Radiation exposure — particularly in children — has been a bedrock concern in radiology for years. Dose level control is so important it spawned both the Image Gently and Image Wisely campaigns, both based on the ALARA principle.
But, what if the basis of the ALARA principle was incorrect? According to an article published in the June issue of The Journal of Nuclear Medicine, that could be the case. Author Jeffry Siegel, PhD, president and CEO of New Jersey-based Nuclear Physics Enterprises, asserts the linear no-threshold hypothesis (LNT), a belief that radiation risk remains proportionately the same for both high-dose and low-dose exposure, is misleading.
Diagnostic Imaging recently discussed his thoughts on why LNT is harmful for radiology and potentially impedes the most beneficial use of imaging in pediatric patients.
Diagnostic Imaging: What prompted your interest into studying the effects of radiation exposure in children?
Siegel: It wasn't the radiation effect in children that started me out. It was the universal application of the linear non-threshold (LNT) model by every regulatory body in the world. That's the linear extrapolation from the observed effects of high levels of radiation all the way down to zero dose. Every exposure is, thus, presumed to be associated with some level of risk — and the damage caused will go on to produce cancer. It's inevitable. It's that belief that prompted the whole thing for me. I've written probably 30 or more articles about LNT and its evil step-child, the ALARA principle. The two can't exist separately. ALARA only makes sense if the effect of low dose is linear. If you half the dose, then you half the risk. But that's all falsehood. It's not true in adults, and it's not true in children either.
Diagnostic Imaging: What science brings you to the conclusion that radiation exposure in children is not unsafe?
Siegel: Basically, every radiobiology course and textbook says children are believed to be more radiation sensitive because cell division is faster when we're younger. This is true, and the belief is that's what leads to greater mutation rates. However, the increase in mutations doesn't necessarily increase cancer risk. In fact, it doesn't. The human body is able to respond to radiation exposure, particularly low-dose, as well as every imaginable external stressor. Our body, through a myriad of adaptive protections, can either repair the damage or eliminate it by cell death or the immune system. The immune system is more vigorous in children than adults, as you can imagine. The immune system weakens as we get older. That's one of the reasons why the probability of cancer increases as we age.
Diagnostic Imaging: What do you see as being incorrect about LNT?
Siegel: This article is based on low-dose radiation from imaging by CT, nuclear studies, or chest X-rays. Credible evidence of imaging-related low-dose (<100-200 mGy) carcinogenic risk is nonexistent. It is a hypothetical prediction derived from the demonstrably false LNT model. On the contrary, low-dose radiation does not cause, but more likely helps, prevent cancer. It must be noted and appreciated that radiation is an extremely weak carcinogen, even at relatively high doses, let alone at the low doses associated with medical imaging.
The body responds differently to high and low-dose radiation exposure. There is plenty of scientific research demonstrating that the body repairs or eliminates low-dose radiation damage, and at the same time is stimulated to repair the much greater endogenous metabolic damage due to oxygen metabolism. This results in a net benefit. At high doses, repair is overwhelmed, indicating a different mechanism of action. LNT ignores this difference. The body can, in fact, mitigate damage at low doses, thereby invalidating LNT.
LNT extrapolates from observed high-dose harm to assumed low-dose harm, entailing that all radiation exposure is harmful by denying any biological response to damage and asserting cumulative lifetime harm, regardless of dose or dose rate. All aspects of LNT are demonstrably false.
Diagnostic Imaging: In your opinion, what's driving support for LNT?
Siegel: Most people are understandably afraid of radiation as a result of the atomic bomb detonations in Japan. This radiophobia is because they have been fed inaccurate information for decades by the media due to various experts. LNT is a well-ensconced paradigm, one that is backed by worldwide regulatory agencies and advisory organizations whose overlapping members have invested reputations and labor. They all subscribe to LNT because of its simplicity and the belief that even if LNT is wrong, at least any derived policies will be protective. Not true. The problem is radiophobia, not low-dose radiation exposure.
Most people are unaware that no health effects are expected to result from the radiation exposure to the population in the aftermath of the Fukushima nuclear accident, but that over 1,600 individuals who were needlessly evacuated did actually die. For radiologic imaging, significant collateral negative consequences of lowering dose arise. Reducing patient doses to mitigate purely hypothetical cancer risks increases other well-known risks, including imaging avoidance and misdiagnoses due to nondiagnostic image quality. These risks are much higher than the cancer risks falsely predicted by LNT and putatively avoided by ALARA-based dose reduction strategies. Medical imaging's low-dose exposure has no documented pathway to harm, while LNT and ALARA most assuredly do.
Diagnostic Imaging: What have been the effects of controlling radiation exposure in children?
Siegel: It's a controversial topic, and a lot of physicians likely haven't given this much thought. The use of LNT and the advocacy for ALARA dosing by various groups, such as the Image Gently Alliance, are misguided and not science-or evidence-based. These groups serve only to frighten rather than to educate, since they offer fictitious protection against nonexistent risks, further enhancing the probability of negative outcomes. It is precisely the proven benefit of low-dose radiation that renders ALARA dosing a source of radiophobia. The goal of the Image Gently Alliance is to lower the potential risk of CT-caused cancer in children, but this risk is hypothetical. Further, based on the atomic bomb survivor data, children are not more radiosensitive than adults in the imaging dose range.
Most radiation protection professionals accept unquestionably the ICRP-recommended fundamental principles of justification and optimization, but these are mutually contradictory and without merit for radiological imaging. All medical procedures require the justification of medical indication, but such justification does not involve imaging's radiation levels. Dose "optimization" efforts only multiply illnesses, injuries, and deaths without justification. Even though many grant the absence of low-dose harm, they nevertheless advocate lower imaging dose as a prudent approach. But this conflates actual prudence, restricting medical procedures to those clinically indicated, with the prejudice-based false prudence of limiting clinically indicated imaging doses.
Diagnostic Imaging: What data supports this assertion?
Siegel: I have noted the well-known risks due to fear of imaging, namely imaging avoidance, nondiagnostic image quality, and use of alternative imaging procedures, such as longer-duration MRI study, requiring risk-incurring sedation for young children. The goal of dose management should be aimed at achieving diagnostic quality images, not reducing dose in the beneficial imaging-dose ranges. It has been suggested that 1 in 20 pediatric abdominal CT scans may be inadequate for diagnostic purposes because of radiation dose reduction efforts. This will negatively influence the care of some patients because of misguided treatment. The hypothetical risks of medical imaging pale in comparison to these actual risks.
Diagnostic Imaging: You identify radiophobia as the culprit. What can be done to combat it?
Siegel: Radiophobia, promoted by the use of LNT (and ALARA), has prompted three petitions for rulemaking to the U.S. NRC requesting that it cease using this model in favor of a model indicating radiation-induced benefit at low doses. Petitions should also be filed with other regulatory agencies and scientific advisory bodies must start to be held to account.
I have been trying to combat radiophobia for years. There is plenty of misinformation out there and there are many individuals and groups with varied agendas promoting LNT and ALARA. I, as well as many others, have been trying to provide accurate information. While it may seem logical for us to attempt to assuage the public's fears by accommodating to their misperceptions and focusing on "optimization" in the absence of harm, I contend that this will only reinforce their misperception. The public's trust in medical practitioners can only be preserved if we can convince them (public and physicians alike) that there is no harm to begin with. Indeed, accurate information about low-dose radiation exposure is the only way to undo the fears.
Diagnostic Imaging: What administrative guidelines would be beneficial to implement?
Siegel: Imaging is a medical procedure that should be governed by the highest, science-based principles and policies, including use of proper procedures and appropriately calibrated equipment. It should not be managed by LNT, an invalidated hypothesis, that has spawned the ALARA principle.
Diagnostic Imaging: Based on your assertions, how should clinical practice change?
Siegel: Medical imaging procedures, as is the case for all medical procedures, should be performed only when clinically indicated. Obtaining correct diagnoses and avoiding riskier alternatives should be paramount so exposure should not be reduced below the required level to achieve this purpose. It is incumbent on the medical imaging community to finally and unambiguously denounce LNT and, unencumbered by false beliefs, act as advocates for the safety and life-saving benefits of medical imaging.
Diagnostic Imaging: What do you say to critics of your claims who will point to years of studies that indicate risk?
Siegel: Most people will read the last sentence of the abstract and the conclusion of a study, and they'll believe it. I say again, there is no credible evidence of imaging-related low-dose carcinogenic risk. The atomic bomb survivor population, considered to be the gold-standard data for estimating radiation effects in humans, does not support LNT and low-dose risk. Epidemiological studies purporting to support LNT and indicating low-dose risk have all been effectively rebutted. Bottom line is that linearity at low dose does not exist. Rather, it is forced by the high-dose extrapolation of the LNT model. This would be patently obvious if there were no high-dose data.
Diagnostic Imaging: What is the take-away message from your study?
Siegel: Children are not more sensitive than adults in the medical imaging dose range. We need a massive education campaign. Radiophobia is the problem, not low-dose radiation exposure.
Accurate information about low-dose effects is the only way to undo fear, as decades of failed alternative approaches and concessions have shown. Radiophobia is detrimental to patients and parents, induces stress, and leads to suboptimal image quality or avoidance of imaging, both of which produce misdiagnoses. Misperception can only be overcome by rejection of the LNT fiction along with ALARA, and by termination of the Image Gently Alliance.