EVALUATION OF A DUAL BIAS DUAL METAL-OXIDE-SILICON SEMICONDUCTOR FIELD-EFFECT TRANSISTOR DETECTOR AS RADIATION DOSIMETER

A new type of direct reading semiconductor dosimeter has been investig ated as a radiation detector for photon and electron therapy beams of various energies. The operation of this device is based on the measure ment of the threshold voltage shift in a custom-built metal oxide-sili con semiconductor field effect transistor (MOSFET). This voltage is a linear function of absorbed dose. The extent of the linearity region i s dependent on the voltage controlled operation during irradiation. Op erating two MOSFETS at two different biases simultaneously during irra diation will result in sensitivity (V/Gy) reproducibility better than +/-3% over a range in dose of 100 Gy and at a dose per fraction greate r than 20X10(-2) Gy. The modes of operation give this device many adva ntages, such as continuous monitoring during irradiation, immediate re ading, and permanent storage of total dose after irradiation. The avai lability and ease of use of these MOSFET detectors make them very prom ising in clinical dosimetry.