Improvement of a detection system for in-vivo Al measurements, and in-vivo Al measurements of a population of miners.

Abstract

The following thesis seeks to investigate potential alternatives to the 4π system employed by the Tandem Accelerator Laboratory (TAL) at McMaster University for use in the investigation of in-vivo aluminum levels using in-vivo neutron activation analysis. It also aims to measure the levels of aluminum in miners who were exposed to it via inhalation of the Aluminum containing McIntyre powder from ~ 1944-1979. The same protocol for creation and irradiation of phantoms was followed as in [1], namely tissue equivalent phantoms were created and irradiated under a proton current of 400 μA, with a proton energy of 2.3 MeV which led to neutron energies of 0.55 MeV. These phantoms were then counted using three different detectors. These detectors consisted of two scintillators (the currently used 4π NaI(Tl) system, and a single LaBr3(Ce)) and a semi-conductor, a single closed-end coaxial HPGe. MDLs for these detectors were found to be 15.85 μgAl/gCa (236.17 μgAl) for the 4π NaI(Tl) system, 56.51 μgAl/gCa (842.0 ugAl) for the HPGe and 98.67 μgAl/gCa (1470.20 μgAl) for the LaBr3(Ce). The next part of the thesis involved in-vivo measurements on a group of 15 miners from Northern Ontario who had been exposed to McIntyre powder previously throughout their careers in the mines. Each patient was irradiated under the same proton current and energy as above, and was transferred to the 4π system for counting for 10 1 minute cycles. The MDL for these in-vivo measurements was found to be 22.57 μgAl/gCa. The highest value was 206.36±14.76 μgAl/gCa and the lowest value was 18.55±3.95 μgAl/gCa, with a median value of 18.56±11.28 μgAl/gCa and average value of 21.78±2.27 μgAl/gCa for IVWM, and 17.43±13.78 μgAl/gCa for regular mean . Of the miners, 7 had negative concentrations, indicating that the concentrations were below the detection limit of the system. Data analysis for all experiments was performed the same way. The Al/Cl peak for the NaI was fit using a FORTRAN algorithm, as well as the Ca peak. The areas for these peaks were then calculated, then the MDL was calculated by taking the average of the low concentration phantoms, and the error was multiplied by 2, then was divided by the calibration slope for the first three time cycles. These values were then added via the inverse variance weighted mean (IVWM) method, and the final concentration of μgAl/gCa was calculated . Given that the HPGe had a significantly better MDL than the LaBr3(Ce) (56.51 vs 98.67 μgAl/gCa), that the HPGe may be a good candidate to improve the current 4π in-vivo system. Also given the high amount of Al found in the bones of the miners, this indicates that it can be a good indicator of how much Al each miner was exposed to and may help with assessing the health effects of McIntyre powder.