Monte Carlo based optimization of source configurations for calibration of quick scan whole body monitor

NaI(Tl) based standing geometry whole body counter, Quick Scan Whole Body Monitor (QSWBM), has been used for in-vivo detection of high-energy photon emitters in various laboratories across India. Conventionally, the Indian reference BOMAB phantom (BOMAB-I) is being used for the periodic calibration of QSWBM. For calibration purposes, various monitoring laboratories follow diverse source configurations in a phantom, such as uniform distribution, axial cavity distribution, and central axial cavity distribution, depending on the source availability and phantom type. In the present study, simulations using FLUKA code were performed for QSWBM using numerical BOMAB-I phantom for uniform and various axial cavity distributions. The results from different source configurations were compared to understand the optimum number of sources to be procured for accurate calibration of a standing geometry whole body counter using BOMAB-I phantom. The study demonstrated that the axial source based calibration can be performed effectively using BOMAB-I phantom with a minimum of one source instead of a configuration in which multiple sources are distributed along the entire axial cavity. The deviation of QSWBM calibration in axial source configurations as compared to uniform source distribution was found to be 9-13 % for various energies. This suggests that uniform source distribution in BOMAB-I should be preferred over axial source distribution to perform more accurate calibration for QSWBM. An experimental validation of QSWBM calibration using single source methodology was also carried out, and deviations <10 % were observed for ¹³⁷Cs and ⁶⁰Co emissions.