RADIATION RISK: A PERSONAL POINT OF VIEW By Dr J A Siegel, C W Pennington & Dr B Sacks The linear no-Threshold assumption and its alara principle: non-science that is inapplicable to medical imaging INTRODUCTION MEDICAL IMAGING AND THE ADAPTIVE RESPONSE The linear no-threshold assumption (hereinafter referred While medical imaging, particularly CT, is thought by most to as simply LNT) is the purported scientific basis for virtu- radiologists and referring physicians, as well as by most ally all regulatory policies throughout the world involving patients or their parents, to raise the cancer risk later in life, exposure to ionizing radiation. In particular, those involving hundreds of experimental and observational studies dem- medical imaging and occupational exposures are wrapped onstrate that such low-dose radiation more likely confers a in the authoritative mantle of LNT. But LNT derives from health benefit and actually helps prevent future cancers [4]. invalid, early-20th-century conclusions, a fact, until recently, Many radiologists and health physicists defensively point to unreported by other scientists [1]. Hermann Muller, in his epidemiological studies that purport to demonstrate elevated 1946 Nobel Lecture about his work on radiogenic mutations radiogenic risk of leukemias and solid cancers from low- in fruit flies, asserted that no threshold exists below which doses and dose rates. However, as we have shown, these stud- radiation is harmless, but his claim was based on experi- ies generally ignore the basic sciences of biology, chemistry, ments using doses greater than 4,000 mGy, a stunningly and physics, and employ circular reasoning, cherry picking unwarranted over-extrapolation. of data, and illegitimate statistical manipulations, thereby rendering their conclusions completely false [5]. In the 1950s, Edward Lewis, with no more scientific justi- fication, further extrapolated LNT to human carcinogen- LNT is a linear extrapolation from evidence-supported, esis. Indeed, carcinogenicity of low-dose radiation exposure high-dose effects to putative low-dose responses down to (<100 – 200 mGy) has never been validated. The LNT theory zero, but the body’s responses to high- and low-dose expo- says all acute radiation exposure down to zero is harm- sure are different. The primary fallacy in LNT, and its off- ful (proportionally to dose) and, furthermore, that it yields spring ALARA, is their focus solely on radiogenic damage cumulative harm throughout life, independent of dose rate. to cellular components, prominently DNA, while completely Both claims are demonstrably false and harmful, leading to ignoring the many-layered protective biological responses, LNT-derived regulatory policies not protective of the public given a chance to operate at low dose rates and conferred [2,3]. For example, more than 1600 deaths resulted from the by evolution on extant animals and plants through natural LNT-driven radiophobia leading to forced evacuations of selection. In short, LNT is not wholly erroneous; it is simply residents following the Fukushima nuclear accident [3]. incomplete, and therefore wrong, at low doses/dose-rates. Unwarranted fear of low-dose radiation underlies the mis- Moreover, repair of DNA or, that failing, removal of damaged guided doctrine of “prudence” in dosing for medical imaging cells through apoptosis, bystander effects from neighboring – the “as low as reasonably achievable” principle (ALARA) cells, and/or immune system removal – the so-called adap- – that, by often diminishing image quality, increasingly pro- tive response – more than eliminate the damage at low doses. duces suboptimal and even non-diagnostic CTs [4]. Today, In so doing, these multi-level processes, from molecular to 70 years after Muller’s Nobel lecture, this non-scientific LNT cellular to tissue to organismal, also repair and/or remove paradigm and ALARA continue to govern the field of radio- some of the many-orders-of-magnitude-greater damage that logical imaging. results from free radicals created by normal, endogenous, metabolic processes [1,5]. This over-reactive adaptive bio- logical response, stimulated by low-dose and low-dose-rate radiation, is known as hormesis – from the Greek word for The Authors “stimulate,” as in “hormone.” Jeffry A. Siegel, PhD1, Charles W. Pennington, MS, MBA2 & Bill Sacks, PhD, MD3 LNT, however, so completely dominates thought and action 1.President and CEO, Nuclear Physics Enterprises, Marlton, NJ, USA in radiation-related endeavors, particularly medical imaging, 2. NAC International, Norcross, GA, Executive Nuclear Energy that even many imaging professionals who grant the absence Consultant (Retired), Alpharetta, GA, USA of evidence of low-dose harm, nevertheless advocate that 3. US FDA Medical Officer and Clinical Radiologist (Retired), “prudence” be used in selecting imaging doses. The Image Green Valley, AZ, USA Gently Alliance campaign’s advocacy of ALARA-based CT dose optimization/reduction for children, while intended Corresponding author as public reassurance that radiologists are cognizant of their Jeffry A Siegel , email: [email protected] fears of cancer risk, only serves to reinforce those very fears, 70 DI EUROPE MARCH 2017 RADIATION RISK: A PERSONAL POINT OF VIEW unwarranted as they are. If the public CTs, and/or physician-recommended extrapolation underlying LNT/ALARA. learned, over time and through authorita- alternative procedures, including explor- Thus, the insistence on low-dosing is non- tive organizations and agencies, that there atory surgery or anesthesia for longer- scientific, despite its espousal by medical were no risks at all, and even probable duration MRIs in children [4]. practitioners. Further, imaging’s double health benefit (hormesis), there would be benefits are downplayed or ignored. There- no need to reduce dose. The only con- The recommended criteria of justifica- fore, it should be clear that neither LNT siderations for medical imaging would be tion and optimization of the International nor ALARA can further the goal of patient that the procedure, like any medical pro- Commission on Radiological Protection health. Such “dark-ages” policies have no cedure at all, is indicated and that adequate (ICRP) are similarly one-sided. All medi- place in managing imaging’s concerns. exposure is used to provide a diagnos- cal procedures, including imaging, should tic set of images. As it now stands, pub- have medical “justification,” but based on Radiophobia can no longer be ignored lic and professional radiophobia dictates clinical indication, not on radiation expo- or tolerated: low-dose radiation exposure that doses be lowered such that images of sures that are diagnostically necessary, as associated with medical imaging has no non-diagnostic quality are often obtained, well as harmless. “Optimization” in imag- documented pathway to harm, while LNT leading to misdiagnoses and/or failure to ing – for any modality, radiation-related and ALARA most assuredly do. The medi- confirm suspected diagnoses, with con- or not –should be guided only by use cal imaging community must recognize comitant mistreatment of many patients. of proper procedures and technical fac- that it is being pushed to pursue non-sci- tors needed to ensure that appropriately entific and soundly discredited practices THE FALLACY OF APPLYING THE calibrated equipment yields diagnostic that encourage a response prompted by PRECAUTIONARY PRINCIPLE TO images. The problem is radiophobia, not unwarranted fear, and that such pursuit is LOW-DOSE RADIATION radiation. A false application of “optimi- not at all in the best interests of patients or, There are those among LNT/ALARA zation” is without “justification,” and only for that matter, of doctors. advocates who grant that LNT-derived multiplies illnesses, injuries, and deaths. estimates of risk may indeed err on the Thus, the ICRP‘s justification and opti- REFERENCES high side. But they assert that such overes- mization are mutually contradictory in 1. Siegel JA, Pennington CW, Sacks B, Welsh JS. The birth of the illegitimate linear no-threshold model: timates are not harmful and claim instead medical imaging. an invalid paradigm for estimating risk following that they err on the side of caution – ask- low-dose radiation exposure. Am J Clin Oncol 2015 ing rhetorically, “What harm can overes- Importantly, LNT and ALARA mask the Nov 3 [Epub ahead of print]. 2. Siegel JA, Stabin MG. RADAR commentary: use of timating risk possibly do?” However, this dual benefit of radiation-associated imag- linear no-threshold hypothesis in radiation protec- particular (mis)application of the precau- ing [4]: valuable diagnostic information, tion regulation in the United States. Health Phys 2012;102:90-99. tionary principle is based on a one-sided as well as reduction in lifetime cancer risk 3. Siegel JA, Welsh JS. Does imaging technology cause self-delusion. It fails to take into account and increased longevity, the likely health cancer? Debunking the linear no-threshold model of the more significant actual harms pro- benefits of low-dose radiation. radiation carcinogenesis. Technol Cancer Res Treat 2016;15:249-256. duced by actions of others based on their 4. Siegel JA, Pennington CW, and Sacks B. Subjecting falsely believing that LNT-based risk esti- CONCLUSION radiological imaging to the linear no-threshold mates reflect reality. Medical imaging studies are intended to hypothesis: a non sequitur of non-trivial proportion. J Nucl Med 2017;58(1):1-6. Among those many harms