Linear No-threshold (LNT) vs. Hormesis: Paradigms, Assumptions, and Mathematical Conventions that Bias the Conclusions in Favor of LNT and Against hormesis.

The linear no-threshold assumption misunderstands the complex multiphasic biological response to ionizing radiation, focusing solely on the initial physical radiogenic damage. This misunderstanding is enabled (masked and amplified) by a number of mathematical approaches that bias results in favor of linear no-threshold and away from alternatives, like hormesis, that take biological response into account. Here we explore a number of these mathematical approaches in some detail, including the use of frequentist rather than Bayesian statistical rules and methods. We argue that a Bayesian approach cuts through an epidemiological stalemate, in part because it enables a better understanding of the concept of plausibility, which in turn properly rests on empirical evidence of actual physical and biological mechanisms. Misuse of the concept of plausibility has sometimes been used to justify the mathematically simple and convenient linearity-without-a-threshold assumption, in particular with the everywhere-positive slope that is central to linear no-threshold and its variants. Linear no-threshold's dominance in the area of dose regulation further rests on a misapplication of the precautionary principle, which only holds when a putative caution has positive effects that outweigh the negative unintended consequences. In this case the negative consequences far outweigh the presumed hazards.

The BEIR VII Estimates of Low-Dose Radiation Health Risks Are Based on Faulty Assumptions and Data Analyses: A Call for Reassessment.

The 2006 National Academy of Sciences Biologic Effects of Ionizing Radiation (BEIR) VII report is a well-recognized and frequently cited source on the legitimacy of the linear no-threshold (LNT) model-a model entailing a linear and causal relationship between ionizing radiation and human cancer risk. Linearity means that all radiation causes cancer and explicitly excludes a threshold below which radiogenic cancer risk disappears. However, the BEIR VII committee has erred in the interpretation of its selected literature; specifically, the in vitro data quoted fail to support LNT. Moreover, in vitro data cannot be considered as definitive proof of cancer development in intact organisms. This review is presented to stimulate a critical reevaluation by a BEIR VIII committee to reassess the validity, and use, of LNT and its derived policies.

The Birth of the Illegitimate Linear No-Threshold Model: An Invalid Paradigm for Estimating Risk Following Low-dose Radiation Exposure.

This paper examines the birthing process of the linear no-threshold model with respect to genetic effects and carcinogenesis. This model was conceived >70 years ago but still remains a foundational element within much of the scientific thought regarding exposure to low-dose ionizing radiation. This model is used today to provide risk estimates for cancer resulting from any exposure to ionizing radiation down to zero dose, risk estimates that are only theoretical and, as yet, have never been conclusively demonstrated by empirical evidence. We are literally bathed every second of every day in low-dose radiation exposure due to natural background radiation, exposures that vary annually from a few mGy to 260 mGy, depending upon where one lives on the planet. Irrespective of the level of background exposure to a given population, no associated health effects have been documented to date anywhere in the world. In fact, people in the United States are living longer today than ever before, likely due to always improving levels of medical care, including even more radiation exposure from diagnostic medical radiation (eg, x-ray and computed tomography imaging examinations) which are well within the background dose range across the globe. Yet, the persistent use of the linear no-threshold model for risk assessment by regulators and advisory bodies continues to drive an unfounded fear of any low-dose radiation exposure, as well as excessive expenditures on putative but unneeded and wasteful safety measures.

Preserving the Anti-Scientific Linear No-Threshold Myth: Authority, Agnosticism, Transparency, and the Standard of Care.

The linear no-threshold (LNT) assumption is over 70 years old and holds that all ionizing radiation exposure leaves cumulative effects, all of which are harmful regardless of how low the dose or dose rate is. The claimed harm centers on the risk of future radiogenic cancer. This has been shown countless times to be fallacious, and hundreds of scientific studies-both experimental and observational/epidemiological-demonstrate that at low enough doses and dose rates, ionizing radiation stimulates an evolved adaptive response and therefore is beneficial to health, lowering rather than raising the risk of cancer. Yet the myth of uncorrected lifetime cumulative risk still pervades the field of radiation science and underlies the policies of virtually all regulatory agencies around the world. This article explores some of the motivations behind, and methods used to assure, the extreme durability of the LNT myth in the face of the preponderance of contrary evidence and the manifest harms of radiophobia. These include subservience to the voice of authority, tactics such as claiming agnosticism on behalf of the entire field, transparent references to contrary evidence while dismissing the findings without refutation, and seeking shelter behind the legally protective medical standard of care.

Dose Optimization to Minimize Radiation Risk for Children Undergoing CT and Nuclear Medicine Imaging Is Misguided and Detrimental.

A debate exists within the medical community on whether the linear no-threshold model of ionizing radiation exposure accurately predicts the subsequent incidence of radiogenic cancer. In this article, we evaluate evidence refuting the linear no-threshold model and corollary efforts to reduce radiation exposure from CT and nuclear medicine imaging in accord with the as-low-as-reasonably-achievable principle, particularly for children. Further, we review studies demonstrating that children are not, in fact, more radiosensitive than adults in the radiologic imaging dose range, rendering dose reduction for children unjustifiable and counterproductive. Efforts to minimize nonexistent risks are futile and a major source of persistent radiophobia. Radiophobia is detrimental to patients and parents, induces stress, and leads to suboptimal image quality and avoidance of imaging, thus increasing misdiagnoses and consequent harm while offering no compensating benefits.