Medical Diagnostic Tools and the Effects of Nuclear Radiation on the Human Body
Computed axial tomography (CAT) or computer tomography (CT) scanning technologies have been thoroughly incorporated into modern medical diagnostics. In some clinical respects, CT scans are preferable to magnetic resonance imaging (MRI) and much better than traditional X-rays. However, CT scans expose patients to more ionizing radiation and could conceivably contribute to cellular damage and to harmful cellular mutation (i.e. cancer), especially in the long-term. It is not yet understood precisely how much damage is caused by each isolated exposure, largely because it is extremely difficult to isolate clinical radiation exposure from either natural (i.e. non-manmade or man-caused) sources or radiation exposure or from other risk factors and independent variables. Nevertheless, the implication of empirical evidence to date is that certain segments of the patient population in particular are more vulnerable to the detrimental health effects of exposure to the levels of radiation from clinical processes involving nuclear medicine. Therefore, alternatives to the use of CT scans and other forms of nuclear medicine should always be considered, especially in this population.
Modern medicine makes extensive use of nuclear technology in numerous diagnostic and therapeutic applications and processes. That has led to concerns about the potential detrimental effects on the human body of exposure to radiation in connection with these diagnostic and therapeutic tools. In principle, the use of nuclear imaging and nuclear bombardment of cancer cells (in particular) present possible risks of radiation-induced illness that (at least arguably) must be factored into any reasoned decision by patients to undergo nuclear diagnostic imaging or radiation therapy. On one hand, nuclear imaging and radiation therapy can be valuable tools used to extend life by promoting the earliest detection and the most effective treatment of many kinds of human cancers. On the other hand, the undisciplined overuse of nuclear medicine where its advantages may not necessarily outweigh the known or suspected potential harms associated with those technologies.
The weight of the empirical evidence seems to suggest that more research is necessary to understand exactly to what degree nuclear radiation exposure that is harmless in the short-term is more dangerous in the long-term. It seems that low doses of radiation may contribute small but not negligible amounts of cellular damage that are cumulative in their detrimental health effects over the course of a lifetime. Accordingly, physicians should be educated in the relative benefit-to-risk analysis of various clinical tools upon which they are relying more and more routinely.
Certain naturally-occurring elements (and manmade compounds) are different from other elements in that they undergo spontaneous decay in a manner moderated by the so-called weak nuclear force (Bleise, Danesi, & Burkart, 2003). In that nuclear decay process, particles are emitted that, although microscopic in size, move at such great velocities that they are highly energetic, making them capable of passing through organic and inorganic matter (Bleise, Danesi, & Burkart, 2003). Human beings are exposed to myriad sources of benign background radiation other than radiation caused by human activities, but those exposures fall well below the so-called "threshold" amount below which (isolated) radiation exposures are not necessarily detrimental to human health (Brenner & Hall, 2007). Exposure to more intense radiation is known to cause acute illness, such as described by radiation poisoning or radiation disease (Bleise, Danesi, & Burkart, 2003).
There are principally two mechanisms by which radioactivity causes damage to human beings and other living species: cellular destruction and cellular mutation (Schanz, Schuler, Lorat, Fan, Kaestner, Wennemuth, & Rube, 2012). The former is attributable to the microscopic holes or tunnels carved by radiation particles as they pass into and through the body; the latter is attributable to the spontaneous mutations to which DNA molecules are prone by virtue of bombardment by radioactive particles (Harbron, 2012). In principle, the energy associated with near light-speed velocity of some particles released by the nuclear decay process cause specific types of damage to the cellular DNA, some of which (such as double strand breaks) may be incapable of complete repair (Schanz, Schuler, Lorat, et al., 2012).
The other principal way that radiation exposure causes disease is by triggering the process of DNA mutation (Harbron, 2012). Generally, cancer occurs when the DNA within organic cells is damaged in ways that interfere with the ordinary physiological mechanism by which the growth of tissue cells is regulated (Brenner & Hall, 2007). There is evidence suggesting that radiation exposure is responsible for either causing these mutations or for causing one of several mutations that cause uncontrolled growth when they all occur within the same cell (Brenner & Hall, 2007).
More specifically, as in the case with many human diseases, low-level exposure to radiation is damaging to cellular tissue but does not represent so much damage that it exceeds the physiological capacity of the natural immune (and other) responses by which damaged cells are repaired and the effects of exposure eventually overcome. In that regard, there is considerable debate ongoing as to the degree to which low-level (i.e. sub-threshold) radiation exposure contributes to long-term disease, notwithstanding the apparent ability of the human body to repair acute cellular damage. Moreover, certain patient populations (such as younger patients and women) appear to be more susceptible, in general to the detrimental health consequences of radiation exposure (Einstein, Henzlova, & Rajagopalan, 2007). According to Schanz, Schuler, Lorat, et al. (2012),
"…our results suggest that protracted low-dose radiation causes cumulative changes in the chromatin, posing a serious threat to the preservation of genetic and epigenetic information. Chromatin modified during DSB repair is sometimes not fully restored to the pre-damaged state, resulting in progressive alterations in chromatin-modification patterns. The importance of chromatin in regulating gene expression implies that long-term maintenance of the nuclear architecture is vital for the normal functioning of cells and tissues over a lifetime."
Brenner and Hall (2007) describe the process in greater detail as follows:
"Ionizing radiation, such as x-rays, is uniquely energetic enough to overcome the binding energy of the electrons orbiting atoms and molecules; thus, these radiations can knock electrons out of their orbits, thereby creating ions. In biologic material exposed to x-rays, the most common scenario is the creation of hydroxyl radicals from x-ray interactions with water molecules; these radicals in turn interact with nearby DNA to cause strand breaks or base damage. X-rays can also ionize DNA directly."
Personal Perspective and Objective Implications
The most obvious implications of the current state of knowledge of the mechanisms of cellular damage and cellular mutation caused by radiation exposure would be to heed the warnings of Brenner and Hall (2007), Einstein, Henzlova, and Rajagopalan (2007), and Schanz, Schuler, Lorat, et al. (2012) to emphasize the risk-to-benefit analysis in diagnostic uses (especially) of nuclear medicine. In that regard, Brenner and Hall (2007), in particular, point out that among radiologists and emergency-room physicians surveyed, three-quarters of those physicians "significantly underestimated" the amount of radiation represented by each clinical use of CT scanning, and 53% of radiologists and 91% of emergency-room physicians were unaware that the use of CT scanning corresponds to higher cancer rates. Naturally, addressing this type of knowledge gap would be the most logical place to start any efforts to emphasize risk management in this area of modern medicine.
There can be no doubt that nuclear medicine in the form of diagnostic imaging and radiation therapy for cancer are both valuable tools that enable contemporary physicians to identify and treat human cancers more successfully than could even have been imagined less than a century ago. However, there is mounting empirical evidence that the clinical use of nuclear medicine modalities must be weighed in a risk-to-benefit analysis owing to the apparent connection between radiation exposure and human diseases and cancer-causing cellular mutations attributable to the consequences of irradiating living organic tissue. The risks…