The dose distribution in an X-ray irradiation field is important information for work planning and design safety. A novel Monte Carlo calculation toolkit was developed for the purpose of calculating the dose distribution in an X -ray diagnostic room. The developed toolkit provides easy preparation of input files of EGS5 Monte Carlo code and executes them. The toolkit is useful for estimation of the detailed dose distribution of a simulated three-dimensional geometry in an X-ray diagnostic room, just by inputting required values using Microsoft Excel. An X-ray beam can be defined as entering into a scattering water phantom in arbitrary energy spectra, the incidence direction, and field size. Additional definitions for up to fifty items, such as shield wall, monitor TV, etc., are available by the rectangular parallelepiped. The photon fluence detectors are arranged at fifty arbitrary positions. The absorbed organ doses can be obtained from the calculation result of photon fluence at an arbitrary evaluation position.
The developed toolkit has been made sure by a model calculation and measured dose using a ionization survey meter. The calculated result agrees with the measured value within 10%, except near the surface of room walls. The absorbed organ doses can be obtained from the calculation result of photon fluence at the arbitrary evaluation position.
From comparison of variation of the organ absorbed dose per mAs, while staying at a fixed position of 100 cm from an X-ray incident point in the range of tube voltages from 50 kV to 130 kV, the lens absorbed dose is the highest, and it subsequently decreases in the order of male genital organs, breast, thyroid gland, and skin. These calculation results clarify what should be carefully considered regarding protection of the thyroid gland or whether a lens should be used with continuous-energy X-ray beams.
The developed Monte Carlo calculation toolkit is well suited for optimizing safe instrument arrangements and undertaking radiation protection actions.

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We simulated three-dimensional (3D) computed tomography images from the 3D object functions of ideal spheres, assuming solitary pulmonary nodules, by using the point spread function measured in a scanner. On the simulated images, we calculated the sphere volumes with a simple threshold technique in which the relationship between the threshold and the volume was analyzed. First, we confirmed that the results obtained by the simulation agreed well with those obtained by the experiment using a sphere phantom. Subsequently, we determined the threshold (defined as Tʹ) so that the sphere volume in simulated images was equal to its object function (true volume). We quantitatively determined that the Tʹ changed with the object diameter while maintaining a constant density in the object, and Tʹ depended on the reconstruction kernel, slice thickness and slice location. When the half maximum of the sphere density in the simulated image, which corresponds to the half maximum in a well known term full-width at half maximum (FWHM), was used as the threshold, the accuracy for the obtained volume fluctuated in relation to the above Tʹ change. Our simulation technique and present results will be effective for basic research on 3D nodule analysis.

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