1 2
other intracavitary methods or interstitial techniques,
MICRO-HEAT-PIPE CATHETER such as placing heating elements directly into the tumor. The use of interstitial techniques permits the
SUMMARY OF THE INVENTION achievement of therapeutic temperature levels without
Millions of people are afflicted with some form of 5 appreciable heating of normal tissues, regardless of the cancer every year, and new techniques for cancer treat- tumor geometry. The use of a number of heating element are continually being developed. The use of local ments permits the regulation of the heat rate to the hyperthermia, or elevating the temperature of a cancer- appropriate level. Interstitial hyperthermia devices inous part of the body to a slightly higher temperature has elude sets of implanted electrodes connected to a radio received increased attention over the past few years. 10 frequency generator, combinations of implanted and Localized heating of a cancerous tumor (including the external electrodes, and implanted microwave antennas, edges of the tumor) to therapeutic temperatures of 42.5° Implanted or injected thennoseeds are also considered C. (108.5° F.) to 43.0° C. (109.4° F.) for periods of 20 to an invasive heating technique. 30 minutes will in most cases destroy the rapidly grow- Each of these invasive techniques has drawbacks, ing cancer cells and lead to the arrest of tumor growth. 15 The use of implanted electrodes, while simple, involves
Total body temperatures above 41.8° C. (107.2° F.) placing an array of needles into the tumor and connect
are detrimental to the functions of the central nervous ing them to an RF generator. The temperature field for
system, heart, liver, and kidney, and may even cause such electrodes is very difficult to control, and the
histologically obvious damage to tissue cells, whereas volume that can be heated effectively is rather small,
tumorcidal effects are generally not observed below 20 requiring many implants. Such an arrangement may
42.5° C. (108.5* F.). At brain temperatures of over 41.8° resuit m non-uniform heating with excessive tempera
C. (107.2* F.), the mechanism for regulation of body tures. Further, the use of high frequencies and high
temperature can be incapacitated and there is danger of voltage may interfere with the electronic thermometers
'malignant' or 'runaway' hyperthermia. Further, tern- md could be harmful to the patient.
peratures of up to 45* C. (113.0° F.) may cause soft 25 x lanted electrodes require connections t0 an exter
Ossue necroses and fistulas as well as skin burns. There- na, r sonnje- A j number of connection wires,
fore accurate temperature control is critical to success- of feed lin major blems. These
ful hyperthermia. As a consequence, there is a sigmfi- b,ems mdude ^ 0ver-heating of feed lines, as well
cant need for development of a simple hyperthermia temperature inhomoeeneity
device which will generate a precisely controllable heat 30 £ ... ^ from
rate that is confined to the tumor region in order to ., v .. . . . . . ~ ,j — .
minimize the risk of damage to the surrounding normal n"%*PI*«> magnetic induction field Each acts as a
tissue and the overall body functions. sma" heatm8 urat' transfernng heat to the tumor by
Local hyperthermia must elevate the temperature of conduction. Implanting microwave antennas is probaa cancerous tumor to a therapeutic level while maintain- 35 «y the most popular invasive heating technique and has ing the temperature of the surrounding tissue at normal been used ln manv treatments Generally, an array of levels. Numerous heating methods for tumor treatment sfds or an1tennas are Ranted m the tumor and left m have been proposed over the past few decades, and Place for the duration of the treatment, several methods are currently in practice. These heating Thermoseeds are generally small cylinders and retechniques may be classified from a clinical point of 40 °«mre careful placement m the tumor because the onenview as non-invasive and invasive. mioa respect to the induced magnetic field dic
Non-invasive hyperthermia techniques involve the tates the degree of tumor heating. As a consequence,
use of electromagnetic or ultrasound energy focused on each cylinder must be implanted individually. As with
the region to be heated by means of external systems. °th.er invasive methods, the use of thermoseeds has
This energy heats the body tissues to the desired tern- 45 limited temperature control. Further, areas with poor
peratures. While it is possible to focus this energy, the blo°d flow may overheat while regions with high blood
resulting effect is regional heating rather than local flow may not attain therapeutic temperatures,
heating, and the blood flow carries much of the heat Small ferromagnetic microspheres may be injected
away. This approach often exhibits large fluctuations in into the tumor or into the blood supply. The appropri
heating due to variations in blood flow and tissue ther- 50 ate region is then subjected to a high intensity, low
mal conductivity. frequency magnetic field. The microspheres absorb
Both electromagnetic and ultrasound energy must be energy from the magnetic field and heat the cancerous
carefully focused, and the wavelength of the beam must tissue by conduction heating. This technique, however,
be small compared to the tumor dimensions. As a conse- has not been used on humans.
quence, microwave heating is not useful for deep tu- 55 AH non-invasive and invasive techniques require a mors, but may be used on diseased areas only a few complete knowledge of the temperature distribution in centimeters into the body. Thus, microwave energy is the diseased region. As a consequence, these techniques restricted to superficial tumors or diseased areas not require the insertion of a large number of invasive temrequiring deep penetration. Ultrasound also exhibits a perature probes or an improvement in the thermal modfrequency-dependent penetration depth. Bones are very 60 eling of the region between temperature probes, strong absorbers of ultrasound beams while air cavities An ideal heating technique must account for the are almost perfect reflectors. Further, reflections occur three-dimensional character of a tumor and its surat dissimilar tissue interfaces, causing additional prob- roundings. Microwave antennas and implanted needle lems. Coupling between the applicator and skin also electrodes lack this ability. However, a technique emposes a problem in some cases. 65 ploying a micro-heat-pipe can account for this charac
Invasive heating techniques include the perfusion of teristic.
the extremities with extracorporally heated blood, the Micro-heat-pipe technology is well known to those in
irrigation of the urinary bladder with heated saline, and the field, and small heat-pipes and miniature heat-pipes
