Design and Evaluation of a 434 MHz Circular Ring Microwave Hyperthermia Applicator for Improved SAR in Superficial Cancer Treatment

This work presents the design of a circular ring applicator operating at a frequency of 434 MHz for superficial cancer. A simulation study is carried out on a homogeneous model to optimize the parameters of antenna design. The proposed antenna has a bandwidth of 39 MHz at −10 dB, power coupling > 90%, the tangential component of the electric field in the tissue is 94%, and the aperture size is 11.34 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. It achieves a specific absorption rate (SAR) of 10.26 W/kg at a depth of 1 cm in homogeneous tissue, which is at least 80% higher than the SAR values in literature. The improved SAR reduces the input power required for treatment. Thermal effective penetration depth (TEPD) and thermal effective field size (TEFS) are 2.66 cm and 28.89 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, respectively. Simulations on heterogeneous breast model, chest wall recurrence model, head model, and lower and upper extremities have shown promising SAR metrics, indicating effective power deposition for superficial applications, and its effective field size (EFS) values are 27.29 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 25.84 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 28 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, 28.84 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, and 29.16 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, respectively. Measurements using homogeneous tissue phantoms and ex-vivo bovine tissues reveal localized power deposition. Both cases have TEFS values of 27.3 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 25.12 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>, and TEPD values of 2.45 cm and 1.95 cm, respectively, which are consistent with the simulation results. The results indicate that the proposed applicator can be used to treat superficial tumors.