Y. Oguri

Transport mechanism of MeV protons in tapered glass capillaries

To investigate the transport mechanism of MeV protons in tapered glass capillaries, spatially resolved energy spectra were measured for proton microbeams focused by 20-μm-outlet capillaries having various taper angles. Three-dimensional Monte Carlo (MC) simulations were also performed to support the experiments and trace each particle in the capillary in more detail. The dependence of the proton energy distribution on the outgoing angle proved that the capillary-focused proton beam consists of two different components, protons traveling straight through the capillary without colliding with the capillary wall and protons scattered by the capillary inner wall. Moreover, the focusing effect of the tapered glass capillary was found to be mainly due to the scattered beam component. The MC simulations well reproduced the experimental results and showed that beam focusing ratios of 1.6–2.4 are possible with capillaries having a convex inner wall. The flight distance of the scattered proton in the capillary glass...

Experimental and numerical study of dose distribution around a syringe needle-type proton-induced X-ray source for radiotherapy

A syringe needle-type proton-induced monochromatic X-ray source was proposed to solve the issue that could occur in practical brachytherapy, such as loss of seed sources and radiation exposure to surgical staff. This paper discusses comparison between experimental results and a Monte Carlo numerical simulation of the dose distribution around the needle. Some simulation results for different source designs are presented as a first step of the design optimization.

Production of quasimonochromatic X-ray microbeams using MeV-protons and a polycapillary X-ray half lens

In this paper, we have proposed monochromatic X-ray microbeams, produced by a proton-induced X-ray technique and a polycapillary X-ray half lens, as a tool for micro-X-ray fluorescence (XRF) analysis. A 30 μm thick planar Cu target was irradiated by a 2.5 MeV proton beam to produce Cu Kα X-rays (8.0 keV), and a polycapillary X-ray half lens was utilized to focus the X-rays emitted behind the Cu target. The focal spot size of the focused X-ray beam was 250 μm at full width at half maximum, which was verified using a knife-edge scanning method. The output focal distance and the depth of focus of the optics were measured to be 47 mm and 1 mm, respectively. A square grid pattern of Co thin films, formed on a thick Cu substrate by thermal evaporation, was used as a test sample for evaluation of the analytical performance of the micro-XRF setup. Two-dimensional mapping of the Co distribution on the Cu substrate was successful, and the spatial resolution was consistent with the beam spot size. For this Co layer, a minimum detection limit of 2.3 ng was achieved.

A PHANTOM TEST OF PROTON-INDUCED DUAL-ENERGY X-RAY ANGIOGRAPHY USING IODINATED CONTRAST MEDIA

Characteristic-line radiation from heavy metal targets bombarded by MeV proton beams has been tested as an X-ray source for dual-energy K-edge subtraction imaging for human angiography (blood vessel imaging) based on iodinated contrast media. To utilize the strong absorption by iodine (Z = 53) at its K-absorption edge (33.2 keV), we used Kα-line of La (lanthanum, Z = 57) at 33.4 keV. As a reference, also KαX emission of Sn (tin, Z = 50) at 25.2 keV was employed. Metallic plates of La and Sn were irradiated by 7-MeV protons to produce these characteristic X-rays. Energy-subtraction method was tested using Lucite phantoms which contain aqueous solutions of KI (potassium iodide) with different concentrations. Also Ca(H2PO4)2 powder was stuffed in these phantoms to simulate bones. The transmission images of the phantoms were recorded on imaging plates. During the exposure, the energy spectra of the X-rays were monitored by a CdTe detector. We found that the contrast of images of iodide solutions taken with La X-rays was higher than that with Sn X-rays. Also the energy subtraction procedure was successfully applied to reduce the graphical noise due to the bones and inhomogeneity of the soft tissue. However, to apply the present method to actual clinical use, the X-ray intensity must be increased by several orders of magnitude. Also the transmission of the “lower-energy” photons has to be a few orders higher for imaging of objects as thick as human chest.

Direct observation of dose distribution around a syringe-needle type proton-induced X-ray source using liquid scintillator and a CCD camera

This paper discusses a method to directly observe the dose distribution around a syringe-needle-type proton-induced monochromatic X-ray source proposed to avoid the risk that could exist in conventional brachytherapy. Images taken by using liquid scintillator and a high sensitivity CCD camera are presented and the dose distribution is qualitatively evaluated by comparing it with a Geant4 Monte Carlo simulation result.

Selective internal radiotherapy using proton-induced monochromatic X-rays and cancer-targeting nanoparticle sensitizers

In this paper, we propose a highly-selective radiotherapy based on monochromatic X-rays and cancer-targeting gold nanoparticle (GNP) sensitizer. In order to deliver the low-energy monochromatic X-rays which selectively ionize the Au L-shell into the cancerous tissue deep inside the patient’s body, we employ a syringe-needle type X-ray source driven by an MeV proton beam. From a simple numerical evaluation, we found that optimization of the primary X-ray energy was essential to enhance the dose around the nanoparticle. In order to confirm the above idea qualitatively, we performed a simulation experiment in the atmosphere, where 100 nm Au foils were used instead of the GNPs. The experimental result showed that the dose around the Au foils was much higher than that at positions away from the foils, owing to short-range secondary electrons from the foils.

Digital subtraction cineangiography using proton-induced quasi-monochromatic pulsed X-rays

Two different kinds of metallic plates on a rotating disk target were irradiated with a MeV proton beam, and quasi-monochromatic pulsed X-rays with different energies around the absorption edge of the contrast medium were alternately produced. By using these dual-energy X-rays and a high-sensitivity X-ray movie camera, we took a motion picture of the transmission image of a periodically moving phantom, which simulated a rat heart as a test animal. We found that the enhanced movie imaging of the contrast agent is available by subtraction between adjacent picture frames.