STUDIES IN BONE LEAD: A NEW 109CD K-XRF MEASUREMENT SYSTEM; MODELING BONE LEAD METABOLISM; INTERPRETING LOW CONCENTRATION DATA

Abstract

Source induced K x-ray fluorescence (XRF) has been used for in vivo bone lead measurement for more than two decades. Recently, the need for the improvement of this system has been emphasized due to the increased awareness of effects of low level lead exposures, the need to examine potentially sensitive populations, such as children and pregnant woman, for whom minor exposure might be important, and the necessity to distinguish relatively small differences between groups in different exposure categories. In this thesis, a new XRF in vivo bone lead measurement system will be studied. The new system consists of a cloverleaf-shaped detector system made of four detectors, and four sets of electronics. The projected performance of this system was investigated in my Master’s program. The result showed an overall minimum detectable limit (MDL) improvement of a factor of about 3.6. Two such systems were purchased in our group. Three different types of electronics were tested to get the optimal setup for the system. After the initial system testing, a dosimetry study was carried out to investigate the dose delivered to the measured individual by using this system. Three age groups were involved in this dosimetry study. The doses were predicted by calculations, MC simulations, and experiments. The result shows that the dose delivered is small, even for 5 years old children (effective dose: ~9pSv). An approval to conduct human measurements on this system has been received from the Research Ethics Board of Hamilton Health Sciences based on this study. Twenty volunteers had their tibia bone measured by both the new system and the conventional system for 30 minutes clock time. The median MDLs for the conventional system and the new system are 8.75 pg/g bone mineral and 3.48 pg/g bone mineral. The source strength used for the new system is 2.45GBq, and this could go up to lOGBq. So the extrapolated median MDL for the new system is 1.74 μg/g bone mineral. Two other minor projects were also described in the thesis. One is about an investigation of a model of lead metabolism in human body. The study shows that one of the current lead metabolism models cannot correctly reflect lead transfer between blood and bone. KXRF bone lead measurement data were used to regulate the transfer rates and the result shows a great improvement. The other is about a statistical approach for the analysis of the KXRF bone lead measurement data. Some left-censoring methods were discussed in this project and the study shows that left-censoring is a good way to handle the censored data.