Interstitial Hyperthermia in Combination with Radiation Brachytherapy for Treatment of Breast Tumor

Combination of interstitial hyperthermia and radiation brachytherapy has been shown to be effective for treatment of a tumor. After increasing the temperature, the tumor becomes sensitive to radiation dose, and as a result the radiation dose can be reduced. The purpose of this study was to identify the appropriate invasive antenna array which can be effectively used on a deep-seated breast tumor to increase the temperature to more than 42.5°C, and to examine the effect of a smaller cumulative radiation dose of 30 Gy. We have found coaxial-slot antenna array to be the most appropriate for applying hyperthermia on a deep-seated breast tumor. The temperature distributions were measured with a breast phantom, and specific absorption rate (SAR) distributions were calculated using a simulation software. A coaxial-slot antenna array, consisting of two coaxial-slot antennas, separated by 5 mm, and using a microwave power of 15 W increased the temperature of a tumor phantom, in an area of 30 mm in diameter, to over 42.5°C in 30 min. The temperature as well as SAR were observed to have increased more in the tumor tissue than in the other types of tissues which were tested. Thereafter, we have examined the radiation dose distribution of brachytherapy using a treatment planning software. Simulations were conducted on the Computed Tomography image of an anonymous breast tumor patient; the tumorʼs dimensions were 40 mm (length)×30 mm (width). A radiation dose of 30 Gy given in 5 fractions of 6 Gy each, which is lesser than the conventional radiation doses used in external beam radiation therapy, was applied to the tumor. Harm to adjacent tissues is also expected to be minimized due to lower radiation dose. As a result of this study, there is a possibility of local control of deep-seated small breast tumors using a combination of interstitial hyperthermia by using coaxial-slot antenna array to increase the temperature to over 42.5°C and radiation brachytherapy by applying cumulative dose of 30 Gy.