Application of a gamma extremity monitoring system in a radiopharmaceutical dispensary.

A new gamma extremity monitoring system (GEMS) was used to assess finger doses of staff working in a hospital radionuclide dispensary. The system is designed to give a continuous readout of dose rate from a small probe which may be attached to a finger. It allows the contributions to radiation dose to the fingers from different parts of a procedure to be measured for the first time and the detailed pattern of radiation exposure to be determined. The dose reduction benefits of small changes in procedure and the use of syringe shields were easily demonstrated after monitoring staff for a few sessions using GEMS, which would not have been possible using thermoluminescent or other integrating dosemeters. GEMS was calibrated against 99Tc(m), 241Am, 137Cs and 131I. The main disadvantage of the system is that the response of the detector increases significantly at lower radiation energies, with that at 60 keV being approximately 70 times the response at 662 keV. In addition, the response of the current detector is nonlinear and saturates around 7000 counts s(-1), which corresponds to a dose rate of 2200 microGy h(-1) for 99Tc(m). Despite these drawbacks, GEMS can play a significant part in the analysis of finger dose patterns and assist in dose reduction.