The two-parameter-fitting method (PFM) is commonly used to calculate the stopping-power ratio (SPR). This study proposes a new formalism: a three-PFM, which can be used in multiple spectral computed tomography (CT). Using a photon-counting CT system, seven rod-shaped samples of aluminium, graphite, and poly(methyl methacrylate) (PMMA), and four types of biological phantom materials were placed in a water-filled sample holder. The X-ray tube voltage and current were set at 150 kV and 40 μA, respectively, and four CT images were obtained at four threshold settings. A semi-empirical correction method that corrects the difference between the CT values from the photon-counting CT images and theoretical values in each spectral region was also introduced. Both the two- and three-PFMs were used to calculate the effective atomic number and electron density from multiple CT numbers. The mean excitation energy was calculated via parameterisation with the effective atomic number, and the SPR was then calculated from the calculated electron density and mean excitation energy. Then, the SPRs from both methods were compared with the theoretical values. To estimate the noise level of the CT numbers obtained from the photon-counting CT, CT numbers, including noise, were simulated to evaluate the robustness of the aforementioned PFMs. For the aluminium and graphite, the maximum relative errors for the SPRs calculated using the two-PFM and three-PFM were 17.1% and 7.1%, respectively. For the PMMA and biological phantom materials, the maximum relative errors for the SPRs calculated using the two-PFM and three-PFM were 5.5% and 2.0%, respectively. It was concluded that the three-PFM, compared with the two-PFM, can yield SPRs that are closer to the theoretical values and is less affected by noise.

We have proposed a method to obtain the electron density and effective atomic number from the attenuation coefficients of multi-energy X-rays. The simulations were performed using NIST’s database and demonstrate that our approach can facilitate electron density measurements within accuracy of 1% in a human body. The proposed method exhibited an improvement in the accuracy of electron density measurements, which were obtained from experimental linear attenuation coefficients using a conventional laboratory X-ray source with energy spectrum.

We have developed a GUI(Graphical User Interface)-based Monte Carlo simulation tool for electron beam lithography. Simulation was executed by changing initial energy, thickness of resist, and target material. We focused on penetration range, backscattering coefficient and spatial distribution of lost energy. Comparison with other theory indicates that our simulation is reliable in the 10-50keV range of the energy of the electron. It seems that backscattering coefficient is strongly affected by the kind of atoms in the target, not initial energy.

We studied DNA damages in heavy ion irradiation for its radiotherapy using molecular dynamics (MD) method. We adopted semi-empirical hybrid quantum mechanics/molecular mechanics (QM/MM) method of Amber in order to investigate the cleavage of chemical bond by heavy ion in our simulation. We found the cleavage of chemical bond, although the simulated energy of heavy ion turned out to be slightly higher than the one determined by experiment.

We developed the photon counting CT system by using a conventional laboratory X-ray source and a CdTe line sensor. Attenuation coefficients were obtained from the measured CT image data. Our suggested method for deriving the electron density and effective atomic number from the measured attenuation coefficients was tested experimentally. The accuracy of the electron densities and effective atomic numbers are about <5 % (the averages of absolute values are 2.6 % and 3.1 %, respectively) for material of 6< Z and Zeff <13. Our suggested simple method, in which we do not need the exact source X-ray spectrum and detector response function, achieves comparable accuracy to the previous reports.