1. What is Hyperthermia?
Hyperthermia is a relatively new cancer treatment which is gaining favor among radiation therapists in the U.S. It is the application of heat (temperatures ranging from 108°- 113°F) to solid tumor cancer. Physicians have known for over a century that cancer cells are vulnerable at higher temperatures, and within the past decade the mechanisms by which the therapy works have become understood. The problem has been finding an accurate method for directing, measuring, and monitoring the heal Hyperthermia is used in conjunction with other cancer therapies, such as radiation therapy and chemotherapy.
2. How does Hyperthermia increase the effectiveness of treatment when used in conjunction with radiation and chemotherapy?
Excessive heat in normal cells is reduced or dissipated by changes in blood flow. Circulation within tumors becomes more restricted as the tumor outgrows its blood supply. Consequently, a tumor retains heat for a longer period of time, which destroys cellular components essential for the survival and reproduction of that tumor.
Another consequence of inadequate blood supply is reduced oxygen. Radiation is more effective in destroying well-oxygenated cells while hyperthermia destroys cells lacking oxygen. When the treatments are used together, both types of cells can be destroyed. Cancer cells are also more vulnerable to heat because of insufficient nutrition and a greater acidity. In addition, heated cells are often more permeable to the drugs used in chemotherapy.
Hyperthermia, when used correctly, has minimal side effects, in contrast to the recognized side effects of radiation and chemotherapy.
3. How is heat applied to cancer tumors in hyperthermia treatments?
Whole Body Heating Techniques
Originally, hyperthermia techniques involved heating the entire body. In the late 1800's several doctors reported complete disappearance of tumors in some patients who had cancer and who had also developed high fevers in reaction to other infections. Since that time, several methods of heating the entire body have evolved, including the artificial induction of fever, the wrapping of an anesthetized patient in plastic and dipping them in hot wax, and heating the blood supply. However, many undesirable side effects are associated with whole body heating. This has lead research efforts towards more localized and precise application, control and measurement of heat.
Local Applications of Heat
Microwave: Heat produced by microwaves can be directed at tumors that are 1-3 cm from the surface of the skin. Microwaves are rapidly absorbed as they penetrate deeper into the body. Thus, tumors located at depths greater than 3 cm from the surface of the body cannot be effectively heated with presently used microwave techniques.
Interstitial Radiofrequency: Interstitial treatments send RF energy through small needles placed into the tumor. After heating, interstitial radioactive therapy material can be introduced into the tumor site through the same probes used to introduce heal (This is called brachytherapy and has been used as a cancer treatment for many years.) Interstitial hyperthermia can also be used with external beam radiation. This technique allows greater control of heat application, but is an, invasive procedure (the placement of needles can be painful and restricts the movement of the patient).
Ultrasound: This technique uses ultra-high frequency soundwaves to produce heat within the tumor. Ultrasound is more easily focused than other energy modalities and can be applied to tumors located from the skin to 8 cm within the body. This allows the treatment of tumors unreachable by other external modalities. Ultrasound doesn't require the use of radiowave shielding devices to protect medical personnel during treatment.
4. Which treatment is best: Microwave, Radiofrequency, or Ultrasound?
There is no "best" hyperthermia method. Microwave, radiofrequency, and ultrasound treatments are appropriate in different situations. It is more difficult to direct and focus microwave and radiofrequency energy. This sometimes results in the heating and damaging of normal cells. Ultrasound is more easily focused, which eliminates these problems. Also, ultrasound can be used for tumors at those deeper locations which microwave and radiofrequency cannot reach. On the other hand, ultrasound is not appropriate for most tumors involving bone or behind gas-filled cavities, such as bowel or lung. In these situations, microwaves would be more useful. However, with increasing control of application, ultrasound can be used for tumors located closer and closer to bone.
5. Where in the body can hyperthermia be used?
Hyperthermia is well suited for a wide variety of tumor locations, including chest wall, axilla, head & neck, breast, groin, and all tumors located directly on or under the skin. It has also been used to reduce the size of tumors prior to surgery, increasing the likelihood of successful removal of cancerous tissue.
6. If local hyperthermia is so effective, why isn't it used more often?
The use of local hyperthermia is limited to solid tumor cancer. Blood diseases (like leukemia) and certain tumor locations within the body (lung cancer, for example) are difficult to heat.