Absolute Activity Measurement of 125I Seed Brachytherapy by Two-dimensional Photon-photon Coincidence Spectroscopy

Photon-photon coincidence counting is a primary standardization technique used for the absolute activity measurement of short half-life radionuclides. In this study, a coincidence spectrometer based on digital signal processing was developed for the absolute standardization of 125I seed Brachytherapy. The spectrometer includes a waveform digitizer that samples at the preamplifier signals directly from two similar 2ʺ × 2ʺ NaI (Tl) detectors. The sampled signals were shaped into trapezoidal signals for pulse height analysis. These detected signals were then recorded in a list file and the software was used to recognize coincidence events. Detailed discussions were included on the formulas for determining absolute activity measurement. The activity of a 125I seed was measured and showed good agreement with the reference values. This presented technique is a quick method for measuring the activity of 125I at nuclear hospitals. The standardized source can also serve as a tracer for measuring the activity of the 109Cd source