Apparatus for medical treatment by hyperthermia

Hyperthermia apparatus including a power amplifier, remote electrode apparatus receiving a high power electrical supply from the power amplifier, power transmission apparatus arranged to electrically couple the power amplifier to the remote electrode apparatus for supply of electrical power thereto and capacitive matching apparatus for providing real time capacitive matching between the power amplifier and the capacitive load across the electrode apparatus.

FIELD OF THE INVENTION 
The present invention relates to apparatus for medical treatment by 
hyperthermia generally and specifically to apparatus for capacitive 
matching between a power amplifier and a capacitive load along a power 
transmission line in such apparatus. 
BACKGROUND OF THE INVENTION 
The use of hyperthermia in treatment of malignant tumors is well known and 
documented. A summary report reflecting the state of the art in 1982 
appears in the following publication: 
Manning, M. R., T. C. Cetas, R. C. Miller, J. R. Oleson, W. G. Connort, and 
E. W. Gerner, "Clinical Hyperthermia, Results of a Phase I Trial Employing 
Hyperthermia Alone or in Combination with External Beam or Interstitial 
Radiotherapy," Cancer Vol. 49, pp. 205-216, 1982. 
One type of hyperthermia treatment employs capacitive heating of the tumor 
by means of a pair of electrodes placed on opposite sides thereof. Because 
significant amounts of electrical energy are involved, the problem of 
capacitive matching between the power amplifier and the capacitive load 
arises. As is well known, absence of good capacitive matching in a system 
causes a relatively large amount of wasted reflected power, thus requiring 
a much larger power amplifier than would otherwise be necessary, unwanted 
heating of the electrodes resulting in heat damage to the skin and 
subcutaneous layers of the patient's body. 
In hyperthermia applications, it has been found by the inventors that 
adjustments in the capacitive matching should be made continually, in 
response to even minor movements of the patient, even those occasioned by 
normal breathing. Adjustments in the capacitive matching must also be made 
in response to the output power supplied to the electrodes. Prior art 
apparatus does not enable adjustments in capacitive matching to be readily 
made. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide a hyperthermia system having 
extremely efficient capacitive matching apparatus operative in real time. 
There is thus provided in accordance with a preferred embodiment of the 
present invention hyperthermia apparatus including a power amplifier, 
remote electrode apparatus receiving a high power electrical supply from 
the power amplifier, power transmission apparatus arranged to electrically 
couple the power amplifier to the remote electrode apparatus for supply of 
electrical power thereto and capacitive matching apparatus for providing 
real time capacitive matching between the power amplifier and the 
capacitive load across the electrode apparatus. 
Additionally in accordance with a preferred embodiment of the present 
invention, there is provided for use in hyperthermia apparatus including a 
power amplifier, remote electrode apparatus receiving a high power 
electrical supply from the power amplifier, and power transmission 
apparatus arranged to electrically couple the power amplifier to the 
remote electrode apparatus for supply of electrical power thereto, 
capacitive matching apparatus for providing real time capacitive matching 
between the power amplifier and the capacitive load across the electrode 
apparatus. 
In accordance with a preferred embodiment of the present invention, the 
capacitive matching apparatus comprises a capacitive matching unit and 
step motor apparatus for driving the capacitive matching apparatus. 
Additionally in accordance with a preferred embodiment of the present 
invention there is provided control apparatus for governing the operation 
of the step motor apparatus in accordance with real time sensing of 
reflected power. 
Further in accordance with an embodiment of the present invention, the 
control apparatus comprises apparatus for calculating a vector function 
indicating required capacitance changes. 
Additionally in accordance with an embodiment of the present invention, the 
control apparatus comprises apparatus for governing the operation of the 
step motor in accordance with a Smith chart plot. 
Further in accordance with an embodiment of the present invention, the 
capacitive matching apparatus is operative for providing capacitive 
matching over a range of applied power extending from less than 10 W to at 
least 1.2 KW. 
Additionally in accordance with an embodiment of the present invention, the 
control apparatus comprises a bidirectional coupler, a decoder receiving 
an input from the bidirectional coupler and providing x and y coordinate 
indications of reflected power, and a computer operated controller 
receiving the output of the decoder and providing operating instructions 
to the step motor apparatus in accordance with Smith chart coordinates.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Reference is now made to FIG. 1, which illustrates, in general form, 
hyperthermia apparatus constructed and operative in accordance with a 
preferred embodiment of the invention. The hyperthermia apparatus 
comprises a housing 10 which encloses a high frequency RF power unit 12, 
typically having a variable output power ranging from 0-1200 W, a 
high-frequency capacitance matching unit 14 coupled to RF power unit 12, a 
controller 16 operative in cooperation with the matching unit 14, a system 
computer 18, keyboard and control panel 19, display 20, thermometer 22 and 
cooling unit 24. 
A power transmission line 30 provides electrical power from RF power unit 
12 via capacitance matching unit 14 to electrodes 32, which are placed 
across a body region, portions of which are to be heated for treatment of 
tumors. Power deposition is accomplished through the interaction of 
electric fields produced by the electrodes in the tissues disposed 
therebetween. Surface cooling of the electrodes 32 is provided by cooling 
unit 24 via cooling fluid conduits (not shown) which also communicate with 
electrodes 32. 
Briefly stated, the system illustrated in FIG. 1 and described hereinabove 
is operative to provide RF heating of selected tissue for tumor treatment. 
The capacitance matching unit is provided in order to minimize reflected 
power due to capacitance mismatching between the RF power unit 12 and the 
capacitive load across the electrodes 32. The computer 18, keyboard and 
control panel 19, and display 20, are operative to provide control and 
safety features for this operation as well as to provide data logging as 
desired. 
Reference is now made to FIG. 2, which illustrates the basic structure of 
the HF capacitance matching unit 14 of FIG. 1. A high frequency oscillator 
40, typically operating at 13.56 MHz, and having a variable power output, 
receives a control input from protection circuitry 42 which is operative 
to provide protection to the circuitry of FIG. 2 and to the patient from 
excessive incident and reflected power, cooling failure, and 
destabilization of the output power. The protection circuitry 42 also 
provides an output to switching circuitry 44, operated by an operator 
using control panel 19, to provide provide emergency power cut off. 
The output of oscillator 40 is supplied first to a preamplifier 46 and then 
to a HF power amplifier 47, typically having a rating up to 1200 watts. An 
output sampling circuit 48 receives the output of amplifier 47 and 
supplies samples of the amplifier output back to protection circuitry 42 
and to a stablilization circuitry 43 to stabilize the output power. The 
power output of amplifier 47 is provided via output sampling circuitry 48 
to the capacitive matching apparatus, which is surrounded by dashed lines 
and is illustrated in more detail in FIG. 3. 
It is noted that circuitries 40, 42, 43, 46, 47 and 48 are included in the 
RF power unit 12 (FIG. 1). 
Considering FIG. 2 at this stage, it is seen that the capacitive matching 
apparatus comprises a bidirectional coupler 50 which receives the power 
output of RF power unit 12 and provides it via matching unit 14 (FIG. 1), 
and a suitable transformer 52, to the electrodes 32, across which is 
defined the capacitance of the patient's body. 
It is extremely important to note that the capacitance of the patient's 
body varies over a relatively short time period, measurable in seconds, 
due to changes in body position, breathing and other anatomical variables. 
Accordingly, in accordance with the present invention, the matching unit 
14 must be operated to provide adaptive capacitive management over the 
same general time period. 
Bidirectional coupler 50 provides an output indication to a decoder 56 of 
both the transmitted and reflected power. Decoder 56 is operative to 
provide an indication of the vector coordinates in x-y coordinates, which 
represent the relationship of the reflected power to the transmitted 
power, to a computer controller 58. It has been found in practice that the 
representation of the relationship of the reflected power to the 
transmitted power in x-y coordinates is valid over a range of output power 
from about 10 W to 1200 W. 
Computer controller 58 translates the information received from the decoder 
56 into Smith chart form in accordance with the well-known teachings of P. 
H. Smith, which originally appeared in Smith, P. H., "Transmission-Line 
Calculator," Electronics, Vol. 12, pp. 29-31, January, 1939. An 
explanation of the Smith technique appears in Engineering 
Electromagnetics, International Student Edition, McGraw-Hill Kogakusha, 
Ltd. Tokyo, 1981 on pages 446-452. 
Computer controller 58 provides an output in Smith chart coordinates to a 
motor driver 60 which, in turn, operates step motors 62, 64 of matching 
unit 14 in accordance with instructions received from computer controller 
58 in order to immediately adjust the capacitive matching to changes in 
capacitance across electrodes 32. 
Cooling apparatus comprising a cooling source 63, a pump 65, a cooling coil 
66 associated with the electrodes 32, flow measuring apparatus 68 and 
temperature measuring apparatus 70, is also provided. 
Reference is now made to FIG. 3 which provides a more detailed illustration 
of the capacitive matching apparatus of FIG. 2. The output from 
bi-directional coupler 50 is supplied to decoder 56, which includes a pair 
of series-connected amplifier pairs, each of which inputs to a splitter. 
The two splitters are 90 degrees out of phase and provide respective X and 
Y outputs. These two outputs, together with a power indication output, are 
supplied to computer controller 58. As noted above, the output of computer 
controller 58 is supplied to motor driver 60 which operates motors 62 and 
64 of the matching unit 14. 
Reference is now made to FIGS. 4A-4F, which are detailed schematic 
illustrations of the circuitry of decoder 56, each portion of the 
circuitry being indicated by a reference indication corresponding to the 
number of the corresponding drawings. For the sake of conciseness, it is 
deemed superfluous to describe verbally that which is clearly and 
completely shown in the schematic illustrations of FIGS. 4A-4F. 
Controller 58, with the exception of its Z-80 CPU, is shown in detailed 
schematic form in FIGS. 5A-5D. For the sake of conciseness, it is deemed 
superfluous to describe verbally that which is clearly and completely 
shown in the schematic illustrations of FIGS. 5A-5D. 
The matching unit 14 is illustrated pictorially in FIGS. 6A and 6B and is 
seen to correspond to the circuit diagram thereof in FIG. 3. Two 
multi-tapped inductors, L 1 and L 2, are each rated at 16 microhenries 
overall, and have individual portions rated as shown in FIG. 6A. Eight 
variable capacitors C, rated at 10-150 picofarads each, are arranged as 
shown, such that each motor controls four such variable compacitors 
independently of the other motor. 
Reference is now made to FIGS. 7A and 7B which illustrate two Smith chart 
representations of the operation of the matching unit 14. The closed 
circular traces 80 indicate operation of one of the motors, such as motor 
64, while the central, generally helical, trace 82 indicates the operation 
of the other motor, such as motor 62. The combined operation of the motors 
brings the reflected power to a desired minimum within a few seconds. 
FIG. 7B is provided to illustrate the advantages of employing the x-y 
coordinate information representing the relationship between transmitted 
and reflected power according to the present invention, instead of merely 
considering the absolute values of transmitted and reflected power as in 
the prior art. 
Location 84 represents the point of minimum reflected power. The reflected 
power increases with distance from location 84 in all directions. 
Accordingly circle 88 represents all of the points at which the reflected 
power is identical to that at a location 86. 
The capacitive matching technique of the present invention will now be 
compared with the prior art technique for capacitive matching with 
reference to point 86. In accordance with the present invention, when the 
x and y vector components indicating the relationship between reflected 
and transmitted power are known, motor 62 is operated to change the 
impedance along the trace 91 until the impedance reaches the point closest 
to trace 90. When the impedance has reached trace 90, i.e. at point 93, 
the operation of motor 62 is terminated and motor 64 is then operated to 
vary the impedance along trace 90 until the impedance reaches location 84. 
According to the prior art, each motor is operated individually in an 
effort to reach a local minimum of reflected power. This is an interative 
process which continues until the minimum reflected power is realized, and 
it can sometimes take a significant amount of time. This may be appeciated 
by considering that any movement along traces 88 and 92 from location 86 
increases the reflected power, thus trapping the capacitive matching 
apparatus at a local minimum which is much higher than the minimum 
reflected power at location 84. 
A computer listing of the software employed in controller 58 is appended 
hereto. 
##SPC1## 
It will be appreciated by persons skilled in the art that the present 
invention is not limited to what has been particularly shown and described 
hereinabove. Rather the scope of the present invention is defined only by 
the claims which follow: