Patent Application
20060094923
This invention relates generally to systems and method for accurately locating, tracking or otherwise monitoring a device or target for treating a patient using radiation.
Cancer is a disease that begins in the cells of the patient. Radiation therapy has become a significant and highly successful process for treating breast cancer, lung cancer, brain cancer and many other types of localized cancers. Radiation therapy is particularly useful for treating tissue after a tumor has been removed, centrally located tumors, and/or small cell tumors that cannot be removed surgically. Radiation therapy can be used as a curative treatment or as a palliative treatment when a cure is not possible. Additionally, surgery and chemotherapy can be used in combination with radiation therapy.
Breast cancer has recently been treated by surgically removing cancerous breast tissue and subsequently treating the remaining tissue surrounding the lumpectomy cavity using radiation. Proxima Corporation and Xoft, Inc. have developed devices and systems for treating the breast tissue surrounding the cavity created by a lumpectomy. The existing breast brachytherapy devices have a balloon configured to be implanted in the breast and a radiation source that can be placed within the balloon. After performing a lumpectomy, the balloon is inserted into the surgical cavity and inflated until the balloon presses against the tissue. The balloon is typically left in the patient for approximately five days over which two radiation treatments per day are performed. Each radiation treatment includes inserting the radiation source into the balloon and activating the radiation source to deliver ionizing radiation for approximately 10-15 minutes. After all of the radiation treatments have been performed during the multi-day course of treatment, the balloon is deflated and removed from the patient.
One challenge of these procedures is inflating the balloon to a desired size and monitoring the balloon to ensure that the balloon has maintained the desired size throughout the multi-day course of treatment. The size of the balloon is currently determined by instilling radiopaque contrast into the balloon and measuring a resulting CT or X-ray image using a ruler. The patient must accordingly undergo a CT scan or another type of X-ray to obtain the image, and then a practitioner must evaluate the image to determine if the balloon is at the desired size. This is a time-consuming and expensive process that reduces the efficiency of treating the patients, and it should be performed each day during the course of treatment. This process also exposes the patient to additional radiation. Therefore, there is a need to provide accurate measurements of the size of the balloon throughout the course of treatment.
Another challenge of existing breast brachytherapy systems is assessing the relative position and/or rotational orientation of the balloon within the lumpectomy cavity. The balloon may move within the lumpectomy cavity over the course of treatment, but existing systems do not detect the relative position between the balloon and the breast. Moreover, when the radiation source is asymmetrically positioned within the balloon (e.g., spaced apart from a rotational center line of the balloon), it is important to know the rotational orientation of the balloon within the lumpectomy cavity so that the radiation source is located at a desired distance from the tissue. Conventional techniques that use a radiopaque contrast in the balloon do not identify the relative position or rotational orientation of the balloon. This can be problematic because the balloon can move after it has been implanted over the course of treatment, or the balloon may not inflate as planned. Therefore, it would also be desirable to determine the rotational orientation or other relative movement of the balloon within the cavity.
In the drawings, identical reference numbers identify similar elements or components. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not drawn to scale, and some of these elements are arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not intended to convey any information regarding the actual shape of the particular elements, but rather the shapes have been solely selected for ease of recognition in the drawings.
In the following description, certain specific details are set forth in the context of breast brachytherapy in order to provide a thorough understanding of various embodiments of the invention. However, one skilled in the relevant art will recognize that the invention may be practiced without one or more of these specific details, or with other methods, components, materials, etc. For instance, inflatable devices for temporary or permanent implantation in a patient can have one or more markers as described below for use in beam radiation therapy procedures described in U.S. patent application Ser. No. 11/165,843, filed on 24 Jun. 2005, and Ser. No. 11/166,801, filed on 24 Jun. 2005, both of which are incorporated herein by reference. In other instances, well-known structures associated with target locating and tracking systems have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention.
Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Further more, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention.
A. Overview
One aspect of the invention is directed toward apparatus for facilitating radiation treatment of a target in a patient. One embodiment of such an apparatus comprises a tube configured to receive a radiation source and an expandable member. The tube has a first end configured to be inserted into a patient and a second end that is generally configured to remain external to the patient. The expandable member is at the first end of the tube, and it is configured to contain the radiation source. The expandable member can comprise a balloon, flexible bladder, mechanical linkage (e.g., a cage), a mesh, or other suitable expandable systems. The apparatus further includes a marker associated with the expandable member such that the marker moves with the expandable member. The marker generally comprises a wireless transponder configured to wirelessly transmit a location signal in response to a wirelessly transmitted excitation energy, but in other embodiments the marker can be a radiopaque element. One suitable marker comprises a casing and a magnetic transponder having a coil in a capacitor coupled to the coil.
The marker is associated with the expandable member such that the marker moves with the expandable member to an expanded orientation. In one embodiment, the marker is attached to or otherwise embedded in the wall of the expandable member. In other embodiments, the marker can be attached to a sheath or mesh around the expandable member.
Another aspect of the invention is directed toward methods for facilitating radiation treatment of a target in a patient. One embodiment of such a method comprises positioning an expandable member in the patient with respect to the target, and expanding the expandable member to a desired size within the patient. This method further includes determining a parameter of the expandable member by localizing a marker that moves in association with the expandable member. This method can optionally include inserting an ionizing radiation source into the expandable member and delivering ionizing radiation to the target. This method can further optionally include localizing the position of the ionizing radiation source within the expandable member by localizing a marker attached to the ionizing radiation source.
Before treating the target with radiation, a portion of the tumor may be surgically removed from the patient. In the case of treating breast cancer, for example, a patient undergoes a lumpectomy to remove as much of the tumor as possible while minimizing removal of healthy tissue.
Various embodiments of the invention are described in this section to provide specific details for a thorough understanding and enabling description of these embodiments. A person skilled in the art, however, will understand that the invention may be practiced without several of these details, or that additional details can be added to the invention. Where context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from other items in reference to a list of at least two items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of the items in the list.
B. Embodiments of Apparatus for Facilitating Radiation Treatment
The apparatus 20 further includes a plurality of markers 40 that are associated with the expandable member 25 such that the markers 40 move with the expandable member 25 to an expanded orientation. In several embodiments, the markers 40 comprise wireless transponders configured to wirelessly transmit independent location signals in response to wirelessly transmitted excitation energies. For example, the markers can comprise a casing and a magnetic transponder in the casing as described in more detail below. In several embodiments, the markers 40 are attached to or otherwise embedded in the expandable member 25 such that the markers move in direct correspondence to the movement of the expandable member 25. In other embodiments, the markers 40 are attached to a sheath or a mesh that surrounds the expandable member 25 so that expansion of the expandable member 25 causes a corresponding expansion of the sheath or mesh. In either case, the markers 40 are associated with the expandable member 25 such that the markers 40 move with the expandable member 25 at least when the expandable member 25 approaches the expanded orientation.
The apparatus 20 provides several advantages for performing breast brachytherapy. In several embodiments, the apparatus 20 enables an accurate determination of the size of the expandable member inflated within the breast without taking expensive CT images and manually assessing the images. This aspect is very useful because the diameter or size of the expandable member 25 positions the radiation source 30 at a desired distance from the tissue to deliver a more uniform and penetrating dose of radiation, but the expandable member 25 may change over the course of the treatment. For example, the expandable member 25 may collapse or have a slow leak such that the size and shape of the expandable member may change over the multi-day treatment course. By localizing the relative positions of the markers 40, any changes in the size and shape of the expandable member 25 can be determined before, during, and after each treatment session to ensure that the accurate dose of radiation is delivered from the radiation source 30.
Another advantage of the apparatus 20 is that movement of the expandable member 25 relative to the breast can be determined. In additional embodiments, a separate marker 40 is implanted or otherwise attached to the patient 6 to define a known reference location. The reference marker 40 can be attached to the surface of the breast, or in other applications it is attached to a fixed structure of the patient (e.g., chest wall, etc.). By localizing the reference marker 40 and the markers 40 associated with the expandable member 25, relative movement of the expandable member 25 within the breast can be determined throughout the course of therapy to ensure that the expandable member is positioned at the desired location within the patient. This is also useful for detecting movement of the patient during therapy. As a result, the apparatus 20 is expected to provide accurate measurements to confirm the status and the location of the expandable member throughout the course of therapy.
Another advantage of the apparatus 20 is that the rotational orientation of the expandable member 25 relative to the breast can be determined and assessed throughout the course of treatment. As mentioned above, the rotational orientation of the expandable member 25 may be particularly important in applications in which the radiation source 30 is located asymmetrically relative to the expandable member 25. The markers 40 can be tracked or otherwise located using a localization system to determine the rotational orientation of the expandable member 25, and thus determine the position of the radiation source 30 relative to the tissue. Therefore, the apparatus 20 is expected to be particularly useful in cases that use asymmetric radiation sources.
1. General Operation of Selected Markers and Localization Systems
The localization system 10 includes an excitation source 60 (e.g., a pulsed magnetic field generator), a sensor assembly 70, and a controller 80 coupled to both the excitation source 60 and the sensor assembly 70. The excitation source 60 generates an excitation energy to energize at least one of the markers 40a-c in the patient 6 (
The sensor assembly 70 can include a plurality of coils to sense the location signals L1-3 from the markers 40a-c. The sensor assembly 70 can be a flat panel having a plurality of coils that are at least substantially coplanar relative to each other. In other embodiments, the sensor assembly 70 may be a non-planar array of coils.
The controller 80 includes hardware, software or other computer-operable media containing instructions that operate the excitation source 60 to multiplex the excitation energy at the different frequencies E1-3. For example, the controller 80 causes the excitation source 60 to generate the excitation energy at the first frequency E1 for a first excitation period, and then the controller 80 causes the excitation source 60 to terminate the excitation energy at the first frequency E1 for a first sensing phase during which the sensor assembly 70 senses the first location signal L1 from the first marker 40a without the presence of the excitation energy at the first frequency E1. The controller 80 then causes the excitation source 60 to: (a) generate the second excitation energy at the second frequency E2 for a second excitation period; and (b) terminate the excitation energy at the second frequency E2 for a second sensing phase during which the sensor assembly 70 senses the second location signal L2 from the second marker 40b without the presence of the second excitation energy at the second frequency E2. The controller 80 then repeats this operation with the third excitation energy at the third frequency E3 such that the third marker 40c transmits the third location signal L3 to the sensor assembly 70 during a third sensing phase. As such, the excitation source 60 wirelessly transmits the excitation energy in the form of pulsed magnetic fields at the resonant frequencies of the markers 40a-c during excitation periods, and the markers 40a-c wirelessly transmit the location signals L1-3 to the sensor assembly 70 during sensing phases. It will be appreciated that the excitation and sensing phases can be repeated to permit averaging of the sensed signals to reduce noise.
The computer-operable media in the controller 80, or in a separate signal processor, also includes instructions to determine the absolute positions of each of the markers 40a-c in a three-dimensional reference frame. Based on signals provided by the sensor assembly 70 that correspond to the magnitude of each of the location signals L1-3, the controller 80 and/or a separate signal processor calculates the absolute coordinates of each of the markers 40a-c in the three-dimensional reference frame.
2. Real Time Tracking
The localization system 10 and markers 40 enable real time tracking of the target 2, expandable member 25, and/or the radiation source 30 relative to an external reference frame outside of the patient during treatment planning, set up, irradiation sessions, and at other times of the radiation therapy process. In many embodiments, real time tracking means collecting position data of the markers, determining the locations of the markers in an external reference frame (i.e., a reference frame outside the patient), and providing an objective output in the external reference frame responsive to the location of the marker. The objective output is provided at a frequency/periodicity that adequately tracks the target in real time, and/or a latency that is at least substantially contemporaneous with collecting the position data (e.g., within a generally concurrent period of time).
For example, several embodiments of real time tracking are defined as determining the locations of the markers and calculating the locations relative to an external reference frame at (a) a sufficiently high frequency/periodicity so that pauses in representations of the target location at a user interface do not interrupt the procedure or are readily discernable by a human, and (b) a sufficiently low latency to be at least substantially contemporaneous with the measurement of the location signals from the markers. Alternatively, real time means that the location system 10 calculates the absolute position of each individual marker 40 and/or the location of the target at a periodicity of approximately 1 ms to 5 seconds, or in many applications at a periodicity of approximately 10-100 ms, or in some specific applications at a periodicity of approximately 20-50 ms. In applications for user interfaces, for example, the periodicity can be 12.5 ms (i.e., a frequency of 80 Hz), 16.667 ms (60 Hz), 20 ms (50 Hz), and/or 50 ms (20 Hz). Additionally, real time tracking can further mean that the location system 10 provides the absolute locations of the markers 40, the target 2, the expandable member 25 and/or the radiation source 30 to a memory device, user interface, linear accelerator or other device within a latency of 10 ms to 5 seconds from the time the localization signals were transmitted from the markers 40. In more specific applications, the location system generally provides the locations of the markers 40, target 2, or an instrument within a latency of about 20-50 ms. The location system 10 accordingly provides real time tracking to monitor the position of the markers 40 and/or the target 2 with respect to an external reference frame in a manner that is expected to enhance the efficacy of radiation therapy.
Alternatively, real time tracking can further mean that the location system 10 provides the absolute locations of the markers 40 and/or the target 2 to a memory device, user interface or other device within a latency of 10 ms to 5 seconds from the time the localization signals were transmitted from the markers 40. In more specific applications, the location system generally provides the locations of the markers 40 and/or target 2 within a latency of about 20-50 ms. The location system 10 accordingly provides real time tracking to monitor the position of the markers 40 and/or the target 2 with respect to an external reference frame in a manner that is expected to enhance the efficacy of radiation therapy because higher radiation doses can be applied to the target and collateral effects to healthy tissue can be mitigated.
Alternatively, real-time tracking can further be defined by the tracking error. Measurements of the position of a moving target are subject to motion-induced error, generally referred to as a tracking error. According to aspects of the present invention, the localization system 10 and at least one marker 4 enable real time tracking of the target 2 or other instrument relative to an external reference frame with a tracking error that is within clinically meaningful limits.
Tracking errors are due to two limitations exhibited by any practical measurement system, specifically (a) latency between the time the target position is sensed and the time the position measurement is made available, and (b) sampling delay due to the periodicity of measurements. For example, if a target is moving at 5 cm/s and a measurement system has a latency of 200 ms, then position measurements will be in error by 1 cm. The error in this example is due to latency alone independent of any other measurement errors, and is simply due to the fact that the target or instrument has moved between the time its position is sensed and the time the position measurement is made available for use. If this exemplary measurement system further has a sampling periodicity of 200 ms (i.e., a sampling frequency of 5 Hz), then the peak tracking error increases to 2 cm, with an average tracking error of 1.5 cm.
For a real time tracking system to be useful in medical applications, it is desirable to keep the tracking error within clinically meaningful limits. For example, in a system for tracking motion of a tumor or an instrument for radiation therapy, it may be desirable to keep the tracking error within 5 mm. Acceptable tracking errors may be smaller when tracking other organs for radiation therapy. In accordance with aspects of the present invention, real time tracking refers to measurement of target position and/or rotation with tracking errors that are within clinically meaningful limits.
3. Additional Embodiments of Apparatus for Facilitating Radiation Treatment
C. Specific Embodiments of Markers and Localization Systems
The following specific embodiments of markers, excitation sources, sensors and controllers provide additional details to implement the systems and processes described above with reference to
1. Markers
The magnetic transponder 120 can include a resonating circuit that wirelessly transmits a location signal in response to a wirelessly transmitted excitation field as described above. In this embodiment, the magnetic transponder 120 comprises a coil 122 defined by a plurality of windings of a conductor 124. Many embodiments of the magnetic transponder 120 also include a capacitor 126 coupled to the coil 122. The coil 122 resonates at a selected resonant frequency. The coil 122 can resonate at a resonant frequency solely using the parasitic capacitance of the windings without having a capacitor, or the resonant frequency can be produced using the combination of the coil 122 and the capacitor 126. The coil 122 accordingly generates an alternating magnetic field at the selected resonant frequency in response to the excitation energy either by itself or in combination with the capacitor 126. The conductor 124 of the illustrated embodiment can be hot air or alcohol bonded wire having a gauge of approximately 45-52. The coil 122 can have 800-1000 turns, and the windings are preferably wound in a tightly layered coil. The magnetic transponder 120 can further include a core 128 composed of a material having a suitable magnetic permeability. For example, the core 128 can be a ferromagnetic element composed of ferrite or another material. The magnetic transponder 120 can be secured to the casing 110 by an adhesive 129.
The marker 100 also includes an imaging element that enhances the radiographic image of the marker to make the marker more discernible in radiographic images. The imaging element also has a radiographic profile in a radiographic image such that the marker has a radiographic centroid at least approximately coincident with the magnetic centroid of the magnetic transponder 120. As explained in more detail below, the radiographic and magnetic centroids do not need to be exactly coincident with each other, but rather can be within an acceptable range.
The first and second contrast elements 132 and 134 illustrated in FIGS. 12A-B are continuous rings positioned at opposing ends of the core 128. The first contrast element 132 can be at or around a first end 136a of the core 128, and the second contrast element 134 can be at or around a second end 136b of the core 128. The continuous rings shown in FIGS. 12A-B have substantially the same diameter and thickness. The first and second contrast elements 132 and 134, however, can have other configurations and/or be in other locations relative to the core 128 in other embodiments. For example, the first and second contrast elements 132 and 134 can be rings with different diameters and/or thicknesses.
The radiographic centroid of the image produced by the imaging element 130 does not need to be absolutely coincident with the magnetic centroid Mc, but rather the radiographic centroid and the magnetic centroid should be within an acceptable range. For example, the radiographic centroid Rc can be considered to be at least approximately coincident with the magnetic centroid Mc when the offset between the centroids is less than approximately 5 mm. In more stringent applications, the magnetic centroid Mc and the radiographic centroid Rc are considered to be at least substantially coincident with each other when the offset between the centroids is 2 mm, or less than 1 mm. In other applications, the magnetic centroid Mc is at least approximately coincident with the radiographic centroid Rc when the centroids are spaced apart by a distance not greater than half the length of the magnetic transponder 120 and/or the marker 100.
The imaging element 130 can be made from a material and configured appropriately to absorb a high fraction of incident photons of a radiation beam used for producing the radiographic image. For example, when the imaging radiation has high acceleration voltages in the megavoltage range, the imaging element 130 is made from, at least in part, high density materials with sufficient thickness and cross-sectional area to absorb enough of the photon fluence incident on the imaging element to be visible in the resulting radiograph. Many high energy beams used for therapy have acceleration voltages of 6 MV-25 MV, and these beams are often used to produce radiographic images in the 5 MV-10 MV range, or more specifically in the 6 MV-8 MV range. As such, the imaging element 130 can be made from a material that is sufficiently absorbent of incident photon fluence to be visible in an image produced using a beam with an acceleration voltage of 5 MV-10 MV, or more specifically an acceleration voltage of 6 MV-8 MV.
Several specific embodiments of imaging elements 130 can be made from gold, tungsten, platinum and/or other high density metals. In these embodiments the imaging element 130 can be composed of materials having a density of 19.25 g/cm3 (density of tungsten) and/or a density of approximately 21.4 g/cm3 (density of platinum). Many embodiments of the imaging element 130 accordingly have a density not less than 19 g/cm3. In other embodiments, however, the material(s) of the imaging element 130 can have a substantially lower density. For example, imaging elements with lower density materials are suitable for applications that use lower energy radiation to produce radiographic images. Moreover, the first and second contrast elements 132 and 134 can be composed of different materials such that the first contrast element 132 can be made from a first material and the second contrast element 134 can be made from a second material.
Referring to
One specific process of using the marker involves imaging the marker using a first modality and then tracking the target of the patient and/or the marker using a second modality. For example, the location of the marker relative to the target can be determined by imaging the marker and the target using radiation. The marker and/or the target can then be localized and tracked using the magnetic field generated by the marker in response to an excitation energy.
The marker 100 shown in FIGS. 12A-B is expected to provide an enhanced radiographic image compared to conventional magnetic markers for more accurately determining the relative position between the marker and the target of a patient.
The marker 200 is expected to operate in a manner similar to the marker 100 described above. The marker 200, however, does not have two separate contrast elements that provide two distinct, separate points in a radiographic image. The imaging element 230 is still highly useful in that it identifies the radiographic centroid of the marker 200 in a radiographic image, and it can be configured so that the radiographic centroid of the marker 200 is at least approximately coincident with the magnetic centroid of the magnetic transponder 120.
Additional embodiments of markers in accordance with the invention can include imaging elements incorporated into or otherwise integrated with the casing 110, the core 128 (
The markers described above with reference to
2. Localization Systems
The excitation source 1010 is adjustable to generate a magnetic field having a waveform with energy at selected frequencies to match the resonant frequencies of the markers 40. The magnetic field generated by the excitation source 1010 energizes the markers at their respective frequencies. After the markers 40 have been energized, the excitation source 1010 is momentarily switched to an “off” position so that the pulsed magnetic excitation field is terminated while the markers wirelessly transmit the location signals. This allows the sensor assembly 1012 to sense the location signals from the markers 40 without measurable interference from the significantly more powerful magnetic field from the excitation source 1010. The excitation source 1010 accordingly allows the sensor assembly 1012 to measure the location signals from the markers 40 at a sufficient signal-to-noise ratio so that the signal processor 1014 or the controller 1016 can accurately calculate the absolute location of the markers 40 relative to a reference frame.
a. Excitation Sources
Referring still to
The energy storage device 1042 is capable of storing adequate energy to reduce voltage drop in the energy storage device while having a low series resistance to reduce power losses. The energy storage device 1042 also has a low series inductance to more effectively drive the coil assembly 1046. Suitable capacitors for the energy storage device 1042 include aluminum electrolytic capacitors used in flash energy applications. Alternative energy storage devices can also include NiCd and lead acid batteries, as well as alternative capacitor types, such as tantalum, film, or the like.
The switching network 1044 includes individual H-bridge switches 1050 (identified individually by reference numbers 1050a-d), and the coil assembly 1046 includes individual source coils 1052 (identified individually by reference numbers 1052a-d). Each H-bridge switch 1050 controls the energy flow between the energy storage device 1042 and one of the source coils 1052. For example, H-bridge switch #11050a independently controls the flow of the energy to/from source coil #11052a, H-bridge switch #21050b independently controls the flow of the energy to/from source coil #21052b, H-bridge switch #31050c independently controls the flow of the energy to/from source coil #31052c, and H-bridge switch #41050d independently controls the flow of the energy to/from source coil #41052d. The switching network 1044 accordingly controls the phase of the magnetic field generated by each of the source coils 1052a-d independently. The H-bridges 1050 can be configured so that the electrical signals for all the source coils 1052 are in phase, or the H-bridge switches 1050 can be configured so that one or more of the source coils 1052 are 180° out of phase. Furthermore, the H-bridge switches 1050 can be configured so that the electrical signals for one or more of the source coils 1052 are between 0 and 180° out of phase to simultaneously provide magnetic fields with different phases.
The source coils 1052 can be arranged in a coplanar array that is fixed relative to the reference frame. Each source coil 1052 can be a square, planar winding arranged to form a flat, substantially rectilinear coil. The source coils 1052 can have other shapes and other configurations in different embodiments. In one embodiment, the source coils 1052 are individual conductive lines formed in a stratum of a printed circuit board, or windings of a wire in a foam frame. Alternatively, the source coils 1052 can be formed in different substrates or arranged so that two or more of the source coils are not planar with each other. Additionally, alternate embodiments of the invention may have fewer or more source coils than illustrated in
The selected magnetic fields from the source coils 1052 combine to form an adjustable excitation field that can have different three-dimensional shapes to excite the markers 40 at any spatial orientation within an excitation volume. When the planar array of the source coils 1052 is generally horizontal, the excitation volume is positioned above an area approximately corresponding to the central region of the coil assembly 1046. The excitation volume is the three-dimensional space adjacent to the coil assembly 1046 in which the strength of the magnetic field is sufficient to adequately energize the markers 40.
In the embodiment of
The spatial configuration of the excitation field in the excitation volume 1109 can be quickly adjusted by manipulating the switching network to change the phases of the electrical signals provided to the source coils 1052a-d. As a result, the overall magnetic excitation field can be changed to be oriented in either the X, Y or Z directions within the excitation volume 1109. This adjustment of the spatial orientation of the excitation field reduces or eliminates blind spots in the excitation volume 1109. Therefore, the markers 40 within the excitation volume 1109 can be energized by the source coils 1052a-d regardless of the spatial orientations of the leadless markers.
In one embodiment, the excitation source 1010 is coupled to the sensor assembly 1012 so that the switching network 1044 (
The excitation source 1010 illustrated in
b. Sensor Assemblies
The panel 1604 may be a substantially non-conductive material, such as a sheet of KAPTON® produced by DuPont. KAPTON® is particularly useful when an extremely stable, tough, and thin film is required (such as to avoid radiation beam contamination), but the panel 1604 may be made from other materials and have other configurations. For example, FR4 (epoxy-glass substrates), GETEK or other Teflon-based substrates, and other commercially available materials can be used for the panel 1604. Additionally, although the panel 1604 may be a flat, highly planar structure, in other embodiments, the panel may be curved along at least one axis. In either embodiment, the field sensors (e.g., coils) are arranged in a locally planar array in which the plane of one field sensor is at least substantially coplanar with the planes of adjacent field sensors. For example, the angle between the plane defined by one coil relative to the planes defined by adjacent coils can be from approximately 0° to 10°, and more generally is less than 5°. In some circumstances, however, one or more of the coils may be at an angle greater than 10° relative to other coils in the array.
The sensor assembly 1012 shown in
The sensor assembly 1012 can further include a first exterior cover 1630a on one side of the sensing subsystem and a second exterior cover 1630b on an opposing side. The first and second exterior covers 1630a-b can be thin, thermally stable layers, such as Kevlar or Thermount films. Each of the first and second exterior covers 1630a-b can include electric shielding 1632 to block undesirable external electric fields from reaching the coils 1602. The electric shielding 1632 can be a plurality of parallel legs of gold-plated, copper strips to define a comb-shaped shield in a configuration commonly called a Faraday shield. It will be appreciated that the shielding can be formed from other materials that are suitable for shielding. The electric shielding can be formed on the first and second exterior covers using printed circuit board manufacturing technology or other techniques.
The panel 1604 with the coils 1602 is laminated to the core 1620 using a pressure sensitive adhesive or another type of adhesive. The first and second exterior covers 1630a-b are similarly laminated to the assembly of the panel 1604 and the core 1620. The laminated assembly forms a rigid structure that fixedly retains the arrangement of the coils 1602 in a defined configuration over a large operating temperature range. As such, the sensor assembly 1012 does not substantially deflect across its surface during operation. The sensor assembly 1012, for example, can retain the array of coils 1602 in the fixed position with a deflection of no greater than ±0.5 mm, and in some cases no more than ±0.3 mm. The stiffness of the sensing subsystem provides very accurate and repeatable monitoring of the precise location of leadless markers in real time.
In still another embodiment, the sensor assembly 1012 can further include a plurality of source coils that are a component of the excitation source 1010. One suitable array combining the sensor assembly 1012 with source coils is disclosed in U.S. patent application Ser. No. 10/334,700, entitled PANEL-TYPE SENSOR/SOURCE ARRAY ASSEMBLY, filed on Dec. 30, 2002, which is herein incorporated by reference.
The coils 1602 may be conductive traces or depositions of copper or another suitably conductive metal formed on the panel 1604. Each coil 1602 has a trace with a width of approximately 0.15 mm and a spacing between adjacent turns within each coil of approximately 0.13 mm. The coils 1602 can have approximately 15 to 90 turns, and in specific applications each coil has approximately 40 turns. Coils with less than 15 turns may not be sensitive enough for some applications, and coils with more than 90 turns may lead to excessive voltage from the source signal during excitation and excessive settling times resulting from the coil's lower self-resonant frequency. In other applications, however, the coils 1602 can have less than 15 turns or more than 90 turns.
As shown in
The pitch of the coils 1602 in the array 1605 is a function of, at least in part, the minimum distance between the marker and the coil array. In one embodiment, the coils are arranged at a pitch of approximately 67 mm. This specific arrangement is particularly suitable when the wireless markers 40 are positioned approximately 7-27 cm from the sensor assembly 1012. If the wireless markers are closer than 7 cm, then the sensing subsystem may include sensor coils arranged at a smaller pitch. In general, a smaller pitch is desirable when wireless markers are to be sensed at a relatively short distance from the array of coils. The pitch of the coils 1602, for example, is approximately 50%-200% of the minimum distance between the marker and the array.
In general, the size and configuration of the array 1605 and the coils 1602 in the array depend on the frequency range in which they are to operate, the distance from the markers 40 to the array, the signal strength of the markers, and several other factors. Those skilled in the relevant art will readily recognize that other dimensions and configurations may be employed depending, at least in part, on a desired frequency range and distance from the markers to the coils.
The array 1605 is sized to provide a large aperture to measure the magnetic field emitted by the markers. It can be particularly challenging to accurately measure the signal emitted by an implantable marker that wirelessly transmits a marker signal in response to a wirelessly transmitted energy source because the marker signal is much smaller than the source signal and other magnetic fields in a room (e.g., magnetic fields from CRTs, etc.). The size of the array 1605 can be selected to preferentially measure the near field of the marker while mitigating interference from far field sources. In one embodiment, the array 1605 is sized to have a maximum dimension D1 or D2 across the surface of the area occupied by the coils that is approximately 100% to 300% of a predetermined maximum sensing distance that the markers are to be spaced from the plane of the coils. Thus, the size of the array 1605 is determined by identifying the distance that the marker is to be spaced apart from the array to accurately measure the marker signal, and then arrange the coils so that the maximum dimension of the array is approximately 100% to 300% of that distance. The maximum dimension of the array 1605, for example, can be approximately 200% of the sensing distance at which a marker is to be placed from the array 1605. In one specific embodiment, the marker 40 has a sensing distance of 20 cm and the maximum dimension of the array of coils 1602 is between 20 cm and 60 cm, and more specifically 40 cm.
A coil array with a maximum dimension as set forth above is particularly useful because it inherently provides a filter that mitigates interference from far field sources. As such, one aspect of several embodiments of the invention is to size the array based upon the signal from the marker so that the array preferentially measures near field sources (i.e., the field generated by the marker) and filters interference from far field sources.
The coils 1602 are electromagnetic field sensors that receive magnetic flux produced by the wireless markers 40 and in turn produce a current signal representing or proportional to an amount or magnitude of a component of the magnetic field through an inner portion or area of each coil. The field component is also perpendicular to the plane of each coil 1602. Each coil represents a separate channel, and thus each coil outputs signals to one of 32 output ports 1606. A preamplifier, described below, may be provided at each output port 1606. Placing preamplifiers (or impedance buffers) close to the coils minimizes capacitive loading on the coils, as described herein. Although not shown, the sensing unit 1601 also includes conductive traces or conductive paths routing signals from each coil 1602 to its corresponding output port 1606 to thereby define a separate channel. The ports in turn are coupled to a connector 1608 formed on the panel 1604 to which an appropriately configured plug and associated cable may be attached.
The sensing unit 1601 may also include an onboard memory or other circuitry, such as shown by electrically erasable programmable read-only memory (EEPROM) 1610. The EEPROM 1610 may store manufacturing information such as a serial number, revision number, date of manufacture, and the like. The EEPROM 1610 may also store per-channel calibration data, as well as a record of run-time. The run-time will give an indication of the total radiation dose to which the array has been exposed, which can alert the system when a replacement sensing subsystem is required.
Although shown in one plane only, additional coils or electromagnetic field sensors may be arranged perpendicular to the panel 1604 to help determine a three-dimensional location of the wireless markers 40. Adding coils or sensors in other dimensions could increase the total energy received from the wireless markers 40, but the complexity of such an array would increase disproportionately. The inventors have found that three-dimensional coordinates of the wireless markers 40 may be found using the planar array shown in
Implementing the sensor assembly 1012 may involve several considerations. First, the coils 1602 may not be presented with an ideal open circuit. Instead, they may well be loaded by parasitic capacitance due largely to traces or conductive paths connecting the coils 1602 to the preamplifiers, as well as a damping network (described below) and an input impedance of the preamplifiers (although a low input impedance is preferred). These combined loads result in current flow when the coils 1602 link with a changing magnetic flux. Any one coil 1602, then, links magnetic flux not only from the wireless marker 40, but also from all the other coils as well. These current flows should be accounted for in downstream signal processing.
A second consideration is the capacitive loading on the coils 1602. In general, it is desirable to minimize the capacitive loading on the coils 1602. Capacitive loading forms a resonant circuit with the coils themselves, which leads to excessive voltage overshoot when the excitation source 1010 is energized. Such a voltage overshoot should be limited or attenuated with a damping or “snubbing” network across the coils 1602. A greater capacitive loading requires a lower impedance damping network, which can result in substantial power dissipation and heating in the damping network.
Another consideration is to employ preamplifiers that are low noise. The preamplification can also be radiation tolerant because one application for the sensor assembly 1012 is with radiation therapy systems that use linear accelerators (LINAC). As a result, PNP bipolar transistors and discrete elements may be preferred. Further, a DC coupled circuit may be preferred if good settling times cannot be achieved with an AC circuit or output, particularly if analog to digital converters are unable to handle wide swings in an AC output signal.
c. Signal Processors and Controllers
The signal processor 1014 and the controller 1016 illustrated in
An experimental phantom based study was conducted to determine effectiveness of this system for real-time tracking. In this experiment, a custom 4D stage was constructed to allow arbitrary motion in three axes for speeds up to 10 cm/sec in each dimension, with accuracy to 0.3 mm. Position accuracy was measured by a 3D digitizing arm attached to the stage system. As shown in
As shown in
The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein of the invention can be applied to target locating and tracking systems, not necessarily the exemplary system generally described above.
The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, are incorporated herein by reference, in their entirety. Aspects of the invention can be modified, if necessary, to employ systems, devices and concepts of the various patents, applications and publications to provide yet further embodiments of the invention.
These and other changes can be made to the invention in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all target locating and monitoring systems that operate in accordance with the claims to provide apparatus and methods for locating, monitoring, and/or tracking the position of a selected target within a body. Accordingly, the invention is not limited, except as by the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/615,443 filed on Oct. 1, 2004, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60615443 | Oct 2004 | US |
