A SYSTEM FOR HIGH-PRECISION DOSIMETRY

The automatic dosimetry system described herein is established to perf orm better than 3% three sigma for a single measurement and better tha n 1.5% three sigma for multiple measurements. This performance is demo nstrated at varying photon energy modalities and doses ranging from le ss than 10 mu Gy to over 10 Gy. This system integrates the Harshaw Mod el 5500 automatic hot nitrogen, loose dosemeter, thermoluminescence do simetry (TLD) instrument and an application software package that eval uates and manages the generated TLD data. The automatic, hot gas TLD r eader employs a closely controlled linearly ramped readout cycle. LiF: Mg,Ti dosemeters in the form of I 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 special ly treated and their calibration factors determined to simplify the pr ocess in medical diagnosis and therapy dosimetry. performance of the r eader was evaluated by conducting the following tests according to the IEC 1066 (1991) specified procedures: Detection threshold, Reproducib ility, Sensitivity to ambient light, TL residue, Stability, Power leak age, and Linearity. The portability of the calibration factor was stud ied at different doses, energies, and in different TLD instruments. Th e results are presented and analysed.