How does a microwave hyperthermia system work for cancer treatment and what frequencies are used?

A microwave hyperthermia system for cancer treatment uses focused microwave energy to heat tumors to 40-45 degrees C (hyperthermia range), which damages cancer cells (which are more temperature-sensitive than normal cells) and enhances the effectiveness of radiation therapy and chemotherapy. The system works by delivering microwave power from an external applicator (antenna array) through the body tissue to the tumor location, where the electromagnetic energy is absorbed and converted to heat. The frequencies used for microwave hyperthermia are: 433 MHz (ISM band, Europe; deepest penetration, approximately 5-7 cm effective heating depth in muscle, but lower spatial resolution), 915 MHz (ISM band, US; good balance of penetration approximately 3-4 cm and focusing ability), and 2.45 GHz (ISM band, worldwide; best spatial focusing approximately 1-2 cm spot size, but limited penetration depth approximately 1.5-2 cm, best for superficial tumors). The choice of frequency depends on the tumor depth: deep tumors (>3 cm) require lower frequencies (433 MHz or 915 MHz) for adequate penetration, while superficial tumors benefit from higher frequencies (2.45 GHz) that concentrate heating in a smaller volume. The system includes: a microwave power source (solid-state amplifier, 50-150 W per channel), a phased array applicator (4-16 antennas surrounding the treatment volume), phase and amplitude control for each channel (to steer and focus the heating pattern), and temperature monitoring (fiber-optic temperature probes inserted near the tumor, or MRI thermometry for non-invasive 3D temperature mapping).