Entrance surface dose and induced DNA damage in blood lymphocytes of patients exposed to low-dose and low-dose-rate X-irradiation during diagnostic and therapeutic interventional radiology procedures

Radiation exposure during angiographic interventions in interventional radiology - risk and fate of advanced procedures

PURPOSE

Advanced angiographic procedures in interventional radiology are becoming more important and are more frequently used, especially in the treatment of several acute life-threatening diseases like stroke or aortic injury. In recent years, technical advancement has led to a broader spectrum of interventions and complex procedures with longer fluoroscopy times. This involves the risk of higher dose exposures, which, in rare cases, may cause deterministic radiation effects, e.g. erythema in patients undergoing angiographic procedures. Against this background, these procedures recently also became subject to national and international regulations regarding radiation protection. At the same time, individual risk assessment of possible stochastic radiation effects for each patient must be weighed up against the anticipated benefits of the therapy itself. Harmful effects of the administered dose are not limited to the patient but can also affect the radiologist and the medical staff. In particular, the development of cataracts in interventionalists is a rising matter of concern. Furthermore, long-term effects of repeated and prolonged x-ray exposure have long been neglected by radiologists but have come into focus in the past years.

CONCLUSIONS

With all this in mind, this review discusses different efforts to reduce radiation exposition levels for patients and medical staff by means of technical, personal as well as organizational measures.

Establishment and validation of surface model for biodosimetry based on γ-H2AX foci detection

INTRODUCTION

In the event of a radiation accident detecting γ-H2AX foci is being accepted as fast method for triage and dose assessment. However, due to their disappearance kinetics, published calibrations have been constructed at specific post-irradiation times.

OBJECTIVES

To develop a surface, or tridimensional, model to estimate doses at times not included in the calibration analysis, and to validate it.

MATERIALS AND METHODS

Calibration data was obtained irradiating peripheral mononucleated cells from one donor with radiation doses ranging from 0 to 3 Gy, and γ -H2AX foci were detected microscopically using a semi-automatic method, at different post-irradiation times from 0.5 to 24 h. For validation, in addition to the above-mentioned donor, blood samples from another donor were also used. Validation was done within the range of doses and post-irradiation times used in the calibration.

RESULTS

The calibration data clearly shows that at each analyzed time, the γ-H2AX foci frequency increases as dose increases, and for each dose this frequency decreases with post-irradiation time. The γ-H2AX foci nucleus distribution was clearly overdispersed, for this reason to obtain bidimensional and tridimensional dose-effect relationships no probability distribution was assumed, and linear and non-linear least squares weighted regression was used. In the two validation exercises for most evaluated samples, the 95% confidence limits of the estimated dose were between ±0.5 Gy of the real dose. No major differences were observed between donors.

CONCLUSION

In case of a suspected overexposure to radiation, the surface model here presented allows a correct dose estimation using γ-H2AX foci as biomarker. The advantage of this surface model is that it can be used at any post-irradiation time, in our model between 0.5 and 24 h.

Recent advances in γH2AX biomarker-based genotoxicity assays: A marker of DNA damage and repair

The phosphorylation of histone variant H2AX and formation of γH2AX is a primary response to the DNA double-strand breaks (DSBs). Detection of γH2AX is a robust and sensitive tool for diagnosis of DNA damage and repair in pre-clinical drug discovery investigations. In addition, the replication stress also leads to the formation of γH2AX and cell death and so γH2AX can serve as a surrogate marker of drug-induced cytotoxicity. Recent advances in genomic research offer an opportunity to detect γH2AX as a specific biomarker for quantitative analysis of DNA damages and repair using high content screening technology and quantitative imaging analysis. The proposed approaches identify a wide range of genetic disorders and are applied in combination with other assays in drug discovery and also for the evaluation of the efficacy of various developmental drugs. In the current review, we provide recent insights into the potential of γH2AX biomarker as a powerful tool in genotoxicity analyses for the monitoring and managing of cancer diseases.

Comparative analysis of physical doses and biomarker changes in subjects underwent Computed Tomography, Positron Emission Tomography-Computed Tomography, and interventional procedures

Even though the medical uses of ionizing radiation are well-acknowledged globally as vital tools for the improvement of human health, they also symbolize the major man-made sources of radiation exposure to the population. Estimation of absorbed dose and biological changes after radiation-based imaging might help to better understand the effects of low dose radiation. Because of this, we measured the Entrance Surface Dose (ESD) at different anatomical locations using Lithium tetraborate doped with manganese (Li₂B₄O₇: Mn), recorded Dose Length Product (DLP) and Dose Area Product (DAP), analyzed Chromosomal Aberration (CA), Micronucleus (MN), gamma-H2AX (γ-H2AX), and p53^ser15 proteins in the blood lymphocytes of patients (n = 267) underwent Computed Tomography (CT), Positron Emission Tomography-CT (PET/CT), and interventional procedures and healthy volunteers (n = 19). The DLP and effective doses obtained from PET/CT procedures were significantly higher (p < 0.05) when compared to CT. Fluoroscopic time and DAP were significantly higher (p < 0.05) in therapeutic compared to diagnostic interventional procedures. All the anatomical locations registered a significant amount of ESD, the ESD obtained from CT and interventional procedures were significantly (p < 0.05) higher when compared to PET/CT. Fluoroscopic time did not correlate with the ESD (eye, head, thyroid, and shoulder; R² = 0.03). CA frequency after PET/CT was significantly higher (p < 0.001) when compared to CT and interventional procedures. MN frequency was significantly higher in 24-hs (p < 0.001) post-interventional procedure compared to 2-hs. The mean ± SD of mean fluorescence intensity of γ-H2AX and p53^ser15 obtained from all subjects underwent PET/CT and interventional procedures did not show a significant difference (p > 0.05) between pre- and post-procedure. However, the relative fluorescence intensity of γ-H2AX and p53^ser15 was >1 in 58.5 % and 65.8 % of subjects respectively. Large inter-individual variation and lack of correlation between physical dose and biomarkers suggest the need for robust dosimetry with a large sample size to understand the health effects of low dose radiation.

Radioactive polymeric nanoparticles for biomedical application

Nowadays, emerging radiolabeled nanosystems are revolutionizing medicine in terms of diagnostics, treatment, and theranostics. These radionuclides include polymeric nanoparticles (NPs), liposomal carriers, dendrimers, magnetic iron oxide NPs, silica NPs, carbon nanotubes, and inorganic metal-based nanoformulations. Between these nano-platforms, polymeric NPs have gained attention in the biomedical field due to their excellent properties, such as their surface to mass ratio, quantum properties, biodegradability, low toxicity, and ability to absorb and carry other molecules. In addition, NPs are capable of carrying high payloads of radionuclides which can be used for diagnostic, treatment, and theranostics depending on the radioactive material linked. The radiolabeling process of nanoparticles can be performed by direct or indirect labeling process. In both cases, the most appropriate must be selected in order to keep the targeting properties as preserved as possible. In addition, radionuclide therapy has the advantage of delivering a highly concentrated absorbed dose to the targeted tissue while sparing the surrounding healthy tissues. Said another way, radioactive polymeric NPs represent a promising prospect in the treatment and diagnostics of cardiovascular diseases such as cardiac ischemia, infectious diseases such as tuberculosis, and other type of cancer cells or tumors.

Potential application of γ-H2AX as a biodosimetry tool for radiation triage

Radiation triage and biological dosimetry are two initial steps in the medical management of exposed individuals following radiological accidents. Well established biodosimetry methods such as the dicentric (DC) assay, micronucleus (MN) assay, and fluorescence in-situ hybridization (FISH) translocation assay (for residual damage) have been used for this purpose for several decades. Recent advances in scoring methodology and networking among established laboratories have increased triage capacity; however, these methods still have limitations in analysing large sample numbers, particularly because of the ∼ 48 h minimum culture time required prior to analysis. Hence, there is a need for simple, and high throughput markers to identify exposed individuals in case of radiological/nuclear emergencies. In recent years, a few markers were identified, one being phosphorylated histone 2AX (γ-H2AX), which measured a nuclear foci or nuclear staining intensity that was found to be suitable for triage. Measurement of γ-H2AX foci formed at and around the sites of DNA double-strand breaks is a rapid and sensitive biodosimetry method which does not require culturing and is thus promising for the analysis of a large number of samples. In this review, we have summarized the recent developments of γ-H2AX assay in radiation triage and biodosimetry, focusing chiefly on: i) the importance of baseline frequency and reported values among different laboratories, ii) the influence of known and unknown variables on dose estimation, iii) quality assurance such as inter-laboratory comparison between scorers and scoring methods, and iv) current limitations and potential for future development.

Challenges in the quantification approach to a radiation relevant adverse outcome pathway for lung cancer

PURPOSE

Adverse outcome pathways (AOPs) provide a modular framework for describing sequences of biological key events (KEs) and key event relationships (KERs) across levels of biological organization. Empirical evidence across KERs can support construction of quantified AOPs (qAOPs). Using an example AOP of energy deposition from ionizing radiation onto DNA leading to lung cancer incidence, we investigate the feasibility of quantifying data from KERs supported by all types of stressors. The merits and challenges of this process in the context of AOP construction are discussed.

MATERIALS AND METHODS

Empirical evidence across studies of dose-response from four KERs of the AOP were compiled independently for quantification. Three upstream KERs comprised of evidence from various radiation types in line with AOP guidelines. For these three KERs, a focused analysis of data from alpha-particle studies was undertaken to better characterize the process to the adverse outcome (AO) for a radon gas stressor. Numerical information was extracted from tables and graphs to plot and tabulate the response of KEs. To complement areas of the AOP quantification process, Monte Carlo (MC) simulations in TOPAS-nBio were performed to model exposure conditions relevant to the AO for an example bronchial compartment of the lung with secretory cell nuclei targets.

RESULTS

Quantification of AOP KERs highlighted the relevance of radiation types under the stressor-agnostic intent of AOP design, motivating a focus on specific types. For a given type, significant differences of KE response indicate meaningful data to derive linkages from the MIE to the AO is lacking and that better response-response focused studies are required. The MC study estimates the linear energy transfer (LET) of alpha-particles emitted by radon-222 and its progeny in the secretory cell nuclei of the example lung compartment to range from 94 - 5 + 5 to 192 - 18 + 15 keV/µm.

CONCLUSION

Quantifying AOP components provides a means to assemble empirical evidence across different studies. This highlights challenges in the context of studies examining similar endpoints using different radiation types. Data linking KERs to a MIE of 'deposition of energy' is shown to be non-compatible with the stressor-agnostic principles of AOP design. Limiting data to that describing response-response relationships between adjacent KERs may better delineate studies relevant to the damage that drives a pathway to the next KE and still support an 'all hazards' approach. Such data remains limited and future investigations in the radiation field may consider this approach when designing experiments and reporting their results and outcomes.

Exposure of patients to low doses of X-radiation during neuro-interventional imaging and procedures: Dose estimation and analysis of γ-H2AX foci and gene expression in blood lymphocytes

Radiation has widespread applications in medicine. However, despite the benefits of medical radiation exposures, adverse long-term health effects are cause for concern. Protein and gene biomarkers are early indicators of cellular response after low-dose exposure. We examined DNA damage by quantifying γ-H2AX foci and expression of twelve candidate genes in the blood lymphocytes of patients exposed to low doses of X-radiation during neuro-interventional procedures. Entrance surface dose (ESD; 10.92-1062.55 mGy) was measured by thermoluminescence dosimetry (TLD). Absorbed dose was estimated using γ-H2AX focus frequency and gene expression, with in vitro dose-response curves generated for the same biomarkers. γ-H2AX foci in post-exposure samples were significantly higher than in pre-exposure samples. Among the genes analysed, FDXR, ATM, BCL2, MDM2, TNFSF9, and PCNA showed increased expression; CDKN1A, DDB2, SESN1, BAX, and TNFRSF10B showed unchanged or decreased expression. Absorbed dose, estimated based on γ-H2AX focus frequency and gene expression changes, did not show any correlation with measured ESD. Patients undergoing interventional procedures receive considerable radiation doses, resulting in DNA damage and altered gene expression. Medical procedures should be carried out using the lowest radiation doses possible without compromising treatment.

Assessment of Genomic Instability in Medical Workers Exposed to Chronic Low-Dose X-Rays in Northern China

The increasing use of ionizing radiation (IR) in medical diagnosis and treatment has caused considerable concern regarding the effects of occupational exposure on human health. Despite this concern, little information is available regarding possible effects and the mechanism behind chronic low-dose irradiation. The present study assessed potential genomic damage in workers occupationally exposed to low-dose X-rays. A variety of analyses were conducted, including assessing the level of DNA damage and chromosomal aberrations (CA) as well as cytokinesis-block micronucleus (CBMN) assay, gene expression profiling, and antioxidant level determination. Here, we report that the level of DNA damage, CA, and CBMN were all significantly increased. Moreover, the gene expression and antioxidant activities were changed in the peripheral blood of men exposed to low-dose X-rays. Collectively, our findings indicated a strong correlation between genomic instability and duration of low-dose IR exposure. Our data also revealed the DNA damage repair and antioxidative mechanisms which could result in the observed genomic instability in health-care workers exposed to chronic low-dose IR.

18F-FDG-induced DNA damage, chromosomal aberrations, and toxicity in V79 lung fibroblast cells

¹⁸F-FDG PET/CT imaging is used in the diagnosis of diseases, including cancers. The principal photons used for imaging are 511 ke V gamma photons resulting from positron annihilation. The absorbed dose varies among body organs, depending on administered radioactivity and biological clearance. We have attempted to evaluate DNA double-strand breaks (DSB) and toxicity induced in V79 lung fibroblast cells in vitro by ¹⁸F-FDG, at doses which might result from PET procedures. Cells were irradiated by ¹⁸F-FDG at doses (14.51 and 26.86 mGy), comparable to absorbed doses received by critical organs during PET procedures. The biological endpoints measured were formation of γ-H2AX foci, mitochondrial stress, chromosomal aberrations, and cell cycle perturbation. Irradiation induced DSB (γH2AX assay), mitochondrial depolarization, and both chromosome and chromatid types of aberrations. At higher radiation doses, increased aneuploidy and reduced mitotic activity were also seen. Thus, significant biological effects were observed at the doses delivered by the ¹⁸F-FDG exposure and the effects increased with dose.

Re-evaluation of the linear no-threshold (LNT) model using new paradigms and modern molecular studies

The linear no-threshold (LNT) model is currently used to estimate low dose radiation (LDR) induced health risks. This model lacks safety thresholds and postulates that health risks caused by ionizing radiation is directly proportional to dose. Therefore even the smallest radiation dose has the potential to cause an increase in cancer risk. Advances in LDR biology and cell molecular techniques demonstrate that the LNT model does not appropriately reflect the biology or the health effects at the low dose range. The main pitfall of the LNT model is due to the extrapolation of mutation and DNA damage studies that were conducted at high radiation doses delivered at a high dose-rate. These studies formed the basis of several outdated paradigms that are either incorrect or do not hold for LDR doses. Thus, the goal of this review is to summarize the modern cellular and molecular literature in LDR biology and provide new paradigms that better represent the biological effects in the low dose range. We demonstrate that LDR activates a variety of cellular defense mechanisms including DNA repair systems, programmed cell death (apoptosis), cell cycle arrest, senescence, adaptive memory, bystander effects, epigenetics, immune stimulation, and tumor suppression. The evidence presented in this review reveals that there are minimal health risks (cancer) with LDR exposure, and that a dose higher than some threshold value is necessary to achieve the harmful effects classically observed with high doses of radiation. Knowledge gained from this review can help the radiation protection community in making informed decisions regarding radiation policy and limits.

DNA damage and the bystander response in tumor and normal cells exposed to X-rays

Monolayer and suspension cultures of tumor (BMG-1, CCRF-CEM), normal (AG1522, HADF, lymphocytes) and ATM-mutant (GM4405) human cells were exposed to X-rays at doses used in radiotherapy (high dose and high dose-rate) or radiological imaging (low dose and low dose-rate). Radiation-induced DNA damage, its persistence, and possible bystander effects were evaluated, based on DNA damage markers (γ-H2AX, p53^ser15) and cell-cycle-specific cyclins (cyclin B1 and cyclin D1). Dose-dependent DNA damage and a dose-independent bystander response were seen after exposure to high dose and high dose-rate radiation. The level of induced damage (expression of p53^ser15, γ-H2AX) depended on ATM status. However, low dose and dose-rate exposures neither increased expression of marker proteins nor induced a bystander response, except in the CCRF-CEM cells. Bystander effects after high-dose irradiation may contribute to stochastic and deterministic effects. Precautions to protect unexposed regions or to inhibit transmission of DNA damage signaling might reduce radiation risks.