A Critical Assessment of the Linear No-Threshold Hypothesis: Its Validity and Applicability for Use in Risk Assessment and Radiation Protection

Interplay of immune modulation, adaptive response and hormesis: Suggestive of threshold for clinical manifestation of effects of ionizing radiation at low doses?

The health impacts of low-dose ionizing radiation exposures have been a subject of debate over the last three to four decades. While there has been enough evidence of "no adverse observable" health effects at low doses and low dose rates, the hypothesis of "Linear No Threshold" continues to rule and govern the principles of radiation protection and the formulation of regulations and public policies. In adopting this conservative approach, the role of the biological processes underway in the human body is kept at abeyance. This review consolidates the available studies that discuss all related biological pathways and repair mechanisms that inhibit the progression of deleterious effects at low doses and low dose rates of ionizing radiation. It is pertinent that, taking cognizance of these processes, there is a need to have a relook at policies of radiation protection, which as of now are too stringent, leading to undue economic losses and negative public perception about radiation.

MIRD Pamphlet No. 28, Part 1: MIRDcalc-A Software Tool for Medical Internal Radiation Dosimetry

Medical internal radiation dosimetry constitutes a fundamental aspect of diagnosis, treatment, optimization, and safety in nuclear medicine. The MIRD committee of the Society of Nuclear Medicine and Medical Imaging developed a new computational tool to support organ-level and suborgan tissue dosimetry (MIRDcalc, version 1). Based on a standard Excel spreadsheet platform, MIRDcalc provides enhanced capabilities to facilitate radiopharmaceutical internal dosimetry. This new computational tool implements the well-established MIRD schema for internal dosimetry. The spreadsheet incorporates a significantly enhanced database comprising details for 333 radionuclides, 12 phantom reference models (International Commission on Radiological Protection), 81 source regions, and 48 target regions, along with the ability to interpolate between models for patient-specific dosimetry. The software also includes sphere models of various composition for tumor dosimetry. MIRDcalc offers several noteworthy features for organ-level dosimetry, including modeling of blood source regions and dynamic source regions defined by user input, integration of tumor tissues, error propagation, quality control checks, batch processing, and report-preparation capabilities. MIRDcalc implements an immediate, easy-to-use single-screen interface. The MIRDcalc software is available for free download (www.mirdsoft.org) and has been approved by the Society of Nuclear Medicine and Molecular Imaging.

The why, who, how, and what of communicating CT radiation risks to patients and healthcare providers

Computed tomography (CT) has witnessed tremendous growth in utilization. Despite its immense benefits, there is a growing concern from the general public and the medical community about the detrimental consequences of ionizing radiation from CT. Anxiety from the perceived risks associated with CT can deter referring physicians from ordering clinically indicated CT scans and patients from undergoing medically necessary exams. This article discusses various strategies for educating patients and healthcare providers on the benefits and risks of CT scanning and salient techniques for effective communication.

Addressing Risk Perceptions of Low-Dose Radiation Exposure

Concern over low-dose radiation (LDR) (exposure of less than 100 milligray (mGy)) is resulting in people refusing diagnostic procedures and medical treatment¹ and also inhibiting revision of the linear no-threshold (LNT) assumption that informs much of science policy. This article reviews representative surveys in Ontario and Saskatchewan and focus groups conducted with science and policy stakeholders in addressing how the public and policy stakeholders understand issues of exposure to LDR and how policy issues can be addressed.

Research results from focus groups demonstrated that policy stakeholders are knowledgeable about issues surrounding the public and perceptions about LDR and implications for policy consistent with LDR literature. Participants understood that the challenge went beyond providing more education about LDR and issues of emotions and biases must be addressed. This research resulted in rich suggestions for public communication and engagement surrounding LDR and a process for addressing the issue of the LNT.

Can computed tomography scanning in adults lead to an increased risk of thyroid cancer? A nationwide nested case-control study

OBJECTIVE

To evaluate the association between computed tomography (CT) scanning and newly diagnosed thyroid cancer cases in relation to the confounding effect of the healthcare utilization rate.

METHODS

This nested case-control study used the Korean National Health Insurance Service-National Sample Cohort 2002-2015: 3557 adult thyroid cancer cases were matched to 17,785 controls by age, sex, and diagnosis date. Odds ratios (ORs) were estimated for thyroid cancer associated with cumulative exposure to CT scanning > 3 years before cancer diagnosis. Changes in estimated ORs with and without adjustment for outpatient visit frequency were investigated.

RESULTS

ORs for newly diagnosed thyroid cancer increased according to the higher number of total CT scans and thyroid-exposing CT scans (CT scans of the head, neck, or chest compartment; OR and 95% confidence interval [CI], 1.09 [1.03-1.16] and 1.28 [1.05-1.57], respectively). ORs for thyroid cancer increased according to higher outpatient visit frequency. The association between thyroid cancer incidence and CT scans became insignificant when outpatient visit frequency was adjusted in the models (OR [95% CI], 1.03 [0.97-1.10]: total CT scans, 1.14 [0.93-1.41]: thyroid-exposing CT scans). Subgroup analyses stratified by age, sex, and history of other malignancies did not reveal independent associations between CT scanning and thyroid cancer.

CONCLUSIONS

The high incidence of thyroid cancer in adults exposed to ionizing radiation during CT scanning can be largely explained by the confounding effect of the healthcare utilization rate. These effects should be considered to avoid overestimation of the CT scanning-associated risk of thyroid cancer.

KEY POINTS

• Studies indicate that diagnostic imaging using low-ionizing radiation may increase risks for thyroid cancer in adults. • Our findings suggest that the risk for radiation-induced thyroid cancer following CT scanning in adults may have been overestimated in observational studies due to medical surveillance-related biases.

Radiophobia Overreaction: College of Chiropractors of British Columbia Revoke Full X-Ray Rights Based on Flawed Study and Radiation Fear-Mongering

Fears over radiation have created irrational pressures to dissuade radiography use within chiropractic. Recently, the regulatory body for chiropractors practicing in British Columbia, Canada, the College of Chiropractors of British Columbia (CCBC), contracted Pierre Côté to review the clinical use of X-rays within the chiropractic profession. A "rapid review" was performed and published quickly and included only 9 papers, the most recent dating from 2005; they concluded, "Given the inherent risks of radiation, we recommend that chiropractors do not use radiographs for the routine and repeat evaluation of the structure and function of the spine." The CCBC then launched an immediate review of the use of X-rays by chiropractors in their jurisdiction. Member and public opinion were gathered but not presented to their members. On February 4, 2021, the College announced amendments to their Professional Conduct Handbook that revoked X-ray rights for routine/repeat assessment and management of patients with spine disorders. Here, we highlight current and historical evidence that substantiates that X-rays are not a public health threat. We also point out critical and insurmountable flaws in the single paper used to support irrational and unscientific policy that discriminates against chiropractors who practice certain forms of evidence-based X-ray-guided methods.

Radiophobic Fear-Mongering, Misappropriation of Medical References and Dismissing Relevant Data Forms the False Stance for Advocating Against the Use of Routine and Repeat Radiography in Chiropractic and Manual Therapy

There is a faction within the chiropractic profession passionately advocating against the routine use of X-rays in the diagnosis, treatment and management of patients with spinal disorders (aka subluxation). These activists reiterate common false statements such as "there is no evidence" for biomechanical spine assessment by X-ray, "there are no guidelines" supporting routine imaging, and also promulgate the reiterating narrative that "X-rays are dangerous." These arguments come in the form of recycled allopathic "red flag only" medical guidelines for spine care, opinion pieces and consensus statements. Herein, we review these common arguments and present compelling data refuting such claims. It quickly becomes evident that these statements are false. They are based on cherry-picked medical references and, most importantly, expansive evidence against this narrative continues to be ignored. Factually, there is considerable evidential support for routine use of radiological imaging in chiropractic and manual therapies for 3 main purposes: 1. To assess spinopelvic biomechanical parameters; 2. To screen for relative and absolute contraindications; 3. To reassess a patient's progress from some forms of spine altering treatments. Finally, and most importantly, we summarize why the long-held notion of carcinogenicity from X-rays is not a valid argument.

Systematic mapping of disaster risk management research and the role of innovative technology

Globally, disaster risk management (DRM) has gone through a criterion transpose from static to a technology-based proactive approach in managing disasters including natural and anthropogenic disasters. This study aimed at exploring this research niche and to identify the main topical issues currently underway, such as the most disaster risk management techniques and prevalent geographical locations using scientometrics techniques. The result reveals that studies on DRM during the period of investigation witnessed an increase from early 2000 and peaking in 2017 followed by 2016 with a Kolmogorov-Smirnoff goodness-of-fit of 0.9672. More so, there exists a decline in year 2018 with about 144 published articles on DRM. However, research output fluctuated during the survey period between 1990 and 2004; for instance, the result shows that the research published on DRM in year 1990, 1991, 1992, 1993, 1994 and 1995 are six, seven, five, seven, three and seven articles, respectively. In this study, the contribution of different nations and country collaboration to different sub-categories of disasters was examined. Global distributions of scientific articles tailored to DRM research across different environmental and disaster issues that demonstrate the development of analytical tools used to detect them and the researchers' production from various nations in both developed and developing countries were evaluated. Despite the recurrence of climate-related disasters in some parts of the world, relevant studies, disaster impacts and support systems remain poorly understood and not well explored.

Are Continued Efforts to Reduce Radiation Exposures from X-Rays Warranted?

There are pressures to avoid use of radiological imaging throughout all healthcare due to the notion that all radiation is carcinogenic. This perception stems from the long-standing use of the linear no-threshold (LNT) assumption of risk associated with radiation exposures. This societal perception has led to relentless efforts to avoid and reduce radiation exposures to patients at great costs. Many radiation reduction campaigns have been launched to dissuade doctors from using radiation imaging. Lower-dose imaging techniques and practices are being advocated. Alternate imaging procedures are encouraged. Are these efforts warranted? Based on recent evidence, LNT ideology is shown to be defunct for risk assessment at low-dose exposure ranges which includes X-rays and CT scans. In fact, the best evidence that was once used to support LNT ideology, including the Life Span Study data, now indicates thresholds for cancer induction are high; therefore, low-dose X-rays cannot cause harm. Current practices are safe as exposures currently encountered are orders of magnitude below threshold levels shown to be harmful. As long as imaging is medically warranted, it is shown that efforts to reduce exposures that are within background radiation levels and that are also shown to enhance health by upregulating natural adaptive protection systems are definitively wasted resources.

5 Reasons Why Scoliosis X-Rays Are Not Harmful

Radiographic imaging for scoliosis screening, diagnosis, treatment, and management is the gold standard assessment tool. Scoliosis patients receive many repeat radiographs, typically 10-25 and as many as 40-50, equating to a maximum 50 mGy of cumulative exposure. It is argued this amount of radiation exposure is not carcinogenic to scoliosis patients for 5 main reasons: 1. Estimated theoretical cumulative effective doses remain below the carcinogenic dose threshold; 2. Scoliosis patient x-rays are delivered in serial exposures and therefore, mitigate any potential cumulative effect; 3. Linear no-threshold cancer risk estimates from scoliosis patient cohorts are flawed due to faulty science; 4. Standardized incidence/mortality ratios demonstrating increased cancers from aged scoliosis cohorts are confounded by the effects of the disease entity itself making it impossible to claim cause and effect resulting from low-dose radiation exposures from spinal imaging; 5. Children are not more susceptible to radiation damage than adults. Radiophobia concerns from patients, parents, and doctors over repeat imaging for scoliosis treatment and management is not justified; it adds unnecessary anxiety to the patient (and their parents) and interferes with optimal medical management. X-rays taken in the evidence-based management of scoliosis should be taken without hesitation or concern about negligible radiation exposures.

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.

Until There Is a Resolution of the Pro-LNT/Anti-LNT Debate, We Should Head Toward a More Sensible Graded Approach for Protection From Low-Dose Ionizing Radiation

Current regulation of ionizing radiation is based on the linear no-threshold (LNT) model where any radiation dose increases cancer risk and is independent of dose rate, resulting in large amounts of time and money being spent protecting from extremely small radiation exposures and hence extremely small risk. There are animal studies which demonstrate that LNT is incorrect at low doses, supporting a threshold or hormesis model and thus indicating that there is no need to protect from very low doses. This has led to a sometimes bitter debate between pro-LNT and anti-LNT camps, and the debate has been at a stalemate for some time. This commentary is not aimed at taking either side of the debate. It is likely that the public, workers, and the environment are adequately protected under current regulation, which is the most important outcome. Until those on one side of the debate can convince the other, it would be sensible to move forward toward a graded (risk-based) approach to regulation, where the stringency of control is commensurate with the risk, resulting hopefully in more sensible practical thresholds. This approach is gradually being put forward by international radiation protection advisory bodies.

Death of the ALARA Radiation Protection Principle as Used in the Medical Sector

ALARA is the acronym for "As Low As Reasonably Achievable." It is a radiation protection concept borne from the linear no-threshold (LNT) hypothesis. There are no valid data today supporting the use of LNT in the low-dose range, so dose as a surrogate for risk in radiological imaging is not appropriate, and therefore, the use of the ALARA concept is obsolete. Continued use of an outdated and erroneous principle unnecessarily constrains medical professionals attempting to deliver high-quality care to patients by leading to a reluctance by doctors to order images, a resistance from patients/parents to receive images, subquality images, repeated imaging, increased radiation exposures, the stifling of low-dose radiation research and treatment, and the propagation of radiophobia and continued endorsement of ALARA by regulatory bodies. All these factors result from the fear of radiogenic cancer, many years in the future, that will not occur. It has been established that the dose threshold for leukemia is higher than previously thought. A low-dose radiation exposure from medical imaging will likely upregulate the body's adaptive protection systems leading to the prevention of future cancers. The ALARA principle, as used as a radiation protection principle throughout medicine, is scientifically defunct and should be abandoned.