MICROWAVE ANTENNA SYSTEM FOR INTRACAVITARY INSERTION

Abstract: A microwave antenna system for intracavitary insertion for inducing hyperthermia by microwave irradiation is provided for cancer treatment and the like. An elongated antenna (11) is adapted to laterally propagate a generally uniform field of microwaves of a wavelength of85 to 120cm. A dielectric jacket (22) surrounds the antenna having a closed outer end (24), but open at its inner end (26). The jacket is equipped with air circulation conduits (30, 32) to cool the tissue in the immediate vicinity of the jacket.

Description: MICROWAVE ANTENNA SYSTEM FOR INTRACAVITARY INSERTION TECHNICAL FIELD Microwave treatment of cancer is currently in clinical trial. The microwaves, which are believed by many to be less harmful than X-rays and gamma rays, heat the tissue upon ir¬ radiation. Malignant tumors often turn out to be more sen¬ sitive to heat than normal tissue, so that upon prolonged heating by microwave irradiation, the tumors can be destroyed while the normal tissue is unharmed. In the article by Petrowicz et al. entitled "Experi¬ mental Studies on the Use of Microwaves for the Localized Heat Treatment of the Prostrate: J. Microwave Power 14(2) : 167-171 (1979) a newly developed microwave applicator emit- ting microwaves at 433.9 MHz was tested on 15 dogs. The ap¬ plicator was inserted rectally, followed by 15 to 20 minutes of irradiation of the prostrate. It is, however, reported that unwanted tissue damage did occur, presumably through burning which was aggravated by the fact that microwaves of 400 MHz and higher have relatively limited capability to penetrate tissue. For example, microwaves at 433 MHz can penetrate tissue for effective heating about 4 cm. To the contrary, in accordance with ' this invention, penetrations of 5 to 6 cm. , a 25 to 50 percent increase in depth, can be achieved. Furthermore, the burning of adjacent tissues to the electrode is a common problem with microwave therapy which must particularly be carefully guarded against when a micro¬ wave antenna is inserted into a body cavity, since it may not be easy to determine whether the interior of the body cavity has been burned until after the fact. In accordance with this invention, an intracavitary microwave applicator is provided having improved tissue pen- ' etration due to the use of an optimal lower frequency and longer wavelength so that, as stated before, 5 to 6 cm. of penetration may be obtained. This permits the extensive irradiation of large tumors of the bowel and the like, so that the entire tumor area can be irradiated. For example the bowel, esophagus, or surgically-created, temporary bod apertures may be entered by the antenna of this invention , and irradiated. Furthermore, the microwave antenn .system of this in vention provides an improved cooling system for prevention of burning, which is critical to avoid in unseen, interior portions of the body. DISCLOSURE OF THE INVENTION In accordance with this invention,- a microwave anten system is provided, being adapted for • intracavitary' insert for inducing hyperthermia by microwave irradiation for can treatment. The antenna system comprises an elongated ante adapted to laterally propagate a generally uniform field o microwaves of a wavelength of 85 to 120 cm. A preferably flexible dielectric jacket surrounds the antenna, with the jacket having an* enclosed outer end, but open at its inner end. A plurality of air flow conduits pass through the in end of the jacket and terminate within the jacket at diffe ent distances from the outer end. As the result of this, air entering the flow conduits is released within differen portions of the jacket interior, which may preferably cor- respond to the "hot spots" of the microwave antenna system for optimum cooling. The released air then exits the jack from the inner end. It is also preferable for electronic temperature mea suring means to be positioned on the jacket, with lead wires extending from the electronic temperature measuring means through the inner end of the jacket to connection wi temperature readout means. It is also desirable for impedance matching means to be provided in electrical connection with the antenna to permit matching the impedance of surrounding tissue volume when the antenna system is inserted into a body cavity. Preferably, the microwave antenna system of this in¬ vention is operated at essentially a 100 cm. wavelength. The use of the specified wavelengths of microwaves propagated in accordance with this invention provides not only improved effective penetration of the'microwaves through tissue, so that large areas may be irradiated, but also the size of the antenna capable of effectively propagating such microwaves is substantially reduced from the corresponding sizes of the antennas of the prior art utilized for propa- gating microwaves of lower frequency. This is an obvious significant advantage for an antenna which is intended to be inserted into body cavities. It is preferred for the microwave antenna system of this invention to include a coaxial cable antenna defining an inner conductor and outer cylindrical conductor. The outer con¬ ductor is folded rearwardly beginning at a point from 10 to 16 centimeters from the end of the antenna and extending from such a point in the direction away from the end of the an¬ tenna by a distance essentially, equal to the.spacing of the point from the end of the antenna. The antenna is adapted to radiate microwaves of a wave¬ length of 85 to 120 centimeters, with the microwave antenna system being enclosed in the jacket as described above. Such an antenna structure provides relatively uniform lateral emission of microwaves with the suppression of "hot spots" _ in_. he-pattern of microwave emission. Also, as can be seen, the size of the antenna is not excessive, which is an ad¬ vantageous feature, coupled with the improved penetrability of microwaves of the wavelength specified above, so that an antenna which is both insertable into a body orifice, coup¬ led with an antenna that radiates microwaves having the de¬ sirable 5 to 6 centimeters of tissue penetration, is pro¬ vided. Additionally, the cooling system of this invention preferably includes the pair of air conduits, one of which extends through the sleeve to the forward end of the anten¬ na, and the other of which extends to said point of folding of the outer conductor, which is a point of particularly strong microwave emission.. Thus a special and selected pattern of air flow, is provided to counteract excessive h ing of the antenna in an optimal way. Preferably, the wavelength of the microwaves radiat is from 90 to 110 centimeters and specifically 100 centi¬ meters. When the wavelength emitted is essentially 100 ce timeters, it is preferable for the distance of said point folding to the end of the antenna to be essentially 12.5 c timeters, with the length of said folded portion of the o cylindrical conductor being also 12.5 centimeters, a total of 1/4 wavelength. It may also be desirable fo ■ a detuning sleeve to be carried by the cylindrical outer conductor, the detuning sleeve being connected to the cylindrical conductor at a position of the outer conductor. Furthermore, it is prefe red for a gap of 2 to 3 centimeters to be present between the folded portion of the outer cylindrical conductor and the detuning sleeve, with the detuning sleeve extending toward the outer end of the antenna from its point of con¬ tact with the outer cylindrical conductor. Additionally, it is preferred for the temperature se ing means to have connected lead wires that pass through a inner tubular conduit means. This tubular conduit means m in turn reside in a dielectric tube that is carried by the sleeve and communicates with the interior of said sleeve through an aperture thereof. When desired, the inner tubular conduits containing the lead wire and the temperature sensing means may be re- moved from the dielectric sleeve when desired for maintena and the like, and also may be placed into the dielectric sleeve as desired for use, with the electronic temperature sensing means being positioned generally in the aperture o the sleeve. Typically, the electronic temperature sensing means a microthermocouple. O BRIEF DESCRIPTION OF DRAWINGS In the drawings, Figure 1 is a longitudinal sectional view of one embodiment of the .microwave antenna system of this invention, shown partly schematically, .and with portions broken away. Figure 2 is another embodiment of the microwave an¬ tenna system of this invention, also shown partly schema¬ tically.. Figure 3 is a detailed, enlarged sectional view of the dielectric sleeve and related parts. DESCRIPTION OF SPECIFIC EMBODIMENT Referring to Figure 1, the microwave antenna system of this invention is adapted for insertion into a body cavity such as the colon for inducing hyperthermia by microwave ' irradiation for cancer treatment. Coaxial cable 10 termin¬ ates in an antenna 11 with its outer tubular conductor 12 being folded back at point 14 to define a folded-back section 16, while central conductor 18 extends outwardly. The length ' of the exposed end 19 of central conductor 18 from its end 20 to point of folding 14 is equal to the length of the folded portion 16, for providing optimum irradiation charac¬ teristics. It is also preferable for the distance between end 20 and point 14, as well as the length of folded portion 16, to each equal one-eight of the length of the wavelength intended for use. Specifically, when a wavelength of " IOTP " centimeters is used, it is preferable for the above two re¬ spective distances to each be 12-1/2 centimeters. Coaxial cable 10 and the antenna portion are surrounded by a dielectric jacket 22, which is closed at its forward end 24 and typically open at its rear end 26. Apertures 28 may be formed in jacket 22, particularly when the antenna system is intended for shallow penetration into a body aper¬ ture, for example in the mouth and upper throat. Typically when the antenna system is intended for deep penetration into the bowel or the like apertures 28 are not used. A plurality of air flow conduits 30, 32 are p passing through inner end 26 of the jacket 22, and termina ting within the jacket at different distances from outer e 24. As specifically shown, one air flow conduit 30 termin ates adjacent to point 14, while the other conduit 32 ter- minates adjacent to end 20 of the antenna. Alternatively, conduit 32, or a third conduit if desired, may terminate a the rear end 34 of folded portion 16 of outer cylindrical antenna number 12. Accordingly, as air passes through con duits 30, 32, jacket 22 is continuously cooled by the acti of the flowing air, with the air flowing from the respecti conduits 30, 32 into the interior of jacket 22 and then ou rear end 26 of the jacket. The presence of conduit 30 ad¬ jacent to point 14 provides added cooling to. the "hot spot which may be generated during microwave Irradiation from t area of the antenna. As a result of this, the tissue within which jacket resides during operation remains cooled by the presence of the continuously cooled jacket, so that burning of the tis sues adjacent the jacket may be avoided. Additionally, the electronic temperature measuringme 36, typically microthermocouples, are positioned on jacket Lead wires 38 extend through inner conduits 40 made of a d electric material, so that microthermocouple 36, lead wire 38, and inner conduits 40 comprise a discrete unit. Outer conduits 42, which may be made of Teflon or the like, are attached at their ends as shown' to jacket 22 and surroundi an aperture 44 in the jacket. Thus the thermocouple 36 ma be threaded into outer conduit 42 and positioned at its de sired place. However, when maintenance or replacement is needed, the thermocouple, inner conduit, and lead wire may be removed as a unit and/or replaced with another unit. • As shown, outer conduit 42 can be threaded through various apertures 46 in jacket 22 for firm retention there Lead wires 38 may then continue to a conventional temperature readout device for the microthermocouple 36, s that the temperatures of the various microthermocouples ma be continuously monitored. O I The above structure provides a convenient system for temperature monitoring of the device of this invention in which the lead wires are protected by the Teflon outer con¬ duits 42, and yet the thermocouples and lead wires may be removed by maintenance or replacement as is required. Also, the latter structure may be preserved for future use, while jacket 22 and the enclosed antenna may be utilized ' only with respect to one patient and then disposed of. Impedance matching means is provided in the form of a tuning stub 48, in communication with coaxial cable 10, to permit matching the impedance of surroundin 'tissue volume when the antenna system is inserted into a body cavity. The embodiment of Figure 2 is similar to that of Fig¬ ure 1, including coaxial cable 10, jacket 22, and the folded antenna portion of the outer sleeve 16a plus the projecting inner antenna portion of identical design to that of the previous embodiment. Air tubes 30a and 32a are also provided to be of equivalent function to the corresponding air tubes of the previous embodiment, along with the related structure which is also of analogous design. The same microwave fre¬ quencies may be used. In this embodiment, jacket 22a is shown to be without perforations and thermocouples, although such'may be used if desired, as previously ^ Also, in accordance with this invention a detuning sleeve " member 50 is provided, it being connected to outer tubular conductor 12a and extending toward folded portion 16a, being preferably of identical length to folded portion 16a. It is preferred for the space 52 between detuning sleeve 50 and the folded tubular portions 16a to be from 2 to 3 centimeters to avoid causing the detuning sleeve to emit radiation. The function of the detuning sleeve 50 is primarily to block rear leakage of radiation, so that the radiation is concentrated in the desired areas. Accordingly, a microwave antenna system is provided which yields the combined advantages of increased tissue penetration, coupled with improved means for eliminating burning of adjacent tissues, and further coupled with an a tenna of manageable size so that it can be effectively use for insertion into the body orifice of a patient. Antenna of lower wavelength and higher frequency exhibit substan¬ tially less penetration of tissue, which is undesirable in many circumstances. Antennas of longer wavelength do not exhibit great improvement in tissue penetrability, and at the same time such antennas must generally be larger and t quite difficult to effectively use clinically for the pene tration of body orifices. Furthermore, a higher percentage of radiation of the particular frequency utilized in this invention is absorbe by the tumor- tissues, relative to that absorbed in healthy tissues, than at the higher frequencies which have been mo ■ commonly used in tumor therapy. Furthermore, an optimum structure for cooling and fo temperature measuring is provided as well as means for re¬ ducing unwanted rearwardly emitted radiation. The above has been > offered for illustrative purposes only, and is not intended to limit the invention of this a plication, which is as defined in the claims below. OM

Claims: THAT WHICH IS CLAIMED IS: 1. A microwave antenna system adapted for intracavi- tary insertion for inducing hyperthermia by microwave irra¬ diation for cancer treatment, which comprises: an elongated antenna, adapted to laterally propagate a generally uniform field of microwaves of a wavelength of 85 to 120 cm. , a dielectric jacket surrounding said antenna, said jacket having a closed outer end but open at its inner end; a plurality of air flow conduits passing through the inner end of the jacket and terminating within said jacket at different distances from said outer end, whereby air en¬ tering said flow conduits is released within different por¬ tions of said jacket interior and then exits said jacket from the inner end. 2. The microwave antenna system of Claim 1 in which electronic temperature measuring means are positioned on said jacket, and lead wires extending from said electronic tem¬ perature measuring means to connection with temperature readout means. 3. The microwave antenna system of Claim 2 in which impedance matching means is provided in electrical connec¬ tion with said antenna to permit matching the impedance of surrounding tissue volume when said antenna system is in- serted into a body cavity. 4. The microwave antenna system of Claim 3 in which said wavelength is essentially 100 cm. 5. A microwave antenna system adapted for intracavi- tary insertion for inducing hyperthermia by microwave irra- diation for cancer treatment, which comprises: a coaxial cable antenna defining an inner conductor and an outer, cylindrical conductor, said outer conductor being folded rearwardly beginning at a point from 10 to 16 cm. from the end of said antenna and extending from said point in the direction away from said end by a distance es sentially equal to the spacing of said point from the end said antenna, said antenna being adapted to radiate micro¬ waves of a wavelength of 85 to 120 cm. , said microwave an¬ tenna system being enclosed in a jacket surrounding said a tenna and having a closed outer end. 6. The microwave antenna system of Claim 5 in which the wavelength emitted is' essentially 100 cm:, and the distance of said point of folding to the end of said anten is essentially 12.5 cm. 7. The microwave antenna system of Claim 6 in which said wavelength emitted is essentially 90 to 110 cm. - 8. The- icrowave antenna system of Claim 5 in which said jacket is perforated. 9. A microwave antenna system adapted for intracavi tary insertion for inducing hyperthermia by microwave irra diation for cancer treatment, which comprises: an elongated coaxial cable antenna defining an inner conductor and outer cylindrical conductor, said outer con¬ ductor being folded rearwardly beginning at a point from 1 to 16 centimeters from the end of said antenna and extendi from said point in the direction away from said end by and essentially equal to the spacing of said point from the en of said antenna, said antenna being adapted to radiate mi¬ crowaves of a wavelength of 85 to 120 centimeters, said mi¬ crowave antenna system being enclosed in a jacket surround¬ ing said antenna and having a closed outer end, and a pair of air tubes passing into said outer jacket from the inner end thereof with one of said air tubes terminating at the end of said coaxial cable, antenna, the other of said air tubes terminating at said point, whereby air entering said flow conduits is released within different portions of said jacket interior and then exits said jacket from the inner end. 10. The microwave antenna system of Claim 9 in which electronic temperature measuring means are positioned on said jacket, and lead wires extending from said electronic temperature measuring means to connection with temperature "readout means. 11. The microwave antenna system of Claim 10 in which said wavelength emitted is essentially 90 to 110 cm. 12. The microwave antenna system adapted for intra- cavitary insertion for inducing hyperthermia by microwave irradiation for cancer treatment, which comprises: an elongated antenna, adapted to laterally propagate a generally uniform field of microwaves, a dielectric jacket surrounding said antenna having a closed outer end and an open inner end, an electronic temperature measuring means positioned on said jacket, dielectric tubes extending from said electronic temperature measuring means rearwardly of said jacket, an inner tubular member inserted within each of said dielectric tubes, said inner tubular members enclos¬ ing lead, wires and communicating between said electronic temperature measuring means at one end and temperature read¬ out means at their other ends, whereby said inner tubular means, lead wires, and electronic temperature measuring means may be installed and removed through said dielectric tubes. 13. The microwave antenna system of Claim 12 which includes an air flow conduit means passing through " the inner end of the jacket and terminating within said jacket, where¬ by air entering said flow conduits is released in said ja¬ cket interior and then exits said jacket from the inner end. 14. The microwave antenna system of Claim 13 in wh a plurality of air flow conduits pass through the end of jacket and terminate within said jacket at different dis¬ tances from said outer end,' whereby air entering said air flow conduits is released within different portions of sa jacket interior and then exits said jacket from the inner end. 15. The microwave antenna system adapted for. intra cavitary insertion by inducing hyperthermia by microwave Irradiation for cancer treatment, which comprises: a coaxial cable antenna defining an inner conductor and an outer cylindrical conductor, said outer conductor being folded rearwardly beginning at a point from 10 to 1 centimeters from the end of said antenna and extending fr said point in the direction away from said end by a dista essentially equal to the spacing of said point from the e of said antenna, said antenna being adapted to radiate mi crowaves of a wavelength of 85 to 120 centimeters, said m crowave antenna system being enclosed in a jacket surroun ing said antenna and having a closed outer end, said ante also carrying detuning sleeve means communicating with sa outer conductor at a point spaced farther away from said end than the folded outer conductor, said detuning sleeve means defining a portion extending toward said folded out conductors, but spaced at least 2 centimeters therefrom, whereby rearward leakage of microwave radiation is suppres ed. 16. The microwave antenna system of Claim 15 in wh said detuning sleeve means is spaced no more than 3 centi- meters from the folded antenna. . 17. The microwave antenna system of Claim 16 in wh a plurality of air flow conduits pass through the inner e of the jacket and terminate within said jacket at differe distances from said outer end, whereby air entering said " Ϊ3 ~ flow conduits is released in different portions of said ja¬ cket interior and then exits said jacket from the inner end. 18. The microwave antenna system of Claim 17 in which- electronic temperature measuring means are positioned on said jacket, and lead wires extend from said electronic tem¬ perature measuring means to connection with temperature read¬ out means. 19. Microwave apparatus useful for treating cancer with heat, comprising: , a source of microwave radiation; a hollow member and conductor means delivering said microwave radiation to said hollow member to generate heat; and a source of air and means for delivering said air to said hollow member to control the external jacket tempera¬ ture. 20. Microwave apparatus as defined in Claim 19, in- . eluding thermocouple means mounted on the hollow member for indicating the external temperature thereof. 21. Microwave apparatus as defined in Claim 19 in which the hollow member comprises an elongated flexible . jacket having an open end and a closed end, and including means for delivering said cooling fluid into selected posi¬ tions in said jacket so that the fluid is discharged through the open end from the jacket.

Inventors: BICHER J, HETZEL F, SANDHU T
Applicants: BICHER J, HETZEL F, SANDHU T
Application year: 1981
Main classification: A61N5
IPC codes: A61B17, A61B18