Finite element analysis of the needle type applicator made of shape memory alloy.

In this paper, we propose a new heating method in which we use shape memory alloy (SMA) in a needle type applicator for brain tumor hyperthermia. In order to expand the heating area of a needle type applicator and to control the heating pattern for various sizes of tumors, some kinds of SMA needle type applicators were developed. To apply the proposed heating method safely to clinical hyperthermia, it is necessary to make appropriate thermal distribution to the region of the brain tumor. However, it is not easy to predict the three dimensional temperature distribution during the human brain tumor hyperthermia. Therefore, we estimated the temperature distribution inside the agar phantom by the finite element method (FEM). Here, first, the computer simulation results of temperature distributions under the different heating times are discussed. Second, a comparison of the heating properties obtained by using the needle type electrodes made of different shaped SMA is discussed. From these results, it is confirmed that the proposed heating method can expand the heating area and control the heating pattern for the various sizes of brain tumors.

Improvement of needle type applicator made of shape memory alloy.

This paper discusses radio frequency (RF) interstitial hyperthermia for brain tumors with a developed needle type applicator made of a shape memory alloy (SMA). The problem with the heating method of interstitial hyperthermia is the small heating area. So, we proposed a new heating method using a needle type electrode made of SMA which consists of nickel (Ni), copper (Cu) and titanium (Ti) for expanding the heating area. Here, we proposed the heating method that the leading end of needle type electrode was divided into four parts and the leading end spreads in four directions with a temperature rise. First, the proposed RF interstitial hyperthermia system with the SMA needle was presented. Second, the results obtained by the experimental heating of the agar phantom by using the developed SMA needle type applicator were presented. Third, comparing experimental results, we discussed the heating properties of the developed system. Finally, from these results, it is confirmed that the developed needle type applicator made of SMA is useful for wide heating by invasive hyperthermia.

Development of automatic impedance matching system for hyperthermia treatment using resonant cavity applicator.

In this paper, we discuss a new system to make impedance matching automatically for a re-entrant resonant cavity applicator for brain tumor hyperthermia treatment non-invasively. We have already discussed about the effectiveness of the heating method using manual type impedance matching controller, with experiments of heating an agar phantom and computer simulations. However, it becomes difficult to perform an accurate impedance matching as resonant frequency becomes high. Here, in order to make a more accurate impedance matching, we developed the automatic impedance matching system (AIMS). We noticed that the reflected power was generated when the impedance matching was not complete. In this system, therefore, to reduce the reflected power fed back, the stepping motor to turn the dial of variable capacitors is controlled by developed software. To evaluate the developed AIMS, the experiments of heating the agar phantom were performed. From these results, we found that the temperature rise of the agar phantom by using AIMS was about 180% of using manual type controller under the same heating condition. It was found that the proposed system was very effective for hyperthermia treatment using resonant cavity applicator even when the resonant frequency was high.

Heating properties of re-entrant resonant cavity applicator for brain tumor with simple head model.

We have already confirmed the effectiveness of the re-entrant resonant cavity applicator system with non-invasive experiments of heating cylindrical agar phantoms and computer simulations. This paper discusses the heating properties of the developed heating system with a human head model made of agar for brain tumor hyperthermia treatment. First, we present the results of heating a uniform agar head model with the developed heating system. In the experiments, the temperature rise at the center of the agar was about 8 degrees C, it was found that the center of the agar is heated to maximum temperature non-invasively. Second, we present the results of heating a non-uniform agar head model having an oral cavity and a nasal cavity. We found that the center of the agar can be heated to maximum temperature as well as uniform agar head model. From these results, it is confirmed that the possibility of effective hyperthermia for various types of deep-seated brain tumors.

Heating properties of developed needle type applicator made of shape memory alloy.

This paper discusses radio frequency (RF) interstitial hyperthermia for a brain tumor with a needle type applicator made of a shape memory alloy (SMA). In this method, it is necessary to make appropriate thermal distribution to the region of the brain tumor. However, it is not easy to predict the thermal distribution during the heating. We estimated the temperature distribution inside an agar phantom by the finite element method (FEM), and heated the agar phantom with the developed needle type applicator. Here, first, the developed RF interstitial hyperthermia system with the SMA needle was presented. Second, the results obtained by the computer simulation and the experimental heating results of the agar phantom by using the developed SMA needle type applicator were presented. Comparing computer simulation results and experimental results, we discussed the heating properties of the developed system. Finally, from these results, it is confirmed that the developed needle type applicator made of SMA is useful for wide heating of invasive hyperthermia.

Finite element analysis of the re-entrant type resonant cavity applicator for brain tumor hyperthermia.

In this paper, we have proposed a new heating method in which high frequency electric fields in a re-entrant type resonant cavity are used for the heating of deeply seated tumors. In this method, a human head is placed between the gap of the inner re-entrant cylinders, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human head and the applicator. Here, we proposed a new method to control the heating area. In this method, the resonant frequency inside the cavity was changed, then we use the TM010-like mode and the TM012-like mode from various types of the resonant frequency. First, the computer simulation results of electric and magnetic field patterns are presented. Second, a comparison of the heating properties of TM010-like mode and TM012-like mode are discussed. The heating area of the center of agar phantom is more concentrated by using TM012-like mode than that of using TM010-like mode. From these results, it is confirmed that the proposed method can be controlled to heat the various sizes of deep tumors.

Heating properties of re-entrant resonant applicator for brain tumor by electromagnetic heating modes.

This paper discusses a new method to control the heating area of a re-entrant resonant cavity applicator for brain tumor hyperthermia treatment non-invasively. We have already discussed about the effectiveness of a developed system with experiments of heating an agar phantom and computer simulations. Here, in order to heat a deep brain tumor, we propose the heating method of using several electromagnetic heating modes which are transverse magnetic (TM) modes. In this method, TM010-like and TM012-like modes obtained by selecting resonant frequencies can be used to heat the deep brain tumors. To control the heating area of the modes the agar phantom is used in the heating experiments by the developed system. From these results, we found that the heating area of the agar phantom by using TM012-like mode is about 50% of the heating area of TM010-like mode. It is found that the proposed heating system can be applicable to the hyperthermia treatment of brain tumors corresponding to the size and the position where it occurred.

Experimental heating properties of re-entrant type resonant cavity applicator for deep tumor hyperthermia.

This paper discusses the heating properties of a new type hyperthermia system composed of a re-entrant type resonant cavity applicator for a deep tumor of the abdominal region. In this heating method, a human body is placed between the two inner electrodes, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human body and the applicator. First, the experimental heating results of an agar-muscle equivalent phantom were presented. Second, we performed an experiment with a lard-agar phantom. The center region of the agar phantom could be heated selectively without generating hot spots in the lard layers. From these results, it was found that our newly developed heating method is useful for a deep-seated tumor hyperthermia treatment.

Design and construction of resonant cavity applicator for brain tumor hyperthermia treatment without contact.

A re-entrant type resonant cavity applicator for brain tumor hyperthermia treatment is presented. In this method, a human brain is placed between the gap of the inner re-entrant cylinders without contact. This cavity has a window for insertion of the human head. Here, first, to design and construct a resonant cavity applicator, the results of the temperature distribution inside an agar phantom and electromagnetic field leaked from the attached window to the environment by the computer simulation were presented. Second, The developed resonant cavity and inner electrode, which were made of an aluminum alloy, were presented. Third, the experimental heating result of the agar phantom was presented. In the experiment, the center region of the agar phantom is heated to 42 degrees C. The leaked electric field strength at the position of 10 cm away from the center of the window was less than that of 10% of the center of the agar phantom. It was found that the developed resonant cavity applicator was applicable to both deep and regional brain hyperthermia treatment.

Development of the re-entrant type resonant cavity applicator for brain tumor hyperthermia - experimental heating results.

A re-entrant type resonant cavity applicator for brain tumor hyperthermia treatment is presented. In this method, a human head is placed between the gap of the inner re-entrant cylinders, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human head and the applicator. First, the comparison of the computer simulation and experimental results were presented. The estimated temperature agrees with the measured temperature with an error of 10% or better. Second, a method to control the heating pattern was presented. In the method, a human head was moved towards the electrode. The controllable range of heating pattern was about 70% of the distance from the center of the agar phantom in the direction of depth.

Improvement of the resonant cavity applicator for brain tumor hyperthermia - Experimental heating results -.

A re-entrant type resonant cavity applicator for deep tumor hyperthermia treatment was presented. In this method, a human body is placed between the gap of the inner re-entrant cylinders, and is heated with electromagnetic fields stimulated in the cavity without contact between the surface of the human body and the applicator. In this paper, two methods to control the heating pattern were proposed. In the first method, a human body was moved towards the electrode. In the second method, the diametric ratio of the inner electrode was changed. The controllable range of heating pattern was about 20% of the distance from the center of the agar phantom in the direction of depth.

Improvement of the resonant cavity applicator for brain tumor hyperthermia - Computer simulation results -.

This paper discusses new methods to control the heating pattern of the prototype resonant cavity applicator for deep tumor hyperthermia treatment. We have already confirmed the effectiveness of the developed heating system with experiments using agar phantoms and computer simulations. Here, the following two methods to control the heating pattern were proposed. In the first method, a human body, which was placed in the gap between the two inner electrodes, was only moved towards the electrode. In the second method, in addition to the first method, the diametric ratio of the inner electrodes was changed. According to our computer simulation of heating agar phantoms, we found that the hot spot was moved about 35% of the distance from the center of the agar phantom. It was found that the proposed heating methods were applicable to both deep and regional hyperthermia treatments.