Hyperthermia induction is a medical procedure that involves raising the temperature of body tissue to a controlled, therapeutic level, ranging from 40 to 45 °C (104 to 113 °F). This process is distinct from a fever, where the body’s internal temperature set point is altered; in hyperthermia, external methods achieve the elevated temperature. This treatment is applied to achieve specific biological effects within the heated tissues.
Biological Principles
Elevated temperatures influence cell structure and function. Heat can directly damage diseased cells by causing proteins to unfold and aggregate, disrupting their normal cellular processes. This thermal stress can also affect cell membranes, altering their permeability and leading to cell death.
Beyond direct damage, elevated temperatures can make certain treatments, such as radiation or chemotherapy, more effective. Hyperthermia can improve blood flow and oxygenation within a heated area, counteracting the oxygen deprivation often found in tumors due to their disorganized blood vessels. This improved oxygenation enhances radiation therapy effectiveness. Heat can also interfere with DNA repair enzymes, making cells more susceptible to DNA damage caused by radiation or certain chemotherapy drugs. It may also increase the uptake of some chemotherapy drugs by cells, augmenting their therapeutic impact.
Techniques for Temperature Elevation
Hyperthermia techniques are categorized by the extent of the body heated: local, regional, and whole-body hyperthermia. Local hyperthermia focuses heat on a small, specific area, such as a tumor on or just below the skin, or within a body cavity. Regional hyperthermia targets larger areas like an organ or a limb, or deep-seated tumors within the body. Whole-body hyperthermia involves raising the temperature of the entire body.
Radiofrequency (RF) energy, ranging from 5-27 MHz for deep heating or 150-430 MHz for superficial heating, uses electromagnetic fields to generate heat within tissues. Microwave technologies, operating at frequencies of 1 GHz or greater, are used, particularly for superficial tumors or for focusing continuous-wave energy into specific areas like breast tissue. Ultrasound, especially high-intensity focused ultrasound (HIFU) at frequencies from 300 kHz to 10 MHz, precisely targets and heats tissues through molecular collisions. Infrared sources, particularly water-filtered infrared, are used for superficial heating, penetrating up to about 3 cm. Other methods include heating fluids like blood or chemotherapy drugs and circulating them through the body or a specific region, known as perfusion.
Therapeutic Applications
Hyperthermia finds primary use as an adjuvant therapy, meaning it is used with other treatments. Its most common application is in cancer treatment, where it is often combined with chemotherapy or radiotherapy. This combination enhances the effectiveness of these conventional therapies by sensitizing cancer cells.
The rationale for using hyperthermia in cancer treatment stems from its biological effects on tumor cells. Heat can directly damage cancer cells and also improve the delivery and efficacy of radiation and chemotherapy. Hyperthermia can increase oxygenation within tumors, which can improve the response to radiation therapy, and it may also impair DNA repair mechanisms in cancer cells, making them more vulnerable to DNA-damaging agents. While cancer treatment is the predominant application, hyperthermia has also been explored in other medical fields like orthopedic rehabilitation, physiotherapy, and traumatology.
Safety and Patient Considerations
Hyperthermia induction is a controlled medical procedure conducted by specialists, with continuous patient monitoring. Side effects and risks can vary depending on the type and extent of hyperthermia. Mild side effects may include skin burns, discomfort, pain, or blistering in the heated area.
More severe complications, though less common, can include organ damage or heatstroke, especially with whole-body hyperthermia if temperatures exceed 40 °C (104 °F). Patient suitability is assessed before treatment, considering contraindications such as certain heart conditions or metallic implants for electromagnetic heating. Observation of vital signs, including core body temperature, heart rate, and blood pressure, helps manage risks and ensures patient safety.