[Ionizing radiation]

Classical radiation biology dogma, bystander effects and paradigm shifts

A classical dogma of radiation biology asserts that all effects of radiation on cells are due to it's direct, immediate actions. But evidence accumulated over the last 50 years shows that radiation also has, indirect ‘non-target’ actions including ‘bystander’ effects in which effects of radiation on cells or media are transported to cells or tissues that were not ‘hit’ by the radiation, leading to changes in their function. This important but heretical recognition of radiation actions has been referred to, probably incorrectly, as a ‘paradigm shift.’ What these signals are and how they induce changes is not well understood. Also not clear is how, or if, bystander effects might affect risk estimates for exposure to low doses of radiation. These issues are reviewed and explored in this series of papers.

Implications for human and environmental health of low doses of ionising radiation

The last 20 years have seen a major paradigm shift in radiation biology. Several discoveries challenge the DNA centric view which holds that DNA damage is the critical effect of radiation irrespective of dose. This theory leads to the assumption that dose and effect are simply linked - the more energy deposition, the more DNA damage and the greater the biological effect. This is embodied in radiation protection (RP) regulations as the linear-non-threshold (LNT) model. However the science underlying the LNT model is being challenged particularly in relation to the environment because it is now clear that at low doses of concern in RP, cells, tissues and organisms respond to radiation by inducing responses which are not readily predictable by dose. These include adaptive responses, bystander effects, genomic instability and low dose hypersensitivity, and are commonly described as stress responses, while recognizing that "stress" can be good as well as bad. The phenomena contribute to observed radiation responses and appear to be influenced by genetic, epigenetic and environmental factors, meaning that dose and response are not simply related. The question is whether our discovery of these phenomena means that we need to re-evaluate RP approaches. The so-called "non-targeted" mechanisms mean that low dose radiobiology is very complex and supra linear or sub-linear (even hormetic) responses are possible but their occurrence is unpredictable for any given system level. Issues which may need consideration are synergistic or antagonistic effects of other pollutants. RP, at present, only looks at radiation dose but the new (NTE) radiobiology means that chemical or physical agents, which interfere with tissue responses to low doses of radiation, could critically modulate the predicted risk. Similarly, the "health" of the organism could determine the effect of a given low dose by enabling or disabling a critical response. These issues will be discussed.

Implications for environmental health of multiple stressors

Recent insights into the mechanisms underlying the biological effects of low dose effects of ionising radiation have revealed that similar mechanisms can be induced by chemical stressors in the environment. This means that interactions between radiation and chemicals are likely and that the outcomes following mixed exposures to radiation and chemicals may not be predictable for human health, by consideration of single agent effects. Our understanding of the biological effects of low dose exposure has undergone a major paradigm shift. We now possess technologies which can detect very subtle changes in cells due to small exposures to radiation or other pollutants. We also understand much more now about cell communication, systems biology and the need to consider effects of low dose exposure at different hierarchical levels of organisation from molecules up to and including ecosystems. Furthermore we understand, at least in part, some of the mechanisms which drive low dose effects and which perpetuate these not only in the exposed organism but also in its progeny and in certain cases, its kin. This means that previously held views about safe doses or lack of harmful effects cannot be sustained. The International Commission on Radiological Protection (ICRP) and all national radiation and environmental protection organisations have always accepted a theoretical risk and have applied the precautionary principle and the LNT (linear-non-threshold) model which basically says that there is no safe dose of radiation. Therefore even in the absence of visible effects, exposure of people to radiation is strictly limited. This review will consider the historical context and the new discoveries and will focus on evidence for emergent effects after mixed exposures to combined stressors which include ionising radiation. The implications for regulation of low dose exposures to protect human health and environmental security will be discussed.

Diagnostic imaging guideline for musculoskeletal complaints in adults-an evidence-based approach-part 2: upper extremity disorders

PURPOSE

To develop evidence-based diagnostic imaging practice guidelines to assist chiropractors and other primary care providers in decision making for the appropriate use of diagnostic imaging for upper extremity disorders.

METHODS

A comprehensive search of the English and French language literature was conducted using a combination of subject headings and keywords. The quality of the citations was assessed using the Quality of diagnostic accuracy studies (QUADAS), the Appraisal of Guidelines Research and Evaluation (AGREE), and the Stroke Prevention and Educational Awareness Diffusion (SPREAD) evaluation tools. The Referral Guidelines for Imaging (radiation protection 118) coordinated by the European Commission served as the initial template. The first draft was sent for an external review. A Delphi panel composed of international experts on the topic of musculoskeletal disorders in chiropractic radiology, clinical sciences, and research was invited to review and propose recommendations on the indications for diagnostic imaging. The guidelines were pilot tested and peer-reviewed by practicing chiropractors and by chiropractic and medical specialists. Recommendations were graded according to the strength of the evidence. Dissemination and implementation strategies are discussed.

RESULTS

Recommendations for diagnostic imaging guidelines of adult upper extremity disorders are provided, supported by over 126 primary and secondary citations. The overall quality of available literature is low, however. On average, 44 Delphi panelists completed 1 of 2 rounds, reaching over 88% agreement on all 32 recommendations. Peer review by specialists reflected high levels of agreement and perceived ease of use of guidelines and implementation feasibility.

CONCLUSIONS

The guidelines are intended to be used in conjunction with sound clinical judgment and experience and should be updated regularly. Future research is needed to validate their content.

[The biological effects of very low-doses of ionizing radiation at the occupational exposure level]

The knowledge of the biological effects of very low-doses of ionizing radiation is of particular interest in order to estimate the risk for occupational workers. The epidemiological studies are to date insufficient to predict the risk for doses below 100 mSv. The cellular and molecular interaction of ionizing radiation with the cells, and the mechanisms involved in cell defence allow understanding the cellular response to radiation. The transcriptome analysis in the range of low doses has shown different cell responses according to the dose and dose rate. Here are presented the cellular and molecular action of ionizing radiation, the cellular mechanisms of cell defence and their modulation by the dose and dose rate. A non-linear relationship is drawn in this area.

High background radiation areas of Ramsar in Iran: evaluation of DNA damage by alkaline single cell gel electrophoresis (SCGE)

The hot springs in special areas in Ramsar, a northern coastal town in Iran, contain (226)Ra and (222)Rn. The natural radiation effects, radiosensitivity or adaptive responses, on the inhabitants of high natural radiation in Ramsar were studied. The single cell gel electrophoresis was used to monitor DNA damages. Three groups of volunteers were selected, one from high natural background radiation areas as the case group and two from normal background radiation areas as controls (control 1 and control 2). The latter one had the similar living situation to case group while the other (control 2) had different living situation from the other groups. Peripheral blood mononuclear cells (PMNCs) were separated and irradiated by (60)Co source at five different gamma doses. It was found that the spontaneous level of DNA damage and the induced DNA damage in all challenging doses in case group was considerably higher than control groups (p < 0.05). On the other hand, the repair rate in those volunteers, who received less than 10.2 mSv/y was significantly more than the control groups. In the contrary, individuals who live in homes with more than 10.2 mSv/y had incomplete repair. Additionally the plasma and urinary levels of vitamin C were measured spectrophotometrically. Although the concentration of vitamin C of plasma was equal in case and control 1 groups, the urinary level of vitamin C was found to be lower in the case group.