A miniature MOSFET radiation dosimeter probe.

Prototype miniature dosimeter probes have been designed, built, and characterized employing a small, radiation sensitive metal oxide semiconductor field effect transistor (MOSFET) chip to measure, in vivo, the total accumulated dose and dose rate as a function of time after internal administration of long range beta particle radiolabeled antibodies and in external high energy photon and electron beams. The MOSFET detector is mounted on a long narrow alumina substrate to facilitate electrical connection. The MOSFET, alumina substrate, and lead wires are inserted into a 16 gauge flexineedle, which, in turn, may be inserted into tissue. The radiation dosimeter probe has overall dimensions of 1.6 mm diam and 3.5 cm length. The MOSFET probe signals are read, stored, and analyzed using an automated data collection and analysis system. Initially, we have characterized the probe's response to long range beta particle emission from 90Y sources in solution and to high energy photon and electron beams from linear accelerators. Since the prototype has a finite substrate thickness, the angular dependence has been studied using beta particle emission from a 90Sr source. Temperature dependence and signal drift have been characterized and may be corrected for. Measurements made in spherical volumes containing 90Y with diameters less than the maximum electron range, to simulate anticipated geometries in animal models, agree well with Berger point kernel and EGS4 Monte Carlo calculations. The results from the prototype probes lead to design requirements for detection of shorter range beta particles used in radioimmunotherapy and lower photon energies used in brachytherapy.