the fourth quadrupole 140. The positioning system 160 may be in signal communication with the control system for the dipoles 110, 120, 130, 140. The positioning system 160 receives signal communications from the control system for the dipoles 110, 120, 130, 140 indicating the deflection and trajectory of the electron beam 12. The positioning system 160 may position the head 162 and, thus, the quadrupole 150, based on signals received from the control system. In some embodiments, the positioning system 160 positions the quadrupole 150 iteratively. For example, the quadrupole 150 may be positioned at a first position, the electron beam 12 may be passed through the quadrupole 150 at the first position, the quadrupole 150 may be repositioned at a second position, and the electron beam 12 may be passed through the quadrupole 150 at the second position.

[0065] Referring to FIG. 12, a method 1000 of forming electron beams in accordance with embodiments, of the present disclosure is described with reference to the magnetic system 100 of FIGS. 1-11.

[0066] The operational status of the magnetic system 100 is selected and the magnetic system 100 is switched thereto (Step 1100). Selecting the operational status of the magnetic system 100 includes selecting a configuration and a mode for the magnetic system 100. A configuration for the magnetic system 100 may be selected from one of the 2D scanning configuration, the linear scanning configuration, the pseudo-2D configuration, or the single beam configuration. A mode for the magnetic system 100 may be selected from one of the planar beam mode, the symmetric beam mode, or the unfocused beam mode. For example, the magnetic system 100 may have an operational status with a 2D scanning configuration and a symmetric beam mode. In some embodiments, the magnetic system 100 may have an operational status with a linear scanning configuration and a planar beam mode.

[0067] In embodiments, the operational status may be selected based on factors including, but not limited to, the energy of the electron beam 12, the location of the target tissue 20, the size of the target tissue 20, the deflection of the electron beam 12 by the dipoles 110, 120, 130, 140, the extent of magnetic focusing of the electron beam 12 by the quadrupole 150, the separations Si, S2, S3, S4, the radial position of the cylinders 112, 114 of the dipoles 110, 120, 130, 140, and the desired center-to- center distance between beamlets. The operational status may be selected by or with the aid of a treatment planning software.

[0068] The quadrupole 150 may be positioned such that the deflected electron beam 12 passes through the quadrupole 150 (Step 1200). If the quadrupole 150 is positioned so that the electron beam 12 passes therethrough, the quadrupole can focus the electron beam 12 and thereby may reduce the diameter of the electron beam 12 along all radial axes or a single axis. For example, the quadrupole 150 may be positioned such that quadrupole aperture 152 coaxially aligns with the electron beam 12. The positioning system 160 may position the quadrupole 150 with respect to the electron beam 12. In some embodiments, the positioning system 160 positions the quadrupole 150 iteratively. For example, the quadrupole 150 may be positioned at a first position, the electron beam 12 may be fired through the quadrupole 150 at the first position, the quadrupole 150 may be repositioned at a second position, and the electron beam 12 may be fired through the quadrupole 150 at the second position. In embodiments, if the quadrupole 150 is positioned so that the electron beam 12 does not pass therethrough, e.g., the quadrupole is positioned outside of the path of the electron beam 12, the magnetic system 100 will deliver unmodified, e.g., unfocused, electron beams 12 toward the target tissue 20 or the target body 24, but the unmodified beams may be positioned by the dipoles 110, 120, 130, and 140.

[0069] The quadrupole 150 may be set to spin about the electron beam 12 as the electron beam 12 passes through the quadrupole 150 (Step 1300). Spinning the quadrupole 150 may produce circular minibeams. Depending on dose rate, the quadrupole 150 may spin at a rate in the range of 50 revolutions per minute (RPM) to 7,500 RPM, e.g., 6,000 RPM for an ultra-high dose rate. The quadrupole 150 may spin clockwise or counterclockwise about the electron beam 12. In embodiments, the quadrupole 150 does not spin about the electron beam 12, the quadrupole 150 may form minibeams having an elongate or planar cross-sectional profile.

[0070] The X-dipoles, e.g., the first dipole 110 and the second dipole 120, are positioned (Step1400). The X-dipoles may be configured to deflect the electron beam 12 in the horizontal plane. TheX-dipoles may be Halbach cylinders as described above. Positioning the X-dipoles may include translating the X-dipoles with respect to each other to space the X-dipoles apart, e.g., the separation Si, and rotating the inner cylinder 112 of each X-dipole relative to the respective outer cylinder 114 to adjust the total magnetic field of the X-dipoles. Translating the X-dipoles and adjusting the total magnetic field of the X-dipoles can change the extent of the deflection of the electron beam 12. In particular, two X-dipoles are positioned with respect to each other such that the total magnetic fields of the two X-dipoles are equal in magnitude and antiparallel to each other. Positioning the two X- dipoles such that the total magnetic fields are equal in magnitude and antiparallel counters the deflection experienced by the electron beam 12 so that the trajectory of the electron beam 12 at the exit from the X-dipoles is parallel to the trajectory of the electron beam 12 at the entry to the X- dipoles but shifted in the horizontal plane.

[0071] The Y-dipoles, e.g., the third dipole 130 and the fourth dipole 140, are positioned (Step 1500). The Y-dipoles may be configured to deflect the electron beam 12 in the vertical plane. The Y-dipoles may be Halbach cylinders as described above. Positioning the Y-dipoles may include translating the Y-dipoles with respect to each other to space the Y-dipoles apart, e.g., the separation53, and rotating the inner cylinder 112 of each Y-dipole relative to the respective outer cylinder 114 to adjust the total magnetic field of the Y-dipoles. Positioning the Y-dipoles may include positioning the Y-dipoles with respect to the X-dipoles. For example, the Y-dipoles may be positioned to be spaced apart from the X-dipoles, e.g., the separation S2, or the quadrupole 150, e.g., the separation54. Translating the Y-dipoles and adjusting the total magnetic field of the Y-dipoles can change the extent of the deflection of the electron beam 12. In particular, the two Y-dipoles are positioned with respect to each other such that the total magnetic fields of the two Y-dipoles are equal in magnitude and are antiparallel to each other. Positioning the two Y-dipoles such that the total magnetic fields are equal in magnitude and antiparallel counters the deflection experienced by the electron beam 12 so that the trajectory of the electron beam 12 at the exit from the Y-dipoles is parallel to the trajectory of the electron beam 12 at the entry to the Y-dipoles but shifted in the vertical plane.

[0072] The electron beam 12 is passed through the magnetic system 100 in the selected operational status (Step 1600). Passing the electron beam 12 through the magnetic system 100 shapes the electron beam 12 for treatment of the target tissue 20. The electron beam 12 may pass through some or all of the dipoles 110, 120, 130, 140 and the quadrupole 150 depending on the selected operational status of magnetic system 100. For example, when the operational status of the magneticsystem 100 is the 2D scanning configuration, the symmetric beam mode, and the single beam state, the electron beam 12 passes through each of the dipoles 110, 120, 130, 140 to be deflected and the quadrupole 150 while the quadrupole is spinning to magnetically focus the electron beam 12. As described above, passing the electron beam 12 through the dipoles 110, 120, 130, 140 allows the electron beam 12 to be steered or aimed at the target tissue 20 or a portion of the target tissue 20 to deliver dose. Passing the electron beam 12 through the quadrupole 150 magnetically focuses the electron beam 12 to reduce the diameter of the electron beam 12 and create electron minibeams.

[0073] In some embodiments, the electron beam 12 may be passed through the magnetic system 100 without being deflected by the dipoles 110, 120, 130, 140. For example, during a treatment process the magnetic system 100 may be aligned with target tissue 20 such that the central aperture 116 of the dipoles 110, 120, 130, 140 and the quadrupole aperture 152 are coaxially aligned with each other. In such an embodiment, the X-dipoles and the Y-dipoles may be positioned such the electron beam 12 is undeflected. For example, the inner cylinder 112 and the outer cylinder 114 of each dipole 110, 120, 130, 140 may be at the second radial position R2 such that each dipole 110, 120, 130, 140 has a zero magnitude magnetic field and the dipoles 110, 120, 130, 140.

[0074] The method 1000 may be repeated as necessary during the course of a treatment. The magnetic system 100 may have the same operational status throughout the course of an entire treatment. For example, the magnetic system 100 may remain in an operational status with the linear scanning configuration and the planar minibeam mode for the entire course of a treatment to deliver a spatially fractionated dose distribution to the target tissue 20. In some embodiments, the magnetic system 100 may switch between operational statuses throughout the course of a treatment. For example, the magnetic system 100 may have an operational status with the 2D scanning configuration and the unfocused beam mode for a portion of a treatment to deliver dose to the medial portions of a target tissue 20. After treatment of the medial portions of the target tissue 20, the magnetic system 100 may be switched to an operational status with the 2D scanning configuration and the symmetric minibeam mode to deliver dose to the periphery of the target tissue 20.

[0075] Although the method steps are described in a specific order, it should be understood that other steps may be performed in between described steps, described steps may be adjusted so that they occur at slightly different times, described steps or sub-steps might occur simultaneously or overlap in time, or the described steps may occur in any order unless otherwise specified.

[0076] Referring to FIGS. 1, 3, 4 and 13-17, hereinbelow an example embodiment in accordance with the present disclosure is described. The underlying data representing the example embodiment is generated by Monte Carlo simulations. The described example embodiment is not limiting and is only illustrative.

[0077] In an example embodiment, with reference to FIGS. 1 and 13-17, the magnetic system 100 is in the linear configuration with two dipoles, e.g., the first dipole 110 and the second dipole 120, and the planar minibeam mode. The quadrupole 150 had a gradient of 42 T / m. Seven electron beamlets with an energy of 9 MeV were passed through and deflected by the dipoles 110, 120 and then focused by the quadrupole 150 to form a spatially fractionated dose distribution of planar beamlets with a 3.5 mm center-to-center separation. The target depth T was 15 mm. The beamlet separation, the separation Si between the dipoles 110, 120, and the strength of the magnetic fields of the dipoles 110, 120 were selected to achieve a quasi-homogeneous dose at the target tissue 20. As shown in FIGS. 13 and 14, when the beamlets exit the quadrupole 150, at the muzzle 104 of the magnetic system 100, and reach the entrance 22 of the target body 24 the beamlets are clearly defined from one another with discrete cross-sections and gaps of low radiation dose between them. As the beamlets travel away from the entrance 22 of the target body 24, each beamlet diverges or spreads until the dose deposited by the beamlets combine at or near the target tissue 20 at the target depth T of 15 mm to form a quasi-homogeneous dose distribution, as shown in FIG. 15. As shown in FIGS. 16 and 17, the beamlets have a high Peak to Valley Dose Ratio (PVDR), greater than 40 at the entrance 22 to the target body 24, and small horizontal FWHM. Specifically, the magnetic system 100 produced single planar beamlets with semi minor diameters as low as 1.1 mm (horizontal FWHM).

[0078] While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Any combination of the above embodiments is also envisioned and is within the scope of the appended claims. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope of the claims appended hereto.

Claims

What is Claimed:

1. A magnetic system capable of creating electron minibeams, the magnetic system comprising: a first dipole defining a first central aperture; a second dipole defining a second central aperture; a third dipole defining a third central aperture; a fourth dipole defining a fourth central aperture, the first central aperture, the second central aperture, the third central aperture, and the fourth central aperture coaxially aligned to define a dipole axis, the first dipole, the second dipole, the third dipole, and the fourth dipole being rotatable about the dipole axis and translatable along the dipole axis relative to each other; and a quadrupole defining a quadrupole aperture, the quadrupole selectively spinnable about a quadrupole axis defined by the quadrupole aperture.

2. The magnetic system according to claim 1, wherein the first dipole, the second dipole, the third dipole, and the fourth dipole each comprise: an outer cylinder; and an inner cylinder defining a respective central aperture of the first dipole, the second dipole, the third dipole, and the fourth dipole, the inner cylinder nested within the outer cylinder, the inner cylinder rotatable with respect to the outer cylinder.

3. The magnetic system according to claim 2, wherein rotating the inner cylinder of a respective dipole with respect to the outer cylinder changes a magnitude of a magnetic field of the respective dipole.

4. The magnetic system according to claim 3, wherein the magnetic field of each dipole is substantially confined within the central aperture of the respective dipole.

5. The magnetic system according to claim 1, wherein the first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole each comprise a plurality of magnetic segments, each magnetic segment of the plurality of magnetic segments being a permanent magnet.

6. The magnetic system according to claim 5, wherein the first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole are Halbach cylinders.

7. The magnetic system according to claim 1, wherein the magnetic system has a first end and a second end opposite the first end, the first dipole positioned adjacent to the first end and the quadrupole positioned adjacent to the second end, the second dipole positioned adjacent to the first dipole between the first dipole and the quadrupole, the third dipole positioned adjacent to the second dipole between the second dipole and the quadrupole, and the fourth dipole positioned adjacent to the third dipole between the third dipole and the quadrupole.

8. The magnetic system according to claim 7, wherein the second dipole is spaced apart from the first dipole a first separation, the third dipole is space apart from the second dipole a second separation, the fourth dipole is spaced apart from the third dipole a third separation, and the quadrupole is spaced apart from the fourth dipole a fourth separation.

9. The magnetic system according to claim 8, wherein translating the first dipole, the second dipole, the third dipole, or the fourth dipole along the dipole axis increases or decreases the first separation, the second separation, the third separation, or the fourth separation.

10. The magnetic system according to claim 8, wherein the first dipole, the second dipole, the third dipole, the fourth dipole, and the quadrupole are spaced apart from one another such that the first separation, the second separation, the third separation, and the fourth separation are equal.

11. The magnetic system according to claim 1, wherein the quadrupole is capable of spinning at a rate in a range of 50 RPM to 7,500 RPM.

12. The magnetic system according to claim 1, wherein the quadrupole has a magnetic field gradient in a range of 5 T / m to 200 T / m.

13. The magnetic system according to claim 1, wherein the first dipole and the second dipole each have a magnetic field, the magnitude of the magnetic field of the first dipole and the magnitude of the magnetic field of the second dipole being equal to each other, and the direction of the magnetic field of the first dipole and the direction of the magnetic field of the second dipole being antiparallel to each other.

14. The magnetic system according to claim 1 , wherein the third dipole and the fourth dipole each have a magnetic field, the magnitude of the magnetic field of the third dipole and the magnitude of the magnetic field of the fourth dipole being equal to each other, and the direction of the magnetic field of the third dipole and the direction of the magnetic field of the fourth dipole being antiparallel to each other.

15. The magnetic system according to claim 1, wherein the first dipole, the second dipole, the third dipole, and the fourth dipole each have a magnetic field in a range of 20 mT to 2 T.

16. The magnetic system according to claim 1 , wherein the first dipole, the second dipole, the third dipole, and the fourth dipole each have a length in a range of 20 mm to 100 mm.

17. A magnetic system capable of creating electron minibeams, the magnetic system comprising: a first dipole; a second dipole, the first dipole and the second dipole configured to steer an electron beam horizontally; a third dipole; a fourth dipole, the third dipole and the fourth dipole configured to steer the electron beam vertically; and a quadrupole that is configured to selectively spin about the electron beam and magnetically focus the electron beam into an electron minibeam.

18. The magnetic system according to claim 17, wherein spinning the quadrupole about the electron beam magnetically focuses the electron beam from a first diameter to a seconddiameter, that is smaller than the first diameter, to form the electron minibeam, the electron minibeam having a circular cross section.

19. The magnetic system according to claim 17, wherein the quadrupole is configured to magnetically focus the electron beam such that the electron minibeam has a planar profile when the quadrupole is stationary with respect to the electron beam.

20. The magnetic system according to claim 17, wherein the first dipole, the second dipole, the third dipole, and the fourth dipole each define a central aperture therethrough, each central aperture defining a dipole axis, the dipole axes of the first dipole and the second dipole coaxially aligned and the dipole axes of the third dipole and the fourth dipole coaxially aligned.

21. The magnetic system according to claim 20, wherein the first dipole is configured to steer the electron beam by deflecting the electron beam in a horizontal direction by a first horizontal angle with respect to the dipole axis and the second dipole is configured to steer the electron beam by deflecting the electron beam in a horizontal direction by a second horizontal angle with respect to the dipole axis, the second horizontal angle being equal to and opposite of the first horizontal angle.

22. The magnetic system according to claim 21, wherein the third dipole is configured to steer the electron beam by deflecting the electron beam in a vertical direction by a first vertical angle with respect to the dipole axis and the fourth dipole is configured to steer the electron beam by deflecting the electron beam in a vertical direction by a second vertical angle with respect to the dipole axis, the second vertical angle being equal to and opposite of the first vertical angle.

23. The magnetic system according to claim 22, wherein the first dipole and the second dipole are configured to steer the electron beam by displacing the electron beam a horizontal deflection with respect to the dipole axis and the third dipole and the fourth dipole are configured to steer the electron beam by displacing the electron beam a vertical deflection with respect to thedipole axis, the horizontal deflection defined by the first horizontal angle and the second horizontal angle and a longitudinal distance traveled by the electron beam between exiting the first dipole and entering the second dipole and the vertical deflection defined by the first vertical angle and the second vertical angle and a longitudinal distance traveled by the electron beam between exiting the third dipole and entering the fourth dipole.

24. The magnetic system according to claim 23, wherein the second dipole is spaced apart from the first dipole a first separation, the third dipole is space apart from the second dipole a second separation, the fourth dipole is spaced apart from the third dipole a third separation, and the quadrupole is spaced apart from the fourth dipole a fourth separation, and wherein increasing or decreasing the first separation increases or decreases the horizontal deflection of the electron beam when the first dipole and the second dipole are configured to deflect the electron beam at the first horizontal angle and the second horizontal angle, respectively, and increasing or decreasing the third separation increases or decreases the vertical deflection of the electron beam when the third dipole and the fourth dipole are configured to deflect the electron beam at the first vertical angle and the second vertical angle, respectively.

25. A system comprising: an electron beam source; and a magnetic system according to claim 17 operably coupled to the electron beam source.

26. A method of shaping an electron beam, the method comprising: selecting an operational status of a magnetic system configured to shape the electron beam; and passing the electron beam through the magnetic system to shape the electron beam.

27. The method according to claim 26, wherein selecting the operational status includes positioning a first dipole and a second dipole such that the electron beam passes therethrough when the electron beam is passed through the magnetic system, the first dipole and the second dipole configured to steer the electron beam to a horizontal position with respect to a target tissue.

28. The method according to claim 27, wherein positioning the first dipole and the second dipole includes rotating the first dipole or the second dipole about a respective dipole axis such that a magnetic field of the first dipole or the second dipole is equal in magnitude and antiparallel to the magnetic field of the other of the first dipole or the second dipole.

29. The method according to claim 27, wherein positioning the first dipole and the second dipole includes rotating an inner cylinder or an outer cylinder of the first dipole or an inner cylinder an outer cylinder of the second dipole such that a magnetic field of the first dipole or the second dipole is equal in magnitude and antiparallel to the magnetic field of the other of the first dipole or the second dipole.

30. The method according to claim 29, wherein rotating the inner cylinder the outer cylinder of the first dipole or the inner cylinder or the outer cylinder of the second dipole changes the magnitude or the direction of the magnetic field of the respective dipole.31 . The method according to claim 27, wherein positioning the first dipole and the second dipole includes translating the first dipole or the second dipole with respect to the other of the first dipole or the second dipole such that the first dipole and the second dipole are spaced apart a first separation.

32. The method according to claim 27, wherein selecting the operational status includes positioning a quadrupole with respect to the electron beam, the quadrupole configured to magnetically focus the electron beam into an electron minibeam.

33. The method according to claim 32, wherein positioning the quadrupole includes spinning the quadrupole about the electron beam to form the electron minibeam such that the electron minibeam has a circular cross-section.

34. The method according to claim 33, wherein selecting the operational status includes positioning a third dipole and a fourth dipole such that the electron beam passes therethrough when the electron beam is passed through the magnetic system, the third dipole and the fourthdipole configured to steer the electron beam to a vertical position with respect to the target tissue.

35. The method according to claim 32, wherein positioning the quadrupole includes coaxially aligning a quadrupole aperture defined by the quadrupole with the electron beam such that the electron beam passes therethrough after being steered by the first dipole and the second dipole.

36. The method according to claim 34, wherein positioning the third dipole and the fourth dipole includes rotating an inner cylinder or an outer cylinder of the third dipole or an inner cylinder or an outer cylinder of the fourth dipole such that a magnetic field of the third dipole or the fourth dipole is equal in magnitude and antiparallel to the magnetic field of the other of the third dipole or the fourth dipole.

37. The method according to claim 36, wherein positioning the third dipole and the fourth dipole includes translating the third dipole or the second dipole with respect to the other of the third dipole or the second dipole such that the second dipole and the third dipole are spaced apart a second separation.

38. The method according to claim 36, wherein positioning the third dipole and the fourth dipole includes translating the third dipole or the fourth dipole with respect to the other of the third dipole or the fourth dipole such that the third dipole and the fourth dipole are spaced apart a third separation.

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