Commentary: ethical issues of current health-protection policies on low-dose ionizing radiation

A study of radiation workers: Dosimetry, chromosomal aberrations, and cancer risk

Cytogenetic analysis of blood lymphocytes can be used as a biomarker of absorbed radiation dose. The frequency of chromosomal aberrations (CA) correlates with subsequent cancer incidence. Healthy medical employees in Hungary - 301 working in an ionizing radiation work area and 732 controls - were studied from 1997 to 2022. Frequencies of chromatid- and chromosome-type aberrations in peripheral blood lymphocytes were significantly higher in the ionizing radiation group. Smoking also affected the frequency of aberrations, which was highest among smokers in the radiation group. Staff working with ionizing radiation were divided into four groups: CT, radiation therapy, diagnostic X-ray, and nuclear medicine. Total aberrations and aberrant cells were significantly higher in the nuclear medicine group than in the CT group. Tumor cases were not more frequent among the ionizing radiation group than among the control group.

Biological effects of ionizing radiation on aquatic biota - A critical review

Ionizing radiation from radionuclides impacts marine aquatic biota and the scope of investigation must be wider than just invertebrates. We intend to detail and illustrate numerous biological effects that occur in both aquatic vertebrates and invertebrates, at various dose rates from all three kinds of ionizing radiation. The characteristics of radiation sources and dosages that would most effectively generate the intended effects in the irradiated organism were assessed once the biological differentiation between vertebrates and invertebrates was determined through multiple lines of evidence. We contend that invertebrates are still more radiosensitive than vertebrates, due to their small genome size, rapid reproduction rates and lifestyle, which help them to compensate for the effects of radiation induced declines in fecundity, life span and individual health. We also identified various research gaps in this field and suggest future directions to be investigated to remedy the lack of data available in this area.

The Radiation-Specific Components Generated in the Second Step of Sequential Reactions Have a Mountain-Shaped Function

A mathematical model for radiation hormesis below 100 mSv has previously been reported, but the origins of the formula used in the previous report were not provided. In the present paper, we first considered a sequential reaction model with identical rate constants. We showed that the function of components produced in the second step of this model agreed well with the previously reported function. Furthermore, in a general sequential reaction model with different rate constants, it was mathematically proved that the function representing the component produced in the second step is always mountain-shaped: the graph has a peak with one inflection point on either side, and such a component may induce radiation hormesis.

The Threshold Effects of Low-Dose-Rate Radiation on miRNA-Mediated Neurodevelopment of Zebrafish

The biological effects and regulatory mechanisms of low-dose and low-dose-rate radiation are still rather controversial. Therefore, in this study we investigated the effects of low-dose-rate radiation on zebrafish neurodevelopment and the role of miRNAs in radiation-induced neurodevelopment. Zebrafish embryos received prolonged gamma-ray irradiation (0 mGy/h, 0.1 mGy/h, 0.2 mGy/h, 0.4 mGy/h) during development. Neurodevelopmental indicators included mortality, malformation rate, swimming speed, as well as the morphology changes of the lateral line system and brain tissue. Additionally, spatiotemporal expression of development-related miRNAs (dre-miR-196a-5p, dre-miR-210-3p, dre-miR-338) and miRNA processing enzymes genes (Dicer and Drosha) were assessed by qRT-PCR and whole mount in situ hybridization (WISH). The results revealed a decline in mortality, malformation and swimming speed, with normal histological and morphological appearance, in zebrafish that received 0.1 mGy/h; however, increased mortality, malformation and swimming speed were observed, with pathological changes, in zebrafish that received 0.2 mGy/h and 0.4 mGy/h. The expression of miRNA processing enzyme genes was altered after irradiation, and miRNAs expression was downregulated in the 0.1 mGy/h group, and upregulated in the 0.2 mGy/h and 0.4 mGy/h groups. Furthermore, ectopic expression of dre-miR-210-3p, Dicer and Drosha was also observed in the 0.4 mGy/h group. In conclusion, the effect of low-dose and low-dose-rate radiation on neurodevelopment follows the threshold model, under the regulation of miRNAs, excitatory effects occurred at a dose rate of 0.1 mGy/h and toxic effects occurred at a dose rate of 0.2 mGy/h and 0.4 mGy/h.

Low-dose ionizing radiation as a hormetin: experimental observations and therapeutic perspective for age-related disorders

Hormesis is any kind of biphasic dose-response when low doses of some agents are beneficial while higher doses are detrimental. Radiation hormesis is the most thoroughly investigated among all hormesis-like phenomena, in particular in biogerontology. In this review, we aimed to summarize research evidence supporting hormesis through exposure to low-dose ionizing radiation (LDIR). Radiation-induced longevity hormesis has been repeatedly reported in invertebrate models such as C. elegans, Drosophila and flour beetles and in vertebrate models including guinea pigs, mice and rabbits. On the contrary, suppressing natural background radiation was repeatedly found to cause detrimental effects in protozoa, bacteria and flies. We also discussed here the possibility of clinical use of LDIR, predominantly for age-related disorders, e.g., Alzheimer's disease, for which no remedies are available. There is accumulating evidence that LDIR, such as those commonly used in X-ray imaging including computer tomography, might act as a hormetin. Of course, caution should be exercised when introducing new medical practices, and LDIR therapy is no exception. However, due to the low average residual life expectancy in old patients, the short-term benefits of such interventions (e.g., potential therapeutic effect against dementia) may outweigh their hypothetical delayed risks (e.g., cancer). We argue here that assessment and clinical trials of LDIR treatments should be given priority bearing in mind the enormous economic, social and ethical implications of potentially-treatable, age-related disorders.

Effects of Low-Dose Gamma-Ray Radiation on Apoptosis and Development of Zebrafish Embryo Brain

To investigate the effects of low-dose γ irradiation on apoptosis and development of the brain in zebrafish embryos, cumulative 15 mGy doses of γ rays from a 137Cs source were used to irradiate zebrafish embryos at 2 h post-fertilization (hpf) for 120 h. Apoptosis of the brain, brain morphological development, cell submicroscopic structure and mRNA expression were analyzed, respectively. Results indicate that after 15 mGy exposure, the apoptosis of zebrafish brain increased, vacuoles appeared in brain tissue, some organelles were damaged and vacuoles appeared locally in brain cells. The mRNA expression level of axin2 was significantly upregulated, and those of frizzled, β-catenin, camk2, TCF/ LEF and bcl9 were significantly downregulated in brain tissue. These genes are involved in the Wnt signaling pathway. The findings of this work suggest that low-dose radiation may influence the apoptosis and development of the brain in the zebrafish embryo by inhibiting the Wnt signaling pathway.

X-Ray Hesitancy: Patients' Radiophobic Concerns Over Medical X-rays

All too often the family physician, orthopedic surgeon, dentist or chiropractor is met with radiophobic concerns about X-ray imaging in the clinical setting. These concerns, however, are unwarranted fears based on common but ill-informed and perpetuated ideology versus current understanding of the effects of low-dose radiation exposures. Themes of X-ray hesitancy come in 3 forms: 1. All radiation exposures are harmful (i.e. carcinogenic); 2. Radiation exposures are cumulative; 3. Children are more susceptible to radiation. Herein we address these concerns and find that low-dose radiation activates the body's adaptive responses and leads to reduced cancers. Low-dose radiation is not cumulative as long as enough time (e.g. 24 hrs) passes prior to a repeated exposure, and any damage is repaired, removed, or eliminated. Children have more active immune systems; the literature shows children are no more affected than adults by radiation exposures. Medical X-rays present a small, insignificant addition to background radiation exposure that is not likely to cause harm. Doctors and patients alike should be better informed of the lack of risks from diagnostic radiation and the decision to image should rely on the best evidence, unique needs of the patient, and the expertise of the physician-not radiophobia.

The prospective mathematical idea satisfying both radiation hormesis under low radiation doses and linear non-threshold theory under high radiation doses

It has yet to be determined whether or not the probability of developing cancer due to radiation exposure levels of low doses is proportional to the dose. Herein, for radiation hormesis occurring at low doses, mathematical models using functions that take a mountain-like shape having two inflection points are considered. The following perspectives were obtained: (i) When the probability of developing cancer decreases at radiation levels above the natural background dose, the radiation hormesis effect occurs up to ~ 12.4 mSv. (ii) When there is a proportional relationship at ≥750 mSv, the radiation hormesis effect occurs up to ~ 225 mSv. Thus, by performing studies at the molecular and cellular levels for radiation doses at ≤16.8 or 307 mSv, it is possible to investigate carcinogenesis resulting from low radiation doses.

Interests, Bias, and Consensus in Science and Regulation

Scientists are human. As such, they are prone to bias based on political and economic interests. While conflicts of interest are usually associated with private funding, research funded by public sources is also subject to special interests and therefore prone to bias. Such bias may lead to consensus not based on evidence. While appealing to scientific consensus is a legitimate tool in public debate and regulatory decisions, such an appeal is illegitimate in scientific discussion itself. We provide examples of decades-long scientific consensus on erroneous hypotheses. For policy advice purposes, a scientific statement or model should be considered as the subject of proper scientific consensus only if shared by those who would directly benefit from proving it wrong. Otherwise, specialists from adjacent fields of science and technology should be consulted.

Developmental toxicity and apoptosis in zebrafish embryos induced by low-dose γ-ray irradiation

In this paper, the developmental toxicity and apoptosis in zebrafish (Danio rerio) embryos induced by 0.01, 0.05, and 0.10-Gy γ-ray irradiation were investigated and verified by single cell gel electrophoresis, acridine orange staining, flow cytometry, transmission electron microscopy, digital gene expression sequencing, and Western blot analysis. DNA damage, deformity rates, and apoptosis of zebrafish embryos were found to increase significantly with the increase of irradiation dose, and survival and hatching rates significantly decreased when the irradiation dose exceeds 0.10 and 0.05 Gy, respectively. Exposure to 0.10-Gy γ-ray irradiation resulted in the swelling of cell mitochondria of zebrafish embryos and changes in their intracellular vacuoles. mRNA and protein expression levels of Shh (sonic hedgehog 19 KDa) and Smo (smoothened 86 KDa) of Hh signaling pathway associated with the development of early embryos significantly increased with the increase of irradiation dose. Expression of the AKT (56 KDa) and PiK3r3 (55 KDa) genes, which are anti-apoptotic and involved with the PI3K/Akt signaling pathway, significantly decreased, while expression of the bada gene, which is pro-apoptotic, significantly increased. The results show that γ-ray irradiations of 0.01 and 0.05 Gy can induce developmental toxicity and apoptosis in zebrafish embryos via Hh and PI3K/Akt signaling pathways, respectively.

Ethics of Adoption and Use of the Linear No-Threshold Model

The linear no-threshold (LNT) model of ionizing radiation–induced cancer assumes that every increment of radiation dose, no matter how small, constitutes an increased cancer risk for humans. Linear no-threshold is presently the most widely applied model for radiation risk assessment. As such, it imposes very heavy burden on the society in both economic and human terms. This model, which was adopted in late 1950s in the wake of massive government investments in science, is controversial and raises important ethical issues. This article identifies 2 issues often missed: scientists usurping the role of policy makers and seeking funding and power. These issues should be considered together with the scientific controversy raging over the validity of the LNT model and the multiple other ethical issues regarding its ongoing use.

Radiophobia: 7 Reasons Why Radiography Used in Spine and Posture Rehabilitation Should Not Be Feared or Avoided

Evidence-based contemporary spinal rehabilitation often requires radiography. Use of radiography (X-rays or computed tomography scans) should not be feared, avoided, or have their exposures lessened to decrease patient dose possibly jeopardizing image quality. This is because all fears of radiation exposures from medical diagnostic imaging are based on complete fabrication of health risks based on an outdated, invalid linear model that has simply been propagated for decades. We present 7 main arguments for continued use of radiography for routine use in spinal rehabilitation: (1) the linear no-threshold model for radiation risk estimates is invalid for low-dose exposures; (2) low-dose radiation enhances health via the body's adaptive response mechanisms (ie, radiation hormesis); (3) an X-ray with low-dose radiation only induces 1 one-millionth the amount of cellular damage as compared to breathing air for a day; (4) radiography is below inescapable natural annual background radiation levels; (5) radiophobia stems from unwarranted fears and false beliefs; (6) radiography use leads to better patient outcomes; (7) the risk to benefit ratio is always beneficial for routine radiography. Radiography is a safe imaging method for routine use in patient assessment, screening, diagnosis, and biomechanical analysis and for monitoring treatment progress in daily clinical practice.

Cancer immunotherapy: how low-level ionizing radiation can play a key role

The cancer immunoediting hypothesis assumes that the immune system guards the host against the incipient cancer, but also "edits" the immunogenicity of surviving neoplastic cells and supports remodeling of tumor microenvironment towards an immunosuppressive and pro-neoplastic state. Local irradiation of tumors during standard radiotherapy, by killing neoplastic cells and generating inflammation, stimulates anti-cancer immunity and/or partially reverses cancer-promoting immunosuppression. These effects are induced by moderate (0.1-2.0 Gy) or high (>2 Gy) doses of ionizing radiation which can also harm normal tissues, impede immune functions, and increase the risk of secondary neoplasms. In contrast, such complications do not occur with exposures to low doses (≤0.1 Gy for acute irradiation or ≤0.1 mGy/min dose rate for chronic exposures) of low-LET ionizing radiation. Furthermore, considerable evidence indicates that such low-level radiation (LLR) exposures retard the development of neoplasms in humans and experimental animals. Here, we review immunosuppressive mechanisms induced by growing tumors as well as immunomodulatory effects of LLR evidently or likely associated with cancer-inhibiting outcomes of such exposures. We also offer suggestions how LLR may restore and/or stimulate effective anti-tumor immunity during the more advanced stages of carcinogenesis. We postulate that, based on epidemiological and experimental data amassed over the last few decades, whole- or half-body irradiations with LLR should be systematically examined for its potential to be a viable immunotherapeutic treatment option for patients with systemic cancer.

Effects of ionising radiation on micronucleus formation and chromosomal aberrations in Chinese radiation workers

This study is aimed to investigate the effects of ionising radiation (IR) on micronuclei (MN) formation and chromosome aberrations (CAs) in Chinese radiation workers. The study was conducted using peripheral blood lymphocytes from 1392 radiation workers from Public Hospitals of the city of Tangshan (the exposed group), and 143 healthy individuals as the control group. Fluorescence in situ hybridisation (FISH) was used to detect the unstable and stable nuclear CAs on metaphase. The MN assay was performed using the cytochalasin B method for cytokinesis-block. The MN and CA frequencies were significantly higher in the exposed group than in healthy controls (both p < 0.001). Examination of the incidence rates of MN and CA showed an increasing trend among workers in some occupations compared with the others (all p < 0.05). There were also significant differences in MN and CA rates among workers with different exposure times (all p < 0.05). Stable CA rates demonstrated an increased trend among workers with different exposure times (all p < 0.05), while no significance of unstable CA rates was found among workers with different exposure times (all p < 0.05). Importantly, the frequencies of CA and MN increased among different cumulative radiation dose groups (all p < 0.05). Correlation analysis showed that the frequencies of MN and CA were positively associated with the cumulative radiation dose. Long-term exposure to IR may have harmful effects on the health of radiation workers. The data obtained here show an increased risk of genetic instability that correlated with occupation, exposure time and equivalent dose among Chinese radiation workers.

Atomic Bomb Survivors Life-Span Study: Insufficient Statistical Power to Select Radiation Carcinogenesis Model

The atomic bomb survivors life-span study (LSS) is often claimed to support the linear no-threshold hypothesis (LNTH) of radiation carcinogenesis. This paper shows that this claim is baseless. The LSS data are equally or better described by an s-shaped dependence on radiation exposure with a threshold of about 0.3 Sievert (Sv) and saturation level at about 1.5 Sv. A Monte-Carlo simulation of possible LSS outcomes demonstrates that, given the weak statistical power, LSS cannot provide support for LNTH. Even if the LNTH is used at low dose and dose rates, its estimation of excess cancer mortality should be communicated as 2.5% per Sv, i.e., an increase of cancer mortality from about 20% spontaneous mortality to about 22.5% per Sv, which is about half of the usually cited value. The impact of the “neutron discrepancy problem” – the apparent difference between the calculated and measured values of neutron flux in Hiroshima – was studied and found to be marginal. Major revision of the radiation risk assessment paradigm is required.

Reconsidering Health Consequences of the Chernobyl Accident

The Chernobyl accident led to major human suffering caused by the evacuation and other counter-measures. However, the direct health consequences of the accident-related radiation exposures, besides the acute effects and small number of thyroid cancers, have not been observed. This absence is challenged by some influential groups affecting public policies who claim that the true extent of radiogenic health consequences is covered up. We consider such claims. The most conservative (in this case - overestimating) linear no-threshold hypothesis was used to calculate excess cancer expectations for cleanup workers, the population of the contaminated areas and the global population. Statistical estimations were performed to verify whether such expected excess was detectable. The calculated cancer excess for each group is much less than uncertainties in number of cancer cases in epidemiological studies. Therefore the absence of detected radiation carcinogenesis is in full correspondence with the most conservative a priori expectations. Regarding the cover-up claims, rational choice analysis was performed. Such analysis shows that these claims are ill-founded. The present overcautious attitude to radiological hazards should be corrected in order to mitigate the present suffering and to avoid such suffering in the future.

Donor-specific cell-based assays in studying sensitivity to low-dose radiation: a population-based perspective

Currently, a linear no-threshold model is used to estimate health risks associated with exposure to low-dose radiation, a prevalent exposure in the general population, because the direct estimation from epidemiological studies suffers from uncertainty. This model has been criticized based on unique biology of low-dose radiation. Whether the departure from linearity is toward increased or decreased risk is intensely debated. We present an approach based on individual radiosensitivity testing and discuss how individual radiosensitivity can be assessed with the goal to develop a quantifiable measure of cellular response that can be conducted via high-throughput population testing.