Biological studies using mammalian cell lines and the current status of the microbeam irradiation system, SPICE

A microbeam irradiation system, SPICE (Single Particle Irradiation system to Cell), is under completion at the National Institute of Radiological Sciences (NIRS). We have improved the beam size, which is now approximately 5 um in diameter, and the cell targeting system, which can irradiated a maximum of 400~500 cells per minute. Two types of cell dishes were specially designed. One is a Si3N4 plate (2.5 mmx2.5 mm area with 1 um thickness) supported by a 7.5 mmx7.5 mm frame of 200 um thickness, and the other is Mylar film stretched by pressing with a metal ring. These cell dishes can be placed on a voice coil stage equipped on the cell targeting system, which also includes of a fluorescent microscope and a CCD camera for capturing the cell images. This microscope system captures all the images of dyed cell nuclei, and computes the coordinates of the cell position according to the fluorescence, and synchronizes this and the voice coil motor stage with a single-particle irradiation system consisting of a scintillation counter and a beam deflector for irradiation. Irradiation of selected cells with a variable preset number of protons can be automatically performed. We employed the simultaneous detection method for visualizing the position of mammalian cells and proton traversal through CR-39 to determine whether the targeted cells are actually irradiated. An Immuno-assay was also performed against gamma-H2AX, to confirm the induction of DNA double-strand breaks in the target cells