NOTE The report of the Committee without its annexes appears as Official Records of the General Assembly, Sixty-third Session, Supplement No. 46. The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries. The country names used in this document are, in most cases, those that were in use at the time the data were collected or the text prepared. In other cases, however, the names have been updated, where this was possible and appropriate, to reflect political changes. Scientific Annexes Annex A. Medical radiation exposures Annex B. Exposures of the public and workers from various sources of radiation INTROdUCTION 1. In the course of the research and development for and the application of atomic energy and nuclear technologies, a number of radiation accidents have occurred. Some of these accidents have resulted in significant health effects and occasionally in fatal outcomes. The application of technologies that make use of radiation is increasingly widespread around the world. Millions of people have occupations related to the use of radiation, and hundreds of millions of individuals benefit from these uses. Facilities using intense radiation sources for energy production and for purposes such as radiotherapy, sterilization of products, preservation of foodstuffs and gamma radiography require special care in the design and operation of equipment to avoid radiation injury to workers or to the public. Experience has shown that such technology is generally used safely, but on occasion controls have been circumvented and serious radiation accidents have ensued. 2. Reviews of radiation exposures from accidents have been presented in previous UNSCEAR reports. The last report containing an exclusive chapter on exposures from accidents was the UNSCEAR 1993 Report [U6]. 3. This annex is aimed at providing a sound basis for conclusions regarding the number of significant radiation accidents that have occurred, the corresponding levels of radiation exposures and numbers of deaths and injuries, and the general trends for various practices. Its conclusions are to be seen in the context of the Committee's overall evaluations of the levels and effects of exposure to ionizing radiation. 4. The Committee's evaluations of public, occupational and medical diagnostic exposures are mostly concerned with chronic exposures of …

sources and effects of ionizing radiation

References http://genesdev.cshlp.org/content/17/5/545.full.html#related-urls Article cited in: http://genesdev.cshlp.org/content/17/5/545.full.html#ref-list-1 This article cites 228 articles, 79 of which can be accessed free at: service Email alerting click here top right corner of the article or Receive free email alerts when new articles cite this article sign up in the box at the Collections Topic (33 articles) Molecular Physiology and Metabolism  (98 articles) Cancer and Disease Models  Articles on similar topics can be found in the following collections

/pdf/molecular-imaging-in-living-subjects-seeing-fundamental-58mg35grjk.pdf

Molecular imaging in living subjects: seeing fundamental biological processes in a new light

There have been few fundamental improvements in clinical X-ray contrast agents in more than 25 years, and the chemical platform of tri-iodobenzene has not changed. Current agents impose serious limitations on medical imaging: short imaging times, the need for catheterization in many cases, occasional renal toxicity, and poor contrast in large patients. This report is the first demonstration that gold nanoparticles may overcome these limitations. Gold has higher absorption than iodine with less bone and tissue interference achieving better contrast with lower X-ray dose. Nanoparticles clear the blood more slowly than iodine agents, permitting longer imaging times. Gold nanoparticles, 1.9 nm in diameter, were injected intravenously into mice and images recorded over time with a standard mammography unit. Gold biodistribution was measured by atomic absorption. Retention in liver and spleen was low with elimination by the kidneys. Organs such as kidneys and tumours were seen with unusual clarity and high spatial resolution. Blood vessels less than 100 mm in diameter were delineated, thus enabling in vivo vascular casting. Regions of increased vascularization and angiogenesis could be distinguished. With 10 mg Au ml 21 initially in the blood, mouse behaviour was unremarkable and neither blood plasma analytes nor organ histology revealed any evidence of toxicity 11 days and 30 days after injection. Gold nanoparticles can be used as X-ray contrast agents with properties that overcome some significant limitations of iodine-based agents.

/pdf/gold-nanoparticles-a-new-x-ray-contrast-agent-3nrxuskv5q.pdf

Gold nanoparticles: a new X-ray contrast agent

The charge of Task Group 186 (TG-186) is to provide guidance for early adopters of model-based dose calculation algorithms (MBDCAs) for brachytherapy (BT) dose calculations to ensure practice uniformity. Contrary to external beam radiotherapy, heterogeneity correction algorithms have only recently been made available to the BT community. Yet, BT dose calculation accuracy is highly dependent on scatter conditions and photoelectric effect cross-sections relative to water. In specific situations, differences between the current water-based BT dose calculation formalism (TG-43) and MBDCAs can lead to differences in calculated doses exceeding a factor of 10. MBDCAs raise three major issues that are not addressed by current guidance documents: (1) MBDCA calculated doses are sensitive to the dose specification medium, resulting in energy-dependent differences between dose calculated to water in a homogeneous water geometry (TG-43), dose calculated to the local medium in the heterogeneous medium, and the intermediate scenario of dose calculated to a small volume of water in the heterogeneous medium. (2) MBDCA doses are sensitive to voxel-by-voxel interaction cross sections. Neither conventional single-energy CT nor ICRU∕ICRP tissue composition compilations provide useful guidance for the task of assigning interaction cross sections to each voxel. (3) Since each patient-source-applicator combination is unique, having reference data for each possible combination to benchmark MBDCAs is an impractical strategy. Hence, a new commissioning process is required. TG-186 addresses in detail the above issues through the literature review and provides explicit recommendations based on the current state of knowledge. TG-43-based dose prescription and dose calculation remain in effect, with MBDCA dose reporting performed in parallel when available. In using MBDCAs, it is recommended that the radiation transport should be performed in the heterogeneous medium and, at minimum, the dose to the local medium be reported along with the TG-43 calculated doses. Assignments of voxel-by-voxel cross sections represent a particular challenge. Electron density information is readily extracted from CT imaging, but cannot be used to distinguish between different materials having the same density. Therefore, a recommendation is made to use a number of standardized materials to maintain uniformity across institutions. Sensitivity analysis shows that this recommendation offers increased accuracy over TG-43. MBDCA commissioning will share commonalities with current TG-43-based systems, but in addition there will be algorithm-specific tasks. Two levels of commissioning are recommended: reproducing TG-43 dose parameters and testing the advanced capabilities of MBDCAs. For validation of heterogeneity and scatter conditions, MBDCAs should mimic the 3D dose distributions from reference virtual geometries. Potential changes in BT dose prescriptions and MBDCA limitations are discussed. When data required for full MBDCA implementation are insufficient, interim recommendations are made and potential areas of research are identified. Application of TG-186 guidance should retain practice uniformity in transitioning from the TG-43 to the MBDCA approach.

Report of the Task Group 186 on model-based dose calculation methods in brachytherapy beyond the TG-43 formalism: current status and recommendations for clinical implementation.

For a given radiation dose, virtual monochromatic spectral images at approximately 70 keV reconstructed from split 80- and 140-kVp data showed less image noise and a higher contrast-to-noise ratio than did 120-kVp CT images.

Virtual monochromatic spectral imaging with fast kilovoltage switching: Improved image quality as compared with that obtained with conventional 120-kVp CT

We explored the potential for clinical research of computed tomography (CT) with monochromatic x-rays using the preclinical multiple energy computed tomography (MECT) system at the National Synchrotron Light Source. MECT has a fixed, horizontal fan beam with a subject apparatus rotating about a vertical axis; it will be used for imaging the human head and neck. Two -photodiode array detectors with different spatial resolutions were used. A 10.5 cm diameter acrylic phantom was imaged with MECT at 43 keV and with a conventional CT (CCT) at 80 kVp: spatial resolution line pairs (lp)/cm for both; slice height, 2.6 mm for MECT against 3.0 mm for CCT; surface dose, 3.1 cGy for MECT against 2.0 cGy for CCT. The resultant image noise was 1.5 HU for MECT against 3 HU for CCT. Computer simulations of the same images with more precisely matched spatial resolution, slice height and dose indicated an image - noise ratio of 1.4:1.0 for CCT against MECT. A 13.5 cm diameter acrylic phantom imaged with MECT at above the iodine K edge and with CCT showed, for a solution, an image contrast of 26 HU for MECT and 13 and 9 HU for the 80 and 100 kVp CCT, respectively. The corresponding numbers from computer simulation of the same images were 26, 12, and 9 HU, respectively. MECT's potential for use in clinical research is discussed.

https://iopscience.iop.org/article/10.1088/0031-9155/42/2/009/pdf

Single- and dual-energy CT with monochromatic synchrotron x-rays

Computed tomography (CT) with monochromatic X-ray beams was used to image phantoms and a live rabbit using the preclinical multiple energy computed tomography (MECT) system at the National Synchrotron Light Source. MECT has a horizontal fan beam with a subject apparatus rotating about a vertical axis. Images were obtained at 43 keV for single-energy studies, and at energies immediately below and above the 33.17 keV iodine K-edge for dual-energy subtraction CT. Two CdWO/sub 4/-photodiode array detectors were used. The high-resolution detector (0.5 mm pitch, uncollimated) provided 14 line pair/cm in-plane spatial resolution, with lower image noise than conventional CT. Images with the low-resolution detector (1.844-mm pitch, collimated to 0.922 mm detector elements) had a sensitivity for iodine of /spl ap/60 /spl mu/g/cc in 11-mm channels inside a 135 mm-diameter acrylic cylindrical phantom for a slice height of 2.5 mm and a surface dose of /spl ap/4 cGy. The image noise was /spl ap/1 Hounsfield Unit (HU); it was /spl ap/3 HU for the same phantom imaged with conventional CT at approximately the same dose, slice height, and spatial resolution (/spl ap/7 1p/cm). These results show the potential advantage of MECT, despite present technical limitations.

/pdf/dual-energy-iodine-contrast-ct-with-monochromatic-x-rays-3kn2aw31rt.pdf

D.J. Krus

Papers

Single- and dual-energy CT with monochromatic synchrotron x-rays

Dual energy iodine contrast CT with monochromatic X-rays