US 20070203551 A1
A dipole microwave applicator emits microwave radiation into tissue to be treated. The applicator is formed from a thin coax cable having an inner conductor surrounded by an insulator, which is surrounded by an outer conductor. A portion of the inner conductor extends beyond the insulator and the outer conductor. A ferrule at the end of the outer conductor has a step and a sleeve that surrounds a portion of the extended inner conductor. A tuning washer is attached to the end of the extended inner conductor. A dielectric tip encloses the tuning washer, the extended inner conductor, and the sleeve of the ferrule. The sleeve of the ferrule and the extended inner conductor operate as the two arms of the dipole microwave antenna. The tuning washer faces the step in the ferrule, and is sized and shaped to cooperate with the step in balancing and tuning the applicator.
1. A dipole microwave applicator for emitting microwave radiation into tissue, the assembly comprising:
an outer conductor having an end;
an inner conductor disposed within the outer conductor, and including a section that extends outwardly beyond the end of the outer conductor;
a ferrule disposed at the end of the outer conductor, and having a sleeve portion that surrounds a portion of the outwardly extending section of the inner conductor; and
a dielectric tip surrounding the sleeve portion of the ferrule and the outwardly extending section of the inner conductor,
whereby the sleeve portion of the ferrule and at least a portion of the outwardly 1l extending section of the inner conductor operate as corresponding arms of the dipole microwave applicator.
2. The dipole microwave applicator of
3. The dipole microwave applicator of
4. The dipole microwave applicator of
5. The dipole microwave applicator of
the ferrule further includes a step adjacent to the sleeve portion, and
the tuning element and step cooperate to balance the corresponding arms of the dipole microwave applicator.
6. The dipole microwave applicator of
7. The dipole microwave applicator of
8. The dipole microwave applicator of
9. The dipole microwave applicator of
the ferrule is formed from copper, and
the tip is formed from itrium stabilized zirconia.
10. The dipole microwave applicator of
the sleeve is formed from stainless steel,
the ferrule is formed from copper, and
the tip is formed from itrium stabilized zirconia.
11. The dipole microwave applicator of
12. The dipole microwave applicator of claim of
the spacer abuts an end of the sleeve of the ferrule and the insulator terminates within the sleeve so as to define a gap within the sleeve of the ferrule around the inner conductor.
13. The dipole microwave applicator of
14. The dipole microwave applicator of
the dielectric tip has open end that abuts the step in the ferrule and a closed end opposite the open end, and
the closed end is configured for one of cutting or piercing tissue.
15. The dipole microwave applicator of
This application is a continuation-in-part (CIP) of application Ser. No. 10/577,414 filed Apr. 26, 2006, which in turn is a national stage application of International Application Serial Number PCT/EP2005/007103 filed Jul. 1, 2005.
This application also claims priority to foreign patent application serial number GB0600018.6 filed Jan. 3, 2006.
1. Field of the Invention
The present invention relates generally to medical technology, and more specifically to microwave radiation applicators and methods of thermal ablative treatment of tissue using radiated microwaves.
2. Background Information
Thermal ablative therapies may be defined as techniques that intentionally decrease body tissue temperature (hypothermia) or intentionally increase body tissue temperature (hyperthermia) to temperatures required for cytotoxic effect, or to other therapeutic temperatures depending on the particular treatment. Microwave thermal ablation relies on the fact that microwaves form part of the electromagnetic spectrum causing heating due to the interaction between water molecules and the microwave radiation. The heat being used as the cytotoxic mechanism. Treatment typically involves the introduction of an applicator into tissue, such as tumors. Microwaves are released from the applicator forming a field around its tip. Heating of the water molecules occurs in the radiated microwave field produced around the applicator, rather than by conduction from the probe itself. Heating is therefore not reliant on conduction through tissues, and cytotoxic temperature levels are reached rapidly.
Microwave thermal ablative techniques are useful in the treatment of tumors of the liver, brain, lung, bones, etc.
U.S. Pat. No. 4,494,539 discloses a surgical operation method using micro-waves, characterized in that microwaves are radiated to tissue from a monopole type electrode attached to the tip of a coaxial cable for transmitting microwaves. Coagulation, hemostasis or transaction is then performed on the tissue through the use of the thermal energy generated from the reaction of the microwaves on the tissue. In this way, the tissue can be operated in an easy, safe and bloodless manner. Therefore, the method can be utilized for an operation on a parenchymatous organ having a great blood content or for coagulation or transaction on a parenchymatous tumor. According to the method, there can be performed an operation on liver cancer, which has been conventionally regarded as very difficult. A microwave radiation applicator is also disclosed.
U.S. Pat. No. 6,325,796 discloses a microwave ablation assembly and method, including a relatively thin, elongated probe having a proximal access end, and an opposite distal penetration end adapted to penetrate into tissue. The probe defines an insert passage extending therethrough from the access end to the penetration end thereof. An ablation catheter includes a coaxial transmission line with an antenna device coupled to a distal end of the transmission line for generating an electric field sufficiently strong enough to cause tissue ablation. The coaxial transmission line includes an inner conductor and an outer conductor separated by a dielectric material. A proximal end of the transmission line is coupled to a microwave energy source. The antenna device and the transmission line each have a transverse cross-sectional dimension adapted for sliding receipt through the insert passage while the elongated probe is positioned in the tissue. Such sliding advancement continues until the antenna device is moved to a position beyond the penetration end and further into direct contact with the tissue. However, a drawback with the existing techniques include the fact that they are not optimally mechanically configured for insertion into, and perforation of, the human skin, for delivery to a zone of soft tissue to be treated. Typically, known radiation applicator systems do not have the heightened physical rigidity that is desirable when employing such techniques.
In addition, some radiation applicators made available heretofore do not have radiation emitting elements for creating a microwave field pattern optimized for the treatment of soft tissue tumors.
Also, given the power levels employed in some applicators and treatments, there can be problems of unwanted burning of non-target, healthy tissue due to the very high temperatures reached by the applicator or the components attached thereto.
Further, although small diameter applicators are known, and liquid cooling techniques have been used, there has been difficulty in designing a small diameter device with sufficient cooling in applications employing power levels required to deal with soft is tissue tumors.
Accordingly, there is a need for methods of treatment of soft tissue tumors, and for radiation applicators that overcome any or all of the aforementioned problems of the prior art techniques, and provide improved efficacy.
Briefly, the present invention is directed to a microwave applicator for ablating tissue. The applicator is a dipole microwave antenna that transmits microwave radiation into the tissue being treated. The applicator is formed from a thin coaxial cable having an inner conductor surrounded by an insulator, which is surrounded by an outer conductor or shield. The end of the coaxial cable is trimmed so that a portion of the insulator and inner conductor extend beyond the outer conductor, and a portion of the inner conductor extends beyond the insulator. The applicator further includes a tubular ferrule defining an aperture therethrough. One end of the ferrule is attached to the outer conductor, while the other end, which forms a sleeve, extends out beyond the end of the insulator and around a portion of the extended inner conductor. A step is preferably formed on the outer surface of the ferrule between its two ends. A solid spacer having a central bore to receive the inner conductor abuts an end of the ferrule and surrounds the extended inner conductor. A tuning element is attached to the end of the extended inner conductor, and abuts an end of the spacer opposite the ferrule. The tuning element faces the step in the ferrule, and the step and the tuning element are both sized and shaped to cooperate in balancing and tuning the applicator. A hollow tip, formed from a dielectric material, has an open end and a closed end. The tip encloses the tuning element, the spacer, and the extended inner conductor. The tip also encloses the sleeve of the ferrule, thus defining outer surface of the ferrule that is surrounded by the dielectric tip. The open end of the tip preferably abuts the step in the ferrule. A rigid sleeve surrounds the coaxial cable and extends away from the ferrule opposite the tip. The sleeve, which abuts the step of the ferrule opposite the tip, has an inner diameter that is larger than the coaxial cable, thereby defining an annular space between the outside of the coaxial cable and the inner surface of the sleeve. The sleeve further includes one or more drainage holes, which permit fluid communication between the annular space around the coaxial cable and the outside of the applicator.
In operation, microwave energy from a source is applied to the coaxial cable, and is conveyed to the tip. The portion of the inner conductor that extends beyond the end of the ferrule forms one arm of the dipole, and emits microwave radiation. In addition, the microwave energy flowing along the inner conductor of the coaxial cable and in the aperture of the ferrule induces a current to flow along the outer surface of the sleeve of the ferrule that is surrounded by the tip. This, in turn, causes microwave radiation to be emitted from the sleeve of the ferrule, which operates as the second arm of the dipole. In this way, microwave energy is emitted along a substantial length of the applicator, rather than being focused solely from the tip. By distributing the emission of microwave radiation along a length of the applicator, higher power levels may be employed.
To keep the coaxial cable and the applicator from overheating, a cooling fluid is introduced from a source into the annular space defined by the outside of the coaxial cable and the inside of the sleeve. The cooling fluid flows along this annular space, and absorbs heat from the coaxial cable. The cooling fluid, after having absorbed heat from the coaxial cable, then exits the annular space through the one or more drainage holes in the sleeve, and perfuses adjacent tissue.
The closed end of the tip is preferably formed into a blade or point so that the microwave applicator may be inserted directly into the tissue being treated. The tip, ferrule, and rigid sleeve, moreover, provide strength and stiffness to the applicator, thereby facilitating its insertion into tissue.
The present invention further provides a method of treating target tissue, such as a tumor, the tumor being formed of, and/or being embedded within, soft tissue. The method includes inserting the microwave applicator into the tumor, and supplying electromagnetic energy to the applicator, thereby radiating electromagnetic energy into the tumor.
Embodiments of the invention will now be described, by way of example, with is reference to the accompanying drawings, in which:
FIGS. 10A-E show a preferred sequential assembly of the radiation applicator of
In the following description, like references are used to denote like elements, and where dimensions are given, they are in millimeters (mm). Further, it will be appreciated by persons skilled in the art that the electronic systems employed, in accordance with the present invention, to generate, deliver and control the application of radiation to parts of the human body may be as described in the art heretofore. In particular, such systems as are described in commonly owned published international patent applications WO95/04385, WO99/56642 and WOOO/49957 may be employed (except with the modifications described hereinafter). Full details of these systems have been omitted from the following for the sake of brevity.
In assembly of the applicator 102, the washer 108 is soldered to a small length 122 of the central conductor 124 of the cable 104 that extends beyond the end 110 of the insulator 126 of the cable 104. The ferrule 106 is soldered to a small cylindrical section 15 128 of the outer conductor 118 of the cable 104. Then, the tube 114, which is preferably stainless steel, but may be made of other suitable materials, such as titanium or any other medical grade material, is glued to the ferrule 106 by means of an adhesive, such as Loctite 638 retaining compound, at the contacting surfaces thereof, indicated at 130 and 132. The tip 112 is also glued preferably, using the same adhesive, on the inner surfaces thereof, to corresponding outer surfaces of the ferrule 106 and the insulation 126.
When assembled, the applicator 102 forms a unitary device that is rigid and stable along its length, which may be of the order of 250 or so millimeters including tube 114, thereby making the applicator 102 suitable for insertion into various types of soft tissue. The space 116 and holes 120 enable cooling fluid to extract heat from the applicator 102 through contact with the ferrule 106, the outer conductor 118 of the cable 104 and the end of the tube 114. The ferrule 106 assists, among other things, in assuring the applicator's rigidity. The exposed end section 134 of cable 104 from which the outer conductor 118 has been removed, in conjunction with the dielectric tip 112, are fed by a source of radiation of predetermined frequency. The exposed end section 134 and dielectric tip 112 operate as a radiating antenna for radiating microwaves into tissue for therapeutic treatment. The applicator 102 operates as a dipole antenna, rather than a monopole device, resulting in an emitted radiation pattern that is highly beneficial for the treatment of certain tissues, such as malignant or tumorous tissue, due to its distributed, spherical directly heated area.
It will be noted that the transverse dimensions of the applicator 102 are relatively small. In particular, the diameter of applicator 102 is preferably less than or equal to about 2.4 mm. The tip 112, moreover, is designed to have dimensions, and be formed of the specified material, so as to perform effective tissue ablation at the operating microwave frequency, which in this case is preferably 2.45 Gigahertz (GHz). The applicator 102 of the present invention is thus well adapted for insertion into, and treatment of, cancerous and/or non-cancerous tissue of the liver, brain, lung, veins, bone, etc.
The end 210 of the tip 112 is formed by conventional grinding techniques performed in the manufacture of the tip 112. The end 210 may be formed as a fine point, such as a needle or pin, or it may be formed with an end blade, like a chisel, i.e. having a transverse dimension of elongation. The latter configuration has the benefit of being well suited to forcing the tip 112 into or through tissue, i.e. to perforate or puncture the surface of tissue, such as skin.
In use, the tip 112 is preferably coated with a non-stick layer such as silicone or paralene, to facilitate movement of the tip 112 relative to tissue.
Further, in an embodiment used in a different manner, the tube 114 may be omitted. In this case the treatment may comprise delivering the applicator to the treatment location, e.g., to the tumorous tissue, by suitable surgical or other techniques. For example, in the case of a brain tumor, the applicator may be left in place inside the tumor, the access wound closed, and a sterile connector left at the skull surface for subsequent connection to the microwave source for follow-up treatment at a later date.
FIGS. 10A-E show a preferred sequential assembly of components forming the radiation applicator 102 of
As shown in
Syringe pump 1110 operates a syringe 1112 for supplying cooling fluid 1114 via conduit 1116 and connector 1118 attached to handle 602, to the interior of the handle section 602. The fluid is not at great pressure, but is pumped so as to provide a flow rate of about 1.5 to 2.0 milliliter(ml)/minute through the pipe 114 in the illustrated embodiment. However, in other embodiments, where the radiation applicator 102 is operated at higher powers, higher flow rates may be employed, so as to provide appropriate cooling. The cooling fluid is preferably saline, although other liquids or gases may be used, such as ethanol. In certain embodiments, a cooling liquid having a secondary, e.g., cytotoxic, effect could be used, enhancing the tumor treatment. In the illustrative embodiment, the cooling fluid 1114 exits the tube 114, as shown by arrows B in
As shown, the cooling system is an open, perfusing cooling system that cools the coaxial cable connected to the radiation applicator 102. That is, after absorbing heat from the coaxial cable, the cooling fluid perfuses the tissue near the radiation applicator 102.
The methodology for use of the radiation applicator 102 of the present invention may be as conventionally employed in the treatment of various soft tissue tumors. In particular, the applicator 102 is inserted into the body, laparoscopically, percutaneously or surgically. It is then moved to the correct position by the user, assisted where necessary by positioning sensors and/or imaging tools, such as ultrasound, so that the tip 112 is embedded in the tissue to be treated. The microwave power is switched on, and the tissue is thus ablated for a predetermined period of time under the control of the user. In most cases, the applicator 102 is stationary during treatment. However, in some instances, e.g., in the treatment veins, the applicator 102 may be moved, such as a gentle sliding motion relative to the target tissue, while the microwave radiation is being applied.
As described above, and as shown in
An alternative embodiment of the present invention is shown in
Applicator 1202 further includes a spacer 1220. The spacer 1220 is preferably cylindrical in shape with a central bore 1222 sized to receive the inner conductor 1210 of the coaxial cable 1204. The outer diameter of the spacer 1220 preferably matches the outer diameter of the third section 1218 of the ferrule 1212. Applicator 1202 also includes a tuning element 1224 and a tip 1226. The tuning element 1224, which be may be disk-shaped, has a central hole 1228 sized to fit around the inner conductor 1210 of the coaxial cable 1204. The tip 1226 is a hollow, elongated member, having an open end 1230, and a closed end 1232. The closed end 1232 may be formed into a cutting element, such as a trocar point or a blade, to cut or pierce tissue. Applicator 1202 also includes a rigid sleeve 1234. The sleeve 1234 has an inner diameter that is slightly larger than outer diameter of the coaxial cable 1204. As described below, an annular space is thereby defined between the outer surface of the coaxial cable 1204 and the inner surface of the sleeve 1234. The sleeve 1234 further includes one or more drainage holes 1236 that extend through the sleeve.
Next, the spacer 1220 is slid over the exposed portion of the inner conductor 1210, and is brought into contact with the second end 1212 b of the ferrule 1212. In the preferred embodiment, the spacer 1220 is not fixedly attached to the ferrule 1212 or the inner conductor 1210. The spacer 1220 is sized so that a small portion 1210 a (
With the tuning element 1224 in place, the next step is to install the tip 1226 as shown in
Those skilled in the art will understand that the applicator 1202 may be assembled in different ways or in different orders.
As illustrated in
Preferably, the sleeve 1234 is formed from stainless steel, and the ferrule 1212 is formed from gold-plated copper. The tip 1226 and the spacer 1220 are formed from dielectric materials. In the illustrative embodiment, the tip 1226 and the spacer 1220 are formed from an itrium stabilized zirconia, such as the Technox brand of ceramic material commercially available from Dynamic Ceramic Ltd. of Stoke-on-Trent, Staffordshire, England, which has a dielectric constant of 25. The tip 1226 may be further provided with a composite coating, such as a polyimide undercoat layer, for adhesion, and a paralyne overcoat layer, for its non-stick properties. Alternatively, silicone or some other suitable material could be used in place of paralyne. The composite coating may also be applied to the ferrule and at least part of the stainless steel sleeve, in addition to being applied to the tip.
Those skilled in the art will understand that alternative materials may be used in the construction of the radiation applicator 1202.
In the preferred embodiment, the holes 1236 are placed far enough behind the closed end 1232 of the tip 1226 such that the discharged cooling fluid does not enter that portion of the tissue that is being heated by the radiation applicator 1202. Instead, the discharged cooling fluid preferably perfuses tissue outside of this heated region. Depending on the tissue to be treated, a suitable distance between the closed end 1232 of the tip 1226 and the holes 1236 may be approximately 30 mm.
A first end 1220 a of the spacer 1220 abuts the second end 1212 b of the ferrule 1212, while a second end 1220 b of the spacer 1220 abuts the tuning element 1224. Accordingly a space, designated generally 1240, is defined within the ferrule 1212 between the end 1208 a of the insulator and the second end 1212 b of the ferrule. In the illustrative embodiment, this space 1240 is filled with air. Those skilled in the art will understand that the space may be filled with other materials, such as a solid dielectric, or it may be evacuated to form a vacuum. The inside surface of the tip 1226 preferably conforms to the shape of the tuning element 1224, the spacer 1220, and the third section 1218 of the ferrule 1212 so that there are no gaps formed along the inside surface of the tip 1226.
As indicated above, operation of the radiation applicator 1202 causes a current to be induced on the outer surface of the third section 1218 of the ferrule 1212, which is enclosed within the dielectric material of the tip 1226. This induced current results in microwave energy being radiated from this surface of the ferrule 1212, thereby forming one arm of the dipole. The section of the inner conductor 1210 that extends beyond the ferrule 1212 is the other arm of the dipole. Both the length of the inner conductor 1210 that extends beyond the ferrule 1212, and the length of the third section 1218 of the ferrule 1212, which together correspond to the two arms of the dipole, are chosen to be approximately ¼ of the wavelength in the dielectric tip 1226, which in the illustrative embodiment is approximately 6 mm. Nonetheless, those skilled in the art will understand that other factors, such as tissue permittivity, the action of the tuning element, etc., will affect the ultimate lengths of the dipole arms. For example, in the illustrative embodiment, the two arms are approximately 5 mm in length.
The tuning element 1224, moreover, cooperates with the second section or step is 1216 of the ferrule to balance the radiation being emitted by the two arms of the dipole.
In particular, the size and shape of the tuning element 1224 and the step 1216 are selected such that the coherent sum of the microwave power reflected back toward the cable at the aperture of the ferrule is minimized. Techniques for performing such design optimizations are well-known to those skilled in the relevant art.
In use, the radiation applicator 1202 is attached to a source of microwave radiation in a similar manner as described above in connection with the applicator 102 of
The foregoing has been a detailed description of illustrative embodiments of the invention. Various modifications and additions can be made without departing from the spirit and scope thereof. For example, the materials described herein are not exhaustive, and any acceptable material can be employed for any component of the described system and method. In addition, modifications can be made to the shape of various components. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of the invention.