Where can I find more information?

This depends on the type of information—general, detailed, textbook—and the form or topic of the information—teaching tools, games, radiation in medicine, radiation in industry, cell phones. We’ve included some additional detail on some topics in our appendices. We’re also providing a list of resources we used in gathering information for this Web site. 

Scientific Reports

Web Sites and Reference Documents

Books

  • Hall EJ, Giaccia AJ. Radiobiology for the radiologist. 6th ed. New York: Lippincott Williams & Wilkins; 2006.
  • Wagner LK, Lester RG, Saldana LR. Exposure of the pregnant patient to diagnostic radiation: a guide to medical management. 2nd ed. Madison, WI: Medical Physics Publishing; 1997.
  • Wolbarst AB. Looking within: how x-ray, CT, MRI, ultrasound, and other medical images are created and how they help physicians save lives. Los Angeles: University of California Press; 1999.
  • Turner JE. Atoms, radiation, and radiation protection. 2nd ed. New York: John Wiley & Sons, Inc.; 1995.
  • Mettler FA, Upton AC. Medical effects of ionizing radiation. 3rd Ed. New York:: Elsevier; 2008 (expected publication is 08Jan08).
  • Kereiakes JG, Rosenstein M. Handbook of radiation doses in nuclear medicine and diagnostic x ray. Boca Raton, FL: CRC Press; 1980.
  • Weingart J. Waste is a terrible thing to mind. Princeton, NJ: Center for Analysis of Public Issues; 2001.
  • International Atomic Energy Agency. Chernobyl’s legacy: health, environmental and socio-economic impacts. IAEA 06-09181. Vienna: IAEA; 2006.
  • Eisenbud M, Gesell T. Environmental radioactivity from natural, industrial and military sources. 4th ed. Boston: Academic Press, Inc.; 1997.

Articles

  1. Adelstein SJ. Administered radionuclides in pregnancy. Teratology 59:236-239; 1999.
  2. Amis ES Jr, Butler PD, Applegate KE, Birnbaum SB, Brateman LF, Hevezi JM, Mettler FA, Morin RL, Pentecost MJ, Smith GG, Strauss KJ, Zeman RK. American College of Radiology white paper on radiation dose in medicine. J Am Coll Radiol 4:272-284; 2007.
  3. Boice JD Jr, Miller RW. Childhood and adult cancer after intrauterine exposure to ionizing radiation. Teratology 59:227-233; 1999.
  4. Brent RL. Utilization of developmental basic science principles in the evaluation of reproductive risks from pre- and postconception environmental radiation exposures. Teratology 59:182-204; 1999.
  5. International Atomic Energy Agency. The Chernobyl Forum: 2003-2005. IAEA/PI/A.87 Rev.2/06-09181. Vienna: Published April 2006.
  6. International Atomic Energy Agency. Beyond the visible: managing heart disease and cancer with nuclear science. 2007. Accessed 19Sept07.
  7. National Electrical Manufacturers Association. How medical imaging has transformed health care in the U.S. 2006.. Accessed 19Sept07.
  8. Strzelczyk J, Damilakis J, Marx MV, Macura KJ. Facts and controversies about radiation exposure, Part 2: Low-level exposures and cancer risk. J Am Coll Radiol 4:32-39; 2007.

 


[linked from page 15]

Why don’t people, even the experts, agree about the effects of radiation?

The short answer to this question is that experts don’t agree because experts can’t scientifically observe if there is an effect on a human due to exposure to radiation at low doses. Why can’t they observe whether there is an effect or not? Because if there is an effect at the doses we are interested in for protecting the public and the worker, it is so small it can’t be conclusively seen in scientific studies. Therefore, the fact there is disagreement provides some comfort that the effect can’t be very large, or it would be conclusively seen. Experts do agree that radiation can and does cause effects at high doses (doses greater than 50 rem). It’s when we get down to low doses (doses less than 50 rem) that we see very different opinions about possible effects. With the lack of conclusive scientific evidence comes the need to develop theories and hypotheses about how low-dose radiation may, or may not, cause an effect. This opens the door for non-science to enter into the issue with the need to make social decisions about when to control radiation exposure and when it is “safe.”

In the rest of this section, we are going to examine some of the reasons for disagreement. Some are social, some political, and some scientific.

Scientific

Please bear with us while we try to explain why even some of the best international experts disagree about the effects of radiation at low doses. As a basis, it is important to realize that a disease caused by radiation will generally not look or act any different than the same disease caused by something else. So if someone has cancer or a child has a birth defect, we can’t simply look at it and determine what caused it. Plus, since approximately one in every two of us will get cancer in our lifetime (the actual number is 1 in every 2.4), it is very difficult to see an extra cancer that might be caused by radiation exposure; for example, if approximately 50,000 people out of 100,000 people will get cancer in their lifetime, it is very hard to tell if 50,010 cancers is really more than the expected 50,000 or if 49,090 cancers is really less than the expected or if both are just a normal variation. Exactly who and how many people in the group of 100,000 will actually get a cancer is unknown. The estimate that one out of two will get a cancer is based on statistics, like rolling dice. If you roll dice six times and don’t get a four, does that mean the dice are loaded or is that just a statistical variation?

As was indicated earlier in this section, most experts agree that high doses of radiation cause harmful effects. Even as early as the 1950s, when scientific groups were creating radiation protection guidelines, no one really knew what the effects of radiation at low doses were or if there were any. For many reasons, some political, it was decided at that time that it would be assumed that the radiation dose and the effect of the dose were linear and proportional—this means for a given dose of radiation to a person, that person has some possibility of a radiation effect; if the dose of radiation is doubled, that person has twice the possibility and so on. It was also decided that at any dose, no matter how small, there could be an effect (or no threshold). We really had only the knowledge that a lot of radiation was harmful, but we needed to make some assumptions about low doses of radiation so protection standards could be set. Setting radiation protection standards required “erring” in these assumptions on the “safe” side, that is, setting a standard lower than it may have to be if the real level of hazard could be known. This, then, was and still is the basis for the Linear No-Threshold Hypothesis (LNT).

Even though LNT was intended for scientists to set radiation protection standards and not for general use, it quickly became “fact” by media and the public because it was easy to use and explain rather than saying we don’t know the effects of low doses of radiation or that low doses of radiation are safe. So, for several decades now, we have simply been assuming that low doses of radiation carry a risk. That still works well when setting radiation protection standards. Now, however, since no activity is risk free, we really need to ask ourselves what dose of radiation is safe—not risk-free, but safe.

Later in this discussion we are going to share what recent science has found and why it can be difficult to determine what effect a low dose of radiation has on a human body. Keep that in mind as you are reading because you are going to read that sometimes radiation might produce “good” effects and sometimes it might produce “bad” effects—at low doses of radiation, the possibility of an effect depends on many things. That is why it can be confusing. It is also how some people are able to say low-dose radiation is harmful while others can say it isn’t—because they can take the information we are sharing and use it so that it appears to support their case. Before we go into more detail on the scientific aspects of low-dose radiation exposure we want to first discuss two other important influences in this area of disagreement—social and political influences. For now, here’s the bottom line: at low doses of radiation, there is no consistent evidence of an effect in humans. Saying that doesn’t mean nothing occurs, it’s just that, if it does, we simply can’t detect it with current studies.

Social

What is “safe”? We could certainly look at a dictionary for a definition, but “safe” or feeling safe is different to each of us. This Web site uses “safe” to mean something about which there is no need to fear or worry about the liability of harm or injury. Since there is no activity that is completely without risk, we individually decide whether an activity is safe for us or our children. For instance, some parents allow their kids to play contact sports believing that it is safe because of all the protective equipment being worn. Some parents believe that even with the protective gear, the potential for injury is too high and they won’t allow their children to play.

Some activities that we initially believe to be pretty risky, for example, crossing a busy highway on foot, we later find out we can do without being injured if we are careful and take our time. There still is a risk, but it can be done safely. Sometimes we learn the hard way—we know we can safely use a knife to cut up veggies, but occasionally we cut our finger. It is a reminder that while cutting veggies with a knife is a safe activity, there is some level of risk.

Like in these examples, people’s feelings about the risks of radiation are based on their idea of “safe.” Some of us grew up with the threat of nuclear weapons being used and had bomb shelters in our backyards. Today we are still worrying about radiation as a weapon, but in the form of a dirty bomb or an improvised nuclear device rather than a whole-scale attack. Much of this worry continues to be promoted in the media when depictions of the “mushroom cloud” imply that all radiation is bad.

And what about nuclear power and those medical x rays? How can some people believe nuclear power is safe while others think it is a bad thing? How can some people voluntarily get a CT scan just to see what it says and others are fearful of x raying a broken arm? Again, like the contact sports or using a knife to cut, it is each person’s perspective. How much do we know about radiation? The less we know, the more we tend to think it isn’t safe. The more we know, the more likely we are to understand that it can be dangerous if used maliciously or it can be beneficial if used to diagnose disease, treat cancer, or generate electrical power.

The social aspect of the safe-ness or risky-ness of radiation is very personal. And we know it doesn’t help that those who are considered experts on this topic disagree about its safety and risk. However, with the information provided throughout this Web site, our hope is that you are able to make an informed decision about those radiation issues affecting you.

Political

What does politics have to do with experts disagreeing and whether radiation is safe? Because allowable uses of radiation in our society can have an impact on public, worker, and environmental health, its use is subject to political decision making and oversight. Well, as with most things political, the decisions are not necessarily based on science or safety. Sometimes our political choices actually impact our social choices—whether radiation is safe or not is one of those decisions.

Sometimes fortunately and sometimes unfortunately, social and cultural ideas impact political decisions. This might be a good thing when society acts out on an issue and our political representatives act in our best interest (banning the use of lead-based paint because it can lead to serious harmful effects if it chips off and children eat it). Sometimes it might not be good when our representatives act on behalf of a small group of people with a special interest (like outlawing alcohol during prohibition because a small group of people thought it wasn’t proper for a church-going person to drink) or if they jump on a bandwagon being driven by emotions rather than accurate, factual information (like enacting a law that no radioactive materials are allowed to enter a sewer system, which means no one can use a toilet since all bodily excretions are radioactive).

Another piece of this is how various people with differing viewpoints on the safety of radiation can be used as centerpieces for political gain, whether it is a special interest group trying to get Congress to make decisions in its favor or whether it is a political faction with certain social views trying to convince others that there is only one correct viewpoint.

Science in more detail

As promised earlier we’re going to discuss some issues with how the science is conducted as it relates to how radiation might harm a human.

Bystander Effect, Hormesis, and Genomic Instability

There are two types of bystander effect when we’re discussing radiation. Both are at a cellular level. Both are ways that cells not touched by radiation can be affected by that radiation anyway if the cell is close by.

The first type of bystander effect is based on studies suggesting that when a cell within a group of cells is “hit” by a radiation photon or particle and killed, that cell releases chemicals into the area where all the cells are sitting. Those chemicals can either offer a protective or a harmful effect on the cells that are left. This implies that the remaining cells are somehow affected by a cell close by that dies, even though they were not hit by the radiation. The exact mechanism is still not known. If, in some instances, a protective effect occurs, this means the cells would be more resistant to radiation damage. If, in some instance, a harmful effect occurs, this means the cells would be more sensitive to radiation damage. Depending on the type of cell, the type of radiation, and the radiation dose, either of these effects could occur.

The second type of bystander effect is based on studies suggesting that cells close together signal each other, causing other cells to protect themselves or to die. Some studies have shown that in a group of cells that are clustered together, causing the death of one cell by radiation can cause the death of other cells very nearby. They have to be clustered very closely, though, because the same effect is not seen if they are even a cell width apart from each other. And, again, the exact mechanism for this effect is still not known. So, as with the first bystander effect discussed, we might have a positive effect (a signal to other cells to protect themselves) that makes cells more resistant to radiation effects or we might have a negative effect (a signal to other cells to die).

This point would be a good time to discuss the concept of hormesis (hor-meee-sis) that, by definition, is a response by cells that makes them more resistant to radiation exposure. There have been some studies in which the authors report that cells exposed to a small amount of radiation (called a conditioning dose) can actually produce what they refer to as an adaptive response that makes cells more resistant to another dose of radiation. Some potential issues with this are that many of the results cannot be reproduced (meaning that other scientists have tried to do the same testing and get the same results, but haven’t been able to; this suggests that the initial results might have been just due to chance), that no type of cell has this capacity for an adaptive response, and that the adaptive response does not appear to last long (so the second radiation dose would have to occur soon after the conditioning dose). So, is it real or not? Scientists can’t agree because the results of studies are so inconsistent.

If that isn’t enough, we’re going to add one more cellular concept—genomic instability. First, the genome of a cell is the DNA-containing portion of the cell. The DNA is what contains our genetic information that is used for the development and functioning of the cell, tissue, or organ that contains the DNA. Thus, as you can probably tell, the DNA is very important to how we function. Genomic instability refers to a situation that can occur if the same genome is somehow changed time and time again. These changes could be the result of radiation interaction, chemical exposure, or another agent. The idea is that the genome is changed once and nothing happens, then in a year or so, it is changed again and nothing happens, then in another year or so, it is changed again and this time it becomes unstable. The number of changes required to make the genome become unstable varies, but the take-away point is that a change can take place and maybe nothing will happen for years to come until another change to that same genome occurs. What does this mean in terms of radiation being harmful? Well, if radiation interacts with a genome and isn’t that “final” change to make it become unstable, then it is likely nothing will happen. If radiation interacts with a genome and it is the “final” change, then it might be the initiating event for a tumor.

How Studies Are Done

There are several factors to think about when looking at various studies and their results. Often, it is not enough just to know the result; we see this commonly in media headlines—“Soda pop found to cause deaths in people with diabetes” and when we dig deeper, we find that someone with diabetes would need to drink more than 48 bottles of non-diet soda a day to cause any effect. [That example is for explanation purposes only and is not real.] The point is that you have to know more than the headline whether it is results of a radiation study or any other study.

We are not going to get in to the different types of human studies. We are only going to explain a few of the issues that complicate how to interpret the results which, again, make it difficult to say whether radiation is good, bad, or neither.

  1. In vitro versus In vivo
    In vitro experiments are those performed outside of a living system (a human or an animal) and usually consist of cells or tissues. In vivo experiments are those performed on a living system, which is usually a human or an animal. The questions here are, Can we take results from radiation exposure to cells sitting outside a human body or from radiation exposure to an animal and determine the impact on a human? Can we say that the effect on a cell outside the body would be the same if that cell were inside the body? When experiments such as these are conducted, scientists try to create a setting for the cells that is as true to what it would be in the human body as possible, or they pick an animal that most closely resembles a human for the organ system they are studying. Scientists work hard to let the reader of the study know the assumptions they had to make to come to any conclusion about the effects of low radiation doses on humans. Even with this, the questions still linger.

  2. Population Studies
    Based on Item 1, it would seem that looking at populations of people who have been exposed to radiation might give us the best answers about low radiation dose effects than studies in cells or animals. True. But these are not without their complications, too. Each person has different activities and different family traits: some might smoke, some might drink, some might have an occupation that exposes them to some type of hazard, some might live in a poor air-quality city, some might be vegetarians, some might have a family history of cancer, and on and on.

If a group of people is exposed to radiation, how do we find a good “control” group of people (a group not exposed to the extra radiation) with which to compare them? Do they all eat the same thing? Were they all raised in the same area? Do they all have the same job? This is one of the complications that make it difficult to see differences in disease rates when we are dealing with low radiation doses. Most studies try to match the control group with the exposed group by having people about the same age, same gender distribution, and usually from the same region of the world, but many other factors cannot easily be accounted for.

Probably the largest complicating factor in a population study looking at harmful effects of low radiation doses is that background rates (rates of disease if no one was exposed to radiation) are very high. That means we need a lot of people to study to get good statistical results. This is equivalent to rolling the dice more than six times to decide if they are loaded or if the results are statistical variation. Results from a low-dose radiation study with 10 people in it probably won’t be seen by scientists as being any good. Results from a low-dose radiation study with 1,000 people or more in it would be good. Results from a low-dose radiation study with a million radiation-exposed people in it and a million matched controls would be the best . . . but we’ll never have that because it is economically impossible to identify, characterize (smoker or nonsmoker, etc), and follow that many people. So what we do is look at several of the smaller studies to see if they’re getting similar results and, if so, draw some conclusions based on that.

Studies known as ecological population studies are performed that involve large populations, like studying the cancer rates in the entire population of the state of Colorado versus the population of Connecticut, where Colorado’s natural radiation levels are more than two times higher than Connecticut’s natural radiation levels. These types of studies are interesting, but they cannot answer the question of how low doses of radiation affect disease in an individual because they don’t include any information about the individuals in the population of those states. For example, the cancer rate in Colorado is 11 percent lower than in Connecticut, but the radiation dose to the population is about 100 percent higher. However, this does not provide scientific evidence that higher radiation exposure reduces cancer rates. It just means that other lifestyle differences between the populations of Colorado and Connecticut are more important in determining cancer rates than low-dose radiation effects.

Concluding Statements

Bottom line? Low doses of radiation can be considered safe; that is to say, their risk of causing a harmful effect is small in relation to other risks we take on a daily basis. We can sometimes see changes in human cells when they are exposed to radiation, but what does that mean for us—is it a bad thing, is it a good thing, or does it really matter? There are thousands of daily interactions with cells that cause damage (not from radiation) and we are okay. It is unlikely that radiation interactions with cells are any different—the radiation may not damage the cell and we are okay; the radiation might damage the cell and there is a high probability that we are still okay.

Study results for humans exposed to low-level radiation simply are not consistent; however, most show that there is no change in the rates of disease with low-dose radiation exposure in humans. Remember, though, that there are some studies that show a decrease in disease and some that show an increase in disease with low radiation doses. This means that individuals and the media can create the conclusion they want others to believe and they can find studies to back up their claim even though not all studies may have the same conclusion. That is why information on this Radiation Answers Web site is based on what we can consider safe and when we need to worry rather than on low-level radiation study results that differ and often don’t offer us basic information we can use right now.

References

Breyer S. Breaking the vicious cycle: toward effective risk regulation. Boston: Harvard Press; 1993.

Brooks AL. Developing a scientific basis for radiation risk estimates: goal of the DOE low dose research program. Health Phys 85(1):85-93; 2003.

Chadwick KH, Leenhouts HP. Radiation risk is linear with dose at low doses. Br J Radiol 78:8-10; 2005.

Hall EJ. The bystander effect. Health Phys 85(1):31-35; 2003.

Huang L, Kim PM, Nickoloff JA, Morgan WF. Targeted and nontargeted effects of low-dose ionizing radiation on delayed genomic instability in human cells. Cancer Res 67(3):1,099-1,104; 2007.

Little JB. Lauriston S. Taylor lecture: Nontargeted effects of radiation: implications for low-dose exposures. Health Phys 91(5):416-426; 2006.

Martin CJ. The LNT model provides the best approach for practical implementation of radiation protection. Br J Radiol 78:14-16; 2005.

Morgan WF, Schwartz JL. Environmental Mutagen Society symposium on risks of low dose, low dose rate exposures of ionizing radiation to humans. Int J Radiat Biol 83(7):491-499; 2007.

Mothersill C, Seymour CB. Radiation-induced bystander effects and the DNA paradigm: An “out of field” perspective. Mutation Res 597:5-10; 2006.

Preston DL, Pierce DA, Shimizu Y, Ron E, Mabuchi K. Dose response and temporal patterns of radiation-associated solid cancer risks. Health Phys 85(1):43-46; 2003.

Prise KM, Folkard M, Michael BD. A review of the bystander effect and its implications for low-dose exposure. Radiat Prot Dosimetry 1,104(4):347-355; 2003.

Ron E. Cancer risks from medical radiation. Health Phys 85(1):47-59; 2003.

Siegel M. False alarm: the truth about the epidemic of fear. Hoboken, NJ: John Wiley & Sons, Inc; 2005.

Smith LE, Nagar S, Kim GJ, Morgan WF. Radiation-induced genomic instability: Radiation quality and dose response. Health Phys 85(1):23-29; 2003.

Strzelczyk J, Damilakis J, Marx MV, Macura KJ. Facts and controversies about radiation exposure, part 2: Low-level exposures and cancer risk. J Am Coll Radiol 4:32-39; 2007.

Upton AC. The state of the art in the 1990s: NCRP Report No. 136 on the scientific bases for linearity in the dose-response relationship for ionizing radiation. Health Phys 85(1):15-22; 2003.

Wall BF, Kendall GM, Edwards AA, Bouffler S, Muirhead CR, Meara JR. What are the risks from medical x rays and other low dose radiation? Br J Radiol 79:285-294; 2006.