Efficiency calibration for in vivo measurement of Pb-210 in the skull using phantoms developed for Chinese adult reference male

Efficiency calibration is a critical step that enables the conversion of the detectors counts rate into the activity of radionuclides in the examined parts for in vivo measurement. However, to date, there hasnt been a well-accepted framework for efficiency calibration. As such, it is often found researchers employ various kinds of anthropomorphic phantoms with considerably different patterns of radionuclide distribution coupling with drastically different numbers of detectors to derive the calibration factor, rendering the cross-comparison among studies challenging. Moreover, some studies employ virtual calibration, whereas others prefer experimental calibration, though their equivalency has not been fully explored. In this paper, focusing on in vivo measurement of Pb-210 in the skull, a promising technique for individualized reconstruction of radon exposure is presented, and a detailed framework for efficiency calibration covering key issues mentioned above is provided. To be specific, physical phantoms of Pb-210 in the skull are developed based on the anatomical characteristics of a Chinese adult reference male, along with the corresponding computational phantoms constructed from computed tomography scan. In comparison, the average deviations between simulation and experimental results are within 4% for efficiency calibration at the top, left, and right sides of the head across varying detection distances. Furthermore, based on the investigation of Pb-210 distribution regions reported in literature, the calculation method for Pb-210 activity is improved to account for different source distributions and joint measurements with multiple detectors. The results are useful for determining the appropriate conversion procedure under different measurement conditions.