We developed a practical spectroscopic system using the white X-rays that arise from a medical X-ray tube. As monochromatic X-rays are more desirable than white X-rays to examine the energy characteristic of the system's image detector, we generated monochromatic X-rays, using a Si crystal, it examine the characteristic. The FWHM (full width at half maximum) and the output X-ray intensity were measured. The following results were obtained. (1) The developed system can be used in the energy region of diagnostic radiography. (2) The FWHM is from 0.15 to 1.4 keV. (3) The intensity of monochromatized X-rays at 50 keV is about 1 % of the total intensity of white X-rays.
Absorbed dose conversion factors, (Cλ)acryl of 8 types of commercially available cylindrical ionization chambers were calculated for conditions using an acrylic plastic phantom and high energy X-rays of 4 MV,6 MV,10 MV and 15 MV and 60Co γ rays. The calculations were according to a Japan Association of Radiological Physicists (JARP) protocol (1986). In comparison with the (Cλ)acryl for the JARP ionization chamber (C-110) having a wall and build-up cap of acrylic plast ic, the difference for the other 7 ionization chambers is small, being from -1.1% to +0.4%. Among them, the (Cλ)acryl for the NE 2581 chamber with a wall of A-150 plastic and Lucentine build-up cap is the most different value of about -1.1% and that for the NE 2505/3B chamber with a wall of nylon and acrylic build-up cap is the second most different value of about -0.7%. With a wall and build-up cap of the same acrylic plastic, the difference between PTW 30001 and PTW 23333chambers is very small, being within ±0.1%. In order to compare the absorbed dose given according to the absorbed dose conversion factors calculated, twin ionization chambers were installed in the acrylic plastic intercomparison phantom for each exposure and 5 types, the PTW 30001, JARP C-110, PTW 23333, NE 2571 and NE 2581 chambers were used for 4 MV and 10MV X-rays. The measured absorbed doses for these ionization chambers show good agreement within ±0.35%, although the difference in the measured doses between PTW 30001 and 4 chambers increases from - 0.44% to +0.71%.
Computerized optimization in stereotactic treatment planning using a linear programming method is presented. A three-dimensional model of dose distribution is built first, and then the required irradiation is decided inversely. In conventional interactive trial and error methods, the treatment parameters are chosen by the operator's experience and improved successively. Compared with such time-consuming methods, the present method is desirable not only for its timesaving capability but also for its capability to obtain a mathematically optimal solution for a treatment plan. Moreover, by employing a linear programming algorithm, no empirical parameters are needed. The validity of the present methodology is demonstrated using Monte Carlo simulation.
The relationships of optical density of a heavy ion radiograph with residual range and with absorbed dose are discussed, and the experimentally obtained results of the residual range for the small animal tissue phantom are shown. It is found that the curve of optical density against PMMA equivalent thickness does not show a peak as seen in the depth dose distribution curve measured with an ionization chamber. This reflects the difference between the film and ionization chamber in their responses to high LET particles. The shapes of the curves of the optical density against the thickness of the range shifter are almost identical, but the amount of shift along the thickness differs depending on the density of the phantom tissues and corresponds to the difference of the residual range. Therefore the optical density curves against absorber thickness are suitable for estimating residual range of the heavy ions emitted from the downstream side of the phantom, pixel by pixel.