Computed tomography is a transmission tomography technique; this technique allows reconstructing the cross-section images or slices of the real object. The CT was developed in the 1970s for medical diagnostic purposes. Today, the CT technique has evolved to the 7th generation using cone-beam configuration (CBCT) and Flat Panel Detector (FPD) instead of fan-beam arrangement and one dimension detector array. CBCT has greater X-ray efficiency and higher spatial resolution than the previous generation; therefore, it can be used in industrial applications such as metrology of precision machined and None-Destructive Testing (NDT). In this research, the first CBCT system in Vietnam was manufactured; this system can acquire and reconstruct three dimensions of a real object with a maximum size of 200 × 300 mm within ten minutes. The resolution of the reconstructed image is around 49 µm.

This study used PHITS and Geant4 code packages to simulate a Leksell Gamma Knife system in order to determine radiation dose distribution in two types of phantoms. The results observed in the water phantom with configurations of single source and 201 sources are in good accord with the prior research, including both simulation and experiment. Several characteristics of Leksell Gamma Knife 4C, such as dose profiles, output factor, FWHM, and penumbra size, are calculated based on Monte Carlo simulations, which show the best consistency with other results. The output factors for collimators of 14 mm, 8 mm, and 4 mm are 0.984, 0.949, and 0.872, respectively. The simulation results with an adult mesh-type reference phantom reveal considerable similarities with the established radiosurgery plans. It indicates that the absorbed dose in brain tumors was highest when utilizing the 18 mm collimator and subsequently reduced with collimator size to 0.65, 0.25, and 0.5 with the 14 mm, 8 mm, and 4 mm collimators, respectively. The absorbed dose has a very low value for other essential organs and decreases with distance from the brain tumor. These findings may explain why the dose to organs decreases linearly as target distance, volume, and collimator size increase.