System to generate therapeutic radiation

Some embodiments include a ring anode to emit radiation, and a conical monochromator to monochromatize the emitted radiation. According to some aspects, an outer diameter of the ring anode is greater than an outer diameter of a base of the monochromator.

BACKGROUND

The present invention relates generally to the generation of radiation, and more particularly to systems for delivering such radiation for therapeutic purposes.

According to conventional radiation therapy, a radiation beam is directed toward a tumor located within a patient. The radiation beam delivers a predetermined dose of therapeutic radiation to the tumor according to an established therapy plan. The delivered radiation kills cells of the tumor by causing ionizations within the cells. In this regard, radiation therapy systems are designed to maximize radiation delivered to the tumor while minimizing radiation delivered to healthy tissue.

A conventional radiation therapy system utilizes X-radiation energies in excess of 1 MeV. State-of-the-art therapy systems generate this “MegaVolt X-Radiation” (MVR) using linear accelerators. In contrast, tube-based X-ray systems generate “KiloVolt X-Radiation” (KVR) having photon energies roughly between 20 keV to 200 keV. These KVR systems have long have been used for imaging and for other purposes. KVR systems may be much cheaper, simpler and more reliable than the linear accelerators used in MVR systems. Environmental safety is also of less concern with KVR systems, which typically require 3 mm of lead shielding as opposed to the 2 m of concrete shielding required for MVR systems.

Despite the foregoing advantages of KVR, MVR is often preferred for therapeutic use because of the high-energy electrons created by Compton scattering of MVR. Most tissue damage caused by KVR results from photoelectric absorption. Particularly in the case of low-energy KVR (photon energy<20 keV), damage resulting from photoelectric absorption is greatest at the surface of a radiation/tissue interaction and decreases with depth into the tissue. Consequently, a KVR beam of uniform or decreasing flux density (i.e., a divergent beam) may cause greater tissue damage at a patient's skin than at a therapy area within the patient's body.

Several existing techniques attempt to address this drawback of KVR therapy. A KVR therapy system such as those described in U.S. Pat. No. 6,366,801 to Cash et al uses a point radiation source which produces a divergent beam of traditional medical X-rays having energies in the kilovoltage range and focuses the beam on a target using a lens designed for this purpose. By focusing the radiation onto the target, the energy per unit area increases with proximity to the target. As a result, tissue damage at a portion of the target is greater than tissue damage at a same-sized portion of the radiation/skin interaction site. Efforts to increase the target-to-skin dose ratio include the development of lenses for focusing the radiation at greater angles of convergence and/or the injection of radiation-absorbing contrast agents at the target.

Also proposed are methods in which a patient is positioned, a target is irradiated by a radiation beam, the patient is repositioned such that a subsequent radiation beam would intercept an area of the patient's skin that was not irradiated by the previous radiation beam, and the target is irradiated again. The patient may be repositioned and the target irradiated several times. Still other methods include moving the radiation beam so as to scan the target. None of these existing techniques have proved to be satisfactorily efficient and/or effective in providing therapeutic KVR.

SUMMARY

To address the foregoing, some embodiments provide a ring anode to emit radiation, and a conical monochromator to monochromatize the emitted radiation. In some aspects, an outer diameter of the ring anode is greater than an outer diameter of a base of the monochromator.

In some embodiments, the present invention provides a radiation source to emit radiation from at least a first location and a second location, the first and second locations being separated by a first distance, and a monochromator comprising a surface of diffracting material, the surface comprising a third location and a fourth location separated by a second distance, the second distance being less than the first distance. The third location is to receive the radiation emitted from the first location and the fourth location is to receive the radiation emitted from the second location.

Embodiments may provide a radiation source to release radiation and one or more blocking devices to substantially block the radiation except for a portion of the radiation traveling along a substantially convergent three-dimensional path.

The claimed invention is not limited to the disclosed embodiments, however, as those of ordinary skill in the art can readily adapt the teachings herein to create other embodiments and applications.

DETAILED DESCRIPTION

The following description is provided to enable any person of ordinary skill in the art to make and use the claimed invention and sets forth the best modes contemplated by the inventors for carrying out the claimed invention. Various modifications, however, will remain readily apparent to those in the art.

FIG. 1illustrates radiation therapy room1pursuant to some embodiments of the claimed invention. Radiation therapy room1includes KVR therapy unit10, therapy table20and operator station30. The elements of radiation therapy room1are used to deliver KVR to a patient according to a therapy plan. In this regard, KVR refers herein to any radiation having energies ranging from 20 to 200 keV. However, it should be noted that some embodiments may be used in conjunction with any radiation.

Therapy unit10is used to deliver therapeutic radiation to a target area through therapy head11. Therapy head11includes a radiation source to emit KVR. KVR may include photon radiation having energies from 20 to 200 keV. Other types of radiation may be used in conjunction with some embodiments, including but not limited to neutron radiation such as thermal neutron radiation.

According to some embodiments, therapy head11may include a ring anode to emit radiation, and a conical monochromator to monochromatize the emitted radiation. In some embodiments, an outer diameter of the ring anode is greater than an outer diameter of a base of the monochromator. Further details of therapy head11according to some embodiments will be described below.

C-arm12is slidably mounted on base13and can therefore be moved in order to change the position of therapy head11with respect to table20and, more particularly, with respect to a patient lying on table20. In some embodiments, c-arm12provides therapy head11with several degrees of freedom relative to a patient lying on table20. These degrees of freedom may include translation along axis13, rotation around axis13, rotation around an axis perpendicular to the geometric center of c-arm12, and translation along axis14of therapy head11. Each of these degrees of freedom may assist in positioning a focal point of therapy head11at a desired target.

Base15may include one or more voltages sources such as high-voltage generators for supplying power used by therapy head11to generate KVR. Many c-arm/base configurations may be used in conjunction with some embodiments, including configurations in which base15is rotatably mounted to a ceiling of room1, configurations in which one c-arm is slidably mounted on another c-arm, and configurations incorporating multiple independent c-arms.

Examples of c-arm KVR units include Siemens SIREMOBIL™, MULTISTAR™, BICOR™ and POLYSTAR™ units as well as other units designed to perform tomography and/or angiography. These units are often less bulky and less costly than MVR systems. Of course, any system for emitting radiation may be used in conjunction with some embodiments.

Imaging system16produces an image based on radiation emitted by therapy head11. The image reflects the attenuative properties of objects located between therapy head11and imaging system16while the radiation is emitted. Imaging system16may comprise a camera-based or a flat panel-based imaging system.

A patient is placed on therapy table20during therapy in order to position a target between therapy head11and imaging system16. Accordingly, table20may comprise mechanical systems for moving itself with respect to unit10.

Operator station30includes processor31in communication with an input device such as keyboard32and an output device such as operator display33. Operator station30is typically operated by an operator who administers actual delivery of radiation therapy as prescribed by an oncologist.

Each of the devices shown inFIG. 1may include less or more elements than those shown. In addition, embodiments of the claimed invention are not limited to the devices described herein.

FIG. 2is a cut away view andFIG. 3is a longitudinal cross-sectional view of therapy head11according to some embodiments. These views include pictorial representations of some elements of therapy head11and illustrate some relationships therebetween. Neither the elements nor their physical relationships to one another are necessarily drawn to scale.

Therapy head11of the present embodiment includes a photon radiation source and other elements arranged to provide radiation to a target at a sufficiently large angle of convergence. In particular, vacuum tube40of therapy head11includes cathode41and anode42. Cathode41may comprise tungsten or any suitable material for emitting electrons. Cathode41may be used in conjunction with a Wehnelt cylinder to control and focus electrons emitted therefrom.

Anode42ofFIG. 2is ring-shaped and may also comprise tungsten. A radius of anode42may measure from 75 mm to 100 mm in order to produce X-ray radiation having a 30° angle of convergence and a beam path of 200 mm to 300 mm.

In operation, cathode41receives power in the form of a 120–200 kV tube voltage from high-voltage connector43, which is coupled to a high-voltage source (not shown), while anode42is held at a high positive potential with respect to cathode41. The received power heats cathode41, and electrons are ejected from a surface of cathode41via thermal emission. The electrons are attracted to and accelerated by the high positive potential of anode42.

The electrons impact anode42and produce X-rays both as characteristic radiation and Bremsstrahlung. Although only particular bundles of X-rays are illustrated inFIG. 3, X-rays are emitted isotropically from locations throughout ring anode42. The spectrum of the characteristic radiation comprises sharp lines at discrete photon energies. The actual photon energies depend upon the material of which anode42is composed. For example, the dominant characteristic X-ray energy of tungsten is 59.3 keV and the dominant characteristic X-ray energy of thorium is 93.3 keV.

According to some embodiments, a radiation source comprises an anode such as ring anode42and a ring cathode. In other embodiments, a radiation source includes a ring anode and a plurality of cathodes, each located at a different position adjacent to ring anode42. Moreover, anodes used in conjunction with some embodiments may possess any suitable shape. Some embodiments include a cathode adapted to move along a circumference of ring anode42while transmitting electrons thereto

A radiation source according to some embodiments may comprise a conventional electron gun adapted to move along a circular path at high frequency. In some embodiments, a radiation source may include more than one radiation source. These sources may be adapted to move along a continuous path while emitting radiation from several locations on the continuous path. These sources may be fixed at locations delineating a shape, such as a circle or a polygon.

Exit window44maintains a vacuum within tube40but also allows photons to pass with high transmittivity. Window44may comprise a ring-shaped sheet of beryllium, aluminum, copper, and/or another material. In addition to the functions mentioned above, aluminum and copper provide filtering of photons having energies significantly lower than the characteristic energy of anode42.

The portion of radiation that passes through window44subsequently intercepts housing50. Housing50includes blocking devices51and52. Blocking device51defines an opening for allowing a portion of radiation from exit window44to pass therethrough. The portion may comprise a portion of radiation traveling along a substantially convergent three-dimensional path. The portion in some embodiments forms a conical shell with a convergence angle of approximately 30° after passing blocking device51. Blocking device51also comprises blocking material to substantially block radiation other than the portion of radiation.

“Conical” as used herein refers to an area or volume comprising any portion of a cone such as a single cone lobe, a cross section of a cone taken perpendicular to the major axis and of any thickness, an outer surface of a portion of a cone having a particular thickness, and/or any other portion. Moreover, the term “portion” may refer to the entirety or a subset of an element to which the term refers.

The portion of radiation that passes through blocking device51arrives at blocking device52, which also comprises an opening for allowing a portion of the arriving radiation to pass therethrough. Blocking device52also comprises blocking material to substantially block radiation other than the portion of radiation from passing. In some embodiments, the portions of radiation passing through blocking devices51and52travel along a substantially convergent three-dimensional path. Accordingly, the relative positions of anode42, blocking device51, and blocking device52define the substantially convergent three-dimensional path. The illustrated path defines a hollow conical volume, however radiation according to different embodiments may travel along differently-shaped paths.

Filter53receives radiation that passes through blocking device52. As shown inFIG. 3, the filtered radiation passes through patient surface54before reaching target55. Filter53may comprise any material for substantially filtering out low-energy radiation from the received radiation. According to the example ofFIG. 3, filtering low-energy radiation may decrease tissue damage occurring at locations on patient surface54and/or between patient surface54and target55. Moreover, the convergent path of the filtered radiation may provide a greater dose per unit volume in target55than in other patient volumes.

FIG. 4illustrates a cut away view of monochromator60disposed within housing50according to some embodiments.FIG. 5shows a longitudinal cross-section of monochromator60in conjunction with a view of some other elements of therapy head11. Monochromator60monochromatizes radiation received from tube40through blocking device51.

Monochromator60is conical according to some embodiments. According to the illustrated example, an outer diameter of ring anode42is greater than a largest outer diameter of monochromator60. In this regard, the largest outer diameter of monochromator60is equal to a diameter of a base of monochromator60. A longitudinal cross-section through the illustrated monochromator is a straight line.

Monochromator60may comprise other rotationally symmetric shapes, including but not limited to a cylinder, a toroid, an ellipsoid, paraboloids, and logarithmic spirals of rotation. These rotationally symmetric shapes can be approximated by corresponding shapes on multi-sided base areas. For example, cones may be approximated by multi-sided pyramids.

Monochromator60includes conical outer surface61. Surface61consists of crystalline material such as Highly Oriented Pyrolitic Graphite (HOPG). Other well-oriented crystalline materials include but are not limited to beryllium, aluminum, gold, platinum, LiF, and mica, which are known to provide high reflectivity to X-ray radiation.

Blocking device62may block direct radiation that is not monochromatized by monochromator60from reaching target55. Blocking device62defines an opening that is coaxial with axis14of monochromator60. Blocking device62may be movable along axis14. Moreover, the conical opening has a diameter slightly larger than a diameter of monochromator60at areas where monochromator60is surrounded by blocking device62. Accordingly, a diameter of the conical opening increases if blocking device62is moved toward vacuum tube40.

Blocking device control63may control movement of blocking device62along axis14of monochromator60. Blocking device control63may comprise one or more of software, hardware, and firmware elements located in one or more of processor31, therapy head11, base13, a stand-alone device, or another device.

In operation, anode42emits radiation isotropically as described above.FIG. 5illustrates particular bundles of the emitted radiation that pass through exit window44and blocking device51and intercept surface61. Radiation emitted from anode42may follow a substantially convergent path to surface61. For example, radiation emitted from locations A and B of anode42is received at locations C and D of surface61, respectively, and a distance between locations C and D is less than a distance between locations A and B. In some embodiments, the angle of convergence is between 25° and 35°.

Window44and blocking device51may be designed to pass radiation that thereafter intercepts diffracting material of surface61at a particular angle of incidence. This angle of incidence may be substantially equal to a Bragg angle corresponding to the material and to a desired radiation energy. In particular, a corresponding Bragg angle is equal to sin−1(λ/(2*d)), wherein d is the lattice plane distance of the diffracting material and λ is the wavelength (which is inversely proportional to the photon energy E:λ/nm=1.24/(E/keV)) of radiation to be reflected Accordingly, monochromator60Bragg-reflects radiation of wavelength λ that intercepts surface61at an angle of incidence equal to sin−1(λ/(2*d)).

The Bragg reflection monochromatizes the received radiation such that the reflected radiation is of a wavelength substantially equal to λ, and of an energy corresponding to λ. In practice, the wavelength/energy bandwidth of the reflected radiation may be 3% to 5%, depending on a mosaicity of the diffracting material and/or the openings of blocking devices51and52.

The above-described geometric relationship between ring anode42and monochromator60is intended to provide a conical radiation path with an approximately 30° angle of convergence and to provide a monochromatizing reflection such as a Bragg reflection. Specific geometric relationships between anode42and monochromator60may depend on the desired angle of convergence and the magnitudes of desired diffraction angles. Arrangements according to some embodiments may therefore provide angles of convergence and monochromatizing reflections that are difficult, if not impossible, to achieve using a point radiation source.

Monochromatized radiation64passes through an aperture of blocking device52and travels along a substantially convergent three-dimensional path to target55. Blocking devices52and62may be positioned in order to block non-monochromatized radiation from passing through blocking device52.

In contrast to an ideal crystal like Diamond or Silicon, HOPG and other crystalline materials usable in some embodiments are mosaic crystals. According to some embodiments, the mosaicity is less than 5°, and may be 0.5°. This mosaicity allows the crystalline reflector material to reflect monochromatic X-radiation over a certain range of incidence angles, i.e. to reflect X-radiation of a certain source solid angle onto target55. In this regard, a focus of the radiation may comprise a point in space or a larger area. A size and location of the focus may be determined by many factors, including radiation energy, and the geometries and lattice plane distances of the reflector materials61. A detailed explanation of Bragg-Brentano focusing according to some embodiments will be provided below with respect toFIG. 8.

The radiation that exits blocking device52might not terminate at target55. Rather, the radiation may continue thereafter, becoming further attenuated and unfocused as its distance from target55increases. In some embodiments, the divergence of the radiation from target55roughly mirrors its convergence thereto.

Monochromatization and/or focusing of radiation may provide more efficient and accurate radiation therapy than previously available. Particularly, some embodiments produce a focused radiation beam having a narrow band of photon energies. Moreover, some embodiments provide radiation having a significantly greater flux density at an internal target than at a patient's skin. Penetration of an X-radiation beam according to some embodiments may therefore be controlled to efficiently deliver tissue damaging mechanisms to precise locations within a patient, while minimizing damage to other locations.

FIG. 6is a longitudinal cross-section of therapy head11according to some embodiments. Therapy head11ofFIG. 6includes previously-undescribed elements70through74. Initially, monochromator70is conical and coaxial with monochromator60. Monochromator70comprises surface71of diffracting material. The material of surface71may be different from or identical to the material of surface61. Moreover, monochromators60and70may be integrally formed.

Blocking device72defines two coaxial conical openings. An outermost opening allows a first portion of radiation from window44to intercept surface61, while an innermost opening allows a second portion of radiation to intercept surface material71. As described above with respect toFIG. 5, the elements of therapy head11may be configured such that the first portion of radiation intercepts surface61at a Bragg angle corresponding to the material of surface61and to a desired energy of monochromatization. Similarly, the second portion of radiation intercepts surface71at a Bragg angle corresponding to the material of surface71and to a desired energy.

For a given desired energy, the Bragg angle corresponding to the material of surface71may be larger than the Bragg angle corresponding to the material of surface61due to smaller lattice plane distances of the former material. Alternatively, the materials may be identical, however using a higher-order reflection of the material of surface71. In some embodiments, the materials are identical and the elements of therapy head11are arranged such that the radiation intercepts surface61and surface71at substantially identical angles.

Monochromatized radiation64and74passes through corresponding coaxial openings of blocking device73and on to target55. Blocking device62and blocking device73may substantially block non-monochromatized radiation from exiting from housing50. Monochromatized radiation64and74may also be focused on target55as a result of Bragg-Brentano focusing mechanisms.

FIG. 7illustrates a system using monochromator80in conjunction with monochromator60. Monochromator80ofFIG. 7comprises a solid ring defining a conical opening. Interior surface81of monochromator80faces and is separate from surface61of monochromator60. Interior surface81also includes a layer of diffracting material. Blocking device82includes two concentric conical openings, With an innermost opening allowing a first portion of radiation from window44to intercept material61, and with an outermost opening allowing a second portion of radiation to intercept material81.

The elements of therapy head11may be configured such that the first portion of radiation intercepts surface61at a Bragg angle corresponding to the material of surface61and to a desired energy of monochromatization, and such that the second portion of radiation intercepts surface81at a Bragg angle corresponding to the material of surface81and to a desired energy. The Bragg angles may be identical in a case that the two materials and the desired photon energies are identical, and may be different in a case that the two materials possess differing interplanar distances. As mentioned above, the Bragg angles may also be different in a case that the two materials are identical, but either different orders of reflection or desired photon energies are associated with surface61and surface81in such a case.

Blocking device83comprises a conical ring for ensuring that only monochromatized radiation passes to blocking device85. Blocking device83may be movable along a major axis of monochromator60under control of a control device (not shown). Moreover, a diameter of an opening of blocking device83may increase with movement toward tube40. Monochromatized radiation64and monochromatized radiation84pass through corresponding coaxial openings of blocking device85. Blocking devices83and85may therefore block all but monochromatized radiation from passing to target55.

FIG. 8is a longitudinal cross-section of some elements of therapy head11according toFIG. 7.FIG. 8will be used to describe Bragg-Brentano focusing according to some embodiments.

As shown, surfaces61and81are tangent to Rowland circle90. Rowland circle90ofFIG. 8represents the reflection points of all X-ray beams emitted from an area of anode42that correspond to the same Bragg angle of interest. Each of the represented beams therefore corresponds to a same photon energy and wavelength.

Crystallites within surfaces61and81will possess a mosaicity of 0.5° in a case that the surfaces are composed of (00.1) oriented HOPG. As a result, all X-rays that are incident to either of surfaces61or81at an angle of +/−0.5° will encounter a reflecting crystal. Such reflections result in the focusing of the beams as shown on focus95. The mosaicity, the value d of the diffracting material, and the lengths of surfaces61and81may therefore operate in harmony to deliver monochromatized, high-intensity radiation to focus95.

Generally, those in the art will appreciate that various adaptations and modifications of the above-described embodiments can be configured without departing from the scope and spirit of the claimed invention. For example, heavy-element contrast agents may be introduced within target55to increase the effective dose absorbed by target55in the presence of KVR. A contrast agent may include rare earth elements and/or elements having a K absorption edge energy that is just below a characteristic K line energy of a material of the ring anode. In one particular example, the ring anode comprises tungsten and the contrast agent comprises at least one of erbium, holmium, dysprosium, terbium, gadolinium, europium, samarium, neodymium, praseodymium, cerium, and lanthanum.

Some embodiments include two or more coaxial or otherwise disposed ring anodes and a dedicated monochromator to Bragg-reflect radiation released from each ring anode. Some embodiments may utilize two or more ring anodes composed of different materials. Different radiation energies and resulting penetration depths may therefore be achieved by applying different anode voltages to different ones of the ring anodes. Moreover, a point focus radiation source may be positioned to emit a thin beam along axis14of monochromator60for alignment purposes.

Some embodiments utilize rotationally-symmetric elements that require adjustments only along the rotational axis. In some embodiments, a monochromator may be moved in and out of an operational position to provide a “filtered radiation” mode and a “monochromatized radiation” mode.

Therefore, it is to be understood that, within the scope of the appended claims, embodiments of the invention may be practiced other than as specifically described herein.