Yutaka Noda

Electron density measurement with dual-energy x-ray CT using synchrotron radiation.

Monochromatic x-ray computed tomography (CT) at two different energies provides information about electron density of human tissue without ambiguity due to the beam hardening effect. This information makes the treatment planning for proton and heavy-ion radiotherapy more precise. We have started a feasibility study on dual energy x-ray CT by using synchrotron radiation. A translation-rotation scanning CT system was developed for quantitative measurement in order to clarify what precision in the measurement was achieved. Liquid samples of solutions of K2HPO4 and solid samples of tissue equivalent materials were used to simulate human tissue. The experiments were carried out using monochromatic x-rays with energies of 40, 70 and 80 keV produced by monochromatizing synchrotron radiation. The solid samples were also measured in a complementary method using high-energy carbon beams to evaluate the electron densities. The measured electron densities were compared with the theoretical values or the values measured in the complementary method. It was found that these values were in agreement in 0.9% on average. Effective atomic numbers were obtained as well from dual-energy x-ray CT. The tomographic image based on each of the electron densities and the effective atomic number presents a different feature of the material, and its contrast drastically differs from that in a conventional CT image.

Simple range measurement of therapeutic ion beams using visible rays generated in a bare plastic scintillator block

Abstract In ion-beam therapy, it is necessary to measure the range of the beams in a tissue-equivalent material. We demonstrate a simple method for the range measurement, using a bare plastic scintillator block and a CCD camera. This method presents an instant result for the range measurement of the therapeutic ion beams. The linearity, resolution and application of the method are discussed.

Some Relationships between Dosimetric Quantities in Photon and Electron Beams

Theoretical considerations of photon and electron dosimetry with general cavity are attempted on the basis of partitioning the kerma into its collisional part and its radiative part. A necessary and sufficient condition for the existence of charged-particle equilibrium in a material irradiated by photons is the equality of the collisional kerma with the absorbed dose. The exposure can be determined indirectly without restriction on the photon energies, if a quantity such as the W-value or G-value of the cavity material of the dosimeter is known. The absorbed dose can also be measured by using a dosimeter calibrated in terms of exposure, air kerma, or absorbed dose in the medium. During exposure calibration, air-kerma calibration, or exposure measurement, a material equivalent to the cavity wall must be used as the build-up cap material.

Measurements of effective doses of natural background level of neutrons with etched-track detectors.

Abstract— An etched-track method was applied for a measurement of the effective dose of natural background neutrons. Ten assemblies of polycarbonate film and 10 B were placed at the center of a rem-counter type moderator. The assemblies were put in an air-tight container in order to avoid a continuous contribution from radon. Electrochemical etching was adopted. The sensitivity of the detector was 0.21 ± 0.02 &mgr;Sv pit −1 cm 2. After a period of storage of 4.3 y, the number of recorded artifact pits in the films corresponded to an effective dose rate of 0.8 ± 0.2 &mgr;Sv y −1. The effective dose rate of natural background neutrons was 18.1 ± 3.6 &mgr;Sv year −1 for the same period, with an artifact dose being subtracted. The total net number of etched-track pits of the present detector was 75 ± 15 when used for measuring an effective dose of natural background level neutrons for 1 mo, which gives enough counting statistics. The method can thus be applied for monitoring the effective dose of neutrons around nuclear sites and high-energy accelerator facilities.

Development of Dual‐Energy X‐ray CT using Synchrotron Radiation

Monochromatic x‐ray CT at two different energies provides information about electron density without ambiguity due to the beam hardening effect. This information makes the treatment planning for heavy‐ion radiotherapy more precise. We have started a feasibility study on the dual‐energy x‐ray CT by using synchrotron radiation. We developed a linear scanning CT system in order to evaluate what precision in the measurement was achieved. The experiments were carried out using monochromatic x‐rays of 40, 70 and 80 keV. Comparison of measured electron densities with the theoretical values proved that these values were in agreement in 0.9 % on average. We have developed a 2D‐CT system with a two‐dimensional scintillator array to take images in a short time. At present, it has been proved that the electron density is measured in the precision of about 1 % with the 2D‐CT system. Effective atomic numbers are obtained as well from the dual‐energy x‐ray CT. The CT images are reconstructed based on each of the electro...

Measurements of charge-changing cross sections for therapeutic ion beams

We measured the survival of 290, 400 MeV/u 12C and 400, 600 MeV/u 20Ne beams as a function of the target thickness using ΔE-type plastic scintillators. The total charge-changing cross sections of several target materials for those beams were deduced from the obtained survival data. Although the obtained cross section data agree well with the other experiments, they showed disagreement with the model prediction which was used for the depth-dose calculations.