Thin linear thermometer arrays for use in localized cancer hyperthermia

A thin linear array of silicon diodes has been developed to measure one-dimensional temperature profiles in tissue during treatment of cancer by localized hyperthermia. The array is composed of six discrete diodes on three flexible stainless steel wires, with a maximum cross-sectional dimension of 0.5 mm, so that it can be introduced into a tumor area via a small puncture wound. Temperature data are extracted using an external electronics system under microprocessor control; the present overall accuracy of the system is 0.2°C over the range of 37-45°C. The array has been tested in ultrasound, RF, and microwave heating fields. Computer simulation shows this array to be nonperturbing of the thermal field in tissue, so that it can provide accurate temperature data. Development of a batch-fabricated array of twenty diodes on five leads is under way. A monolithic silicon diode array is shown to produce large temperature perturbations because of its high thermal conductivity, while an alternative technology using silicon micromachining and adaptations of existing techniques for lead fabrication should produce an array of low thermal conductivity which can obtain accurate measurements. The present and future arrays should also be suitable for data collection in many in-vivo situations other than hyperthermia.