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

Sources, Effects and Risks of Ionizing Radiation

We have investigated the effect of the adaptive response on acute myeloid leukemia (AML) induced in CBA/Harwell mice by a chronic radiation exposure. Groups of mice irradiated with a total dose of 1.0 Gy at two different chronic dose rates (0.5, 0.004 Gy/h) had similar frequencies of AML. Compared to control animals that did not develop AML, irradiation at either of these dose rates did not change the longevity of the mice that did not die of leukemia. The survival rates of irradiated mice that did develop leukemia in the two groups were not different from each other, indicating that the dose rates produced similar responses and therefore were both chronic exposures. We then tested the ability of a chronic 10-cGy (0.5 Gy/h) exposure to ionizing radiation, mild hyperthermia (40.5°C whole-body, 60 min) or treatment with interleukin-1 (1500 U i.p.) to induce an adaptive response and modify the frequency or latency of AML which resulted from a subsequent (24 h later) 1.0-Gy (0.5 Gy/h) chronic radiation exposu...

The adaptive response modifies latency for radiation-induced myeloid leukemia in CBA/H mice.

Standard methods for risk assessments resulting from human exposures to mixed radiation fields in Space consisting of different particle types and energies rely upon quality factors. These are generally defined as a function of linear energy transfer (LET) and are assumed to be proportional to the risk. In this approach, it is further assumed that the risks for single exposures from each of the radiation types add linearly. Although risks of cancer from acute exposures to photon radiations have been measured in humans, quality factors for protons and ions of heavier atomic mass are generally inferred from animal and/or cellular data. Because only a small amount of data exists for such particles, this group has been examining tumourigenesis initiated by energetic protons and iron ions. In this study, 741 female Sprague–Dawley rats were irradiated or sham irradiated at approximately 60 days of age with 250 MeV protons, 1 GeV/nucleon iron ions or both protons and iron ions. The results suggest that the risk of mammary tumours in the rats sequentially irradiated with 1 GeV/nucleon 56Fe ions and 250 MeV protons is less than additive. These data in conjunction with earlier results further suggest that risk assessments in terms of only mean LETs of the primary cosmic rays may be insufficient to accurately evaluate the relative risks of each type of particle in a radiation field of mixed radiation qualities.

http://iopscience.iop.org/article/10.1088/0031-9155/49/16/024/pdf

In vivo mammary tumourigenesis in the Sprague-Dawley rat and microdosimetric correlates.

During the past decade, a large number of radiobiological studies have become available for tritium--many of them focusing on the relative biological effectiveness of tritium beta rays. These and previous studies indicate that tritium in body water produces the same spectrum of radiogenic effects (e.g., cancer, genetic effects, developmental abnormalities, and reproductive effects) observed following whole-body exposure to penetrating radiations such as gamma rays and x rays. However, tritium beta rays are of greater biological effectiveness than gamma rays and x rays. For example, tritium in the oxide form is about 2 to 3 times more effective at low doses or low dose rates than gamma rays from 137Cs or 60Co. When tritium is bound to organic molecules, relative biological effectiveness values may be somewhat larger than those for tritium in oxide form. Tritium administered to animals or to cells in vitro as tritiated amino acids results in relative biological effectiveness values that appear similar to those obtained for tritium in oxide form; however, if administered as tritiated thymidine, the relative biological effectiveness values appear to be about two-fold higher. It is clear from the wealth of tritium data now available that relative biological effectiveness values for tritium beta rays are higher than the quality factor of unity generally used in radiation protection.

Tritium radiobiology and relative biological effectiveness

To help resolve uncertainties as to the most appropriate weighting factor for tritium beta rays, a large experiment was carried out to measure the relative biological effectiveness (RBE) of tritiated water compared to X rays for the induction of myeloid leukemia in male mice of the CBA/H strain. The study was designed to estimate the lifetime incidence of myeloid leukemia in seven groups of about 750 mice each; radiation exposures were approximately 0, 1, 2 and 3 Gy both for tritiated water and for X rays. The lifetime incidence of leukemia in these mice increased from 0.13% in the control group to 6-8% in groups exposed to higher radiation doses. The results were fitted to various equations relating leukemia incidence to radiation dose, using both the raw data and data corrected for cumulative mouse-days at risk. The calculated RBE values for tritium beta rays compared to X rays ranged from 1.0 +/- 0.5 to 1.3 +/- 0.3. A best estimate of the RBE for this experiment was about 1.2 +/- 0.3. A wR value of 1 would thus appear to be more appropriate than a wR of 2 for tritium beta rays.

Relative Biological Effectiveness of Tritium for Induction of Myeloid Leukemia in CBA/H Mice

The RBE for tritium was estimated in reference to 200-kVp X rays, using acceleration of breast tumor appearance in the female Sprague-Dawley rat as the end-point. Seventy-five percent of the total tritium dose was delivered to the mammary gland within the first 10 days and 95% within the first 20 days after the start of the tritium exposure. RBE estimations were based on various criteria including the tumor incidence per Gy at 450 days postirradiation and the time required to induce tumors in 50% of the animals at risk. The results suggest that tritium ..beta.. rays are about 1.1-1.3 times more effective than chronic 200-kVp X rays for acceleration of the appearance of rat mammary tumors. However, the uncertainties involved in these calculations are such that the effects of tritium ..beta.. rays could not be reliably distinguished from those of chronic 200-kVp X rays. Measured differences in RBE values were slightly larger for the comparison between acute and chronic X rays than for the comparison between chronic tritium ..beta.. rays and chronic X rays.

Occurrence of Mammary Tumors in Rats after Exposure to Tritium Beta Rays and 200-kVp X Rays

Mammary tumour development was followed in two experiments involving a total of 2229 female Sprague-Dawley rats exposed to various doses of X or gamma rays at different dose rates. The data for another 462 rats exposed to tritiated water in one of these experiments were also analyzed. The incidence of adenocarcinomas and fibroadenomas at a given time after exposure increased linearly in proportion to total radiation dose for most groups. However, no significant increase in adenocarcinomas was observed with chronic gamma exposures up to 1.1 Gy, and the increase in fibroadenomas observed with chronic gamma exposures at a dose rate of 0.0076 Gy h-1 up to an accumulated dose of 3.3 Gy was small compared to that observed after acute exposures. The incidence of all mammary tumors increased almost linearly with the log of dose rate in the range 0.0076 to 26.3 Gy h-1 for 3 Gy total dose of gamma rays. The effects of X rays appeared to be less influenced by dose rate than were the effects of gamma rays.

D. K. Myers

Papers

Relative Biological Effectiveness of Tritium for Induction of Myeloid Leukemia in CBA/H Mice

Occurrence of Mammary Tumors in Rats after Exposure to Tritium Beta Rays and 200-kVp X Rays

Dose-rate effects of mammary tumor development in female Sprague-Dawley rats exposed to X and gamma radiation.

An Experiment Designed to Measure the RBE of Tritium for the Induction of Myeloid Leukaemia in Animals