Patent Number: 
Section: description

It is known to use directed beams of particles, including but not limited to protons, heavier ions (such as carbon), and mesons, to attack and destroy cancer cells. Particle therapy has an advantage over traditional radiation therapy in that the particle beam can be directed to a particular depth within a patient's body; because, unlike an x-ray beam, the particle beam deposits little energy in the tissue through which it passes, but deposits a large amount of energy at its end point, the beam can kill cancer cells with minimal damage to intervening tissue. Dose to the tissue surrounding the tumor is further reduced by arranging for the beam to reach the tumor from many different directions, such as over an arc of up to 360 degrees. Conventional particle therapy involves generating a beam of fast-moving particles in a particle accelerator or a cyclotron. The beam is then directed along a desired path toward a patient. Because the beam must be delivered to the entire circumference of the target site, current systems direct the beam at the patient from a gantry rotating around the patient. Conventional particle therapy devices place the patient in a horizontal position, and use magnets arranged in large gantry assemblies to direct the beam at the patient from locations around a 360-degree circumference. Because of the size of the particle beam generator, the magnets required to deflect the beam by a total of close to 180 degrees, and the gantry, this arrangement requires deep excavation at huge cost. Current systems incorporate gantries four or more meters in diameter, weighing over 90 tons. Further, the varying direction of the beam mandates that extensive radiation shielding is required around the entire circumference of the treatment area. There is, therefore, a need for a particle therapy device and method that requires a smaller and less complicated structure. FIG. 1 shows a representation of an embodiment of the system 10 of the present invention. A beam 12 is generated by a beam generator 14, which may be a cyclotron or similar device. While the beam may be any type of beam, including optical and particle beams, “beam” or “particle beam” as used herein is intended to describe any suitable type of beam. The beam is directed along a path 16 by path guides 18, which are preferably magnets for a particle beam, but which may be any device suitable for deflecting the path of a given type of beam. As shown in FIGS. 2A-2D, the path 16 is bent at a first angle γ and a second angle σ. While the first angle γ and the second angle σ remain constant for a particular treatment cycle, the beam path varies in a rotation around axis B, which is coaxial with the path of the beam 12 prior to deflection at the first angle γ, as shown in FIGS. 1 and 4A. The angles γ and σ can be any angles that provide the desired system geometry. The rotation of the beam path forms a cone 20 with a fixed isocenter 22 at its apex and located along the axis B. The rotation may occur in either the clockwise or counterclockwise direction. While the beam path varies, the beam continually passes through the isocenter, which is positioned at a target site 24 located within or on a body 26, including but not limited to the site of a tumor inside the patient's body. While the system may be used to direct a beam of any type to a target site on a body generally, the system will be generally described herein in the context of the treatment of a tumor in a human patient. As the beam path 16 rotates around the axis B (as shown in FIG. 1), the patient assembly 30 simultaneously rotates around a vertical axis Z, as seen in FIGS. 2A, 2B, 4A, and 4B. The assembly 30 includes a rotating platform 32 and a patient cradle 34. The cradle includes a patient tray 36 mounted to a frame 38. The frame and tray are movable in multiple degrees of freedom, and may be moved by motors 40-46 positioned to adjust the position of the tray in any number of desired directions, in order that the target within the patient remains at the isocenter 22 during rotation of the patient assembly 30. In the embodiment shown in FIGS. 4A and 4B, motor 40 moves the frame 38 in a direction X; motor 42 moves the frame 38 in a direction Y perpendicular to direction X, and motor 44 moves the tray 36 in along axis P. Motor 46 allows the angle α, shown in FIG. 3B, to be adjusted if needed; e.g., to compensate for deflection of the patient cradle or tray, or to adjust the angle at which the beam enters the patient's body. These degrees of freedom allow the patient to be positioned so that the platform's axis of rotation Z passes through the tumor located at target site 24. The rotation of the assembly 30 about axis Z may be in either the clockwise or counterclockwise direction, and corresponds with the rotation of the beam path 16 about axis B. As shown in FIGS. 2A-2D, the respective rotations are synchronized so that the beam 12 always contacts the patient 26 at roughly a right angle to the patient's body without the use of an large-diameter gantry structure, as is the case for a horizontal patient. As will be understood by one of ordinary skill in the art, the respective rates of rotation of the assembly and beam path need not be constant. Similarly, one of ordinary skill will appreciate that the relationship between the rates of rotation of the assembly and the beam, respectively, need not be linear. One embodiment of the relationship between the rates of rotation is shown in FIG. 6, wherein each function line depicts a different direction of rotation of the beam path. FIGS. 2A-2D show how the beam 12 contacts the patient's body at various times during a treatment cycle. FIG. 2A is a side view of the arrangement at a first point in the cycle. The patient is located on the tray 36 of the assembly 30. The beam 12 is directed through first and second angles γ and σ, respectively, and contacts the tumor located at target site 24. As will be described, the position of the patient may be varied in order to maintain the target site in a constant location in space, and to maintain beam contact with the site throughout the treatment cycle. FIG. 2B is a side view of a second point in the cycle. As shown in FIGS. 2A and 2B, the beam contacts the target site 24 at approximately 90 degrees from the axis P. FIG. 2C is a view of a third point in the treatment cycle, as seen from the same location in space as FIGS. 2A and 2B. The assembly 30 has rotated 90 degrees around axis Z, which runs through roughly the center of the tumor located at the target site 24. Because the assembly preferably rotates around an axis passing through the center of the target site, the target site's spatial orientation preferably remains constant; i.e., the site does not move laterally, but rather merely rotates in place. As seen in FIGS. 2A-2C, the rates of rotation are synchronized in a non-linear fashion, so that the beam is still contacting the target site at an angle of roughly 90 degrees from the axis P. As seen in FIG. 2B, the assembly 30 has rotated 180 degrees from its orientation shown in FIG. 2A. The beam 12 has also rotated a corresponding amount, and still contacts the target site 24 at approximately 90 degrees from the axis P. As seen in FIGS. 2A-2D, the beam isocenter 22 remains aligned with the target site 24 throughout the treatment cycle. In order to properly position the patient for treatment and ensure that the beam isocenter remains fixed on the target site, the assembly 30 should be highly adjustable. As seen in FIGS. 3A, 3B, and 4B, the cradle 34, frame 38, and tray 36 may all be adjusted for position. The assembly 30 includes a platform 32, which rotates around an axis Z passing vertically through the target site's approximate center. In order to accomplish this, the frame 38 can be adjusted in directions X and Y, and the tray 36 can be adjusted along axis P to compensate for location of the target site within the body. Depending on the rotational mechanism used, the rotating platform 32 preferably rotates about its own center axis. The motor 40 is used to position the frame 38 in the X direction. The motor 42 is used to position the frame in the Y-direction. The motor 44 is used to position the tray 36 along the axis P, and the motor 46 is used to set the angle α of the tray. The tray may be set at any desired angle α at which the patient is comfortable, but the angle α is preferably maintained at an angle corresponding to the chosen γ and σ angles so that the beam enters the patient's body at the desired angle. While the beam preferably enters the patient's body at a roughly 90-degree angle, any suitable angle may be chosen to minimize potential damage to healthy intermediate tissue. The angle α will generally be set between approximately 30 and 60 degrees, as shown in FIG. 5. The adjustability of angle α may also be used to compensate for deflection of the cradle 34 or frame 38 under a range of patient sizes or weights. The frame is sturdy enough to support the weight of the patient, and may be made of any suitable material, including metal or plastic. While the frame is depicted as being supported at its lower edge, it and the cradle 34 may be any shape or material that does not interfere with the beam path 16. If the target site cannot be positioned along the assembly's axis of rotation, the beam path may be adjusted to ensure full coverage of the target site. As will be understood by those of ordinary skill in the art, the path followed by the particles or other particles may be varied in either or both of two ways for the purpose of accurately covering the full volume of an extended tumor, whose center may lie at the nominal isocenter of the beam. One variation is to introduce a computer-controlled variable-thickness “wedge”, whose effect will be to alter slightly the depth at which the beam deposits its energy, thus reaching from the near side to the far side of the tumor at each angle by which it is irradiated. The other variation is to apply an additional small magnetic field or other deflecting method, so as to move the beam slightly from side to side or in a raster pattern, thus covering the (possibly irregular) width of the tumor. These adjustments can occur sufficiently rapidly to perform a three-dimensional scan of the entire tumor volume at each angle of the radiation. FIG. 5 shows an alternative embodiment of the invention, in which the invention is used to perform a scan, such as a CT scan, of a patient's body. In this embodiment, the beam can be any type of beam necessary to perform the scan. A detecting device 50 can be included in the apparatus. If a 360 degree scan is needed, the detecting device 50 can rotate about an axis M so as to maintain alignment with the beam 12, which may be a thin “pencil” beam, or a beam that forms a cone shape as shown in FIG. 5. The beam may be a particle beam, or it may be another type of beam, such as an x-ray beam generated by a device included along the path of the particle beam. The detector may be any type that is suitable for detecting the beam generated. It is preferred that the beam and patient rotate in a manner identical to that expected to be used during therapy; however, the patient may or may not rotate, depending on the type of image desired. Additionally, if the scan is a linear scan, i.e., along a length of the patient's body, the assembly may remain stationary, and the frame or tray may be moved to ensure proper coverage by the beam of the area to be scanned. Alternatively, any or all of the angles γ, σ, or β may be varied to change the location in which the beam contacts the patient's body, and the detector may move in a corresponding manner. Similarly, the scan may be performed using the same method or device on any object requiring a 3-D scan. FIG. 6 shows a graphical representation of the relation between the conical rotation of the beam about its horizontal axis and the rotation of the patient about its vertical axis, as required to have the beam traverse the exact circumference of the body. Optionally, intentional, controlled variation from the angles depicted in FIG. 6 can widen the points of entry to a belt of varying width, further reducing the dose to the intervening tissue, while still being focused on the target tumor. For example, in the position of FIG. 2A, where the patient is facing toward the beam and is tilted backward (defined as θ=±180° or ±π radians), the beam is in a topmost position (defined as φ=0° or 0 radians). The beam intersects the patient body at the front. In the position of FIG. 2B, where the patient is facing away from the beam (defined as θ=0° or 360°, or 0 or 2π radians), the beam is in its lowest position (defined as φ=±180° or ±2π radians). The beam intersects the patient body at the back. The intermediate cases are less simple, as two positions of the beam are possible. To clarify this, consider a small counterclockwise rotation (as seen from above) of the patient from the position in FIG. 2A toward the viewer. There are then two points on the circumference of the body that intersect the cone 20, one corresponding to a point closer to the viewer, and the other to a point away from the viewer. The former entails a counter-clockwise rotation of the beam around the cone (as seen from the patient), and the other entails a clockwise rotation. For example, if the patient is facing at right angles to the beam, as in FIGS. 2C and 2D, with the patient angle θ=90° or π/2 radians, the beam must be somewhat above or somewhat below the horizontal. In summary, the relationship between the two angles is non-linear in the manner shown in FIG. 6. Either of the curved paths may be followed, as long as the one chosen is consistent for the full 360° or 2π radians of rotation. All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.