A 27 MHz current source interstitial hyperthermia system for small animals

Abstract

Temperature distribution is an important factor in thermo-radiotherapy and it is greatly dependent on the applied heating technique. Consistency of the heating method is therefore important in translating in vivo experimental data to the clinical situation. To further evaluate the combination of interstitial hyperthermia and interstitial radiotherapy, an experimental interstitial hyperthermia system has been developed for small (500-2000 mm3) tumours growing in the flank of a rat. The system used reproduces the properties of our clinical current source interstitial hyperthermia system. The heating system consists of four applicators, each with independent tuning and power control. The applicators are situated inside plastic afterloading catheters and are capacitively coupled with the surrounding tissue. The tumour is heated through dissipation of a 27 MHz current flowing to an external ground plane. An effective RF-filter allows reliable thermocouple temperature measurements when the power is switched on. The tumour temperature is easily controlled by means of a continuous temperature read-out and a clear temperature display. A minimum temperature up to 46 degrees C can be reached within 4-10 min and maintained (+/-0.5 degrees C) throughout the treatment period. Modelling calculations performed for this heating system indicate that the applicator temperatures should be kept equal in order to minimize the difference between maximum and minimum temperature. Significantly higher applicator currents are needed at larger distances from the ground plane. In addition, the homogeneity of the temperature distribution is improved when either the tumour is isolated or when the environmental temperature is increased. The calculations also show that temperature distribution is strongly dependent on effective heat conductivity. A description of the system and its performance is presented.

Temperature measurement errors with thermocouples inside 27 MHz current source interstitial hyperthermia applicators

“…However, this does not mean there is no need to avoid using afterloading catheter material with a high dielectric loss factor. The effect on ERR may be limited but high-loss catheters still considerably increase the inhomogeneity of the temperature distribution in the surrounding tissue (Kaatee et al 1995), because less electromagnetic energy is absorbed directly in the tissue.…”

Implications of using thermocouple thermometry in 27 MHz capacitively coupled interstitial hyperthermia

“…The Multi Electrode Current Source (MECS) interstitial hyperthermia system developed at the Departments of Radiotherapy and Biomedical Engineering of the University Hospital Utrecht and the Department of Clinical Physics of the Daniël Den Hoed Cancer Center in Rotterdam (Lagendijk 1990, Lagendijk et al 1995, Kaatee et al 1995 is based on the capacitively coupled 27 MHz rf heating technique for brachytherapy implant catheters (Visser et al 1989, Marchal et al 1989, Deurloo et al 1991. The three-dimensional power steering of the MECS system is an important feature, as power control on a centimetre scale or better greatly improves temperature uniformity (Crezee and Lagendijk 1992).…”