Frequently Asked Questions: Radiation

1. What is ionizing and non-ionizing radiation?
2. How does radiation cause health effects?
3. How do we know radiation causes cancer?
4. Is diagnostic radiation a major issue?
5. Is it true that using mammography before age 40 can cause more harm than good?
6. What does CT stand for and how does it work?
7. What is the purpose of the CT scan?
8. What risks are associated with whole body CT scans?
9. What is being done to reduce radiation exposure?
10. How concerned should we be about radiation in medicine?
11. What is the future outlook of harm to the population due to radiation?
12. How harmful are CT scans for children?
13. Is the amount of radiation needed to produce a clear image in CT scans the same for children and adults?
14. Is it true that with the increased use of medical radiation, the incidence of some cancers has actually decreased?
15. If radiation exposure is so harmful, why do physicians order imaging examinations so frequently?
16. What efforts have professional societies taken to publicize the risks of inappropriate use of diagnostic radiation?

What is ionizing and non-ionizing radiation?

Radiation that has enough energy to move atoms in a molecule or cause them to vibrate, but not enough to remove electrons, is referred to as non-ionizing radiation. Examples of this kind of radiation are sound waves, visible light, and microwaves. Radiation that can remove electrons is called ionizing radiation, because it has enough energy to remove tightly bound electrons from atoms, thus creating ions and damaging DNA. This is the type of energy that most people think of as radiation. Ionizing or x-ray radiation can be used to ease bone pain for cancer patients, to cause cancerous tumors to die or shrink, to detect fractures, broken bones and to find tumors. Ionizing radiation is also used to produce what is called nuclear energy and in many manufacturing processes.

How does radiation cause health effects?

Radioactive materials that decay spontaneously produce ionizing radiation, which can strip electrons from atoms or break some chemical bonds, including those involved in the basic building block of all living material—our DNA. Any living tissue in the human body can be damaged by ionizing radiation. We all have the capacity to repair DNA damage, although sometimes that repair capacity cannot work well. Mistakes made in the natural repair process can lead to cancerous cells. The most common forms of ionizing radiation are alpha and beta particles, or gamma and X-rays. Other long-term health effects associated with ionizing or x-ray radiation include birth defects or teratogenic (an agent affecting the embryo or fetus) that include smaller head or brain size, poorly formed eyes, abnormally slow growth, and mental retardation, and genetic mutations passed from parent to child.

How do we know radiation causes cancer?

We have learned through observation of people who have been highly exposed. As the use of radioactive materials and reports of illnesses became more frequent, scientists began to notice patterns in the illnesses. People working with radioactive materials and x-rays developed particular types of uncommon medical conditions. Scientists began to keep track of the health effects, and soon set up careful scientific studies of groups of people who had been exposed. The best known long-term studies are those of Japanese atomic bomb blast survivors, other populations exposed to nuclear testing fallout, and uranium miners.

Is diagnostic radiation a major issue?

According to the American College of Radiology white paper, in the United States, we receive as much radiation from diagnostic procedures every year as was released through the Chernobyl accident, which spewed hundred of Hiroshimas into the environment. The American College of Radiology is calling for a summit meeting with emergency room physicians to come up with ways to reduce unnecessary diagnostic radiation.

Is it true that using mammography before age 40 can cause more harm than good?

Along with public health experts in Canada, England, and Scandinavia, and famed surgeon Dr. Susan Love, many believe that mammography screening of women who have no symptoms helps to save lives of women who are age 50 and older who are close to menopause. Lately, mammographic screening has been done on younger women and can carry two risks. One is the risk of unnecessary surgery and the fear that goes along with it. The other risk is the radiation itself.  Radiation to the young breast is a risk, as we know from the girls who were preteens at the time of the Hiroshima bombing that now have a much higher risk of breast cancer when they get to be in their 40s and 50s.

What does CT stand for and how does it work?

CT stands for computer tomography. In traditional medical diagnostic x-ray equipment, low doses of x-rays are passed through tissues in the body onto a series of detailed cross-sectional images. In CT, the x-rays are targeted through the particular internal part of the body of interest at many hundreds of angles for every cross sectional slice. The information from these x-rays after they have passed through the body is analyzed by a computer, which then creates a series of detailed cross-sectional images. Thus, a typical CT scan can involve dozens to hundreds of chest x-rays.

What is the purpose of the CT scan?

CT scans look at the whole body and are used as a means of screening for early signs of illness in people who have no symptoms or disease risk factors. The benefit is that diseases such as cancer can be treated more successfully if they are detected in their early stages. They are most useful in the examination of specific target organs in the body using a narrow beam of x-rays. It is also used to measure the size and precise location of tumors; to elevate the extent of cancer spread, and as an aid to guiding biopsies and radiation treatments.

What risks are associated with whole body CT scans?

Although CT imaging may be useful as an investigative tool for some potentially fatal disease, general whole body CT scanning in otherwise healthy individuals can also have negative consequences. For example, patients who receive a clean bill of health after a whole body scan may be left with a false sense of security about their health, discouraging them from adopting healthier lifestyles, having regular medical check ups or other more appropriate screening tests. On the other hand, people whose scans produce suspicious findings, such as those often found in the thyroid may be subjected to expensive, invasive and sometimes unnecessary follow-up medical procedures.

What is being done to reduce radiation exposure?

The National Council on Radiological Protection and Measurement is developing a set of guidelines on the management of patient dose in CT scanning. The FDA is developing a tutorial on the dangers associated with CT scanning and it will be available on their website when it is completed. The American Society of Radiologic Technologists has supported the introduction of legislation in the US House of Representatives (HR 583, the Consistency, Accuracy, Responsibility and Excellence in Medical Imaging and Radiation Therapy Act, known as the CARE bill [PDF] ) [50] as a means of providing safer medical imaging examinations by setting federal standards for personnel who perform them. This bill specifically requires certification, licensure, testing, training, or experience for individuals who will be involved in performing medical imaging services.

How concerned should we be about radiation in medicine?

In a 2007 white paper on radiation in medicine, the American College of Radiology noted that in the past quarter century, the amount of radiation the U.S. population receives each year from medical imaging has increased fivefold. A single computerized scan of the stomach today can give half the dose that was shown to induce cancer in those who survived the atomic bomb blasts in Japan.

What is the future outlook of harm to the population due to radiation?

A group of Yale researchers, looking at current patterns estimates that in one year, 700 people will die from cancers associated with head CTs and 1,800 will die from radiation-induced cancer from abdominal examinations carried out when they were infants.

How harmful are CT scans for children?

A CT scan to the head of a baby can give you between 200 and 4,000 chest X-rays at once. Therefore, they should be used in a much more limited way.

Is the amount of radiation needed to produce a clear image in CT scans the same for children and adults?

No. The amount of radiation needed to produce a clear image is directly proportional to the subject’s body size. Therefore, children require much less ionizing radiation than adults do when they get X-rays and CT scans. A child, who receives a CT scan for his or her abdominal region using a setting that is meant for adults, ends up being exposed to as much radiation as is used in about 4,000 X-rays. This translates to approximately eight times the amount of ionizing radiation that an adult would be exposed to for a similar procedure.

Is it true that with the increased use of medical radiation, the incidence of some cancers has actually decreased?

No. Lung cancer is decreasing in men because of smoking cessation and breast cancer is leveling off. There is no evidence that increased screening is responsible for this decline, nor is there any reason to suppose that it could account for the decline in lung cancer . Radiation-induced cancers typically do not occur until 1 or 2 decades after exposure. Therefore, any increase in cancer occurrences due to medical exposure in the past two decades may not be evident for many years to come.

If radiation exposure is so harmful, why do physicians order imaging examinations so frequently?

Although some referring physicians are very knowledgeable regarding radiation safety and incorporate it into their imaging decisions, others have had little or no training in radiation exposure and do not routinely consider this factor when referring for these exams. In addition, non –physician health care providers may be granted the authority to order imaging studies and their ordering patterns may be reflected by the behavior of their supervising physicians.

What efforts have professional societies taken to publicize the risks of inappropriate use of diagnostic radiation?

For more than a decade, the FDA and professional radiology groups such as the American College of Radiology have provided a number of advisories that warn of the dangers of inappropriate radiation.