Development of a new integrated IN-VIVO counting system at the QST.

This article focuses on the development and performance evaluation of a new integrated in-vivo counting system at the National Institutes for Quantum Science and Technology (QST) in Japan, designed to function as both a whole-body counter (WBC) and a lung counter (LC) for internal dose assessment. The system employs three high purity germanium (HPGe) detectors arranged flexibly within a 20-cm-thick iron shielding chamber and was calibrated using three standard phantoms: the BOttle Manikin ABsorption (BOMAB) phantom, the Lawrence Livermore National Laboratory (LLNL) phantom, and the Japan Atomic Energy Research Institute (JAERI) phantom. Monte Carlo simulations supported the optimization of detector placement, showing good agreement with experimental peak efficiencies for photon energies above 100 keV. For lung counting, the system achieved a tentative Minimum Detectable Activity (MDA) of 9.5 Bq for americium-241 (^241Am) in a typical Japanese male subject within a 30-minute counting time. The system is now operational and intended to support radiation emergency medicine preparedness in Japan.