Review of the risk of cancer following low and moderate doses of sparsely ionising radiation received in early life in groups with individually estimated doses

Revisiting an Inverse Dose-Fractionation Effect of Ionizing Radiation Exposure for Ischemic Heart Disease: Insights from Recent Studies

Over the last two decades, there has been emerging evidence suggesting that ionizing radiation exposures could be associated with elevated risks of cardiovascular disease (CVD), particularly ischemic heart disease (IHD). Excess CVD risks have been observed in a number of exposed groups, with generally similar risk estimates both at low and high radiation doses and dose rates. In 2014, we reported for the first time significantly higher risks of IHD mortality when radiation doses were delivered over a protracted period of time (an inverse dose-fractionation effect) in the Canadian Fluoroscopy Cohort Study. Here we review the current evidence on the dose-fractionation effect of radiation exposure, discuss potential implication for radiation protection policies and suggest further directions for research in this area.

A Review of Recent Low-dose Research and Recommendations for Moving Forward

ABSTRACT

The linear no-threshold (LNT) model has been the regulatory "law of the land" for decades. Despite the long-standing use of LNT, there is significant ongoing scientific disagreement on the applicability of LNT to low-dose radiation risk. A review of the low-dose risk literature of the last 10 y does not provide a clear answer, but rather the body of literature seems to be split between LNT, non-linear risk functions (e.g., supra- or sub-linear), and hormetic models. Furthermore, recent studies have started to explore whether radiation can play a role in the development of several non-cancer effects, such as heart disease, Parkinson's disease, and diabetes, the mechanisms of which are still being explored. Based on this review, there is insufficient evidence to replace LNT as the regulatory model despite the fact that it contributes to public radiophobia, unpreparedness in radiation emergency response, and extreme cleanup costs both following radiological or nuclear incidents and for routine decommissioning of nuclear power plants. Rather, additional research is needed to further understand the implications of low doses of radiation. The authors present an approach to meaningfully contribute to the science of low-dose research that incorporates machine learning and Edisonian approaches to data analysis.

Radiation Adverse Outcome pathways (AOPs): examining priority questions from an international horizon-style exercise

PURPOSE

The Organisation for Economic Co-operation and Development (OECD) Adverse Outcome Pathway (AOP) Development Programme is being explored in the radiation field, as an overarching framework to identify and prioritize research needs that best support strengthening of radiation risk assessment and risk management strategies. To advance the use of AOPs, an international horizon-style exercise (HSE) was initiated through the Radiation/Chemical AOP Joint Topical Group (JTG) formed by the OECD Nuclear Energy Agency (NEA) High-Level Group on Low Dose Research (HLG-LDR) under the auspices of the Committee on Radiological Protection and Public Health (CRPPH). The intent of the HSE was to identify key research questions for consideration in AOP development that would help to reduce uncertainties in estimating the health risks following exposures to low dose and low dose-rate ionizing radiation. The HSE was conducted in several phases involving the solicitation of relevant questions, a collaborative review of open-ended candidate questions and an elimination exercise that led to the selection of 25 highest priority questions for the stated purpose. These questions were further ranked by over 100 respondents through an international survey. This final set of questions was judged to provide insights into how the OECD's AOP approach can be put into practice to meet the needs of hazard and risk assessors, regulators, and researchers. This paper examines the 25 priority questions in the context of hazard/risk assessment framework for ionizing radiation.

CONCLUSION

By addressing the 25 priority questions, it is anticipated that constructed AOPs will have a high level of specificity, making them valuable tools for simplifying and prioritizing complex biological processes for use in developing revised radiation hazard and risk assessment strategies.

Association between urinary phthalates and phthalate metabolites and cancer risk: A systematic review and meta-analysis

Phthalates, widely utilized in industrial products, are classified as endocrine-disrupting chemicals (EDCs). Although certain phthalate and their metabolites have been implicated in cancer development, the reported findings have exhibited inconsistencies. Therefore, we conducted the comprehensive literature search to assess the association between phthalate and their metabolites and cancer risk by identifying original studies measuring phthalates or their metabolites and reporting their correlation with cancer until July 4, 2023. The Odds Ratios (ORs) and corresponding 95% confidence intervals (CIs) were extracted and analyzed to estimate the risk. Pooled data from eleven studies, including 3101 cancer patients and 6858 controls, were analyzed using a fixed- or random-effects model based on heterogeneity tests. When comparing extreme categories of different phthalates and their metabolites, we observed a significant association between urinary phthalates and phthalate metabolites (MEHHP, MECPP, DBP and MBzP) and cancer risk. The findings of our meta-analysis reinforce the existing evidence that urinary phthalates and phthalate metabolites is strongly associated with cancer development. Further investigations are warranted to elucidate the underlying mechanisms of this association. These results may offer novel insights into cancer development.

Recurrent medical imaging exposures for the care of patients: one way forward

Medical imaging is both valuable and essential in the care of patients. Much of this imaging depends on ionizing radiation with attendant responsibilities for judicious use when performing an examination. This responsibility applies in settings of both individual as well as multiple (recurrent) imaging with associated repeated radiation exposures. In addressing the roles and responsibilities of the medical communities in the paradigm of recurrent imaging, both the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) have issued position statements, each affirmed by other organizations. The apparent difference in focus and approach has resulted in a lack of clarity and continued debate. Aiming towards a coherent approach in dealing with radiation exposure in recurrent imaging, the IAEA convened a panel of experts, the purpose of which was to identify common ground and reconcile divergent perspectives. The effort has led to clarifying recommendations for radiation exposure aspects of recurrent imaging, including the relevance of patient agency and the provider-patient covenant in clinical decision-making. CLINICAL RELEVANCE STATEMENT: An increasing awareness, generating some lack of clarity and divergence in perspectives, with patients receiving relatively high radiation doses (e.g., ≥ 100 mSv) from recurrent imaging warrants a multi-stakeholder accord for the benefit of patients, providers, and the imaging community. KEY POINTS: • Recurrent medical imaging can result in an accumulation of exposures which exceeds 100 milli Sieverts. • Professional organizations have different perspectives on roles and responsibilities for recurrent imaging. • An expert panel reconciles differing perspectives for addressing radiation exposure from recurrent medical imaging.

A generalisation of the method of regression calibration and comparison with Bayesian and frequentist model averaging methods

For many cancer sites low-dose risks are not known and must be extrapolated from those observed in groups exposed at much higher levels of dose. Measurement error can substantially alter the dose-response shape and hence the extrapolated risk. Even in studies with direct measurement of low-dose exposures measurement error could be substantial in relation to the size of the dose estimates and thereby distort population risk estimates. Recently, there has been considerable attention paid to methods of dealing with shared errors, which are common in many datasets, and particularly important in occupational and environmental settings. In this paper we test Bayesian model averaging (BMA) and frequentist model averaging (FMA) methods, the first of these similar to the so-called Bayesian two-dimensional Monte Carlo (2DMC) method, and both fairly recently proposed, against a very newly proposed modification of the regression calibration method, the extended regression calibration (ERC) method, which is particularly suited to studies in which there is a substantial amount of shared error, and in which there may also be curvature in the true dose response. The quasi-2DMC with BMA method performs well when a linear model is assumed, but very poorly when a linear-quadratic model is assumed, with coverage probabilities both for the linear and quadratic dose coefficients that are under 5% when the magnitude of shared Berkson error is large (50%). For the linear model the bias is generally under 10%. However, using a linear-quadratic model it produces substantially biased (by a factor of 10) estimates of both the linear and quadratic coefficients, with the linear coefficient overestimated and the quadratic coefficient underestimated. FMA performs as well as quasi-2DMC with BMA when a linear model is assumed, and generally much better with a linear-quadratic model, although the coverage probability for the quadratic coefficient is uniformly too high. However both linear and quadratic coefficients have pronounced upward bias, particularly when Berkson error is large. By comparison ERC yields coverage probabilities that are too low when shared and unshared Berkson errors are both large (50%), although otherwise it performs well, and coverage is generally better than the quasi-2DMC with BMA or FMA methods, particularly for the linear-quadratic model. The bias of the predicted relative risk at a variety of doses is generally smallest for ERC, and largest for the quasi-2DMC with BMA and FMA methods (apart from unadjusted regression), with standard regression calibration and Monte Carlo maximum likelihood exhibiting bias in predicted relative risk generally somewhat intermediate between ERC and the other two methods. In general ERC performs best in the scenarios presented, and should be the method of choice in situations where there may be substantial shared error, or suspected curvature in the dose response.

A generalisation of the method of regression calibration and comparison with Bayesian and frequentist model averaging methods

For many cancer sites low-dose risks are not known and must be extrapolated from those observed in groups exposed at much higher levels of dose. Measurement error can substantially alter the dose-response shape and hence the extrapolated risk. Recently, there has been considerable attention paid to methods of dealing with shared errors, which are particularly important in occupational and environmental settings. In this paper we test Bayesian model averaging (BMA) and frequentist model averaging (FMA) methods, the first of these similar to the so-called Bayesian two-dimensional Monte Carlo (2DMC) method, and both fairly recently proposed, against a very newly proposed modification of the regression calibration method, the extended regression calibration (ERC) method. The quasi-2DMC+BMA method performs well when a linear model is assumed, but poorly when a linear-quadratic model is assumed. FMA performs as well as quasi-2DMC+BMA when a linear model is assumed, and generally much better with a linear-quadratic model, although the coverage probability for the quadratic coefficient is uniformly too high. ERC yields coverage probabilities that are too low when shared and unshared Berkson errors are both large (50%), although otherwise it performs well, and coverage is generally better than the quasi-2DMC+BMA or FMA methods, particularly for the linear-quadratic model. The bias of predicted relative risk at a variety of doses is generally smallest for ERC, and largest for quasi-2DMC+BMA and FMA, with standard regression calibration and Monte Carlo maximum likelihood exhibiting bias in predicted relative risk generally somewhat intermediate between ERC and the other two methods. In general ERC performs best in the scenarios presented, and should be the method of choice in situations where there may be substantial shared error, or suspected curvature in the dose response.

Plain film of the abdomen remains a low sensitivity test in A&E

BACKGROUND

Plain film abdomens (PFA) are frequently used in the emergency department to help guide the management of patients presenting with abdominal symptoms. A plain film abdomen contributes minimally to clinical scenarios due to low sensitivity and specificity. Is a PFA useful in the emergency setting or does it serve to further complicate decision making?

AIM

We hypothesise that PFAs in the emergency department are over utilised to falsely reassure clinicians and patients alike.

METHODS

A search of the National Integrated Medical Imaging System (NIMIS) database in an Irish tertiary referral hospital was conducted. All plain film abdominal radiographs requested by the emergency department between 01/01/2022 and 31/08/2022 were identified. Requests where there was suspicion of foreign body were excluded. A retrospective search of the NIMIS database identified subjects who underwent subsequent imaging.

RESULTS

A total of 619 abdominal films were deemed suitable for inclusion. These comprised of 338 male and 282 female subjects. Subjects had an average age of 64 years. Fifty-seven per cent of PFAs detected no abnormality. Forty-two per cent of subjects had subsequent imaging. The plain film findings correlated with further imaging in only 15% of cases. One case of ruptured aortic aneurysm and 11 perforations were detected on computerised tomography, none of these cases were evident on abdominal X-ray.

CONCLUSION

Plain film abdomen requests are over utilised in the emergency department. PFAs are not sensitive for detecting acute pathology and should not be used to decide if a patient requires further imaging or a full clinical assessment.

Non-Habit-Related Oral Squamous Cell Carcinoma: A Review

Oral squamous cell carcinoma (OSCC) is a serious and potentially life-threatening condition that can have a profound impact on an individual's health and well-being. Its etiology is commonly known to be habit induced, such as tobacco consumption, smoking, or alcohol abuse. Apart from these etiologies, certain factors that lead to OSCC are also present but are less frequently encountered in hospitals and clinics. However, these non-habitual factors, with their pathogenesis, can lead to OSCC, which may be confusing to certain medical practitioners. This article discusses the various non-habitual causes that can lead to OSCC, as well as their pathophysiology, molecular expression, and related indicators and prognostic factors.

Radiotherapy for non-cancer diseases: benefits and long-term risks

PURPOSE

The discovery of X-rays was followed by a variety of attempts to treat infectious diseases and various other non-cancer diseases with ionizing radiation, in addition to cancer. There has been a recent resurgence of interest in the use of such radiotherapy for non-cancer diseases. Non-cancer diseases for which use of radiotherapy has currently been proposed include refractory ventricular tachycardia, neurodegenerative diseases (e.g. Alzheimer's disease and dementia), and Coronavirus Disease 2019 (COVID-19) pneumonia, all with ongoing clinical studies that deliver radiation doses of 0.5-25 Gy in a single fraction or in multiple daily fractions. In addition to such non-cancer effects, historical indications predominantly used in some countries (e.g. Germany) include osteoarthritis and degenerative diseases of the bones and joints. This narrative review gives an overview of the biological rationale and ongoing preclinical and clinical studies for radiotherapy proposed for various non-cancer diseases, discusses the plausibility of the proposed biological rationale, and considers the long-term radiation risks of cancer and non-cancer diseases.

CONCLUSIONS

A growing body of evidence has suggested that radiation represents a double-edged sword, not only for cancer, but also for non-cancer diseases. At present, clinical evidence has shown some beneficial effects of radiotherapy for ventricular tachycardia, but there is little or no such evidence of radiotherapy for other newly proposed non-cancer diseases (e.g. Alzheimer's disease, COVID-19 pneumonia). Patients with ventricular tachycardia and COVID-19 pneumonia have thus far been treated with radiotherapy when they are an urgent life threat with no efficient alternative treatment, but some survivors may encounter a paradoxical situation where patients were rescued by radiotherapy but then get harmed by radiotherapy. Further studies are needed to justify the clinical use of radiotherapy for non-cancer diseases, and optimize dose to diseased tissue while minimizing dose to healthy tissue.

Radiation-Related Thyroid Cancer

Radiation is an environmental factor that elevates the risk of developing thyroid cancer. Actual and possible scenarios of exposures to external and internal radiation are multiple and diverse. This article reviews radiation doses to the thyroid and corresponding cancer risks due to planned, existing, and emergency exposure situations, and medical, public, and occupational categories of exposures. Any exposure scenario may deliver a range of doses to the thyroid, and the risk for cancer is addressed along with modifying factors. The consequences of the Chornobyl and Fukushima nuclear power plant accidents are described, summarizing the information on thyroid cancer epidemiology, treatment, and prognosis, clinicopathological characteristics, and genetic alterations. The Chornobyl thyroid cancers have evolved in time: becoming less aggressive and driver shifting from fusions to point mutations. A comparison of thyroid cancers from the 2 areas reveals numerous differences that cumulatively suggest the low probability of the radiogenic nature of thyroid cancers in Fukushima. In view of continuing usage of different sources of radiation in various settings, the possible ways of reducing thyroid cancer risk from exposures are considered. For external exposures, reasonable measures are generally in line with the As Low As Reasonably Achievable principle, while for internal irradiation from radioactive iodine, thyroid blocking with stable iodine may be recommended in addition to other measures in case of anticipated exposures from a nuclear reactor accident. Finally, the perspectives of studies of radiation effects on the thyroid are discussed from the epidemiological, basic science, and clinical points of view.

Radiation exposure during CT procedures in Tanzania

The aim of this study was to evaluate optimisation status during common computed tomography (CT) procedures by determining values of volume computed tomography dose index (CTDIvol) and dose-length product (DLP) per examination. Patient and exposure data were collected from the CT console during various CT procedures. The results show that variations in CTDIvol and DLP values were mainly because of differences in the techniques used. The 75th percentile values were set as the third quartile of the median CTDIvol or DLP values for all hospitals. These values of 40.9, 9.0, 9.4 and 16.2 mGy for CTDIvol were determined for head, high-resolution chest, abdomen-pelvis and lumbar spine, respectively. The corresponding DLP values for the same sequence of CT procedures were 900, 360, 487 and 721 mGy.cm, respectively. The updated results provide a basis for optimising the procedures of CT in this country.

A generalisation of the method of regression calibration and comparison with the Bayesian 2-dimensional Monte Carlo method

For many cancer sites it is necessary to assess risks from low-dose exposures via extrapolation from groups exposed at moderate and high levels of dose. Measurement error can substantially alter the shape of this relationship and hence the derived population risk estimates. Even in studies with direct measurement of low-dose exposures measurement error could be substantial in relation to the size of the dose estimates and thereby distort population risk estimates. Recently, much attention has been devoted to the issue of shared errors, common in many datasets, and particularly important in occupational settings. In this paper we test a Bayesian model averaging method, the so-called Bayesian two-dimensional Monte Carlo (2DMC) method, that has been fairly recently proposed against a very newly proposed modification of the regression calibration method, which is particularly suited to studies in which there is a substantial amount of shared error, and in which there may also be curvature in the true dose response. We also compared both methods against standard regression calibration and Monte Carlo maximum likelihood. The Bayesian 2DMC method performs poorly, with coverage probabilities both for the linear and quadratic dose coefficients that are under 5%, particularly when the magnitudes of classical and Berkson error are both moderate to large (20%-50%). The method also produces substantially biased (by a factor of 10) estimates of both the linear and quadratic coefficients, with the linear coefficient overestimated and the quadratic coefficient underestimated. By comparison the extended regression calibration method yields coverage probabilities that are too low when shared and unshared Berkson errors are both large (50%), although otherwise it performs well, and coverage is generally better than the Bayesian 2DMC and all other methods. The bias of the predicted relative risk at a variety of doses is generally smallest for extended regression calibration, and largest for the Bayesian 2DMC method (apart from unadjusted regression), with standard regression calibration and Monte Carlo maximum likelihood exhibiting bias in predicted relative risk generally somewhat intermediate between the other two methods.

Exposure to low-dose radiation in occupational settings and ischaemic heart disease: a systematic review and meta-analysis

Ionising radiation is a human carcinogen, but the evidence is less clear that exposure to low-dose ionising radiation (LDIR) increases the risk of adverse cardiovascular outcomes. We synthesised the literature of chronic occupational exposure to LDIR and cardiovascular disease, particularly for ischaemic heart disease (IHD).The literature search was conducted using three databases including studies published between 1990 and 2022. A quality assessment of the studies was completed using the Office of Health and Assessment and Translation Risk of Bias Rating Tool. We conducted meta-analyses for IHD mortality using random effects models using measures of excess relative risk per sievert (ERR/Sv) obtained from internal cohort comparisons, as well as with standardised mortality ratios (SMRs) from external cohort comparisons.We identified 2189 articles, and of these, 26 provided data on IHD and were retained. Most studies were classified as having a 'moderate' level of risk of bias. Fourteen and 10 studies reporting external radiation doses were included in meta-analyses using SMR and ERR/Sv, respectively. The meta-summary SMR was 0.81 (95% CI 0.74 to 0.89) with evidence of reduced risk but high heterogeneity across studies. For internal cohort measures, the summary ERR/Sv for a lagged exposure of 10 years was 0.10 (95% CI 0.01 to 0.20) with low heterogeneity. The subgroup analysis by lagged exposure time showed the strongest association were for the 15 and 20 years lag.Our findings suggest that occupational exposure to LDIR increases the risk IHD mortality and highlight the relevance of internal cohort comparisons.

A generalisation of the method of regression calibration

There is direct evidence of risks at moderate and high levels of radiation dose for highly radiogenic cancers such as leukaemia and thyroid cancer. For many cancer sites, however, it is necessary to assess risks via extrapolation from groups exposed at moderate and high levels of dose, about which there are substantial uncertainties. Crucial to the resolution of this area of uncertainty is the modelling of the dose-response relationship and the importance of both systematic and random dosimetric errors for analyses in the various exposed groups. It is well recognised that measurement error can alter substantially the shape of this relationship and hence the derived population risk estimates. Particular attention has been devoted to the issue of shared errors, common in many datasets, and particularly important in occupational settings. We propose a modification of the regression calibration method which is particularly suited to studies in which there is a substantial amount of shared error, and in which there may also be curvature in the true dose response. This method can be used in settings where there is a mixture of Berkson and classical error. In fits to synthetic datasets in which there is substantial upward curvature in the true dose response, and varying (and sometimes substantial) amounts of classical and Berkson error, we show that the coverage probabilities of all methods for the linear coefficient [Formula: see text] are near the desired level, irrespective of the magnitudes of assumed Berkson and classical error, whether shared or unshared. However, the coverage probabilities for the quadratic coefficient [Formula: see text] are generally too low for the unadjusted and regression calibration methods, particularly for larger magnitudes of the Berkson error, whether this is shared or unshared. In contrast Monte Carlo maximum likelihood yields coverage probabilities for [Formula: see text] that are uniformly too high. The extended regression calibration method yields coverage probabilities that are too low when shared and unshared Berkson errors are both large, although otherwise it performs well, and coverage is generally better than these other three methods. A notable feature is that for all methods apart from extended regression calibration the estimates of the quadratic coefficient [Formula: see text] are substantially upwardly biased.

Magnetic resonance imaging pelvimetric measurements as predictors for emergent cesarean delivery in obstructed labor

Objective

This study aimed to investigate the usefulness of various magnetic resonance imaging (MRI) pelvimetric parameters for predicting emergent cesarean delivery due to obstructed labor.

Study design

This was a prospective observational study. MRI pelvimetry was performed in cases of a clinically suspected maternal narrow pelvis, maternal short stature, fetal overgrowth, and abnormal placental position. MRI pelvimetry was performed at 34.7 ± 4.2 gestational weeks using a 1.5 T MRI system. The pelvic inlet angle, pelvic inclination, obstetric conjugate, sacral outlet diameter (SOD), and coccygeal pelvic outlet were measured in the sagittal section. The interspinous diameter and intertuberous diameter were measured in coronal sections. Fetal anomalies, cesarean deliveries before the onset of labor, and non-reassuring fetal status were excluded from the analysis.

Results

MRI pelvimetry was performed in 154 patients. After excluding 76 cases, including 19 cases of absolute cephalopelvic disproportion, 78 cases of trial of labor were included. Of these, 63 were vaginal deliveries and 15 were emergent cesarean deliveries due to obstructed labor. The cut-off value for body mass index (BMI) was 22.2, with an area under the curve (AUC) of 0.69, for predicting obstructed labor. The cut-off value for the SOD was 10.7 cm with an AUC of 0.69. BMI alone had a sensitivity of 80%, specificity of 66%, positive predictive value (PPV) of 36%, and negative predictive value (NPV) of 93%. When BMI and SOD were combined, sensitivity was 53%, specificity was 90%, PPV was 57%, and NPV was 89%. The odds ratio for emergent cesarean delivery was 5.42 (95% confidence interval 1.06-27.6, p = 0.041) if the SOD was less than the cut-off value in the binomial logistic regression analysis in cases with an BMI > 22.

Conclusion

We confirmed that MRI pelvimetry was a reliable tool for better patient selection for obstructed labor. The SOD was the best predictor of obstructed labor, with a cut-off value of 10.7 cm for women with a low BMI.

A generalisation of the method of regression calibration

There is direct evidence of risks at moderate and high levels of radiation dose for highly radiogenic cancers such as leukaemia and thyroid cancer. For many cancer sites, however, it is necessary to assess risks via extrapolation from groups exposed at moderate and high levels of dose, about which there are substantial uncertainties. Crucial to the resolution of this area of uncertainty is the modelling of the dose-response relationship and the importance of both systematic and random dosimetric errors for analyses in the various exposed groups. It is well recognised that measurement error can alter substantially the shape of this relationship and hence the derived population risk estimates. Particular attention has been devoted to the issue of shared errors, common in many datasets, and particularly important in occupational settings. We propose a modification of the regression calibration method which is particularly suited to studies in which there is a substantial amount of shared error, and in which there may also be curvature in the true dose response. This method can be used in settings where there is a mixture of Berkson and classical error. In fits to synthetic datasets in which there is substantial upward curvature in the true dose response, and varying (and sometimes substantial) amounts of classical and Berkson error, we show that the coverage probabilities of all methods for the linear coefficient \(\alpha\) are near the desired level, irrespective of the magnitudes of assumed Berkson and classical error, whether shared or unshared. However, the coverage probabilities for the quadratic coefficient \(\beta\) are generally too low for the unadjusted and regression calibration methods, particularly for larger magnitudes of the Berkson error, whether this is shared or unshared. In contrast Monte Carlo maximum likelihood yields coverage probabilities for \(\beta\) that are uniformly too high. The extended regression calibration method yields coverage probabilities that are too low when shared and unshared Berkson errors are both large, although otherwise it performs well, and coverage is generally better than these other three methods. A notable feature is that for all methods apart from extended regression calibration the estimates of the quadratic coefficient \(\beta\) are substantially upwardly biased.

Noncancer Effects of Ionizing Radiation Exposure on the Eye, the Circulatory System and beyond: Developments made since the 2011 ICRP Statement on Tissue Reactions

For radiation protection purposes, noncancer effects with a threshold-type dose-response relationship have been classified as tissue reactions (formerly called nonstochastic or deterministic effects), and equivalent dose limits aim to prevent occurrence of such tissue reactions. Accumulating evidence demonstrates increased risks for several late occurring noncancer effects at doses and dose rates much lower than previously considered. In 2011, the International Commission on Radiological Protection (ICRP) issued a statement on tissue reactions to recommend a threshold of 0.5 Gy to the lens of the eye for cataracts and to the heart and brain for diseases of the circulatory system (DCS), independent of dose rate. Literature published thereafter continues to provide updated knowledge. Increased risks for cataracts below 0.5 Gy have been reported in several cohorts (e.g., including in those receiving protracted or chronic exposures). A dose threshold for cataracts is less evident with longer follow-up, with limited evidence available for risk of cataract removal surgery. There is emerging evidence for risk of normal-tension glaucoma and diabetic retinopathy, but the long-held tenet that the lens represents among the most radiosensitive tissues in the eye and in the body seems to remain unchanged. For DCS, increased risks have been reported in various cohorts, but the existence or otherwise of a dose threshold is unclear. The level of risk is less uncertain at lower dose and lower dose rate, with the possibility that risk per unit dose is greater at lower doses and dose rates. Target organs and tissues for DCS are also unknown, but may include heart, large blood vessels and kidneys. Identification of potential factors (e.g., sex, age, lifestyle factors, coexposures, comorbidities, genetics and epigenetics) that may modify radiation risk of cataracts and DCS would be important. Other noncancer effects on the radar include neurological effects (e.g., Parkinson's disease, Alzheimer's disease and dementia) of which elevated risk has increasingly been reported. These late occurring noncancer effects tend to deviate from the definition of tissue reactions, necessitating more scientific developments to reconsider the radiation effect classification system and risk management. This paper gives an overview of historical developments made in ICRP prior to the 2011 statement and an update on relevant developments made since the 2011 ICRP statement.

The Future of Radioactive Medicine

The discovery of X rays in the late 19th century heralded the beginning of a new age in medicine, and the advent of channeling the power of radiation to diagnose and treat human disease. Radiation has been leveraged in medicine in a multitude of ways and is a critical element of cancer care including screening, diagnosis, surveillance, and interventional treatments. Modern radiotherapy techniques include a multitude of methodologies utilizing both externally and internally delivered radiation from a variety of approaches. This review provides a comprehensive overview of contemporary radiotherapy methodologies, the field of radiopharmaceuticals and theranostics, effects of low dose radiation and highlights the phenomena of fear of exposure to radiation and its impact in modern medicine.

The scientific basis for the use of the linear no-threshold (LNT) model at low doses and dose rates in radiological protection

The linear no-threshold (LNT) model was introduced into the radiological protection system about 60 years ago, but this model and its use in radiation protection are still debated today. This article presents an overview of results on effects of exposure to low linear-energy-transfer radiation in radiobiology and epidemiology accumulated over the last decade and discusses their impact on the use of the LNT model in the assessment of radiation-related cancer risks at low doses. The knowledge acquired over the past 10 years, both in radiobiology and epidemiology, has reinforced scientific knowledge about cancer risks at low doses. In radiobiology, although certain mechanisms do not support linearity, the early stages of carcinogenesis comprised of mutational events, which are assumed to play a key role in carcinogenesis, show linear responses to doses from as low as 10 mGy. The impact of non-mutational mechanisms on the risk of radiation-related cancer at low doses is currently difficult to assess. In epidemiology, the results show excess cancer risks at dose levels of 100 mGy or less. While some recent results indicate non-linear dose relationships for some cancers, overall, the LNT model does not substantially overestimate the risks at low doses. Recent results, in radiobiology or in epidemiology, suggest that a dose threshold, if any, could not be greater than a few tens of mGy. The scientific knowledge currently available does not contradict the use of the LNT model for the assessment of radiation-related cancer risks within the radiological protection system, and no other dose-risk relationship seems more appropriate for radiological protection purposes.

Lympho-hematopoietic malignancies risk after exposure to low dose ionizing radiation during cardiac catheterization in childhood

Pediatric patients with congenital heart disease (CHD) often undergo low dose ionizing radiation (LDIR) from cardiac catheterization (CC) for the diagnosis and/or treatment of their disease. Although radiation doses from a single CC are usually low, less is known about the long-term radiation associated cancer risks. We aimed to assess the risk of lympho-hematopoietic malignancies in pediatric CHD patients diagnosed or treated with CC. A French cohort of 17,104 children free of cancer who had undergone a first CC from 01/01/2000 to 31/12/2013, before the age of 16 was set up. The follow-up started at the date of the first recorded CC until the exit date, i.e., the date of death, the date of first cancer diagnosis, the date of the 18th birthday, or the 31/12/2015, whichever occurred first. Poisson regression was used to estimate the LDIR associated cancer risk. The median follow-up was 5.9 years, with 110,335 person-years. There were 22,227 CC procedures, yielding an individual active bone marrow (ABM) mean cumulative dose of 3.0 milligray (mGy). Thirty-eight incident lympho-hematopoietic malignancies were observed. When adjusting for attained age, gender and predisposing factors to cancer status, no increased risk was observed for lympho-hematopoietic malignancies RR_/mGy = 1.00 (95% CI: 0.88; 1.10). In summary, the risk of lympho-hematopoietic malignancies and lymphoma was not associated to LDIR in pediatric patients with CHD who undergo CC. Further epidemiological studies with greater statistical power are needed to improve the assessment of the dose-risk relationship.

Phthalazone tethered 1,2,3-triazole conjugates: In silico molecular docking studies, synthesis, in vitro antiproliferative, and kinase inhibitory activities

New phthalazone tethered 1,2,3-triazole derivatives 12-21 were synthesized utilizing the Cu(I)-catalyzed click reactions of alkyne-functionalized phthalazone 1 with functionalized azides 2-11. The new phthalazone-1,2,3-triazoles structures 12-21 were confirmed by different spectroscopic tools, like IR; 1H, 13C, 2D HMBC and 2D ROESY NMR; EI MS, and elemental analysis. The antiproliferative efficacy of the molecular hybrids 12-21 against four cancer cell lines was evaluated, including colorectal cancer, hepatoblastoma, prostate cancer, breast adenocarcinoma, and the normal cell line WI38. The antiproliferative assessment of derivatives 12-21 showed potent activity of compounds 16, 18, and 21 compared to the anticancer drug doxorubicin. Compound 16 showed selectivity (SI) towardthe tested cell lines ranging from 3.35 to 8.84 when compared to Dox., that showed SI ranged from 0.75 to 1.61. Derivatives 16, 18 and 21 were assessed towards VEGFR-2 inhibitory activity and result in that derivative 16 showed the potent activity (IC50 = 0.123 µM) in comparison with sorafenib (IC50 = 0.116 µM). Compound 16 caused an interference with the cell cycle distribution of MCF7 and increased the percentage of cells in S phase by 1.37-fold. In silico molecular docking of the effective derivatives 16, 18, and 21 against vascular endothelial growth factor receptor-2 (VEGFR-2) confirmed the formation of stable protein-ligand interactions within the pocket.

Individual response of the ocular lens to ionizing radiation

PURPOSE

Cataract (opacification of the ocular lens) is a typical tissue reaction (deterministic effect) following ionizing radiation exposure, for which prevention dose limits have been recommended in the radiation protection system. Manifestations of radiation cataracts can vary among individuals, but such potential individual responses remain uncharacterized. Here we review relevant literature and discuss implications for radiation protection. This review assesses evidence for significant modification of radiation-induced cataractogenesis by age at exposure, sex and genetic factors based on current scientific literature.

CONCLUSIONS

In addition to obvious physical factors (e.g. dose, dose rate, radiation quality, irradiation volume), potential factors modifying individual responses for radiation cataracts include sex, age and genetics, with comorbidity and coexposures also having important roles. There are indications and preliminary data identifying such potential modifiers of radiation cataract incidence or risk, although no firm conclusions can yet be drawn. Further studies and a consensus on the evidence are needed to gain deeper insights into factors determining individual responses regarding radiation cataracts and the implications for radiation protection.

Low-dose radiotherapy for COVID-19 pneumonia and cancer: summary of a recent symposium and future perspectives

The lessons learned from the Coronavirus Disease 2019 (COVID-19) pandemic are numerous. Low dose radiotherapy (LDRT) was used in the pre-antibiotic era as treatment for bacterially/virally associated pneumonia. Motivated in part by these historic clinical and radiobiological data, LDRT for treatment of COVID-19-associated pneumonia was proposed in early 2020. Although there is a large body of epidemiological and experimental data pointing to effects such as cancer at low doses, there is some evidence of beneficial health effects at low doses. It has been hypothesized that low dose radiation could be combined with immune checkpoint therapy to treat cancer. We shall review here some of these old radiobiological and epidemiological data, as well as the newer data on low dose radiation and stimulated immune response and other relevant emerging data. The paper includes a summary of several oral presentations given in a Symposium on "Low dose RT for COVID and other inflammatory diseases" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually 3-6 October 2021.

Brain cancer after radiation exposure from CT examinations of children and young adults: results from the EPI-CT cohort study

BACKGROUND

The European EPI-CT study aims to quantify cancer risks from CT examinations of children and young adults. Here, we assess the risk of brain cancer.

METHODS

We pooled data from nine European countries for this cohort study. Eligible participants had at least one CT examination before age 22 years documented between 1977 and 2014, had no previous diagnosis of cancer or benign brain tumour, and were alive and cancer-free at least 5 years after the first CT. Participants were identified through the Radiology Information System in 276 hospitals. Participants were linked with national or regional registries of cancer and vital status, and eligible cases were patients with brain cancers according to WHO International Classification of Diseases for Oncology. Gliomas were analysed separately to all brain cancers. Organ doses were reconstructed using historical machine settings and a large sample of CT images. Excess relative risks (ERRs) of brain cancer per 100 mGy of cumulative brain dose were calculated with linear dose-response modelling. The outcome was the first reported diagnosis of brain cancer after an exclusion period of 5 years after the first electronically recorded CT examination.

FINDINGS

We identified 948 174 individuals, of whom 658 752 (69%) were eligible for our study. 368 721 (56%) of 658 752 participants were male and 290 031 (44%) were female. During a median follow-up of 5·6 years (IQR 2·4-10·1), 165 brain cancers occurred, including 121 (73%) gliomas. Mean cumulative brain dose, lagged by 5 years, was 47·4 mGy (SD 60·9) among all individuals and 76·0 mGy (100·1) among people with brain cancer. A significant linear dose-response relationship was observed for all brain cancers (ERR per 100 mGy 1·27 [95% CI 0·51-2·69]) and for gliomas separately (ERR per 100 mGy 1·11 [0·36-2·59]). Results were robust when the start of follow-up was delayed beyond 5 years and when participants with possibly previously unreported cancers were excluded.

INTERPRETATION

The observed significant dose-response relationship between CT-related radiation exposure and brain cancer in this large, multicentre study with individual dose evaluation emphasises careful justification of paediatric CTs and use of doses as low as reasonably possible.

FUNDING

EU FP7; Belgian Cancer Registry; La Ligue contre le Cancer, L'Institut National du Cancer, France; Ministry of Health, Labour and Welfare of Japan; German Federal Ministry of Education and Research; Worldwide Cancer Research; Dutch Cancer Society; Research Council of Norway; Consejo de Seguridad Nuclear, Generalitat de Catalunya, Spain; US National Cancer Institute; UK National Institute for Health Research; Public Health England.

Low-Dose Extrapolation Factors Implied by Mortality and Incidence Data from the Japanese Atomic Bomb Survivor Life Span Study Data

Assessment of the effect of low dose and low-dose-rate exposure depends critically on extrapolation from groups exposed at high dose and high-dose rates such as the Japanese atomic bomb survivor data, and has often been achieved via application of a dose and dose-rate effectiveness factor (DDREF). An important component of DDREF is the factor determining the effect of extrapolation of dose, the so-called low-dose extrapolation factor (LDEF). To assess LDEF models linear (or linear quadratic) in dose are often fitted. In this report LDEF is assessed via fitting relative rate models that are linear or linear quadratic in dose to the latest Japanese atomic bomb survivor data on solid cancer, leukemia and circulatory disease mortality (followed from 1950 through 2003) and to data on solid cancer, lung cancer and urinary tract cancer incidence. The uncertainties in LDEF are assessed using parametric bootstrap techniques. Analysis is restricted to survivors with <3 Gy dose. There is modest evidence for upward curvature in dose response in the mortality data. For leukemia and for all solid cancer excluding lung, stomach and breast cancer there is significant curvature (P < 0.05). There is no evidence of curvature for circulatory disease (P > 0.5). The estimate of LDEF for all solid cancer mortality is 1.273 [95% confidence intervals (CI) 0.913, 2.182], for all solid cancer mortality excluding lung cancer, stomach cancer and breast cancer is 2.183 (95% CI 1.090, >100) and for leukemia mortality is 11.447 (95% CI 2.390, >100). For stomach cancer mortality LDEF is modestly raised, 1.077 (95% CI 0.526, >100), while for lung cancer, female breast cancer and circulatory disease mortality the LDEF does not much exceed 1. LDEF for solid cancer incidence is 1.186 (95% CI 0.942, 1.626) and for urinary tract cancer is 1.298 (95% CI <0, 7.723), although for lung cancer LDEF is not elevated, 0.842 (95% CI 0.344, >100).

The Evidence for Excess Risk of Cancer and Non-Cancer Disease at Low Doses and Dose Rates

The question of whether there are excess radiation-associated health risks at low dose is controversial. We present evidence of excess cancer risks in a number of (largely pediatrically or in utero exposed) groups exposed to low doses of radiation (<0.1 Gy). Moreover, the available data on biological mechanisms do not provide support for the idea of a low-dose threshold or hormesis for any of these endpoints. There are emerging data suggesting risks of cardiovascular disease and cataract at low doses, but this is less well established. This large body of evidence does not suggest and, indeed, is not statistically compatible with any very large threshold in dose (>10 mGy), or with possible beneficial effects from exposures. The presented data suggest that exposure to low-dose radiation causes excess cancer risks and quite possibly also excess risks of various non-cancer endpoints.

CBTRUS Statistical Report: Pediatric Brain Tumor Foundation Childhood and Adolescent Primary Brain and Other Central Nervous System Tumors Diagnosed in the United States in 2014-2018

The CBTRUS Statistical Report: Pediatric Brain Tumor Foundation Childhood and Adolescent Primary Brain and Other Central Nervous System Tumors Diagnosed in the United States in 2014-2018 comprehensively describes the current population-based incidence of primary malignant and non-malignant brain and other CNS tumors in children and adolescents ages 0-19 years, collected and reported by central cancer registries covering approximately 100% of the United States population. Overall, brain and other CNS tumors are the most common solid tumor, the most common cancer, and the most common cause of cancer death in children and adolescents ages 0-19 years. This report aims to serve as a useful resource for researchers, clinicians, patients, and families.

Application of radiation omics in the development of adverse outcome pathway networks: an example of radiation-induced cardiovascular disease

BACKGROUND

Epidemiological studies have indicated that exposure of the heart to doses of ionizing radiation as low as 0.5 Gy increases the risk of cardiac morbidity and mortality with a latency period of decades. The damaging effects of radiation to myocardial and endothelial structures and functions have been confirmed radiobiologically at high dose, but much less is known at low dose. Integration of radiation biology and epidemiology data is a recommended approach to improve the radiation risk assessment process. The adverse outcome pathway (AOP) framework offers a comprehensive tool to compile and translate mechanistic information into pathological endpoints which may be relevant for risk assessment at the different levels of a biological system. Omics technologies enable the generation of large volumes of biological data at various levels of complexity, from molecular pathways to functional organisms. Given the quality and quantity of available data across levels of biology, omics data can be attractive sources of information for use within the AOP framework. It is anticipated that radiation omics studies could improve our understanding of the molecular mechanisms behind the adverse effects of radiation on the cardiovascular system. In this review, we explored the available omics studies on radiation-induced cardiovascular disease (CVD) and their applicability to the proposed AOP for CVD.

RESULTS

The results of 80 omics studies published on radiation-induced CVD over the past 20 years have been discussed in the context of the AOP of CVD proposed by Chauhan et al. Most of the available omics data on radiation-induced CVD are from proteomics, transcriptomics, and metabolomics, whereas few datasets were available from epigenomics and multi-omics. The omics data presented here show great promise in providing information for several key events of the proposed AOP of CVD, particularly oxidative stress, alterations of energy metabolism, extracellular matrix and vascular remodeling.

CONCLUSIONS

The omics data presented here shows promise to inform the various levels of the proposed AOP of CVD. However, the data highlight the urgent need of designing omics studies to address the knowledge gap concerning different radiation scenarios, time after exposure and experimental models. This review presents the evidence to build a qualitative omics-informed AOP and provides views on the potential benefits and challenges in using omics data to assess risk-related outcomes.

Cancer risks among studies of medical diagnostic radiation exposure in early life without quantitative estimates of dose

BACKGROUND

There is accumulating evidence of excess risk of cancer in various populations exposed at acute doses below several tens of mSv or doses received over a protracted period. There is also evidence that relative risks are generally higher after radiation exposures in utero or in childhood.

METHODS AND FINDINGS

We reviewed and summarised evidence from 89 studies of cancer following medical diagnostic exposure in utero or in childhood, in which no direct estimates of radiation dose are available. In all of the populations studied exposure was to sparsely ionizing radiation (X-rays). Several of the early studies of in utero exposure exhibit modest but statistically significant excess risks of several types of childhood cancer. There is a highly significant (p < 0.0005) negative trend of odds ratio with calendar period of study, so that more recent studies tend to exhibit reduced excess risk. There is no significant inter-study heterogeneity (p > 0.3). In relation to postnatal exposure there are significant excess risks of leukaemia, brain and solid cancers, with indications of variations in risk by cancer type (p = 0.07) and type of exposure (p = 0.02), with fluoroscopy and computed tomography scans associated with the highest excess risk. However, there is highly significant inter-study heterogeneity (p < 0.01) for all cancer endpoints and all but one type of exposure, although no significant risk trend with calendar period of study.

CONCLUSIONS

Overall, this large body of data relating to medical diagnostic radiation exposure in utero provides support for an associated excess risk of childhood cancer. However, the pronounced heterogeneity in studies of postnatal diagnostic exposure, the implied uncertainty as to the meaning of summary measures, and the distinct possibilities of bias, substantially reduce the strength of the evidence from the associations we observe between radiation imaging in childhood and the subsequent risk of cancer being causally related to radiation exposure.

Establishing a Communication and Engagement Strategy to Facilitate the Adoption of the Adverse Outcome Pathways in Radiation Research and Regulation

BACKGROUND

Studies on human health and ecological effects of ionizing radiation are rapidly evolving as innovative technologies arise and the body of scientific knowledge grows. Structuring this information could effectively support the development of decision making tools and health risk models to complement current system of radiation protection. To this end, the adverse outcome pathway (AOP) approach is being explored as a means to consolidate the most relevant research to identify causation between exposure to a chemical or non-chemical stressor and disease or adverse effect progression. This tool is particularly important for low dose and low dose rate radiation exposures because of the latency and uncertainties in the biological responses at these exposure levels. To progress this aspect, it is essential to build a community of developers, facilitators, risk assessors (in the private sector and in government), policy-makers, and regulators who understand the strengths and weaknesses of, and how to appropriately utilize AOPs for consolidating our knowledge on the impact of low dose ionizing radiation. Through co-ordination with the Organisation of Economic Co-operation and Development (OECD) Nuclear Energy Agency (NEA) High-Level Group on Low-Dose Research (HLG-LDR) and OECD's AOP Programme, initiatives are under way to demonstrate this approach in radiation research and regulation. Among these, a robust communications strategy and stakeholder engagement will be essential. It will help establish best practices for AOPs in institutional project development and aid in dissemination for more efficient and timely uptake and use of AOPs. In this regard, on June 1, 2021, the Radiation and Chemical (Rad/Chem) AOP Joint Topical Group was formed as part of the initiative from the NEA's HLG-LDR. The topical group will work to develop a communication and engagement strategy to define the target audiences, establish the clear messages and identify the delivery and engagement platforms.

CONCLUSION

The incorporation of the best science and better decision-making should motive the radiation protection community to develop, refine and use AOPs, recognizing that their incorporation into radiation health risk assessments is critical for public health and environmental protection in the 21st century.

Nuclear and Radiological Emergencies: Biological Effects, Countermeasures and Biodosimetry

Atomic and radiological crises can be caused by accidents, military activities, terrorist assaults involving atomic installations, the explosion of nuclear devices, or the utilization of concealed radiation exposure devices. Direct damage is caused when radiation interacts directly with cellular components. Indirect effects are mainly caused by the generation of reactive oxygen species due to radiolysis of water molecules. Acute and persistent oxidative stress associates to radiation-induced biological damages. Biological impacts of atomic radiation exposure can be deterministic (in a period range a posteriori of the event and because of destructive tissue/organ harm) or stochastic (irregular, for example cell mutation related pathologies and heritable infections). Potential countermeasures according to a specific scenario require considering basic issues, e.g., the type of radiation, people directly affected and first responders, range of doses received and whether the exposure or contamination has affected the total body or is partial. This review focuses on available medical countermeasures (radioprotectors, radiomitigators, radionuclide scavengers), biodosimetry (biological and biophysical techniques that can be quantitatively correlated with the magnitude of the radiation dose received), and strategies to implement the response to an accidental radiation exposure. In the case of large-scale atomic or radiological events, the most ideal choice for triage, dose assessment and victim classification, is the utilization of global biodosimetry networks, in combination with the automation of strategies based on modular platforms.

Age effects on radiation response: summary of a recent symposium and future perspectives

One of the principal uncertainties when estimating population risk of late effects from epidemiological data is that few radiation-exposed cohorts have been followed up to extinction. Therefore, the relative risk model has often been used to estimate radiation-associated risk and to extrapolate risk to the end of life. Epidemiological studies provide evidence that children are generally at higher risk of cancer induction than adults for a given radiation dose. However, the strength of evidence varies by cancer site and questions remain about site-specific age at exposure patterns. For solid cancers, there is a large body of evidence that excess relative risk (ERR) diminishes with increasing age at exposure. This pattern of risk is observed in the Life Span Study (LSS) as well as in other radiation-exposed populations for overall solid cancer incidence and mortality and for most site-specific solid cancers. However, there are some disparities by endpoint in the degree of variation of ERR with exposure age, with some sites (e.g., colon, lung) in the LSS incidence data showing no variation, or even increasing ERR with increasing age at exposure. The pattern of variation of excess absolute risk (EAR) with age at exposure is often similar, with EAR for solid cancers or solid cancer mortality decreasing with increasing age at exposure in the LSS. We shall review the human data from the Japanese LSS cohort, and a variety of other epidemiological data sets, including a review of types of medical diagnostic exposures, also some radiobiological animal data, all bearing on the issue of variations of radiation late-effects risk with age at exposure and with attained age. The paper includes a summary of several oral presentations given in a Symposium on "Age effects on radiation response" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually on 3-6 October 2021.