CA1324414C - Electrostatic deep heating applicators - Google Patents
Electrostatic deep heating applicatorsInfo
- Publication number
- CA1324414C CA1324414C CA000575146A CA575146A CA1324414C CA 1324414 C CA1324414 C CA 1324414C CA 000575146 A CA000575146 A CA 000575146A CA 575146 A CA575146 A CA 575146A CA 1324414 C CA1324414 C CA 1324414C
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- applicator
- tissue
- energy
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- resonant
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
- A61N1/00—Electrotherapy; Circuits therefor
- A61N1/40—Applying electric fields by inductive or capacitive coupling ; Applying radio-frequency signals
- A61N1/403—Applying electric fields by inductive or capacitive coupling ; Applying radio-frequency signals for thermotherapy, e.g. hyperthermia
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- Health & Medical Sciences (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
- Radiology & Medical Imaging (AREA)
- Life Sciences & Earth Sciences (AREA)
- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
- Veterinary Medicine (AREA)
- Thermotherapy And Cooling Therapy Devices (AREA)
- Electrotherapy Devices (AREA)
Abstract
ELECTROSTATIC DEEP HEATING APPLICATOR
ABSTRACT
An electrostatic deep heating applicator deposits RF energy in a relatively uniform manner throughout a given cross-section of the human torso, thus resulting in a similar uniform heating of the region. The applicator uses a pair of identical, rectangular (70), flat (82) or cylindrical applicators which generate a heat-producing electric field predominantly parallel to the major axis of the body (74) so as to minimize excessive surface heating. The applicator finds particular use in the treatment of deep seated cancers in patients. It need only be placed near the torso for satisfactory operation, thus allowing a relatively large air gap between it and the patient. It requires very minimum set-up time, is convenient to use and is non-threatening to the patient.
ABSTRACT
An electrostatic deep heating applicator deposits RF energy in a relatively uniform manner throughout a given cross-section of the human torso, thus resulting in a similar uniform heating of the region. The applicator uses a pair of identical, rectangular (70), flat (82) or cylindrical applicators which generate a heat-producing electric field predominantly parallel to the major axis of the body (74) so as to minimize excessive surface heating. The applicator finds particular use in the treatment of deep seated cancers in patients. It need only be placed near the torso for satisfactory operation, thus allowing a relatively large air gap between it and the patient. It requires very minimum set-up time, is convenient to use and is non-threatening to the patient.
Description
EL~CTROSTATIC DEEP H~ATING APPLICATORS
Field of t~e Invention The present inventlon relates generally to hyperthermia treat~ent of tu~ors and specifically to the selective and unifor~
deposit~ng of RF energy during such treatment Bac~oround of t~e Invention Heating of cancerous tu~ors is now recognized as a valuable ad~unct to the long established ~reat~ent with c~emot~erapy or radiot~erapy because the treatment effectivity is often enhanced when hyperther~ia is lncluded as part of the protocol It ls thus desira~le to elevate t~e tumor temperature as ~uc~ a~ pos~ible ~ithout causing in~ury to healt~y tissue during the hyperthermia treatment ~ `~
Effective heating of a tu~or deep withln the body ~ay at 8 to 10 c~ depth, ~as been a goal of many appllcator deslgners Thi~ l~ very dlfficult to ac~leve, however, and i~ always limited by the allo~able temperature elevatlon of healthy tissue at lesser `~
depth~ a~ well a~ at the muscle-fat interface or at the surface lt~
A prlor art hyperthermla ~ystem used to heat tumors in t~e tor~o of the body co~prlse~ an RF power ~ource coupled via a ~atchlng networ~ and a tran~mi~sion llne to an appllcator, and then to the tor~o of the patlont The RF power sourco typlcally would provlde ~00 to ~000 watts ~hermometry egulp~ent ls connected to the patlent to monltor temperature at various locatlon- via fiber-optlc probes Thls thermal infor~atlon can .,', . ':
~` ~ .. ,:
~ ... ~.
1 32 4 ~ i 4 62196-514 also be used to control the amplitude of the RF power source throug~ a feed back loop if desired.
Various applicators have been successfully devlsed to heat tumors. However, heating has ~ost cons~stently been ac~eved in surface or near surface tu~or t~erapy w~ere the overlying tissue ~s not a basic llmitation. The desi~n of applicators for thi~ type of therapy are relatively straightforward and often operate at ~icrouave frequen~ies where some focuslng can be achie~ed. Other applicators that are ~ore specifically designed for deep heating have also bean developed. These devices qenerally operate ln the lower HF or VHF frequencies where greater depth of penetratlon is possible. Several relevant devices of thls type are d~cussed in the literature.
They are~
1. ~Deep Heating Electrode~, Harri~on, U.S. Patent No.
~,325,~61, Aprll 20, 1982:
Field of t~e Invention The present inventlon relates generally to hyperthermia treat~ent of tu~ors and specifically to the selective and unifor~
deposit~ng of RF energy during such treatment Bac~oround of t~e Invention Heating of cancerous tu~ors is now recognized as a valuable ad~unct to the long established ~reat~ent with c~emot~erapy or radiot~erapy because the treatment effectivity is often enhanced when hyperther~ia is lncluded as part of the protocol It ls thus desira~le to elevate t~e tumor temperature as ~uc~ a~ pos~ible ~ithout causing in~ury to healt~y tissue during the hyperthermia treatment ~ `~
Effective heating of a tu~or deep withln the body ~ay at 8 to 10 c~ depth, ~as been a goal of many appllcator deslgners Thi~ l~ very dlfficult to ac~leve, however, and i~ always limited by the allo~able temperature elevatlon of healthy tissue at lesser `~
depth~ a~ well a~ at the muscle-fat interface or at the surface lt~
A prlor art hyperthermla ~ystem used to heat tumors in t~e tor~o of the body co~prlse~ an RF power ~ource coupled via a ~atchlng networ~ and a tran~mi~sion llne to an appllcator, and then to the tor~o of the patlont The RF power sourco typlcally would provlde ~00 to ~000 watts ~hermometry egulp~ent ls connected to the patlent to monltor temperature at various locatlon- via fiber-optlc probes Thls thermal infor~atlon can .,', . ':
~` ~ .. ,:
~ ... ~.
1 32 4 ~ i 4 62196-514 also be used to control the amplitude of the RF power source throug~ a feed back loop if desired.
Various applicators have been successfully devlsed to heat tumors. However, heating has ~ost cons~stently been ac~eved in surface or near surface tu~or t~erapy w~ere the overlying tissue ~s not a basic llmitation. The desi~n of applicators for thi~ type of therapy are relatively straightforward and often operate at ~icrouave frequen~ies where some focuslng can be achie~ed. Other applicators that are ~ore specifically designed for deep heating have also bean developed. These devices qenerally operate ln the lower HF or VHF frequencies where greater depth of penetratlon is possible. Several relevant devices of thls type are d~cussed in the literature.
They are~
1. ~Deep Heating Electrode~, Harri~on, U.S. Patent No.
~,325,~61, Aprll 20, 1982:
2. ~Focused Blectrouagnetlc Heatlng of Nuscle Tissue~ EE
tran~. NTT-32, ~8, August, 198~, pages 887-888~
tran~. NTT-32, ~8, August, 198~, pages 887-888~
3. ~Annular Phased Array~, IEEE Tran~. BME-31, pages 1-6-106~ , January, 198~
~. ~A T~ree-Dluenslonal Model For The Coaxlal TEH Deep-Body Nypertheruia Applicator,~ Int.J.Hyperther~ia, 1986, Vol. 2, No. 3, pages 2-3-252~ and 5. ~A Ne~ Coaxlal TBN Radlofreguency/Mlcrowave Applicator For Non-Invasive Deep-Body Hyperther~ia, ~ Journal of Hicrowave Po~or, 1983, 18, pages 367-375.
; :,''"
. .
: .
132~
62196-51~
6. "Capacitor Electrodes for Shortwave Dlather~y", Hyperther~la in Cancer Therapy, G.K. Hall Medical Publisbers, pp 284-287 . ;
7. "co~parison o$ Deep-Heating Electrode Concepts for Hyperthermia~, J. Nicrowave Power 1985, pp 1-8.
8. ~Resonant Ridged Naveguide Structure Operating at 27HHz. n U.S. Patent ~4,282,887.
These devices are capable of penetratinq the subcutaneous layers and heatlng imbedded tu~or tissue without serlous surface overheating. However, each has lts limltations. `
1. The patent entitled ~Deep Heating Electrode, n U~ S
Patent No. ~,186,729, conslsts of a single turn, resonant, non-contactlng cylinder that surrounds the body and does not reguire bolus ~ater baqs~ bet~een the electrode and the patient. The conducting ~heet for~s the inductor and the overlapplng sheets for~ the capacltor requlred to resonate the clrcuit. The devlce typlcally operates on the lo~er ISH frequencles, l.e., 13.56, 2~.12 or ~0.68 NHz. N~en ~ed fron an RF power ~ource, the re~ulting lnduced concentrlc electrlc field llne~ are parallel to the body ~urface and energy depo~ition ln the deep ~uscle tlssue ls not dependent upon electrlc field line~ that ~u~t pass through the fat~ln layer. Clinlcal experlence ~lth over lOOO patients ~bo~s that exce~lve ~urface heatlng l~ ~pared and deep heatlng ls often achleved.
Ho~over, tbe concentrlc electric field strength is . .
proportlonal to the radiu~, thus heatlng is al~o dependent upon the relatlve radlal locatlon. Calculatlons and experience have ''.~', '`' ' ' .
shown that the half-power depth of penetratlon ls typloally 6 to 7 cm below the surface of the torso with a patlent havlng a 1 to 2 c~ fat layer.
2. T~e paper ~Focused ElectroDagnetic Heating of Muscle Tlssue HTT-32~ describes an applicator that conslsts of two identical ~etallic cylinders spaced from one another and placed concentrically over a cylindrical phantom s~mulatin~ muscle tigsue to be heated~ A very thin 2 ~ insulator i5 placed between the phanton and the netallic cyllnders. The cylinder diameterr phanton dl~ensions and frequency of operation are chosen to obtain constructive lnterference ln the central region of the l~mb~phantom to be heated. For the case cited in this paper thls approao~ requlre~ an RF po~er source operating at a freguency of 150 NHz.
The concept 18 acceptable when worklng wlth an e~perlmental unlfor~ cyllndrlcal phanto~. However the approach has seriou~ itatlons ~ben dealing ~lth the shape irregularities of a bu~an torso ~here tbe requlred mlnlmum ~paclng to the body cannot be ~alntalned and tnls compro-l~es the necessary radlal pha~e relatlon~blp~ As dlscussed thereln a lO cu dia~eter pbanto- ~as u~ed ~ith ~ust 2 ~ ~paclng between the phantom and the oyllndrical netallio shells l.e. a very preclse spaclng not aohle~able ln a cllnlcal envlronment.
3. Tbe de~lce ln the paper ~Annular Phased Array " conslst~
of a group of as many as 16 dlpole element~ that are radlally spaoed around the patlent ~ tor~o and fed ln phase from a common .:
:,, 132~14 RF source. To obtain sufficlent RF coupllng to the body, .
distilled water bags are placed between the dipoles and the patient. This allows the dipole elements to function in a medium having a dielectric constant similar to muscle tissue (approximately 78), thus enhancing the coupllng and mlnlmlzing the discontinuity between the dipole eleDents and the body surface~
By carefully filling all the voids between ' ~"
'' .
'.:' '"' . ''' ~a ''.
132~ 66-49 the dipole elements and the patient with water bags, efficient RF energy transfer and heating can be achieved at depth From a human usaga point of view, this device also has serious limitations It is very difficult to achieve uni~orm filling of the voids around the patient with wa~er bags Variable fat thickness, with its lower dielectric constant, also creates additional discontinuities When these variations occur, localized lo hot spots will exist that can cause injury or limit the extent of energy input possible without localized thermal damage It is also very time consuming to propQrly position the watQr bags and check for localized heating beforQ treatment begins, thus contribu~ing to patient fatigue and degraded treatment tolerancQ
~. ~A T~ree-Dluenslonal Model For The Coaxlal TEH Deep-Body Nypertheruia Applicator,~ Int.J.Hyperther~ia, 1986, Vol. 2, No. 3, pages 2-3-252~ and 5. ~A Ne~ Coaxlal TBN Radlofreguency/Mlcrowave Applicator For Non-Invasive Deep-Body Hyperther~ia, ~ Journal of Hicrowave Po~or, 1983, 18, pages 367-375.
; :,''"
. .
: .
132~
62196-51~
6. "Capacitor Electrodes for Shortwave Dlather~y", Hyperther~la in Cancer Therapy, G.K. Hall Medical Publisbers, pp 284-287 . ;
7. "co~parison o$ Deep-Heating Electrode Concepts for Hyperthermia~, J. Nicrowave Power 1985, pp 1-8.
8. ~Resonant Ridged Naveguide Structure Operating at 27HHz. n U.S. Patent ~4,282,887.
These devices are capable of penetratinq the subcutaneous layers and heatlng imbedded tu~or tissue without serlous surface overheating. However, each has lts limltations. `
1. The patent entitled ~Deep Heating Electrode, n U~ S
Patent No. ~,186,729, conslsts of a single turn, resonant, non-contactlng cylinder that surrounds the body and does not reguire bolus ~ater baqs~ bet~een the electrode and the patient. The conducting ~heet for~s the inductor and the overlapplng sheets for~ the capacltor requlred to resonate the clrcuit. The devlce typlcally operates on the lo~er ISH frequencles, l.e., 13.56, 2~.12 or ~0.68 NHz. N~en ~ed fron an RF power ~ource, the re~ulting lnduced concentrlc electrlc field llne~ are parallel to the body ~urface and energy depo~ition ln the deep ~uscle tlssue ls not dependent upon electrlc field line~ that ~u~t pass through the fat~ln layer. Clinlcal experlence ~lth over lOOO patients ~bo~s that exce~lve ~urface heatlng l~ ~pared and deep heatlng ls often achleved.
Ho~over, tbe concentrlc electric field strength is . .
proportlonal to the radiu~, thus heatlng is al~o dependent upon the relatlve radlal locatlon. Calculatlons and experience have ''.~', '`' ' ' .
shown that the half-power depth of penetratlon ls typloally 6 to 7 cm below the surface of the torso with a patlent havlng a 1 to 2 c~ fat layer.
2. T~e paper ~Focused ElectroDagnetic Heating of Muscle Tlssue HTT-32~ describes an applicator that conslsts of two identical ~etallic cylinders spaced from one another and placed concentrically over a cylindrical phantom s~mulatin~ muscle tigsue to be heated~ A very thin 2 ~ insulator i5 placed between the phanton and the netallic cyllnders. The cylinder diameterr phanton dl~ensions and frequency of operation are chosen to obtain constructive lnterference ln the central region of the l~mb~phantom to be heated. For the case cited in this paper thls approao~ requlre~ an RF po~er source operating at a freguency of 150 NHz.
The concept 18 acceptable when worklng wlth an e~perlmental unlfor~ cyllndrlcal phanto~. However the approach has seriou~ itatlons ~ben dealing ~lth the shape irregularities of a bu~an torso ~here tbe requlred mlnlmum ~paclng to the body cannot be ~alntalned and tnls compro-l~es the necessary radlal pha~e relatlon~blp~ As dlscussed thereln a lO cu dia~eter pbanto- ~as u~ed ~ith ~ust 2 ~ ~paclng between the phantom and the oyllndrical netallio shells l.e. a very preclse spaclng not aohle~able ln a cllnlcal envlronment.
3. Tbe de~lce ln the paper ~Annular Phased Array " conslst~
of a group of as many as 16 dlpole element~ that are radlally spaoed around the patlent ~ tor~o and fed ln phase from a common .:
:,, 132~14 RF source. To obtain sufficlent RF coupllng to the body, .
distilled water bags are placed between the dipoles and the patient. This allows the dipole elements to function in a medium having a dielectric constant similar to muscle tissue (approximately 78), thus enhancing the coupllng and mlnlmlzing the discontinuity between the dipole eleDents and the body surface~
By carefully filling all the voids between ' ~"
'' .
'.:' '"' . ''' ~a ''.
132~ 66-49 the dipole elements and the patient with water bags, efficient RF energy transfer and heating can be achieved at depth From a human usaga point of view, this device also has serious limitations It is very difficult to achieve uni~orm filling of the voids around the patient with wa~er bags Variable fat thickness, with its lower dielectric constant, also creates additional discontinuities When these variations occur, localized lo hot spots will exist that can cause injury or limit the extent of energy input possible without localized thermal damage It is also very time consuming to propQrly position the watQr bags and check for localized heating beforQ treatment begins, thus contribu~ing to patient fatigue and degraded treatment tolerancQ
4 The dQvice disclosed in the paper ~A Three-Dimensional Model For The Coaxial ~EM Deep-Body Hyparthermia Applicator~ develops a very detailed three dimansional mathematical model showing that deep heating is possibl- using a pair of cylindrical ~leeve-~ as described abovo This rainrorces the theoretical reasons ~hy th pr s nt invention functions wall It concludes, ~For an rficient electromagnQtic coupling, a suffici ntly cooled watar bolus batween the apertur~ and the hu~an body is necessary~
T~ device diQclosed in tha paper ~A New Coaxial TEH Radiofrequency/Microwave Applicator For Non-Inva-iv- De-p-Body Hyperthermia~ provides a limited th or tical evaluation of the same model showing that tho applicator will work with human body di~ensions and verifio~ th-se pr~dictions with a small model operating at an appropriately scaled higher frsquency It also requir s th- use o~ a wat~r bolus The paper concludes, ~To ~atch the patient to the applicator aperture, a 3S distilled water bolus between the patient and the applicator aperture is necessary~
T~ device diQclosed in tha paper ~A New Coaxial TEH Radiofrequency/Microwave Applicator For Non-Inva-iv- De-p-Body Hyperthermia~ provides a limited th or tical evaluation of the same model showing that tho applicator will work with human body di~ensions and verifio~ th-se pr~dictions with a small model operating at an appropriately scaled higher frsquency It also requir s th- use o~ a wat~r bolus The paper concludes, ~To ~atch the patient to the applicator aperture, a 3S distilled water bolus between the patient and the applicator aperture is necessary~
"'. '."''.:. ~
. :',, .
"
1324~14 6. The device described in the paper "Capacltor Electrode~
for Shortwave Diathermy,~ illustrates the serious theoretical and practical limitations of employing either contacting or noncontacting plates when heating a phantom (skin/fat and muscle) with RF energy. The resulting E-field llnes and current flow are perpendicular to the body surface. Thus the current path is ln series with the fat and ~uscle resulting ln t~e hlgher res1stance fat belng seriously over heated.
T~is article further descrlbes where two small plates ::
lin ter~s of body size) are placed on the sa~e surface of the patient. They produce currents flowlng between the~ and t~rough t~e fat and ~uscle tissue. ~ut also a large perpendicular current "`
flo~ passes t~roug~ the fat causlng surface overheating. This reference and discu~sion is included to clearly distlnguish thls -~
approach froa t~at of t~e present lnventlon. T~e present lnvontlon, to be doscrlbed, e~ploys large plates, ln terDs of body ~lze and t~ey forn a resonant aperture by which longitudlnal E-fleld energy ls transferred.
. :',, .
"
1324~14 6. The device described in the paper "Capacltor Electrode~
for Shortwave Diathermy,~ illustrates the serious theoretical and practical limitations of employing either contacting or noncontacting plates when heating a phantom (skin/fat and muscle) with RF energy. The resulting E-field llnes and current flow are perpendicular to the body surface. Thus the current path is ln series with the fat and ~uscle resulting ln t~e hlgher res1stance fat belng seriously over heated.
T~is article further descrlbes where two small plates ::
lin ter~s of body size) are placed on the sa~e surface of the patient. They produce currents flowlng between the~ and t~rough t~e fat and ~uscle tissue. ~ut also a large perpendicular current "`
flo~ passes t~roug~ the fat causlng surface overheating. This reference and discu~sion is included to clearly distlnguish thls -~
approach froa t~at of t~e present lnventlon. T~e present lnvontlon, to be doscrlbed, e~ploys large plates, ln terDs of body ~lze and t~ey forn a resonant aperture by which longitudlnal E-fleld energy ls transferred.
7~ Tho artlclo ~onparl~on of Deep Heatlng Electrode Concopts for Hypert~ernia~ further discus~es the u~e of oppo~ing plates and thelr linitations and also provldes depth of pen~tratlon details for various applicators.
. ~ " .
. ~ " .
8. U.S. Patent ~,282,8a7 entitled "Resonant Ridged ~aveguldo Structure Operatlng at 27 NHz.~ describes a rldge waveguide structure t~at is fllled witb water to lncrease lts , ~ .
62196-51g effective dimensions to make it resonant at 27MHz and yet small enough to fit on the body. A rubber bag, filled wlth delonized water, fits over the waveguide opening. A second rubber bag ls placed over top of the first. It is filled with a saline 6a ;
A ;
. . .... :
~ 56 absorption solution to prevent over heating of the fringe area around the periphery This second bag hac its center removed so that the third water cooled bag A ~ employing circulating water, is placed in the void s and used to cool the fat layer that is excessively heated Energy is coupled into the body im~ via these multiple water bags Power to the device is applied to the applicator wit~ a coax to waveguide transition l3~
The various prior art devices described above have the limitation of being close fitting around the object heated or using a water bolus to fill the void between the applicator and ob;ect to be heated The IJH paper concludes, ~For an efficient electromagnetic coupling, a sufficiently cooled water bolus between the aperture and the human body is necessary ~ The JMP paper concludes, ~To matc~ ths patient to the applicator aperture, a distilled water bolus between the patient and the applicator aperture is necessary ~
Prior art devices 2 through 5 are not resonant devic-s and a sorious impedance mismatch with the 50 ohm lino to th- RF pow r sourc- will result unless a water bolus is us d as described~ Moreover, the lack of a resonant structur limits the frequencies which may be employed in the d~vices Additionally, in a clinical environment, it is pr fer~bl~ t~ us- as simplified a device a~ possible and preferably ~ d~vice that does not surround the patient Accordingly, it is the principal ob~ect of the pres nt inv ntion to deposit RF energy in a uniform manncr in tissuo It is anoth-r ob~ect of the present invention to tr-at tu~ors by hyperthermia treat~ent without the need for a water bolus or an applicator closely fitting around the patient ''' ''. ~'`
66-~9 132~
Yet another object of the invantion is to allow an applicator to function at vario~s frequencies and to optimally couple the RF energy to the applicator A further object of the invention is to employ structures that do not surround the patient, to eliminate the need for side coupling elements and shield plates sum~ary of the Invention T~e present invention, in a broad aspect, includes lo a pair of identical metallic cylindrical or rectangular applicator sleeves spacQd along the torso The applicator sleeves are resonated with inductors The sleeves ar~ wQll spaced from the body (radial spacing) and ~o not require the USQ of a water bolus between the applicator and thQ patient This is possible because thQ sleeves becom~ part of the resonant circuit employed to raise thQ imp~dance of the applicator and obtain the necessary coupling to the torso without a water bolus betweQn the patient and applicator The r~onant circuit also becomes a part of th~ matching circuit that precisely matchQs the cylinder imp~dance to the 50 ohm RF power sourcQ To work on differ nt fr~qu ncies, it is simply necessary for the presQnt devic- to be re-resonatQd at the new desired fr gu ncy by changing th~ I/C values in the circuit Tho measured thermal r~Qpon-Qe of the present inv ntion ~bows relativ-ly uniform heating at depth in cro~s-s~ction~ equivalent to that of the human torso In an alternat~ e~bodiment the preQent invention consists o~ two, three or four larg- metallic plates, that aro position~d in a non-contacting manor above and b~low the tor_o, i ~, typically spaced 3 inches from the patient RF i~ connectQd to the plates so as to produce a longitudinal E-field within the body They are made part of a resonant circuit with the addition of -` ~32~414 -inductors. A water bolus between the plates and the patient is not required.
While t~e power distribution is less uniform, the use of just two plates is also very attractive because of its performance characteristics, convenience and extreme simplicity. (The plates can be placed in the table under the patient~ The E-field mapping and phantom experiments show that remarkably good depth of penetration is achieved while applying power from the one surface.
Tbis configuration can be beneficial in some cases where it is desirable to li~it t~e overall heating to a more specific reg~on~
It also completely eliminates any patient constraint incurred by positioning of surrounding applicator hardware~ -~ dditional inductive and capacitive loadlng can be e~ployed to eli~inate any E-fleld asymmetry or resonance sensitivity~ It can also be used to purposely create an asymmetry if an E-field concentratlon at a specific location is desired~
A beneficial ~ethod of providing unlform heatlng ls also pro~ided ~it~ the invention~
Accordlng to a broad aspect of the invention there is provided an electrostatlc deep heating applicator for tissue conprising-sleeve ~eans, axlally spaced and disposed in a non-contacting relatlonship around said tlssue, for forming a gap for depositlng RF energy to sald tissue; and resonant neans, coupled to a source of RF energy, for coupllng said energy to sald sleeves to establish an electric :. . .
field across said gap, ~hereby the resulting currents in said 9 ' ' ' ::':.:
.,~.
.
i~2~414 tissue cause preferential and uniform heating in said gap According to another broad aspect of the invention there is provided a method of unifor~ly heating animal tissue comprising the steps of placing caid tissue in a non-contacting relationship w~t~in two sleeves disposed coaxially around said tissue and spaced to provide a gap between them; and exciting said sieeves with radio frequency energy to establish an electric field across said gap, whereby the resulting lo currents flowing in the ani~al tissue cause preferential heating in the gap region~
According to another broad aspect of the lnvention there is provlded an electrostatic deep heating applicator for tlssue corprislng plate ~eans, spaced and disposed in a non-contacting relationshlp near said tissue, for forming a gap for depositing RF
energy to said tissue; and resonant ~eans, coupled to a source of RF energy, for ` `
coupling ~ald energy to said plates to establish an electric fleld ` `
acro~s ~aid gap, ~hereby the resultlng currents in said tissue `
cause preferentlal and uniform heating in said gap Accordlng to another broad aspect of the lnvention there `
18 provlded an electrostatlc deep heatlng applicator for tissue corpri~ingt gap-for~lng ~eans, axlally spaced and dlsposed in a non-contactlng relationshlp around said tissue, for for~ing a gap for deposltlng RF energy to sald tlssue; and 9 :.. : , .
a `
:~ .
1324~1~
; 62196-51g resonant means, ~oupled to a source of RF energy, for coupling said energy to said gap-forming means to establish an electric field across said gapt whereby ~he resulting currents in said tissue cause preferential and uniform heating in said gap.
Other objects, features, and advantages of the present invention will become apparent from a consideration of the following detailed description and the accompanying drawings.
Brief DescriDtion of the Dra~inqs Fig. 1 is a schematic block diagra~ of a prior art hypertheraia systea designed to heat the torso of the body;
Fig. 2 is a cross-sectional view of a prior art -applicator e~ploying a single turn resonant cylinder with a aagnetic induction technique of heating the torso;
Fig. 3 is a perspective view of a prior art applicator enploy1nq two close f1tt1ng sleeves ~here the '``': : ' `' , ' ''`' ' ,"~
''~',''' '`' ;' . ` ' `', .'', ' '.
` ' ` . '`
9b `
, ~ . :, .. : . .
~32~14 65-~9 diameter and frequency of operation are chosen to establish a reinforced radial standing wave in the center of the phantom being treated;
Figs. 4 (a) '-d (b) illustrate a prior art applicator using a series of radial dipole elements inserted in water bags that are in contact with the patient;
Fig 5 is an end view of an electrostatic deep heating applicator according to the present invention;
lo Fig~ 6 is a top view of an electrostatic deep heating applicator system according to the present invention Fig. 7 is a top view showing an alternative embodi~ent of t~e present invention;
Fig 8 is an end view of t~e embodiment shown in Fig 7:
Pig 9 is a side view of the embodiment~shown in Pig ?:
Pig 10 is a graph showing thQ measured relative electric fi-ld strength in an experiment employing the pres nt inv ntion as observed in a saline water tank design d to ~imulata thQ cro~_-section and conductivity of tho human tor~o:
Fig 11 i~ a graph showing the mea~urQd thermal pattern in an ~xperi~ent employing th~ present invention as observ~d in a muscle eguivalent phaneom of the torso having tho same cross-section aQ used in E-field moasurem nts of Fig 10;
Fig 12 is a ~imilar measurement as that shown in Fig 11 whcre the duration of heating has been increased to obtain a more pronounced temperature increase;
Fig 13 i~ a cross sectional view of a prior art applicator employinq a pair of conductive plates placed on oppo~ito ~id-s of the torso to be heated;
~J `,`''`,, .~ ' -10- "", ,,," ,.
''.'''''' '"'`'.''. '`'' ,`,'~''," '''' '. '. `','"' " '~'' 132~14 66-49 Fig 14 is a cross sectional view of a prior art applicator employing two small conductive plates placed - --side by side on or near the torso to be heateds ~ig 15 is a side view of a prior art water loaded ridge waveguide applicator that must be used in con-junction with several water bags positioned between the applicator and the patient;
Figs 16(a) and (b) are top and side views respectively of an alternate embodiment of the present lo invention employing 4 plates Fig 1~ shows the measurQd relative specific absorption rate vs location in a saline water tank p~antom for the device shown in ~ig 16 Figs 18(a) and (b) ar~ top and side views respectively of an alternate embodiment of the present invention employing 3 plates;
Fig l9 shows the measured relativQ SAR vs iocation in a salinQ water tank phantom while using 3 plates Figs 20(~) and (b~ ar- top and side views respectively of an alternate embodiment of the present invention ~mploying 2 plateQ; `;
Fig 21 showQ th- measured relative SAR with 2 plates ~ount d in the table;
Figs 22(a) and (b) are top and side views reQpectively of the 3 plate embodiment shown in Figs 18(a) and (b~ ~owing plac-n nt of a pig and thermometer plac~o~nt; and Figs 23 shows ther~al data obtained through the midsection of a liv~ _edated pig while using the 3 plate ~`
applicator configuration Det~ ri~ n `~
R-~erring mor- particularly to the drawings, a new applicator, as shown in Figs 5-9, has ~een developed that deposits RF energy in a nearly uniform manor throughout a cross-section of the human torso without -11- :` .
' ;'`' ' `
1~24~1~ 66-~3 the undesired characteristics of the previous devices described The basic applicator system and the method relating thereto, as shown in Figs S and 6, consists of two identical metallic rectangular sleeves 70, spaced from one another by a gap 72 Other shapes, such as cylindrical, elliptical, or square could be used They are placed concentrically around the torso-simulating phantom 74 As will be shown, heating occurs lo principally in the gap region between the two sleeves The sleeves dimensions (width and heigbt) are typically 30% to 50% greater than the torso so that the applicator sleeves allow a relatively large air gap 76 to exist betwe_n the patient and the metallic sleeves lS Th~ two sleeves 70 surrounding the torso 74 are electrically connected to each other, in the example, by a coil 78~ The inductance of the coil and the`capacity developed between the sleeves and the torso form a rQsonant circuit through which RF power 77 can be appli~d as s~own The RF en-rgy can be coupled directly to t~- sl~-v s by an impedance matching circuit and a bolus, by tap coupllng of the RF energy through one of thQ inductors, (as shown in Figure 6) or by tap coupling of tho RF energy employing the shield plates discussed b-lo~ as ~ ground return Evon tnough the sl~ev~s surrounding the torso are ~mall in teros of wavelength, a non-uniform E-field distr~bution occurs in tho phantom cross-s-ction if the two sle~ves are simply resonated with an inductor attach~d at a single point to each sleev- as shown in Fig 6 The resonant condition produced by the sleeve/torso capacity and inductor is also sensitive to movemont and torso size Any E-field asymmetry and resonance sensitivity can be corrected by the proper placement of additional inductive and capacitive loading as shown in the - 66-~9 ~32~
alternative embodiment of the invention depicted in Figs 8 and 9 The two sleeves 70 surrounding the torso 74 are electrically connected, in the figures, by four coils 78 in conjunction with eight identical capacitors -80 and two shield plates 82 The shield plates 82 are --placed along both sides of the applicator between the -phanto~ ond the applicator sleeves Electrically, the shield plate surfaces form equal capacitancQ to both sleeves so that a neutral RF potantial exists on the shield plates, i.Q-, they are at ground potential By positioning the plates as shown in the figures, the E-field level around tha minor axis of the elliptical phantom was reduced to a level equal to tbat established elsewhere The addition of the coils and fixed capacitors are arranged so that the field distribution around the sleeves is very uniform Likewise, the added càpacitive loading stabilizes the resonant circuit so that it is ;
not significantly affected by patient to patient 20 variation `;
In a prototype of the present invention, the circuit was r~sonatod at 27 12 MHz ThiQ frequency rosult-d in conv ni~nt inductor and capacitor values and good coupling to the torso was possible Since 27 12 NHz is also an ISM froquoncy, its use does not require a scraen roo~ to furth-r mini~izo RF radiation The same applicator principle~ howQver can be used at other ~`
fr qu ncie~ by prop r choico of the circuit element values Th- elongatQd elliptical cross-section phantom 74 was u~-d to make RF E-field and thermal measurements in a salino tank with the new applicator because it more noarly duplicated the human torso The resulting electric field patt-rn was measured as shown in Fig 10 ;~;
Differencos in th- right and left side field-strength response shape may be seen However, since the levels ; . .. :.: .
:' .'' ' .' ": ", ..
,'.` : ' , ~' ` ~324414 66-~9 did not exceed that produced in the center, it is not considered a problem Fig 10 was plotted in terms of the relative Specific Absorption Rate, SAR The tank was ~illed with a saline solution where the salt content was adjusted to provide the approximate conductivity of human muscle tissue at 27 M~z, i e , 0 62 mhos per meter T~e corresponding heating patterns for two different heating times are shown in Figs 11 and 12 and the plots represent the ~easured thermal increase The thermal patterns were measured in the same tank as used for the E-field measurements but with the tank filled with finely powdered silicon saturated with a saline solution Again, the required salinity was experimentally determined, by measurement, to produce a phanto~ conductivity equivalent to muscle tissue Fig~ 11 shows the thermal response a~ter applying 800 watts for 8 minutes Fig 12 shows that a similar heating pattern was obtained when the duration was increased to 15 minutes As is shown, relatively uniform heating i~ obtained at any depth in thQ desired cros~-~ection The thQrmal increaæe in the center of the phantom was approximately 15% less than that obtained at th~ bottom surface, but it was also about 10% greator than that ~t the top surface T~e r lative SAR E-field mea~urement~ of Fig 10 ~hows th~t ~ contrally located tumor (at 10 cm depth) would receiv~ essentially the ~ame SAR within mea~urement accuracy a~ that ob~-rved at the top and botto~ surfac-s, i e , a very uniform oxcitation pattern that s~ould result in a unifor~ heating pattern; the ob~ect of thi~ invention The thermal differences noted in Fig~ 11 and 12, while minor when compared to other methods of heating, appear to be due to an inadvertent variation in the conductivity of the phantom material Following the -14- ~
132~ 66-~9 thermal experiments, sample conductivity measurements were made as follows top -- o 50 mhos/m, center -- 0 68 mhos/m and bottom surface -- o 85 mhos/m.
It is important to note that maximum heating - -occurred in the material having thQ higher cond~ctivity of muscle tissue This characteristic is a very desireable feature since it discriminates against the heating of fat a lower conductivity tiSSUQ that often heats excessively while attempting deep heating An a`-ernate serie~ of embodiments employing the present invention is shown in Fig 16, 18, 20, and 22 Those shown in Figs 16 and 18 deposit RF energy in a nearly uniform manor throughout a cross-section o~ the human torso without the undesired characteristics of many devices Figure 20, an abbreviation of the above two applicator~, forms a very convenient device that also provides deQp penetr~tion but favors~ the side nearest the applicator plates ~"
The basic applicator system and the method relating 20 thereto of thQ alternate embodiment, as shown in Fig `~
16, consiQts of four large rectangular thin metal plates ``
82 and 8~, spac d from one another by a gap 86 They are placed abov~ and below th- torso-simulating phantom 88 Th~ plat-s ar~ 20 to 24 inch-s long, i e , so as to xc- d th~ body width The s~aller plate dimension is 10 to 12 inches m e plates are spaced 2 to 4 inches ``~
above and below the body -Qurfac- 88 allowing an air gap The low~r plat-~ 82 can be imbedded in the patient table m ~ dimansion~ given are typical and can be varied considerably with minor effect Th~ plat ~ becom part of a resonant circuit by placing coils 95 across the gap and connecting them to `~
the lower plates as shown RF power i-~ then applied via the coaxial lln- 94 The lower plates 82 are connected to the upp-r plates 84 by ~etal straps 92 so that they are on~ ~etallic structure That is, the upper and -15- `
-...~". . .
"~ .
~` 66-Ç9 132~14 lower plates are at the same RF potential The two sets of plates 82-84 are connected by the coils 95 and RP
I energy is coupled to one of the coils as shown at 94.
Thus the plates on opposite sides of the gap produce a di~ference of potential across the gap region 86 that is an aperture or RF coupling mecbanism through which energy is transferred to the body The relatively large s~rfaces of the plates, in terms of body dimensions, provide a large distributed capacitive coupling to the body on eith~r side of the gap region that provides an efficient aperture through which the RF ,energy is launched into the body This is further verified with ~easurement dat~
The 4-plate version of the pr~sent invention also extends over the torso in a non-contacting manner but has no side plates aQ shown in Fig 5-9 This configuration eli~inates excessive ~ide heating of clliptical shapes whil~ still retaining the ability to produce central heating Th~ ~bre- plat- version of thQ present invention as shown in Fig 18 will also produce an E-field distribution nearly a~ uniform aQ that obtained with the four plato ver~ion B~cause the plates are large and extand over a significant portion of the body, the three 2S plat- vorsion is ~uch mor convenient in a clinical sotting By r moval of the on- plate (that would nornallr protrud- over the necX-nosQ region when heating a c~ast tu~or), tha region near th- patient's face is unobstruct d ~aking the procedure much less threatening for tho pat nt Tbe two plata version of the present invention is -~hown in Fig 20 Both plates can be placed in the patiQnt table so that it is simply necessary to position the pati~nt so that the portion to be heated is over the gap region ~':.
1324~1~ 66-49 E-field intensity patterns, that are representative of the heating patterns, were measured while using the present inventions These are shown in Figs 17, 19, and 21 where central heating is uniform to within 8 7% with four plates, 11.1% with t~ree plates and 20% with the use of two plates ~ -With reference to Fig 23, the t~ermal performance of the present invention was demonstrated by heating a 125 pound sedated pig 96 The pig was placed on its 10 side and positioned with its mid-section in the gap of --the three plate version o~ the present invention A
catheter 98 was inserted through the mid-section into --which a ~iberoptic thermal probQ was inserted and moved to various locations to obtain a thermal profile ~-~emperature measurements were made before heating and after 15, 30 and 45 minutes of heating as shown in ;~
Figure 23 ~s may ~e seen, the upper surface~ (skin and thick fat lay~r of a pig~ was not superficially heated, as would be the case if signi~icant perpQndicular E-20 fields w re pres nt The ther~al pattern is also ~`
remarkabl~ uniforo, espQcially when considering the heterog neous body ~aterial in the cross-section T~us the over~h~lming utility of the present invention is authentic~t d In t~e foregoing description of the present inv ntion, ~ pre~err~d embodiment o~ the invention has been disclosed It is to be understood that other mechanical and design variations are within the scope of the pr-sQnt inv ntion Accordingly, the preQent invention i~ not limit-d to the particular arrangement which h~s b~en illustrat-d and described herein ~;
DOCS 06649PAT OlD -~
:
: :~
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''' '' ''~'' ', ~-.''''
62196-51g effective dimensions to make it resonant at 27MHz and yet small enough to fit on the body. A rubber bag, filled wlth delonized water, fits over the waveguide opening. A second rubber bag ls placed over top of the first. It is filled with a saline 6a ;
A ;
. . .... :
~ 56 absorption solution to prevent over heating of the fringe area around the periphery This second bag hac its center removed so that the third water cooled bag A ~ employing circulating water, is placed in the void s and used to cool the fat layer that is excessively heated Energy is coupled into the body im~ via these multiple water bags Power to the device is applied to the applicator wit~ a coax to waveguide transition l3~
The various prior art devices described above have the limitation of being close fitting around the object heated or using a water bolus to fill the void between the applicator and ob;ect to be heated The IJH paper concludes, ~For an efficient electromagnetic coupling, a sufficiently cooled water bolus between the aperture and the human body is necessary ~ The JMP paper concludes, ~To matc~ ths patient to the applicator aperture, a distilled water bolus between the patient and the applicator aperture is necessary ~
Prior art devices 2 through 5 are not resonant devic-s and a sorious impedance mismatch with the 50 ohm lino to th- RF pow r sourc- will result unless a water bolus is us d as described~ Moreover, the lack of a resonant structur limits the frequencies which may be employed in the d~vices Additionally, in a clinical environment, it is pr fer~bl~ t~ us- as simplified a device a~ possible and preferably ~ d~vice that does not surround the patient Accordingly, it is the principal ob~ect of the pres nt inv ntion to deposit RF energy in a uniform manncr in tissuo It is anoth-r ob~ect of the present invention to tr-at tu~ors by hyperthermia treat~ent without the need for a water bolus or an applicator closely fitting around the patient ''' ''. ~'`
66-~9 132~
Yet another object of the invantion is to allow an applicator to function at vario~s frequencies and to optimally couple the RF energy to the applicator A further object of the invention is to employ structures that do not surround the patient, to eliminate the need for side coupling elements and shield plates sum~ary of the Invention T~e present invention, in a broad aspect, includes lo a pair of identical metallic cylindrical or rectangular applicator sleeves spacQd along the torso The applicator sleeves are resonated with inductors The sleeves ar~ wQll spaced from the body (radial spacing) and ~o not require the USQ of a water bolus between the applicator and thQ patient This is possible because thQ sleeves becom~ part of the resonant circuit employed to raise thQ imp~dance of the applicator and obtain the necessary coupling to the torso without a water bolus betweQn the patient and applicator The r~onant circuit also becomes a part of th~ matching circuit that precisely matchQs the cylinder imp~dance to the 50 ohm RF power sourcQ To work on differ nt fr~qu ncies, it is simply necessary for the presQnt devic- to be re-resonatQd at the new desired fr gu ncy by changing th~ I/C values in the circuit Tho measured thermal r~Qpon-Qe of the present inv ntion ~bows relativ-ly uniform heating at depth in cro~s-s~ction~ equivalent to that of the human torso In an alternat~ e~bodiment the preQent invention consists o~ two, three or four larg- metallic plates, that aro position~d in a non-contacting manor above and b~low the tor_o, i ~, typically spaced 3 inches from the patient RF i~ connectQd to the plates so as to produce a longitudinal E-field within the body They are made part of a resonant circuit with the addition of -` ~32~414 -inductors. A water bolus between the plates and the patient is not required.
While t~e power distribution is less uniform, the use of just two plates is also very attractive because of its performance characteristics, convenience and extreme simplicity. (The plates can be placed in the table under the patient~ The E-field mapping and phantom experiments show that remarkably good depth of penetration is achieved while applying power from the one surface.
Tbis configuration can be beneficial in some cases where it is desirable to li~it t~e overall heating to a more specific reg~on~
It also completely eliminates any patient constraint incurred by positioning of surrounding applicator hardware~ -~ dditional inductive and capacitive loadlng can be e~ployed to eli~inate any E-fleld asymmetry or resonance sensitivity~ It can also be used to purposely create an asymmetry if an E-field concentratlon at a specific location is desired~
A beneficial ~ethod of providing unlform heatlng ls also pro~ided ~it~ the invention~
Accordlng to a broad aspect of the invention there is provided an electrostatlc deep heating applicator for tissue conprising-sleeve ~eans, axlally spaced and disposed in a non-contacting relatlonship around said tlssue, for forming a gap for depositlng RF energy to sald tissue; and resonant neans, coupled to a source of RF energy, for coupllng said energy to sald sleeves to establish an electric :. . .
field across said gap, ~hereby the resulting currents in said 9 ' ' ' ::':.:
.,~.
.
i~2~414 tissue cause preferential and uniform heating in said gap According to another broad aspect of the invention there is provided a method of unifor~ly heating animal tissue comprising the steps of placing caid tissue in a non-contacting relationship w~t~in two sleeves disposed coaxially around said tissue and spaced to provide a gap between them; and exciting said sieeves with radio frequency energy to establish an electric field across said gap, whereby the resulting lo currents flowing in the ani~al tissue cause preferential heating in the gap region~
According to another broad aspect of the lnvention there is provlded an electrostatic deep heating applicator for tlssue corprislng plate ~eans, spaced and disposed in a non-contacting relationshlp near said tissue, for forming a gap for depositing RF
energy to said tissue; and resonant ~eans, coupled to a source of RF energy, for ` `
coupling ~ald energy to said plates to establish an electric fleld ` `
acro~s ~aid gap, ~hereby the resultlng currents in said tissue `
cause preferentlal and uniform heating in said gap Accordlng to another broad aspect of the lnvention there `
18 provlded an electrostatlc deep heatlng applicator for tissue corpri~ingt gap-for~lng ~eans, axlally spaced and dlsposed in a non-contactlng relationshlp around said tissue, for for~ing a gap for deposltlng RF energy to sald tlssue; and 9 :.. : , .
a `
:~ .
1324~1~
; 62196-51g resonant means, ~oupled to a source of RF energy, for coupling said energy to said gap-forming means to establish an electric field across said gapt whereby ~he resulting currents in said tissue cause preferential and uniform heating in said gap.
Other objects, features, and advantages of the present invention will become apparent from a consideration of the following detailed description and the accompanying drawings.
Brief DescriDtion of the Dra~inqs Fig. 1 is a schematic block diagra~ of a prior art hypertheraia systea designed to heat the torso of the body;
Fig. 2 is a cross-sectional view of a prior art -applicator e~ploying a single turn resonant cylinder with a aagnetic induction technique of heating the torso;
Fig. 3 is a perspective view of a prior art applicator enploy1nq two close f1tt1ng sleeves ~here the '``': : ' `' , ' ''`' ' ,"~
''~',''' '`' ;' . ` ' `', .'', ' '.
` ' ` . '`
9b `
, ~ . :, .. : . .
~32~14 65-~9 diameter and frequency of operation are chosen to establish a reinforced radial standing wave in the center of the phantom being treated;
Figs. 4 (a) '-d (b) illustrate a prior art applicator using a series of radial dipole elements inserted in water bags that are in contact with the patient;
Fig 5 is an end view of an electrostatic deep heating applicator according to the present invention;
lo Fig~ 6 is a top view of an electrostatic deep heating applicator system according to the present invention Fig. 7 is a top view showing an alternative embodi~ent of t~e present invention;
Fig 8 is an end view of t~e embodiment shown in Fig 7:
Pig 9 is a side view of the embodiment~shown in Pig ?:
Pig 10 is a graph showing thQ measured relative electric fi-ld strength in an experiment employing the pres nt inv ntion as observed in a saline water tank design d to ~imulata thQ cro~_-section and conductivity of tho human tor~o:
Fig 11 i~ a graph showing the mea~urQd thermal pattern in an ~xperi~ent employing th~ present invention as observ~d in a muscle eguivalent phaneom of the torso having tho same cross-section aQ used in E-field moasurem nts of Fig 10;
Fig 12 is a ~imilar measurement as that shown in Fig 11 whcre the duration of heating has been increased to obtain a more pronounced temperature increase;
Fig 13 i~ a cross sectional view of a prior art applicator employinq a pair of conductive plates placed on oppo~ito ~id-s of the torso to be heated;
~J `,`''`,, .~ ' -10- "", ,,," ,.
''.'''''' '"'`'.''. '`'' ,`,'~''," '''' '. '. `','"' " '~'' 132~14 66-49 Fig 14 is a cross sectional view of a prior art applicator employing two small conductive plates placed - --side by side on or near the torso to be heateds ~ig 15 is a side view of a prior art water loaded ridge waveguide applicator that must be used in con-junction with several water bags positioned between the applicator and the patient;
Figs 16(a) and (b) are top and side views respectively of an alternate embodiment of the present lo invention employing 4 plates Fig 1~ shows the measurQd relative specific absorption rate vs location in a saline water tank p~antom for the device shown in ~ig 16 Figs 18(a) and (b) ar~ top and side views respectively of an alternate embodiment of the present invention employing 3 plates;
Fig l9 shows the measured relativQ SAR vs iocation in a salinQ water tank phantom while using 3 plates Figs 20(~) and (b~ ar- top and side views respectively of an alternate embodiment of the present invention ~mploying 2 plateQ; `;
Fig 21 showQ th- measured relative SAR with 2 plates ~ount d in the table;
Figs 22(a) and (b) are top and side views reQpectively of the 3 plate embodiment shown in Figs 18(a) and (b~ ~owing plac-n nt of a pig and thermometer plac~o~nt; and Figs 23 shows ther~al data obtained through the midsection of a liv~ _edated pig while using the 3 plate ~`
applicator configuration Det~ ri~ n `~
R-~erring mor- particularly to the drawings, a new applicator, as shown in Figs 5-9, has ~een developed that deposits RF energy in a nearly uniform manor throughout a cross-section of the human torso without -11- :` .
' ;'`' ' `
1~24~1~ 66-~3 the undesired characteristics of the previous devices described The basic applicator system and the method relating thereto, as shown in Figs S and 6, consists of two identical metallic rectangular sleeves 70, spaced from one another by a gap 72 Other shapes, such as cylindrical, elliptical, or square could be used They are placed concentrically around the torso-simulating phantom 74 As will be shown, heating occurs lo principally in the gap region between the two sleeves The sleeves dimensions (width and heigbt) are typically 30% to 50% greater than the torso so that the applicator sleeves allow a relatively large air gap 76 to exist betwe_n the patient and the metallic sleeves lS Th~ two sleeves 70 surrounding the torso 74 are electrically connected to each other, in the example, by a coil 78~ The inductance of the coil and the`capacity developed between the sleeves and the torso form a rQsonant circuit through which RF power 77 can be appli~d as s~own The RF en-rgy can be coupled directly to t~- sl~-v s by an impedance matching circuit and a bolus, by tap coupllng of the RF energy through one of thQ inductors, (as shown in Figure 6) or by tap coupling of tho RF energy employing the shield plates discussed b-lo~ as ~ ground return Evon tnough the sl~ev~s surrounding the torso are ~mall in teros of wavelength, a non-uniform E-field distr~bution occurs in tho phantom cross-s-ction if the two sle~ves are simply resonated with an inductor attach~d at a single point to each sleev- as shown in Fig 6 The resonant condition produced by the sleeve/torso capacity and inductor is also sensitive to movemont and torso size Any E-field asymmetry and resonance sensitivity can be corrected by the proper placement of additional inductive and capacitive loading as shown in the - 66-~9 ~32~
alternative embodiment of the invention depicted in Figs 8 and 9 The two sleeves 70 surrounding the torso 74 are electrically connected, in the figures, by four coils 78 in conjunction with eight identical capacitors -80 and two shield plates 82 The shield plates 82 are --placed along both sides of the applicator between the -phanto~ ond the applicator sleeves Electrically, the shield plate surfaces form equal capacitancQ to both sleeves so that a neutral RF potantial exists on the shield plates, i.Q-, they are at ground potential By positioning the plates as shown in the figures, the E-field level around tha minor axis of the elliptical phantom was reduced to a level equal to tbat established elsewhere The addition of the coils and fixed capacitors are arranged so that the field distribution around the sleeves is very uniform Likewise, the added càpacitive loading stabilizes the resonant circuit so that it is ;
not significantly affected by patient to patient 20 variation `;
In a prototype of the present invention, the circuit was r~sonatod at 27 12 MHz ThiQ frequency rosult-d in conv ni~nt inductor and capacitor values and good coupling to the torso was possible Since 27 12 NHz is also an ISM froquoncy, its use does not require a scraen roo~ to furth-r mini~izo RF radiation The same applicator principle~ howQver can be used at other ~`
fr qu ncie~ by prop r choico of the circuit element values Th- elongatQd elliptical cross-section phantom 74 was u~-d to make RF E-field and thermal measurements in a salino tank with the new applicator because it more noarly duplicated the human torso The resulting electric field patt-rn was measured as shown in Fig 10 ;~;
Differencos in th- right and left side field-strength response shape may be seen However, since the levels ; . .. :.: .
:' .'' ' .' ": ", ..
,'.` : ' , ~' ` ~324414 66-~9 did not exceed that produced in the center, it is not considered a problem Fig 10 was plotted in terms of the relative Specific Absorption Rate, SAR The tank was ~illed with a saline solution where the salt content was adjusted to provide the approximate conductivity of human muscle tissue at 27 M~z, i e , 0 62 mhos per meter T~e corresponding heating patterns for two different heating times are shown in Figs 11 and 12 and the plots represent the ~easured thermal increase The thermal patterns were measured in the same tank as used for the E-field measurements but with the tank filled with finely powdered silicon saturated with a saline solution Again, the required salinity was experimentally determined, by measurement, to produce a phanto~ conductivity equivalent to muscle tissue Fig~ 11 shows the thermal response a~ter applying 800 watts for 8 minutes Fig 12 shows that a similar heating pattern was obtained when the duration was increased to 15 minutes As is shown, relatively uniform heating i~ obtained at any depth in thQ desired cros~-~ection The thQrmal increaæe in the center of the phantom was approximately 15% less than that obtained at th~ bottom surface, but it was also about 10% greator than that ~t the top surface T~e r lative SAR E-field mea~urement~ of Fig 10 ~hows th~t ~ contrally located tumor (at 10 cm depth) would receiv~ essentially the ~ame SAR within mea~urement accuracy a~ that ob~-rved at the top and botto~ surfac-s, i e , a very uniform oxcitation pattern that s~ould result in a unifor~ heating pattern; the ob~ect of thi~ invention The thermal differences noted in Fig~ 11 and 12, while minor when compared to other methods of heating, appear to be due to an inadvertent variation in the conductivity of the phantom material Following the -14- ~
132~ 66-~9 thermal experiments, sample conductivity measurements were made as follows top -- o 50 mhos/m, center -- 0 68 mhos/m and bottom surface -- o 85 mhos/m.
It is important to note that maximum heating - -occurred in the material having thQ higher cond~ctivity of muscle tissue This characteristic is a very desireable feature since it discriminates against the heating of fat a lower conductivity tiSSUQ that often heats excessively while attempting deep heating An a`-ernate serie~ of embodiments employing the present invention is shown in Fig 16, 18, 20, and 22 Those shown in Figs 16 and 18 deposit RF energy in a nearly uniform manor throughout a cross-section o~ the human torso without the undesired characteristics of many devices Figure 20, an abbreviation of the above two applicator~, forms a very convenient device that also provides deQp penetr~tion but favors~ the side nearest the applicator plates ~"
The basic applicator system and the method relating 20 thereto of thQ alternate embodiment, as shown in Fig `~
16, consiQts of four large rectangular thin metal plates ``
82 and 8~, spac d from one another by a gap 86 They are placed abov~ and below th- torso-simulating phantom 88 Th~ plat-s ar~ 20 to 24 inch-s long, i e , so as to xc- d th~ body width The s~aller plate dimension is 10 to 12 inches m e plates are spaced 2 to 4 inches ``~
above and below the body -Qurfac- 88 allowing an air gap The low~r plat-~ 82 can be imbedded in the patient table m ~ dimansion~ given are typical and can be varied considerably with minor effect Th~ plat ~ becom part of a resonant circuit by placing coils 95 across the gap and connecting them to `~
the lower plates as shown RF power i-~ then applied via the coaxial lln- 94 The lower plates 82 are connected to the upp-r plates 84 by ~etal straps 92 so that they are on~ ~etallic structure That is, the upper and -15- `
-...~". . .
"~ .
~` 66-Ç9 132~14 lower plates are at the same RF potential The two sets of plates 82-84 are connected by the coils 95 and RP
I energy is coupled to one of the coils as shown at 94.
Thus the plates on opposite sides of the gap produce a di~ference of potential across the gap region 86 that is an aperture or RF coupling mecbanism through which energy is transferred to the body The relatively large s~rfaces of the plates, in terms of body dimensions, provide a large distributed capacitive coupling to the body on eith~r side of the gap region that provides an efficient aperture through which the RF ,energy is launched into the body This is further verified with ~easurement dat~
The 4-plate version of the pr~sent invention also extends over the torso in a non-contacting manner but has no side plates aQ shown in Fig 5-9 This configuration eli~inates excessive ~ide heating of clliptical shapes whil~ still retaining the ability to produce central heating Th~ ~bre- plat- version of thQ present invention as shown in Fig 18 will also produce an E-field distribution nearly a~ uniform aQ that obtained with the four plato ver~ion B~cause the plates are large and extand over a significant portion of the body, the three 2S plat- vorsion is ~uch mor convenient in a clinical sotting By r moval of the on- plate (that would nornallr protrud- over the necX-nosQ region when heating a c~ast tu~or), tha region near th- patient's face is unobstruct d ~aking the procedure much less threatening for tho pat nt Tbe two plata version of the present invention is -~hown in Fig 20 Both plates can be placed in the patiQnt table so that it is simply necessary to position the pati~nt so that the portion to be heated is over the gap region ~':.
1324~1~ 66-49 E-field intensity patterns, that are representative of the heating patterns, were measured while using the present inventions These are shown in Figs 17, 19, and 21 where central heating is uniform to within 8 7% with four plates, 11.1% with t~ree plates and 20% with the use of two plates ~ -With reference to Fig 23, the t~ermal performance of the present invention was demonstrated by heating a 125 pound sedated pig 96 The pig was placed on its 10 side and positioned with its mid-section in the gap of --the three plate version o~ the present invention A
catheter 98 was inserted through the mid-section into --which a ~iberoptic thermal probQ was inserted and moved to various locations to obtain a thermal profile ~-~emperature measurements were made before heating and after 15, 30 and 45 minutes of heating as shown in ;~
Figure 23 ~s may ~e seen, the upper surface~ (skin and thick fat lay~r of a pig~ was not superficially heated, as would be the case if signi~icant perpQndicular E-20 fields w re pres nt The ther~al pattern is also ~`
remarkabl~ uniforo, espQcially when considering the heterog neous body ~aterial in the cross-section T~us the over~h~lming utility of the present invention is authentic~t d In t~e foregoing description of the present inv ntion, ~ pre~err~d embodiment o~ the invention has been disclosed It is to be understood that other mechanical and design variations are within the scope of the pr-sQnt inv ntion Accordingly, the preQent invention i~ not limit-d to the particular arrangement which h~s b~en illustrat-d and described herein ~;
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Claims (24)
1. An electrostatic deep heating applicator for tissue comprising:
sleeve means, axially spaced and disposed in a non-contacting relationship around said tissue, for forming a gap for depositing RF energy to said tissue; and resonant means, coupled to a source of RF energy, for coupling said energy to said sleeves to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
sleeve means, axially spaced and disposed in a non-contacting relationship around said tissue, for forming a gap for depositing RF energy to said tissue; and resonant means, coupled to a source of RF energy, for coupling said energy to said sleeves to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
2. An applicator as defined in claim 1, wherein said sleeve means comprises a pair of metallic sleeves each having a circular cross-section to form a capacitive heating applicator.
3. An applicator as defined in claim 1, wherein said sleeve means comprises a pair of metallic sleeves each having rectangular cross-section to form a capacitive heating applicator.
4. An applicator as defined in claim 1, wherein said sleeve moans comprises a pair of metallic sleeves each having a elliptical cross-section to form a capacitive heating applicator.
5. An applicator as defined in claim 1, wherein said resonant means comprises inductor means, attached to said sleeve means and said source of RF energy, for forming a resonant circuit with said sleeve means.
6. An applicator as defined in claim 5, wherein said applicator further comprises control means for controlling the distribution of said field in said tissue and the sensitivity of said resonant circuit.
7. An applicator as defined in claim 6, wherein said control means comprises:
capacitor means, coupled to said inductor means, and a plurality of shield plate means disposed adjacent said sleeve means.
capacitor means, coupled to said inductor means, and a plurality of shield plate means disposed adjacent said sleeve means.
8. An applicator as defined in claim 6, wherein:
said sleeve means comprises a pair of rectangular metallic sleeves;
said inductor means comprises multiple inductors, connected between corresponding sides of said sleeves;
said capacitor means comprises multiple capacitors mounted pair-wise on said multiple inductors; and said shield plate means comprises a pair of elongated shield plates disposed in facing relation on opposing sides of said sleeves.
said sleeve means comprises a pair of rectangular metallic sleeves;
said inductor means comprises multiple inductors, connected between corresponding sides of said sleeves;
said capacitor means comprises multiple capacitors mounted pair-wise on said multiple inductors; and said shield plate means comprises a pair of elongated shield plates disposed in facing relation on opposing sides of said sleeves.
9. An applicator as defined in claim 7, wherein said resonant means includes means for coupling said RF
energy to said sleeve means.
energy to said sleeve means.
10. An applicator as defined in claim 9, wherein said means for coupling comprises an inpedance matching circuit coupled between said resonant means and said RF
energy source.
energy source.
11. A method of uniformly heating animal tissue comprising the steps of:
placing said tissue in a non-contacting relationship within two sleeves disposed coaxially around said tissue and spaced to provide a gap between them; and exciting said sleeves with radio frequency energy to establish an electric field across said gap whereby the resulting currents flowing in the animal tissue cause preferential heating in the gap region.
placing said tissue in a non-contacting relationship within two sleeves disposed coaxially around said tissue and spaced to provide a gap between them; and exciting said sleeves with radio frequency energy to establish an electric field across said gap whereby the resulting currents flowing in the animal tissue cause preferential heating in the gap region.
12. The method of claim 11, wherein said method further comprises the step of resonating said sleeves to couple said energy to said applicator at a selected resonant frequency.
13. An electrostatic deep heating applicator for tissue comprising:
plate means, spaced and disposed in a noncontacting relationship near said tissue, for forming a gap for depositing RF energy to said tissue; and resonant means, coupled to a source of RF energy, for coupling said energy to said plates to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
plate means, spaced and disposed in a noncontacting relationship near said tissue, for forming a gap for depositing RF energy to said tissue; and resonant means, coupled to a source of RF energy, for coupling said energy to said plates to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
14. An applicator as defined in claim 13, wherein said plate means comprises two generally flat metallic plates disposed in opposing relation to form a capacitive heating applicator.
15. An applicator as defined in claim 13, wherein said plates means comprises at least a pair of curved metallic plates to form a capacitive heating applicator.
16. An applicator as defined in claim 13, wherein said resonant means comprises inductor means, attached to said plate means and said source of RF energy, for forming a resonant circuit with said plate means.
17. An applicator as defined in claim 16, wherein said applicator further comprises control means for controlling the distribution of said field in said tissue and the resonant frequency of said resonant means.
18. An applicator as defined in claim 17, wherein said resonant means and control means comprises capacitor means, coupled to said inductor means, for forming a resonant circuit and controlling distribution of said fiels in said tissue.
19. An applicator as defined claim 18, wherein said resonant means includes means for coupling said RF
energy to said plate means.
energy to said plate means.
20. An applicator as defined in claim 19 wherein said means for coupling comprises an impedance matching circuit coupled between said resonant means and said RF
energy source.
energy source.
21. An applicator as defined in claim 13, wherein said plate means comprises four generally flat rectangular plates disposed pair-wise in opposing relation.
22. An applicator as defined in claim 13, wherein said plate means comprises two generally flat plates disposed in linear relation.
23. An applicator as defined in claim 13, wherein said plate means comprises a pair of flat plates disposed in opposing relation and a third plate adjacent one of said flat plates.
24. An electrostatic deep heating applicator for tissue comprising:
gap-forming means, axially spaced and disposed in a non-contacting relationship around said tissue, for forming a gap for depositing RF energy to said tissue:
and resonant means, coupled to a source of RF energy, for coupling said energy to said gap-forming means to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
gap-forming means, axially spaced and disposed in a non-contacting relationship around said tissue, for forming a gap for depositing RF energy to said tissue:
and resonant means, coupled to a source of RF energy, for coupling said energy to said gap-forming means to establish an electric field across said gap, whereby the resulting currents in said tissue cause preferential and uniform heating in said gap.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/006,219 US4823811A (en) | 1987-01-23 | 1987-01-23 | Electrostatic deep heating applicator |
| US07/052,246 US4823813A (en) | 1987-01-23 | 1987-05-19 | Electrostatic deep heating applicators |
| CA000575146A CA1324414C (en) | 1987-01-12 | 1988-08-18 | Electrostatic deep heating applicators |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/002,301 US4723665A (en) | 1987-01-12 | 1987-01-12 | Telescoping closet garment organizer |
| CA000575146A CA1324414C (en) | 1987-01-12 | 1988-08-18 | Electrostatic deep heating applicators |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1324414C true CA1324414C (en) | 1993-11-16 |
Family
ID=25672062
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000575146A Expired - Fee Related CA1324414C (en) | 1987-01-12 | 1988-08-18 | Electrostatic deep heating applicators |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1324414C (en) |
-
1988
- 1988-08-18 CA CA000575146A patent/CA1324414C/en not_active Expired - Fee Related
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