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Radiation applicator and method of radiating tissue

Radiation applicator and method of radiating tissue description/claims

The present application is related to commonly owned copending International patent application no. WO 2006/002943, concerning a Radiation Applicator and Method of Radiating Tissue and which is hereby incorporated by reference in its entirety.

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 microwaves, 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 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.

In accordance with one aspect of the present invention, there is provided 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 extending section of the inner conductor operate as corresponding arms of the dipole microwave applicator.

Particular embodiments are set out in the dependent claims.

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.

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