FEASIBILITY OF MEASURING SELENIUM IN HUMANS USING IN VIVO NEUTRON ACTIVATION ANALYSIS

Abstract

Selenium (Se), an essential trace element, plays an important role in the normal function of a number of Se-dependent biological processes. Many studies have demonstrated that selenium deficiency in the body may contribute to an increased risk for certain neoplastic diseases (including colonic carcinoma, gastric carcinoma, pulmonary carcinoma and prostate carcinoma), as well as diseases of the cardiovascular, osseous, nervous systems and retardation of bone formation. However, at higher concentrations Se is cytotoxic. For these reasons it is desirable to have a means of monitoring selenium concentration in humans. The feasibility of measuring selenium in humans using the in vivo neutron activation analysis (IVNAA) technique was studied. For this purpose human hand tissue equivalent phantoms were prepared with varying amounts of selenium and irradiated by a low energy neutron beam produced by the 7Li(p,n)7Be reaction by employing the high beam current Tandetron accelerator. The counting data saved using the 4π NaI(TI) detection system in anticoincidence, coincidence and singles modes of detection were analyzed. The selenium was detected via the neutron capture reaction, 76Se(n,γ)77mSe, whereas calcium was detected through the 48Ca(n,γ)49Ca reaction. The peak areas of Se and Ca were computed and the Se concentrations were normalized to the Ca concentrations for various time segments of detection. The calibration lines were drawn between Se/Ca concentration and Se/Ca counts ratio. The minimum detection limits (MDL) were obtained and the inverse variance weighted mean value of MDL was finally calculated for three time segments. During the analysis of counting data it was also found that 18O is activated in water phantoms and becomes short lived radioactive 19O having T1/2=26.9 s. To the author’s best knowledge, this study for the first time presents the MDL value in terms of Se/Ca concentration for the human hand bone equivalent phantom obtained from in vivo neutron activation analysis and these results will provide a good basis for future investigations.