A System for High Precision Dosimetry

The automatic dosimetry system described herein is established to perform better than 3% three sigma for a single measurement and better than 1.5% three sigma for multiple measurements. This performance is demonstrated at varying photon energy modalities and doses ranging from less than 10 μGy to over 10 Gy. This system integrates the Harshaw Model 5500 automatic hot nitrogen, loose dosemeter, thermoluminescence dosimetry (TLD) instrument and an application software package that evaluates and manages the generated TLD data. The automatic, hot gas TLD reader employs a closely controlled linearly ramped readout cycle. LiF:Mg,Ti dosemeters in the form of 1 mm diam. x 6 mm rods, 3.2 x 3.2 x 0.4 mm 3 square chips, and 1 mm 3 microcubes, are used in applications requiring high spatial resolution. These dosemeters have been specially treated and their calibration factors determined to simplify the process in medical diagnosis and therapy dosimetry. Performance of the reader was evaluated by conducting the following tests according to the IEC 1066 (1991) specified procedures: Detection threshold, Reproducibility, Sensitivity to ambient light, TL residue, Stability, Power leakage, and Linearity. The portability of the calibration factor was studied at different doses, energies, and in different TLD instruments. The results are presented and analysed.