Patent Application
20050245920
The present invention is in the field of microwave thermal therapy of tissue in a body and more particularly is an apparatus and method for treating interior tissue regions with a cell necrosis probe energized by a microwave generator.
Cell necrosis apparatus and methods are known in treatment of a variety of organs including but not limited to the prostate, liver, lungs, breasts and kidneys. In regard to prostate treatment, for example, U.S. Pat. No. 5,301,687 to Wong discloses a method and apparatus using an intracavity approach to the prostate through either the rectum or the urethra.
U.S. Pat. No. 5,273,886 to Edwards discloses an RF tissue heating system which includes a cooling feature where liquid coolant is used to cool the tissue being treated. More specifically sterile coolant water is applied to mucosal tissue at the targeted tissue region and subsequently is aspirated.
U.S. Pat. No. 5,733,319 to Nielson discloses apparatus for trans-urethral microwave thermal therapy of tissue which uses coolant passages arranged in an asymmetrical pattern in the antenna. This produces a corresponding asymmetrical pattern of radiation, which effectively focuses the microwave energy more on one side toward the tissue being treated and less on the opposite side toward tissue not intended for treatment. This cooling configuration further focuses the radiation by concentrating microwave emission at a given length of the antenna rather than spreading it up and down the antenna length.
The Nielson apparatus further includes a coolant-sensor interface module for sensing the temperature and pressure of the circulating liquid coolant. This interface module is relatively complex as is it constructed to prevent the circulating liquid from physically contacting the sensor control unit, which thus avoids a need for time consuming and expensive cleaning and sterilization of the sensor control unit between patents. The three above-referenced prior art patents are incorporated herein by reference.
The new invention is an improved cell necrosis apparatus and method which provide a number of advantages over known prior art systems.
In a first preferred embodiment the new invention includes a microwave generator, coolant circulating system, a flexible cooled transmission line, a probe handle connected to a probe body with its included antenna assembly, and a sharp probe tip for piercing the skin or other body tissue to initiate a percutaneous cell necrosis procedure. A particular aspect of the novelty herein is the configuration of the probe handle and probe body and antenna within the probe body to include a coaxial feedline cable and coaxial coolant entry and exit or return passageways in the probe body, thus establishing a symmetrical structure and a symmetrical radiation pattern emanating from the antenna. In this embodiment a fixed quantity of coolant from a reservoir is circulated by a pump, and temperature and pressure sensors in the probe for the coolant are absent and unneeded, as explained below. The present invention, furthermore, includes the method of cooling a microwave generating cell necrosis apparatus and a method of cell necrosis treatment with a microwave generating probe.
Within the microwave generator system the microwave generator, which generates a frequency of either 915 MHz or 2450 MHz, is connected to the proximal portion of a microwave transmission line whose distal end is coupled to a microwave antenna. The length of the radiating antenna assembly section will differ depending on the operating frequency. The generator should have an input power between 30 200 Watts. More than one output channel could be designed into the generator, so that simultaneous necrosis sites could be generated with multiple devices. The refrigerated coolant and pump system can either be integral to the microwave generator or self standing. Chilled water maintained at 40° F. and at a flow rate between 60 170 cc/min is preferred. By surface cooling the antenna radiating elements, the treatment volume may be extended to larger values of radii.
Examples of hypothetical clinical scenarios are as follows:
A. To create a 4.0 cm necrosis diameter within the patient's liver tumor site, the settings for the probe would be as follows: 200 watts of input power at 2450 MHz with a flow rate of 170 cc/min of 40° F. water. The probe would be placed accordingly within the tumor mass and operated for a total of 15 minutes. This would create a necrosis of at least 5.0 cm in diameter and 5.5 cm in length, and
B. To create a 2.0 cm necrosis lesion diameter within the patient's liver tumor site, the settings for the probe would be as follows: 200 watts of input power at 2450 MHz with a flow rate of 170 cc/min of 40° F. water. The probe would be placed accordingly within each tumor mass and operated simultaneously for a total of 10 minutes. This would create a necrosis of at least 3.0 cm in diameter and 3.5 cm in length.
Obviously, within the scope of this invention, parameters listed above and other parameters may be varied to achieve desired volumetric tissue heating and ablation.
From the microwave generator and coolant circulation pump extends a flexible coaxial feedline cable with coaxial coolant inlet and outlet passageways, whose distal end is coupled to the probe handle having coaxial lumens corresponding to those of the feedline cable. In the preferred embodiment the probe comprises a handle, a body, an antenna assembly, a tip and a temperature sensor at the tip.
The handle is used to manipulate the probe during the cell necrosis procedure. The handle also provides a communication link for the flexible transmission line and the coolant passageways with the corresponding elements in the probe body.
The purpose of the probe body is to contain and protect the distal portion of the cable chassis which includes the antenna radiating element. Depending on the type of procedure, insertion forces of different magnitudes are applied to the probe. For instance in percutaneous procedures, the probe must be capable of penetrating the patient's skin as well as the other body tissues that are in the insertion pathway to the tumor. With open and laparoscopic procedures these insertion forces are significantly less, since the organ of the patient is typically exposed and the probe can be directly placed.
The probe body consists of two single lumen tubes, which create a coaxial system. The outer lumen tube, which has a circular profile, is constructed of a plastic and metal composite. Non metallic materials such as plastic must be used to create the radiating element segment since metal in the field of the radiating element will disrupt the radiation pattern generated by the microwave antenna. This would result in uncontrollable and ineffective cell necrosis. The proximal portion of the outer lumen tube is constructed primarily of metal in order to minimize the potential for buckling of the probe shaft during insertion. Roughly 3.0 cm of the distal portion of the outer lumen is constructed of plastic in order to cover the 2.5 cm active length of the microwave antenna.
The inner lumen is constructed entirely of plastic and resides within the outer lumen. Plastics with high flexural moduli such as PEEK (Polyetheretherketone) and PEI (Polyetherimide) are optimal. Various fillers can be added to these resins in order to enhance their flexural moduli. The profile of the inner tube lumen is circular. However, a splined profile can further enhance the overall rigidity and integrity of the probe body. The splines reduce the flexure of the body during loading. To further reduce drag, the metallic portion of the outer lumens surface can be coated with a non stick surface such as PTFE.
At the distal end of the probe body, a tip is grafted to the outer lumen. To further minimize the insertion force of the probe, various tip designs can be used. These tips can be constructed of either plastic or metal. A metal edge at the distal end of the tip allows for a sharper and harder penetrating surface thereby minimizing the insertion force.
At the proximal end of the probe body a hub exists which supports both the inner and outer lumens. This hub is mounted to the probe handle. It should be noted that the construction of the probe body is not limited to a metal and plastic composite. Other variations exist. Alternatively, the probe body can be constructed entirely of plastic or high performance carbon fiber tubing.
The antenna assembly consists of the flexible coaxial feedline cable leading to the probe handle, a hermetically sealed splice or junction within the probe handle, a semi-rigid feedline cable and a radiating element within the probe body. The seal is both air tight and water tight so that coolant can be applied over the entire antenna assembly without causing an electrical short. Typically, electrical characteristics for each of these cables include excellent power handling and insertion loss properties. Calculations for antenna output are set forth later herein in the description of the preferred embodiment.
The antenna consists of conventional proximal, central and distal elements, but with changed and additional new construction for coaxial coolant lumens and an entire coolant delivery and control system.
The semi rigid coaxial cable is coated with a material of low dielectric property such as PTFE, which coating can be applied via means of spray coating or can be in the form of heat-shrink tubing. The antenna comprises proximal and distal elements joined to a central element positioned between them. The inner conductor of the transmission cable terminates at the distal element of the antenna. The proximal element of the antenna communicates with the distal end of the semi rigid cable's outer conductor. This junction is formed by means of welding the outer conductor of the semi rigid coaxial cable to the proximal element. Both the proximal and distal elements are constructed of medical grade metal. The central element is constructed of either epoxy or PTFE filler. The entire assembly is insulated with PTFE shrink tubing.
The coolant system circulates chilled water from the generator throughout the entire probe assembly for several reasons. First, chilling allows the antenna and transmission line to operate at higher powers over an extended period of time. Larger burn profiles result at higher wattages along with more time. Second, chilling of the antenna portion allows for a greater depth of penetration. By cooling the outer probe surface around the antenna, the therapeutic heating radius is increased. This is based on maximizing the coolant power in order to minimize the overall power difference of the system. This is more fully described later in the Description of the Preferred Embodiment. Third, lesions created by microwave antennas typically yield tear drop profiles resulting in tracking. This is caused by conductive energy, which tracks proximally beyond the antenna. Cooling eliminates this profile and allows for a more elliptical to spherical lesion with no tracking. Fourth, cooling of the probe body allows for patient comfort during the procedure at the entry site. This is extremely important during percutaneous procedures. It also allows the practitioner to hold the feedline during the procedure. All of these design features translate into large, controllable lesions.
An additional feature of the probe is a temperature sensor (either a thermocouple or a fiber optic sensor) is placed at the distal portion of the probe. The sensor is attached by means of an adhesive and runs proximally along the inner lumen to the connector. Temperature measuring is normally conducted only when the microwave system along with the pump is off. Temperature sensing is possible during the ablation process with more advanced measuring techniques; however, the information may be less useful. The purpose of the temperature sensing is twofold. First, it allows the practitioner to determine whether the device is working. Second, it allows the physician to re guide the probe into an untreated area by a simple temperature measurement.
In use of this new cell necrosis apparatus, the probe body is inserted into the tumor mass by means of advancing the probe handle. Through ultrasound or CT guidance, the practitioner can place the probe's radiating element into the tumor mass. Placement can be performed via an open surgery, laparoscopic or percutaneous procedure.
In preferred embodiments the diameter of the probe body can range from 7 to 9 Fr in size. For smaller tumor masses the size of the probe body can be reduced. Various exposure lengths can be constructed. A typical probe would be 8 Fr in diameter with an exposed length (distance from hub to the tip of the probe) of 20 cm. The probe handle is to be held by the practitioner during placement. A microwave antenna, housed within the distal tip of the probe body, has a 2.5 cm active length. The transmission line cable is roughly 7 ft long, which length allows the microwave generator system to be at a satisfactory distance away from the patient's bedside, considering space restrictions within procedural rooms. The length also allows the practitioner freedom to move the probe without obstruction during placement. The probe at its proximal end has a connector for attachment to a compatible microwave generator with an integral coolant system. Chilled water is circulated throughout the entire probe assembly. A temperature sensor is placed at the distal tip for temperature monitoring after necrosis. The entire probe is disposable.
An objective of this invention is to cool a probe of a cell necrosis apparatus by flowing coolant along the length of the antenna's outer surface via a passageway that circumferentially surrounds said surface. It is a further objective to establish by inner and outer concentric lumens, an inner annular flow path that surrounds the outer surface of the antenna and an outer flow path radially outward of and generally surrounding the inner flow path. In this embodiment the coolant from a source initially flows in the outer flow path in a distal direction lengthwise of the antenna, and then reverses direction and flows in the proximal direction along the surface of the antenna to produce a generally symmetric radiation pattern. It is a further objective to measure the temperature in the region of the distal end of the antenna, preferably when the antenna is inactive, and to thereafter adjust the coolant temperature and/or flow rate as needed. In establishing said coolant flow passageways it is an additional object to electrically insulate the antenna from the coolant flow. An additional objective is to cool via these coaxial flow passageways the microwave feedline within the probe body and within the transmission cable extending between the microwave generator and the probe handle.
In one preferred embodiment the present invention is a cell necrosis apparatus for delivering thermal microwave energy to a specific site in a body, comprising:
A further embodiment of this invention is a method of cell necrosis treatment with a cell necrosis apparatus including a microwave antenna in a probe, comprising the steps:
Features and advantages of the preferred embodiments of this invention are set forth in the following description and drawings, as well as in the appended claims.
A preferred embodiment of the new cell necrosis apparatus 1 is seen in
To better understand the present invention the environment of its use is indicated in
The new cell necrosis apparatus will now be described in terms of: (a) the probe handle, body and tip, (b) the cable chassis terminating in the microwave antenna, (c) the cooling system and (d) the microwave generator.
The probe will be described first with reference to
The diameter of the probe body can range from 7 to 9 Fr in size. For smaller tumor masses the size and exposure lengths of the probe body can be reduced. A typical probe would be 8 Fr in diameter with an exposed length (distance from hub to the tip of the probe) of 20 cm. The probe handle 6 is to be held by the practitioner during placement. The microwave antenna housed within the distal tip of the probe body has a 2.5 cm active length. The transmission line cable is roughly 7 feet in length which allows the practitioner freedom to move the probe without obstruction during placement. The probe has a connector at its proximal end for attachment to a compatible microwave generator with an integral coolant system. Chilled water is circulated throughout the entire probe assembly. A temperature sensor is placed at the distal tip for temperature monitoring after necrosis. The entire probe is disposable.
Regardless of procedure, the proposed device is capable of handling insertion forces because of its adequate construction described later herein. In the probe body the outer lumen tube, which has a circular profile, is constructed of a plastic and metal composite. Non-metallic materials such as plastic must be used to create the radiating element segment, since metal in the field of the radiating element will disrupt the radiation pattern generated by the microwave antenna, which would result in uncontrollable and ineffective cell necrosis. The proximal portion of the outer lumen tube is constructed primarily of metal in order to minimize the potential for buckling of the probe shaft during insertion. Roughly 3.0 cm of the distal portion of the outer lumen is constructed of plastic in order to cover the 2.5 cm active length of the microwave antenna. This plastic tube has a diameter for 3.0 cm along its distal portion, the same as the diameter of the metal lumen. The balance of the plastic tube is ground down to a diameter less than that of its distal portion, thus establishing a step at this junction. The metal lumen is then inserted over the proximal end of the plastic tube so that it abuts against the junction.
The inner lumen 16 is constructed entirely of plastic and resides within the outer lumen 17. Plastics with high flexural moduli such as PEEK (Polyetheretherketone) and PEI (Polyetherimide) are preferred, and various fillers can be added to these resins to further enhance their flexural moduli. The profile of the inner lumen seen in
At the distal end of the probe body 5 a tip 12 of plastic or metal is grafted to the outer lumen. Various manufacturing methods can be used to graft the tip including radio frequency energy and the application of medical grade adhesives. To minimize the insertion force of the probe, various tip designs 12A, 12B can be used as illustrated in
The probe handle 6 is shown in
Referring again to
The semi-rigid coaxial cable 36 is coated with a material of low dielectric property such as PTFE, which can be applied via means of spray coating or installed in the form of heat-shrink tubing. The inner conductor of the cable terminates at the distal element of the antenna 10. The proximal element communicates with the distal end of the semi-rigid cable's outer conductor, this junction being formed by means of welding the outer conductor of the semi-rigid coaxial cable to the proximal element. Both the proximal and central elements are constructed of medical grade metal. The central element is constructed of either epoxy or PTFE filler. The entire assembly is insulated with PTFE shrink tubing.
The bipolar choked antenna design allows for minimal insertion losses and optimal performance. With conventional (non-choked) microwave antennas, the radiating performance is a function of insertion depth. For optimal radiation the antenna must have sections that are equal in length and that correspond to a quarter wavelength in tissue. In most cases, this is not clinically practical since insertion depth is a function of the clinical situation. As a result, conventional microwave antennas typically have increased reflected power at the antenna junction, which results in increased input power requirements and ohmic heating of the transmission and antenna feed lines. Moreover, the overall antenna may have unbalanced radiating patterns. A variety of different connectors can be used at the proximal section of the antenna chassis including but not limiting to SMA, N and SMB connectors which are standard in the industry.
The coolant system and pathways are illustrated in
Third, lesions created by microwave antennas typically yield tear drop profiles resulting in tracking. This is caused by conductive energy which tracks proximally beyond the antenna. Cooling eliminates this profile and allows for a more elliptical to spherical lesion with no tracking. Finally, cooling of the probe body allows for patient comfort during the procedure at the entry site. Cooling also allows the practitioner to hold the feedline during the procedure, all of these design features enhancing the capability and controlability of this apparatus and procedure for treating lesions.
The coolant pathways are illustrated in the elevational views of
A microwave generator, which generates a frequency of either 915 MHz, or 2450 MHz, is connected to the proximal portion of the probe transmission line. Note that the length of the antenna would differ depending on the operating frequency. The generator should have an input power between 30-200 Watts. More than one output channel could be designed into the generator. Hence simultaneous necrosis sites could be generated with multiple devices. The refrigerated coolant and pump system can either be integral to the microwave generator or self-standing. Chilled water maintained at 40° F. and at a flow rate between 60-170 cc/min is preferred. By surface cooling the antenna radiating elements, the treatment volume may be pushed to larger values of radius.
A temperature sensor 58, either thermocouple or fiber optic sensor, is placed at the distal tip of the probe, as seen in
An optional sheath (not shown) can be placed over the probe. Such sheath would be connected to the distal portion of the probe delivery systems body by means of a luer lock, which would prevent the sheath from separating from the probe delivery system during the treatment session. The purpose of the sheath is twofold. First it can be used to inject chemicals such as ethanol, acetic acid or saline solution into the target treatment area in order to aid in the treatment process. Second, the sheath can provide a means for tracking the wound site after the procedure. This would allow the practitioner to plug the wound site after the treatment session has been completed and the probe delivery system has been removed from the patient. Typically a practitioner would infuse a fibrin material through the sheath side arm to minimize bleeding from the wound site. The sheath has a valve within its proximal hub to prevent blood and other bodily fluids from leaving the wound site.
Although the present invention has been described with reference to preferred embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
