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Radiation and Cancer Risks: Is it safe to have X-Rays? 
  Submitted By: Robert H. Wagner, MD, FACNP

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Radiation and Cancer Risks: Is it safe to have X-Rays?


Article Authored by: Robert H. Wagner, MD, FACNP


The association between cancer and radiation is a well-documented one and has led to fear and anxiety among patients who are supposed to receive diagnostic radiology studies. Shortly after the discovery of x-rays by Wilhelm Roentgen in 1895, and radioactivity by Henri Bequerel the following year, radiation became the wonder of the new century. The following decades would see radiation used as an elixir of health, a tool to measure shoe sizes, a diagnostic and therapeutic tool in medicine, a means to produce electricity, and a devastating weapon of war. Initially thought to be safe, it was later discovered that radiation had the potential to cause cancer. The initial enthusiasm for radiation slowly turned to fear. The entertainment industry produced many films on the unknown mutating effects of radiation on living creatures. Even today, popular television will use radiation in less than accurate ways to create an aura of excitement. These stories promote misconceptions about radioactivity and lead to misunderstanding by the general public. Despite all of the myth and mystery that surrounds radiation, the fact remains that radiation is the best-studied carcinogen known to mankind.

When discussing radiation carcinogenesis it is important to understand several concepts first. The first is that there are two broad categories of effects, those that occur directly as a result of radiation exposure and those that occur on a statistical basis. For example, exposing a person to approximately 100 rads of radiation (0.1 Gray) or the equivalent of 100 CT scans to the total body results in a slight decrease in the circulating white cells and platelets. This will happen in everyone exposed to this dose. The induction of cancer or genetic abnormalities occurs in a percentage of those exposed to a certain dose of radiation. The Biologic Effects of Ionizing Radiation report (BEIR V) states that if 100,000 people are exposed to 10 rads of radiation, then there will be 800 additional cancers in that population above the normally occurring amount. Thus, you have a statistically increased chance of developing a cancer.

Doses and dose rates are also important considerations. Sit out in the Caribbean sun without any sun block for two hours and you’re likely to get sunburn. Sit in the same sunlight for two minutes a day for 60 days, and you probably won’t even develop a tan. In both cases, you’ve spent a total of 120 minutes in the sun. The difference is that when you extend the exposure, there is some healing of the damage over time. The same is true for radiation damage. Fifteen rads (0.15 Gray) given all at once will temporarily decrease the number of sperm cells that are being produced. Extend that exposure over a period of weeks or months, and you won’t see those changes.

Cancer may be caused by damage to the DNA. DNA damage occurs on a regular basis even without the presence of radiation, and may be the reason that one out of four people will develop a cancer of some kind. Normal cells have mechanisms that repair this genetic damage. If the damage is not identified or if the rate of damage is too high for the repair mechanisms, it may result in a cancer being formed. Thus, there is a definite link with high dose radiation and cancer. Cancers caused by radiation are biologically the same when compared with cancers that occur naturally. Under a microscope, there is no difference from a thyroid cancer that occurs spontaneously and a thyroid cancer caused by radiation. Although large doses of radiation are known to cause cancer, what happens at the small diagnostic doses that are used in medicine is still unknown. There are several theories that attempt to describe the effects of low-level radiation.

Most radiation safety models make the assumption that there is no safe dose of radiation and even the tiniest amount increases your risk for cancer. If you expose one million people to 1 rad of radiation, you will expect to see 800 additional cancers during their lifetime. By extrapolation, exposing the same million people to 10 millirads of radiation (a chest x-ray) you will expect to see 8 additional cancers over their lifetime. Statistically however 250,000 of that million people will get cancer anyway. The difference of a chest x-ray to a million people in causing cancer (250,000 vs. 250,008) is impossible to measure. Many people disagree with this model since it does not take into account normal cellular repair of genetic damage.

A recently advanced theory is one called hormesis. It makes the assumption that the additional radiation given at lower doses does cause some genetic damage, but also stimulates the cells to fix the naturally occurring genetic damage at an earlier stage. A naturally occurring DNA abnormality that might later lead to development of a cancer could be repaired because the additional radiation damage triggered the repair mechanism. The result is that this theory makes the claim that there are actually fewer cancers when people are exposed to small amounts of radiation. While it may be difficult to believe that a small amount of radiation may be healthy for you, there are a growing number of scientists and studies to support this claim.

All of the diagnostic studies performed in your radiology or nuclear medicine department fall into this low-level radiation group. The risk of developing a cancer from any of these studies is very small, but the benefit can be significant. There is no question that mammography identifies breast cancers at an early stage and therefore improves the chance of survival. The small number of cancers that might be caused by the mammogram is far overwhelmed by the number of cancers that are detected at an early stage. On the other hand, performing a total body CT scan for screening purposes only is not justified. The important thing to consider is the risk versus the benefit of the study.

In conclusion, radiation does indeed have the potential to cause cancer at larger doses, but the effects of smaller doses such as those used in diagnostic medicine are still unknown. If it does cause cancer at these low doses, the overall risk is very small, especially when compared to the potential benefit of improving the diagnosis and treatment of many different diseases.

Robert H. Wagner, M.D.
Associate Professor of Radiology
Loyola University Medical Center 


 


Additional Authors:  

Works Cited:  
  Brenner DJ, Elliston CD. Estimated Radiation Risks Potentially Associated with Full-Body CT Screening. Radiology 2004 232:735-738

Pierce DA, Preston DL. Radiation-related cancer risks at low doses among atomic bomb survivors. Radiat Res 2000; 154:178-186.

Brenner DJ, Doll R, Goodhead DT, et al. Cancer risks attributable to low doses of ionizing radiation: assessing what we really know. Proc Natl Acad Sci U S A 2003; 100:13761-13766

Luckey TD. Hormesis with Ionizing Radiation. CRC Press, Inc. Boca Raton, FL 1980.

Health Effects of Exposure to Low Levels of Ionizing Radiation BEIR V. National Academy Press 1990.
 
 


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