Brain hyperthermia: I. Interstitial microwave antenna array techniques--the Dartmouth experience

Area of Science:

• Biomedical Engineering
• Oncology
• Medical Physics

Background:

• Hyperthermia therapy, using heat to treat cancer, is an established modality.
• Microwave heating offers precise temperature control for targeted tumor treatment.
• Developing effective microwave antenna arrays is crucial for uniform tumor heating.

Purpose of the Study:

• To evaluate the efficacy of various microwave antenna designs for hyperthermia treatment of brain tumors.
• To achieve target temperatures of 43.0 degrees C throughout the tumor volume.
• To assess the heating capabilities and temperature distribution of different antenna configurations.

Main Methods:

• Flexible microwave antennas (dipole, choke dipole, modified dipole, helical) were tested at 915 or 2450 MHz in brain-equivalent phantoms and patient arrays.
• Phase shifting and rotation techniques, guided by a treatment planning computer, were used to direct power within the tumor.
• Choke antennas were specifically designed to minimize insertion depth dependency for consistent power delivery.

Main Results:

• Twenty-three patients received treatment with one to six microwave antennas.
• Average tumor temperatures ranged from 37.2-44.3°C (mean 40.0°C) minimum and 46.5-60.1°C (mean 49.1°C) maximum.
• 70.9% of all measured temperatures reached the therapeutic threshold of ≥43.0°C, with T50 at 44.2°C.

Conclusions:

• An array of four dipole antennas spaced 2.0 cm apart demonstrated the ability to heat a significant volume.
• This configuration could heat a volume of 5.9 cm x 2.8 cm x 2.8 cm, indicating effective tumor coverage.
• The study validates the use of microwave antenna arrays for targeted hyperthermia in brain tumor treatment.