Waveguide-based applicators for superficial hyperthermia treatment: is tuning really required?

Waveguide-based applicators are used for hyperthermia treatment of superficial tumors, e.g. chest wall recurrences. During superficial hyperthermia treatment (SHT), the patient is in the near field of these antennas, so its radiating properties may vary. To maximize the transfer power from generators towards treatment area, waveguide-based applicators usually feature means for tuning the applicators. The purpose of this study was to investigate whether waveguide-based applicators for SHT really require such tuning. Hereto, we designed and optimized a waveguide lucite applicator at 434 MHz, applying a muscle phantom and a layered (skin, fat and muscle) phantom to mimic the patient.Applicator performance was measured for different water bolus temperatures and temperatures of the water circulating the applicator by studying impedance matching. S₁₁ ≤ -15 dB was measured for nine locations at the skin of a volunteer and three different water bolus temperatures.We conclude that tuning of waveguidebased applicators is not required when the applicator is properly designed.