Automated data collection and analysis system for MOSFET radiation detectors

Metal oxide semiconductor field effect transistors (MOSFET) have been used as radiation dosimeters. Because of their small detector size, minimal power requirements, and signal integration characteristics, they offer unique possibilities as real-time dose monitors in radiotherapy. An automated data collection and analysis system for use with MOSFET radiation dosimeters has been designed and built. The objective was to design a system which can acquire and process the MOSFET signals in real time, in any radiation field encountered in radiotherapy. In particular, major problems have been solved arising from the intrinsic drifts of the MOSFET signal during low dose rate measurements. These signal drifts are significant when the MOSFET detector is used in applications such as on-line monitoring of radiation dose delivery in brachytherapy or radioimmunotherapy. The data collection and analysis system includes a portable IBM-compatible personal computer fitted with digital-to-analog and analog-to-digital converter boards. A single-chip programmable current supply is used to power the MOSFET dosimeters. Intrinsic and extrinsic drifts in signal due to ion diffusion and electron tunneling are corrected by deconvolution of the collected data in real time or after data collection. The data acquisition system and signal-processing methodologies are described.