Demonstration of inter- and intracellular distribution of boron and gadolinium using micro-proton-induced X-ray emission (Micro-PIXE)

Micro-proton-induced X-ray emission (Micro-PIXE) was applied to determine inter- and intracellular distribution of boron (¹⁰B) and gadolinium (¹⁵⁷Gd), the capture atoms used to kill tumor cells in neutron capture therapy (NCT). Cultured 9L gliosarcoma cells on Mylar film were exposed to sodium borocaptate (BSH) and gadobenate dimeglumine (Gd-BOPTA). To analyze the inter- and intracellular distribution of ¹⁰B and ¹⁵⁷Gd in 9L gliosarcoma cells, the cells were irradiated using a proton beam of 1.7 or 3 MeV energy collimated to 1 μm diameter and emission X-ray was detected. The distribution of ¹⁰B and ¹⁵⁷Gd in 9L gliosarcoma cells was then examined. In this study, we could directly analyze the inter- and intracellular distribution of ¹⁰B and ¹⁵⁷Gd elements in 9L gliosarcoma cells directly using Micro-PIXE. This is the first report on the distribution of ¹⁰B employing a method to detect γ-rays resulting from the nuclear reaction of ¹⁰B using particle-induced γ-ray emission (PIGE). These results show that the distribution of ¹⁵⁷Gd elements was correctly measured using micro-PIXE. ¹⁵⁷Gd should have the same tendency as ¹⁰B in cultured 9L gliosarcoma cells and agree with the distribution in 9L gliosarcoma cells. Further investigation is necessary for a higher spatial resolution and optimization of the measurement time or improvement of the sampling method. In the future, it will be possible to employ this method to analyze the intracellular microdistribution of the capture element and in the development of new drugs for NCT.