This project will address the need for real-time, continuous measurement of radiation dose in vivo. Single- and dual-dielectric radiation sensing field effect transistor (RADFET) fabrication sequences will be developed. A mask set for semiconductor processing will be designed and manufactured. These masks will be used to fabricate both isolated transistors and arrays of RADFETs of both types for evaluation and optimization of the process as well as characterization of the sensors. The process will be incorporated into an integrated circuit fabrication sequence so that RADFETs and circuits can be manufactured on a single silicon substrate. Smart radiation sensors, containing a sensor as well as excitation, control and analog to digital conversion will be developed under Phase II. These chips will be assembled into a multisite, digital output probe. Each year close to l million new cases of cancer are reported in the US alone; nearly 60% or 600,000 of those cases are treated with radiation. Radioimmunoassay therapy (RIT) is currently under investigation and in clinical trials as a novel technique of targeting tumors. The instrument will allow real time dose rate and total accumulated dose measurements during RIT treatment. This information, unobtainable by any current techniques, will result in better pre-treatment planning and post-treatment evaluation as well as potential optimization of radiation exposure during radioimmunotherapy. In addition, the small RADFET sensors can be used for brachytherapy stereotactic radiotherapy and on-patient monitoring.