Method of eigenvectors for numerical studies of multilayer gratings

A new approach to numerical studies of lamellar multilayer gratings is developed. It stands out against the existing modal and differential methods by its applicability to thick multilayer gratings with a small grating period, and also to the case of grazing incidence of radiation. The diffraction properties of multilayer gratings are calculated for x rays with the angles of incidence down to zero. Reflection curves are calculated for multilayer gratings with the grating periods down to 5 nm and the number of bilayers up to 1000. The diffraction pictures are developed for all the range of x-ray radiation (soft and hard x rays). It is directly demonstrated that the multilayer grating can be regarded as a two-dimensional crystal. Numerical calculations based on the newly proposed method were used for the interpretation of experimental data on the performance of the Ni/C multiplayer grating.     

Theoretical and experimental investigation of x-ray diffraction by a lamellar multilayer amplitude grating

We present experimental and theoretical studies of the diffraction by an x-ray lamellar multilayer amplitude grating. The main diffraction properties of such a device are given. Experimental efficiency curves are obtained at 800 eV photon energy using synchrotron radiation. The features observed in these curves are identified and interpreted by means of two theoretical methods. Particular emphasis is given to structures observed for the first time which had been theoretically predicted.     

Characterization of a Flat-Field Grazing-Incidence XUV Spectrometer

We describe a XUV spectrometer for the study of dense hot microplasmas at wavelengths between ≈50 and ≈300 ?. It uses a commercially fabricated grazing incidence flat-field reflection grating with 1200 grooves per millimeter. The spectral resolution was optimized by imaging the source on a narrow slit with the help of a curved grazing incidence mirror. The instrument was tested with a laser-produced plasma as a source. The limit of the resolving power due to imaging aberrations of the flat-field grating ranges from 1500 at 50 ? to 3600 at 200 ? and has been achieved with a 5-μm slit. We also measured and calculated the grating efficiencies for the first to fifth diffraction order as a function of wavelength.     

Radiation therapy for prostate cancer

In Japan, where the mortality rate of prostate cancer is lower than in Western countries, radical prostatectomy or hormonal therapy has been applied more frequently than radiation therapy. However, the number of patients with prostate cancer has been increasing recently and the importance of radiation therapy has rapidly been recognized. Although there have been no randomized trials, results from several institutions in Western countries suggest that similar results of cancer control are achieved with either radiation therapy or radical prostatectomy. For higher-risk cases, conformal high-dose therapy or adjuvant hormonal therapy is more appropriate. In this article, the results of radiation therapy for prostate cancer were reviewed, with a view to the appropriate choice of therapy in Japan.     

Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons: an arrangement for irradiating dry or hydrated DNA with monochromatic photons

PURPOSE: Theoretical modelling techniques are often used to simulate the action of ionizing radiations on cells at the nanometre level. Using monoenergetic vacuum-UV (VUV) radiation to irradiate DNA either dry or humidified, the action spectra for the induction of DNA damage by low energy photons and the role of water and can be studied. These data provide inputs for the theoretical models. METHODS: Various combinations of monochromator, grating and VUV window have been used to obtain monochromatic photons from the 2 GeV electron synchrotron at the CLRC, Daresbury Laboratory. A sample chamber containing plasmid DNA is installed at the end of the beamline. The chamber can be evacuated or water can be introduced (as water vapour or humidified helium). In this way, DNA can be irradiated either dry or humidified. RESULTS: An arrangement for irradiating dry or humidified DNA using monoenergetic photons from 7 eV to 150 eV has been developed. At the energies used, exposure rates vary from about 5 x 10(10) to 3 x 10(12) photons cm(-2) s(-1) over a 1 cm2 sample area. At all but the lowest energies this is sufficient to produce significant levels of DNA damage in just a few minutes. The measured dose variation over the sample area is typically 30%, but this is reduced significantly using sample scanning techniques.     

MRI of radiation myelitis: a report of a case treated with hyperbaric oxygen

Radiation therapy is commonly applied as a primary or adjuvant therapy for malignancies. One of the major complications following radiation therapy is the necrosis of the otherwise normal surrounding soft tissues and/or bone. Post-radiation myelopathy rarely occurs when the spinal cord is included within the radiation field, in cases of high total radiation doses or for high radiation doses per fractionation. Up until the present, no tolerance dose for the spinal cord has accurately been defined and no treatment has proved satisfactory. Hyperbaric oxygen therapy is already currently used as adjuvant treatment for osteoradionecrosis and for radionecrosis of soft tissues with satisfactory results, whereas results for the treatment of post-attinic myelitis were contradictory. The aim of our report is to describe a case of radiation myelitis with a progressive improvement in the clinico-radiologic picture following hyperbaric oxygen treatment. Received: 18 March 1999; Revised: 7 September 1999; Accepted: 15 November 1999     

辐射防护基因治疗现状与展望

放射治疗是恶性肿瘤的主要治疗手段之一,超过50%的肿瘤患者在病程的不同阶段都需要接受放疗。尽管影像引导靶向治疗技术不断发展,使患者受到的辐射剂量大大降低,但仍然存在严重的不良反应——正常组织细胞的辐射损伤。为了减少正常组织损伤,研究人员一直在寻找辐射防护的新方法。目前的辐射防护方法多是采用化学合成小分子物质及天然植物提取物作为辐射防护剂使用,但疗效并不十分理想,研究人员迫切想找到一种高效可行的辐射防护新方法。基因治疗以其靶向明确、细胞毒性小、不良反应少等优点在增强细胞和组织相关性能上具有很大优势,使其成为极好的辐射防护新方法。笔者对辐射防护的基因治疗研究及其未来的改进方向做一综述。     

Planning mantle radiation therapy in patients with Hodgkin disease: role of gallium-67 scintigraphy

Detection of all sites of lymphoma is imperative for accurate planning of radiation therapy. In patients with Hodgkin disease, mantle radiation is used to treat the thoracic lymph nodes; in those with early-stage or nonbulky disease, mantle and paraaortic radiation may be the only treatment given. CT scanning of the chest adds important information to that obtained from chest radiographs. Gallium-67 scintigraphy has also been used to provide additional information on sites of active tumor. To determine the usefulness of 67Ga-citrate scintigraphy in planning the portals for radiation therapy, we analyzed the radiation treatment plans in 26 consecutive patients with Hodgkin disease; in all 26 patients, the disease had been staged by chest radiographs, chest CT scans, and gallium-67 images. Gallium-67 imaging alone provided unique information that affected the treatment plans in three patients (12%). The combined results of gallium-67 imaging and CT scans influenced the planning of radiation therapy in eight patients (31%). Gallium-67 imaging was found to be an important adjunctive study for optimal planning of radiation therapy in patients with Hodgkin disease.     

A survey of annual radiation dose for radiation workers from occupational and medical exposures in Kyushu]

This study was carried out to determine annual dose equivalents of exposure in workers exposed to medical radiation and occupational radiation in an enterprise associated with nuclear power plants. The results indicated that medical exposure is much higher than occupational exposure. Average annual effective dose equivalents for medical and occupational exposure were 4.0-7.5 mSv and 2.4-3.6 mSv, respectively. Individual occupational exposure limits have been well controlled and maintained at one-fifth of the dose limit for radiation workers (50 mSv/yr). On the other hand, medical exposure in the older workers of this enterprise has been increasing as a result of X-ray diagnosis with barium meal.     

Void effects and the determination of “patches” for radiation distributions in heterogeneous multilayer shields

The effect on radiation distributions in heterogeneous multilayer shield configurations containing cylindrical air-filled voids of different diameters have been investigated. The heterogeneous shield assemblies were placed in front of one of the horizontal channels of the ET-RR-1 reactor. The measurements of δ-rays and slow neutrons were carried out using LiF-7 and LiF-6 Teflon disc dosimeters, respectively. It was found that the presence of air-filled voids increases the radiation along and perpendicular to the void axis.An empirical formula has been derived to calculate the radiation distribution in the multilayer shields and a good agreement between the measured and calculated values was obtained.The formulae developed by Chase have been checked experimentally to determine the minimum amount of “patching” required on the outside of the voided shields to maintain a uniform emergent radiation distribution on the outer surface of the shielding assembly. The applicability of this formula has been defined and a semi-empirical formula developed to describe the experimental results obtained for the required “patching”.     

Changes in practice of breast cancer radiotherapy 1998-2002: an Australasian survey

In order to assess the impact on radiation oncology practice of the publication of evidence-based guidelines for technical aspects of therapeutic radiation for breast cancer, the Radiation Oncology Expert Advisory Group of the National Breast Cancer Centre conducted two postal surveys of radiation oncologists practising in Australia and New Zealand. Results from a survey conducted in 1998, prior to distribution of the guidelines, have been published previously. This article reports on results from a survey undertaken in 2002 and contains data from 102 respondents who manage women with breast cancer. The results show several important changes in practice since 1998, including increased use of CT scanning in breast cancer treatment planning and increased use of immobilization devices for patient treatment. There is also evidence of increased attention to technical aspects of treatment planning that reduce the potential risk of treatment toxicity. The influence of the guidelines, the wider availability of modern equipment and results from landmark clinical trials on change in radiation therapy practice is discussed.     

Color-specific effects of intense laser exposure on visual evoked potentials in rhesus monkeys

Color-specific visual impairments following exposure to intense laser flashes were investigated using visual evoked potentials (VEPs) recorded from four anesthetized rhesus monkeys. Steady-state VEPs were recorded from the primary visual cortex in response to counterphasing high-contrast sine-wave gratings composed of either luminance contrast (red-black, green-black, and blue-black) or chromatic contrast (red-green). The effects of laser flashes in the red (647 nm), green (514 nm), and blue (476 nm) regions of the visible spectrum were assessed. Only slight wavelength-specific effects were demonstrated, primarily for the red-black grating relative to the other two luminance gratings. Recovery functions for VEPs to the red-green chromatic grating were similar to those of the three luminance gratings. The results are discussed in terms of nonopponent (luminance) and opponent (chromatic) processing.     

The patterns of care study: a specialty effort to improve care

The Patterns of Care Study is a comprehensive ongoing review of radiation therapy practice in the United States. Outcome studies have established national benchmarks for six cancer sites. Analysis of the factors influencing recurrence and complications have established important causal relationships that the radiation oncologist can manipulate to improve results. Care processes have been identified, and outcome correlations established.     

Science and perception of radiation risk.

The risks, real and supposed, of the use of radiation in medical practice as perceived by patients, their families, and the general public have a substantial impact on medical practice. Attempts to quantify low-level radiation effects involve much conjecture and supposition. This causes considerable uncertainty in results. Conflicting perceptions follow from this. Radiation exposure limits have been established, and changes in these limits have been made on the basis of the best available judgment at the time. Dose limitations have been lowered over the years. The perceived risk that the public will accept for a given benefit, in part, determines what is permissible. The radiologist must be well informed about radiation effects and must effectively communicate this risk information so that the public will be well informed.     

Characterization of a Multilayer Coated Laminar Reflection Grating at λ = 0.154 nm

A laminar grating of 1200 1/mm was coated with an x-ray reflecting multilayer coating. The multilayer coating consisted of 41 alternating layers of ReW and C having a period of 2.3 nm. In this paper we report on diffraction measurements of the coated grating at the CuKα emission line. We describe its reflection behavior using a simple theoretical model and derive two diffraction conditions, corresponding to the grating relation and the Bragg law, for which peak intensities are to be observed. We find that grating order efficiencies are modulated by the multilayer reflection.     

Venoruton as a radioprotector: a haematological assessment

Efficacy of Venoruton--O-(hydroxyethyl) Rutoside--as a radioprotector has been tested on haematological profile of rats which were subjected to whole body radiation (500 rads). The results show radiation induced lesions in respect of total (TLC) and differential leukocyte counts (DLC)/and haemoglobin are significantly lessened when Venoruton was administered prior to radiation exposure.     

A Soft X-Ray/EUV Reflectometer Based on a Laser Produced Plasma Source

A soft x-ray reflectometer is described which is based on a laser-produced plasma source and is continuously tunable over the range 40 ? < λ < 400 ?. The source is produced by focusing 0.532-μm light from a Q-switched Nd:YAG laser on a solid target. The x-ray wavelength is defined using a high throughput spherical grating monochromator with moderate resolving power (λ/Δλ ≈ 100 to 500). A time-averaged monochromatized flux of more than 109 photons/s in a 1% bandwidth at 100 eV is obtained. Photon "shot noise" limited measurements are obtained by the use of an I0 detector to normalize out the shot-to-shot variations in source intensity. Measurements with submillimeter spot sizes are readily obtainable. Various detectors have been used and the advantages and disadvantages of each are discussed. The higher order contamination of the monochromator output has been analyzed using a second grating for the purpose of making measurement corrections. The reflectometer thus provides the capability for precision absolute measurements of the reflectance of gratings and multilayer mirrors, the transmittance of thin film filters, or other properties of x-ray optical elements.     

Dose reduction technique in diagnostic X-ray computed tomography by use of 6-channel multileaf collimators

Recently, region-setting computed tomography (CT) has been studied as a region of interest imaging method. This technique can strongly reduce the radiation dose by limiting the irradiation field. Although mathematical studies have been performed for reduction of the truncation artifact, no experimental studies have been performed so far. In this study, we developed a three-dimensional region-setting CT system and evaluated its imaging properties. As an experimental system, we developed an X-ray CT system with multileaf collimators. In this system, truncated projection data can be captured by limiting of the radiation field. In addition, a truncated projection data correction was performed. Finally, image reconstruction was performed by use of the Feldkamp–Davis–Kress algorithm. In the experiments, the line profiles and the image quality of the reconstructed images were evaluated. The results suggested that the image quality of the proposed method is comparable to that of the original method. Furthermore, we confirmed that the radiation dose was reduced when this system was used. These results indicate that a 3D region-setting CT system using 6-channel multileaf collimators can reduce the radiation dose without in causing a degradation of image quality.     

Computed tomography and patient risk: Facts,perceptions and uncertainties

Since its introduction in the 1970s, computed tomography (CT) has revolutionized diagnostic decision-making. One of the major concerns associated with the widespread use of CT is the associated increased radiation exposure incurred by patients. The link between ionizing radiation and the subsequent development of neoplasia has been largely based on extrapolating data from studies of survivors of the atomic bombs dropped in Japan in 1945 and on assessments of the increased relative risk of neoplasia in those occupationally exposed to radiation within the nuclear industry. However, the association between exposure to low-dose radiation from diagnostic imaging examinations and oncogenesis remains unclear. With improved technology, significant advances have already been achieved with regards to radiation dose reduction. There are several dose optimization strategies available that may be readily employed including omitting unnecessary images at the ends of acquired series, minimizing the number of phases acquired, and the use of automated exposure control as opposed to fixed tube current techniques. In addition, new image reconstruction techniques that reduce radiation dose have been developed in recent years with promising results. These techniques use iterative reconstruction algorithms to attain diagnostic quality images with reduced image noise at lower radiation doses.