Generation of Controllable Heating Patterns by Two Types of Thin Microwave Antennas for Interstitial Microwave Thermal Therapy

In recent years, various types of medical applications of microwaves have widely been investigated and reported [1]. In particular, minimally invasive microwave thermal therapies using thin coaxial antennas are of a great interest. They are interstitial microwave hyperthermia [2] and microwave coagulation therapy (MCT) [3] for medical treatment of cancer, cardiac catheter ablation for ventricular arrhythmia treatment [4], thermal treatment of BPH (Benign Prostatic Hypertrophy) [5], etc. Up to now, the authors have been studying such thin coaxial antennas for the interstitial microwave hyperthermia. Hyperthermia is one of the modalities for cancer treatment, utilizing the difference of thermal sensitivity between tumor and normal tissue. In this treatment, the tumor is heated up to the therapeutic temperature between 42 and 45 °C without overheating the surrounding normal tissues. We can enhance the treatment effect of other cancer treatments such as radiotherapy and chemotherapy by using them together with the hyperthermia. There are a few methods for heating the cancer cells inside the body. Especially, the authors have been studying a coaxial-slot antenna [6], which is one of the thin microwave antennas, for the interstitial microwave hyperthermia. As a result of these investigations, actual treatments could be realized in some cases by use of our developed antenna and the effectiveness of the treatments has been confirmed [7]. Figure 1 shows an example of photograph during the treatment. In the treatments, control of the heating region is important especially for the treatment of critical organs such as brain. It is possible to change the heating pattern in the perpendicular direction of the antenna axis by varying the number of elements and the antenna insertion points. In addition, control of the heating pattern in the longitudinal direction of the antenna axis is realized by changing the structure of the antenna elements while keeping the thin structure. In this paper, heating characteristics of the thin coaxial antennas, which generate the controllable heating patterns in the longitudinal direction of the antenna axis, are described.