About Hyperthermia

When cells are heated beyond their normal temperature they can become sensitized to therapeutic agents such as Radiation and Chemotherapy. If they are heated higher still the heat will irreparably damage them. The application of heat in a therapeutic setting is called Hyperthermia. Tumor cells have been shown to be more sensitive to some levels of hyperthermia than normal tissue cells. This has given investigators great hope of using Hyperthermia as an effective cancer therapy. Biological studies have shown that there is a time - temperature relationship for the effectiveness of heat; two different temperatures may cause the same biological effect if the time is adjusted to account for the difference in temperatures. This phenomenon is known as thermal dose and has led to different applications of Hyperthermia: using moderate temperatures as therapeutic sensitizers, or using higher temperatures as a method of ablating tissue minimally invasively or noninvasively.

In clinical practice, Hyperthermia has been shown to be effective in the treatment of cancer. Different types of thermal therapies with different goals may raise the temperature to different levels.

• Several centers are conducting investigational work with whole body hyperthermia. This generally involves temperatures of 40 -42 o C (104-107.5 Farenheit) and requires specialized equipment with careful monitoring and medical support.
• Localized heating to temperatures in the range of 41 - 45 o C (106 - 113 Farenheit) have been used to sensitize cancer cells to the effects of other therapies such as Radiation therapy, Chemotherapy, and biological therapies. Although these temperatures may seem high, the heating is confined just to the area of the tumor and generally it is very well tolerated. This type of treatment can be delivered to superficial sites (such as the breast or chest wall, head and neck, etc.), to sites deep in the pelvic and abdominal region, or to the whole body.
• Other techniques are used to achieve much higher temperatures in order to completely ablate the tissue being treated. These techniques have been investigated in brain, liver, and prostate and require very precise placement of the energy in the tissue that needs to be ablated.

There is a range of methods used to elevate the temperature:

• Microwaves and ultrasound are the most commonly used modalities to elevate the temperature of superficial tumors. The sources can either be coupled to the heated area externally or interstitially implanted into the tissue. Typical areas of treatment are the chest wall and breast, head and neck areas, and any other sites that allow access and where the tumor is not too deep.
• Radiofrequency waves are typically used to heat deeper pelvic tumors and can be used to heat limbs as well. Typically the area to be heated is surrounded by a ring of radiating elements. The energy is directed into the tissue by including a layer of water between the radiating elements and the patient.
• Whole body hyperthermia typically uses warm-water blankets, inductive coils, or thermal chambers. This method delivers the hyperthermia to the entire body and works well in conjunction with other systemic therapies.
• High temperature thermal ablation therapies typically either implant heating sources in the area to be ablated or "focus" energy into the tissue to be heated noninvasively. This type of therapy requires image guidance in order to ensure the correct tissue is being ablated.

In all types of hyperthermia, temperature monitoring is critical. Presently this is done invasively by placing thin temperature probes into the tissue being heated. However, several investigators are developing methods to measure temperature noninvasively using modalities such as MRI and ultrasound. Developments in this area could have profound effects on the application of thermal therapy.

Clinical studies in hyperthermia are ongoing at several institutions in the United States as well as world wide. Convincing results from randomized (phase III) studies in Europe have demonstrated the ability of hyperthermia as a cancer therapy for breast cancer, head and neck cancer, and melanoma. Biological studies continue to investigate the effects of heat on cell processes as well as helping to determine clinical schemes for fractionation and combinations of hyperthermia with other therapeutic agents. Engineering developments are aimed at the improved delivery and monitoring of thermal therapy.