Everything you ever wanted to know about radiation and cancer, but were afraid to ask


by Julie Bromberg and Laura Covarrubias
2014

 

Click link to jump to section:

Radiation from the Environment
Medical Devices that Use Radiation
Other Manufactured Devices that Use Radiation
Table: Approximate Dose and Cancer Risk of Various Radiation Sources

When most people think of radiation, they think of manufactured devices such as the nuclear bomb or cancer treatments, which emit high doses of radiation.  In reality, however, radiation takes many forms and is always around us.  Some types are much more dangerous than others.1,2

Most researchers agree that there is no such thing as a dose of ionizing radiation that is so low that it will not have some effect on our body, such as damaging cells.  Usually, the damage is small enough that one dose does not lead to any health problems.  It is likely that the increased risk of cancer from low doses of radiation is so low that studies in the general population can’t detect it.3,4

It is important to note that each exposure to radiation builds up in our body and the risk of cancer increases with each radiation exposure.  So even though a single source of exposure to radiation is unlikely to cause cancer by itself, the combined exposures add up throughout our lifetime and increase our risk of cancer over time.5 This is why it is important to limit unnecessary exposures to radiation.  Radiation exposure during certain sensitive times of development, such as during childhood and puberty, also has more health risks than the same exposures in adults.6,7

Since radiation is always around us, we cannot avoid all radiation, but we can try to limit our exposures.  This article will explain the various risks associated with different sources of radiation and how you can avoid getting too much exposure to radiation.

 

Radiation from the Environment

Background radiation

Background radiation refers to radiation that naturally occurs in our environment and does not come from any manufactured devices.  Radiation is emitted from the earth, sun, our galaxy, and other galaxies.  Even the human body naturally contains some radioactive elements.8  People who receive few or no high-dose radiation medical tests usually get more exposure to radiation from the natural environment than from any manufactured device.9

This is because we are constantly exposed to a very low dose radiation for our whole lives, while devices such as x-ray tests expose you to radiation for a very short period of time.  On the other hand, one CT scan can be equal to several years of background radiation exposures, so many people receive much higher doses of radiation from medical devices than they do from the natural environment.

The risk of developing cancer from a lifetime exposure of background radiation is about 1 in 100, or 1% of the population.10It is impossible to avoid all background radiation, but the best ways to limit unnecessary exposure to radiation from the environment is to prevent your exposure to radon and repeated unprotected sun exposure.

 

Radon

Radon is a colorless, odorless gas that comes from decaying rocks and soil.  For the average person, radon accounts for over half their annual exposure to radiation.  Radon comes up from the ground and gets trapped in houses and buildings.

Exposure to a small amount of radon inside is normal, but high levels can cause lung cancer.  Radon is the second leading cause of lung cancer (smoking is the leading cause), and approximately 1 in every 15 houses have too much radon.  The only way to know if you have a safe level of radon in your house is to get it tested.11

 

Cosmic and terrestrial radiation 

Cosmic and terrestrial radiation is radiation that comes from the galaxy and from the earth.  It makes up about 8% of our average yearly exposure to radiation.12 Cosmic radiation includes ultraviolet (UV) rays from the sun that cause tans and sunburns.  UV rays can also damage the DNA in our skin cells and lead to skin cancer.13 Although we cannot avoid UV rays all the time, limiting exposure to direct sun light can reduce your risk of skin cancer.  Tanning beds are also a common source of UV radiation and are just as dangerous as radiation from the sun.  For more information on tanning beds, please read: Tanning Beds: Safe Alternative to Sun?

Being at higher altitudes, such as flying on a plane or living in a “mile high” location, will exposure you to higher levels of cosmic radiation than being at sea level.  While there is technically no “safe” dose of ionizing radiation, the chances of getting cancer from frequent plane trips is very slim.  Studies of airline crew members have not found a significant increase in risk of cancer after many years of working on airplane.14

 In addition, living in Denver or other high altitude locations that receive higher doses of cosmic radiation has not been shown to increase the risk of cancer.15

text-box-environ-rad

Medical Devices that Use Radiation

X-rays

X-rays use ionizing radiation and are used for many types of diagnostic tests such as CT scans, mammograms, fluoroscopy, and simple x-rays.  These tests allow your doctor to see potential problems inside your body and choose an appropriate treatment.  They can help doctors make life-saving decisions, but some doctors are performing unnecessary scans or are using doses of radiation that are too high.16  Since x-rays use ionizing radiation, they can cause damage to our cells and DNA. X-ray tests can lead to cancer, but several common tests (such as mammograms and bone x-rays) use very low doses that have not been shown to cause a significant increased risk of cancer when administered properly.

Over the past few decades, the average level of radiation that Americans are exposed to has increased rapidly due to increased use of medical diagnostic tests such as x-rays (including dental x-rays and mammograms) and CT scans and cancer treatments.  Diagnostic tests and treatments can help improve patients’ quality and length of life, but there are also risks.  Usually, the benefit of receiving one of these tests outweighs the risk, but patients and doctors need to be wary of performing unnecessary tests, particularly if the test uses high doses of radiation.

Not all imaging tests use radiation that has been linked to cancer. Magnetic Resonance Imaging (MRIs) and ultrasounds do not use x-rays.  Instead, they use non-ionizing radiation and have not been found to increase the risk of cancer or other health problems.17

MRIs and Ultrasounds are a safer alternative to diagnostics tests that use x-rays or other ionizing radiation.

Children, young adults, and fetuses of pregnant women should be particularly careful about getting any x-ray tests.  Children, young adults, and fetuses are more sensitive to radiation, and their young age also allows a longer period of time for cancer to develop.18,19,20

Pregnant women should avoid any x-ray exposure, particularly when they are less than 20 weeks pregnant, since radiation exposure in the womb can lead to mental retardation, growth retardation, leukemia, and other cancers later in life.21  If it is necessary for a pregnant women to be x-rayed, the American College of Obstetricians and Gynecologists states a single x-ray test does not harm the fetus, but a protective lead apron should be used to cover the abdomen.22  However, high-dose, multiple-dose, or x-rays of the pelvic region should be avoided for pregnant women, whenever possible.

Many people get simple x-ray tests, such as an arm, leg, chest, or dental x-ray that look for broken bones or other problems.  Simple x-ray tests use very low doses of radiation,23  and studies have not found an increase risk of cancer among humans who have received a very low dose of radiation.24 Although the dose of radiation used to x-ray different parts of the body will vary, most simple x-rays use less radiation than other types of x-ray scans (such as a mammogram or CT scan).

 

Mammograms

Mammograms are an x-ray test that is used to detect breast cancer.  This test uses a higher dose of radiation than a simple x-ray, but less than a CT scan or Fluoroscopy.  According to the U.S. Preventative Services Task Force, a woman above age 50 who is at average risk of breast cancer should get a mammogram test once every two years until age 74.25 These new guidelines would expose women to less than half the amount of radiation from mammograms than following previous recommendations (which included annual mammograms starting at age 40 for women at average risk).

While these doses of radiation could cause new cases of breast cancer, the appropriate use of mammograms has resulted in lives saved, and the benefits of getting regular mammograms are likely to be even greater than the risks when the frequency of mammograms is reduced to every other year.

Women who are carriers of the BRCA genetic mutation were previously recommended to begin yearly mammograms at age 25-30, since this mutation puts them at much higher risk of getting breast cancer.  Newer studies have found that starting yearly mammograms before age 35 has no benefit to these women and may instead be harmful.  They end up with higher exposure to radiation over their lifetime, which increases the chance of getting radiation-induced breast cancer that they may not have gotten otherwise.26

 

Fluoroscopy

Fluoroscopyis an x-ray test that allows doctors to see a continuous x-ray image of your body (like a movie, rather than just a picture as with other x-ray tests).  Fluoroscopy uses an x-ray absorbing dye that is either drunk or injected into the body, which allows doctors to see a better outline of the organ.  This procedure is used to view the digestive system (such as stomach, kidneys, or colon), arteries, or joints.27

Since this test sends x-ray beams over an extended period of time (usually 20-60 minutes),28 it exposes people to much higher doses of radiation than a simple x-ray test, although the doses vary widely depending on the test.

Fluoroscopy and CT scans both use high doses of radiation and pose the greatest and most avoidable risk of radiation-induced cancer.  Limiting the number of CT and fluoroscopy tests you receive is one of the best ways you can avoid getting cancer from radiation.  In addition to increasing cancer risk, this test can damage the skin and cause burns.29

 

Computed Tomographic (CT) scans

CT Scans are a relatively new type of diagnostic imaging technology that allows doctors to view 3-dimentional pictures of various organs in your body.  CT scans use higher doses of radiation than most other types of diagnostic test and are likely to cause new cancers in some patients, compared to their risk if they had not received a CT scan.

Today, an American’s average lifetime dose of radiation from diagnostic procedures is six times higher than it was in the 1980s.30  This is largely due to the increased use of CT scans. Everyday, 19,500 CT scans are performed in the U.S. and this number continues to climb. Each CT scan is equivalent to 30 – 442 chest x-rays, depending on the dose used for the CT scan.31 One study projected that CT scans performed in the U.S. in 2007 alone will result in 29,000 new cancer cases and roughly 15,000 deaths that would not have occurred if they had not received a CT scan.32 These risks would increase with each additional CT scan a person receives.  Low-dose CT scans, which expose patients to less radiation, are now being used to screen for lung cancer, with concerns about whether the benefits outweigh the risks.  For more information on low-dose CTs, click here.

Unfortunately, there is no established guideline for how much radiation should be used for each procedure.  Different scans require different levels of radiation in order to get a clear image, but some doctors are using more radiation than is necessary.  One study found that different medical facilities had huge variations in the dose of radiation used for the same procedure.  On average, the highest dose given for a CT scan was 13 times higher than the lowest does given for the same type of scan.33 The researchers found no pattern in why this dose variation occurred, and no scientific justification.

Children’s exposure to radiation from CT scans is particularly worrisome because children have many more years to develop cancer than adults receiving CT scans and are more sensitive to the effects of radiation.  A June 2012 study found that children receiving higher doses of radiation — through multiple CT scans– were more likely to develop brain tumors and leukemia than children who had only one CT scan.34  However, brain tumors and leukemia are very rare conditions and the increased risk due to CT scans was relatively small: for every 10,000 CT scans performed on children under 10 years-old, there will be one additional diagnosis of leukemia and one additional diagnosis of a brain tumor. The researchers concluded that the benefits of children having necessary CT scans outweighed the risks of later developing cancer.

A study published in May 2013 looked at children from infancy to 19 years of age in Australia and compared those who had undergone CT scans to those who had never had any.35  Ten years after getting scanned,  there were 24% more cases of cancer among  the 680,000 children and teenagers who had CT scans than among the 10 million children and teenagers who did not undergo CT scans. Young people who had CT scans during the 12-month period before being diagnosed with cancer were not counted because the decision to scan them may have had to do with cancer symptoms.  Children 4 and under had the highest increased risk in cancer, and risk for all increased with the number of scans. The researchers concluded that for every 1,800 people under 20 who had a CT scan, there was 1 additional case of cancer that would not have occurred without the radiation from the CT scan. The CT scans in this study took place between 1985 and 2005 when radiation doses where generally higher than they are today.

Parents should make sure that CT scans ordered for their children are medically necessary and ask their doctors if lower-radiation alternatives exist. While parents should not stop their children from receiving a necessary CT scan because of radiation concerns, they should think about keeping the number of scans below age 20 to a minimum.

The FDA and investigative journalists have also released warnings about occurrence of extreme accidental overdoses of radiation from CT scans.36,37

 In January 2010, the FDA reported that over 250 patients at 4 facilities had received as much as 8 times the amount of radiation that they were supposed to receive.38 Accidental radiation overdoses can result in skin redness, hair loss, increased risk of various cancers and cataracts in the future, and death.  While extreme overdoses of radiation are rare, these avoidable mistakes have lead many health professionals to call for more standardized and comprehensive methods of overseeing medical radiation.39

(Click here for more information on heart CT scans and cancer risk).

 

Positron Emission Tomography (PET) scans

PET scans differ from other types of diagnostic imaging in that they allow doctors to see how an organ or system is functioning rather than just seeing the structure.  This test works in a very different way than other tests and does not use x-rays-rather, it uses gamma rays, which usually have a higher level of energy than x-rays.

PET scans work by injecting (or swallowing) small amounts of radioactive material, which then spreads throughout the body. The PET scanner is then used to detect the radiation that is emitting from the radioactive material in your body. Procedures that use radioactive material to diagnose and treat patients is referred to as “nuclear medicine.”40

The dose of radiation from a PET scan is similar to CT, and therefore exposes people to a relatively high dose of radiation in comparison to other types of scans.

Using Radiation to Treat Cancer:

Radiation therapy

Radiation therapy uses high doses of radiation to treat various types of cancers.  Beams of radiation are directed at the cancer to kill off cancerous cells.  This can save lives and prevent recurrence of cancer, but healthy cells that are exposed to radiation may develop into a new cancer.  Fortunately, new cancers caused by radiation therapy are not thought to be very common since radiation technology can precisely irradiate a small part of the body that contains cancer, minimizing the amount of healthy cells that are exposed to radiation.41

Another concern about radiation therapy and diagnostic tests are errors in using this technology. Although relatively uncommon, some patients will accidently receive doses that are too high.  In addition to being at increased risk of developing cancer in the future, the incorrect doses can cause serious wounds to the skin, bone, and other organs, as well as death.42,43

text-box-med-devices

 

Between 1950 and 2006, the frequency of diagnostic radiation increased 10-fold.44 As health professionals continue to find new uses for medical devices that use radiation, people will be exposed to radiation more often. For example, many radiologists have recently started promoting the use of CT scans to screen for colon cancer (known as a virtual colonoscopy), although the FDA has not approved CT scans for this purpose.45

Although many patients would prefer this non-invasive procedure over the traditional direct examinations, it would expose people to high doses of radiation that is roughly equal to 100 chest x-rays (or 3 years of background radiation.46 This means more people are likely to be diagnosed with cancers that are caused by radiation than they would not have gotten otherwise.

 

Other Manufactured Devices that Use Radiation

Airport and Building X-ray Scans

Backscatter and millimeter scanners have begun replacing metal detectors and are designed to scan a person to determine what weapons or explosives they may have beneath their clothing. Currently, there are about 250 backscatter and 264 millimeter wave scanners in the United States. The TSA hopes to have 1,800 scanners of either type installed by the end of 2014 – which would mean that nearly every airport in the country will have one.

Backscatter scanners look like two large blue boxes:

tech_backscatter

 

(Source: Transportation Security Administration, from http://www.tsa.gov/approach/tech/ait/how_it_works.shtm)

People raise their arms and stand sideways between these two boxes when they are scanned.

In contrast, millimeter wave scanners look like circular glass phone booths, and the person being scanned stands with their arms raised while part of the scanner rotates around them:

tech_millimeter_wave

 

(Source: Transportation Security Administration, from http://www.tsa.gov/approach/tech/ait/how_it_works.shtm)

If you are not sure which scanner is in use at your airport, ask a TSA official at the security checkpoint.

While metal detectors and millimeter scans both use non-ionizing radiation, which until recently was assumed to be safe (see our article Can Cell Phones Harm our Health?), backscatter scans use ionizing radiation, which is used in x-rays and known to potentially increase the risk of cancer. Backscatter scans work a little differently from x-rays. X-rays work by sending high-energy radiation to the body and recording the radiation that passes through the body. Dense parts of the body (like bones) block some of the radiation, resulting in lighter areas on the recorded image.  Backscatter scanners also send radiation toward the body, but at much lower energy than an x-ray. Because it is not as strong as the radiation used in x-rays, the radiation does not pass through the body. Instead, the outer layers of the body “scatter” the radiation, which bounces off the body and back toward the machine. People receive most of the radiation that is absorbed by the body is deposited in the outer layers (like the skin and ribs), although a 2012 study showed that radiation from these scans may penetrate to other organs.47  Because the radiation is concentrated in the skin, there are concerns that this could cause skin cancer.

All data on backscatter scans are provided by TSA, a government agency that does not allow independent researchers to examine the machines they use.48 Researchers must therefore make educated guesses using data provided by the TSA, or they must make models of the scanners based on information that the agency releases.

The TSA states that backscatter scans use such low doses of radiation that estimating the potential effects of the scan is extremely difficult.49,50 A 2011 report using information from the TSA found that these backscatter scans expose people to the same amount of radiation that they receive from 3 to 9 minutes of normal daily life or from 1 to 3 minutes of flight.51 To put this into perspective, we would expect only 6 of the 100 million airline passengers each year to develop a cancer in their entire lives due to the backscatter scans.

Dr. David Brenner, a researcher at Columbia University, produced a different estimate based on the risk that the scanners are to the entire population, not just to an individual.52 Dr. Brenner multiplied the risk associated with one scan by the number of scans conducted each year to estimate the number of people who may develop cancer in one year because of the scanners. Because up to one billion scans may be performed each year, Brenner estimated that each year 100 people would develop cancer because of their exposure.

In April 2010, a group of scientists from the University of California, San Francisco wrote a letter of concern to Dr. John Holdren, the Assistant to President Obama for Science and Technology, about the backscatter scans. These researchers pointed out that because backscatter scans only penetrate outer layers of the body, it is possible that these layers receive a higher concentration of radiation than previously believed.

The scientists also expressed concern that sperm may mutate because the testicles are close to the surface of the skin and are exposed to radiation during these backscatter scans. In addition, they noted that the effects of radiation on the cornea (the outer surface of the eye) and the thymus (a part of the immune system located in the chest) have not been studied. While this letter only outlined concerns of the scientists and did not present new data, it called for further testing of backscatter scans.  The scientists called for more rigorous and independent studies to ensure that the scans are safe for the entire population, as well as for all parts of the body.

In a joint reply with the TSA, the FDA stated that the radiation exposures from the backscatter scans were within established legal limits, even for frequent fliers.53 In reply to the scientists’ concerns that the radiation dose to the skin would be higher, the FDA wrote that their calculations showed that a person would have to pass through the scanner 1000 times in a year in order to begin to absorb the annual limit of what is considered safe.54

Not everyone agrees with the FDA, and some people have pointed out that TSA agents operating the scanners may improperly manage the devices or that mechanical errors may occur, either of which could cause the machines to emit more radiation than they are supposed to. From May 2010 to May 2011, there were 3,778 calls for mechanical problems on backscatter machines, but only 2% of those machines were evaluated for radiation safety.55

For a more in-depth look at airport security and radiation, read here.

 

Microwaves, Cell Phones, and Other Manufactured Devices

There is still much debate among scientists about whether non-ionizing (low-energy) radiation such as microwaves can increase your risk of cancer or other health problems. The concern is not about microwave ovens, but rather the long-term exposures to microwaves from other sources, such as communication towers and cell phones.56 Cell phones emit very low doses of microwave radiation, which was long assumed to be safe.

Although generally safer than ionizing radiation, the much longer-term exposure could make these products potentially dangerous. There are studies indicating that long-term exposures to low doses of non-ionizing radiation can damage DNA and may cause cancers and neurological and reproductive harm.57,58

The rapid increase in use of cell phones and other wireless devices intensifies the need for further research on potential health effects of these non-ionizing radiation sources.  Click here to get more information on cell phones and health.

Tobacco, fertilizer, welding rods, smoke detectors, and several other consumer products also contain some radiation, but radiation from these sources is generally very low (approximately 3% of our yearly radiation dose.[10]

Table: APPROXIMATE DOSE AND CANCER RISK OF VARIOUS RADIATION SOURCES: How does it compare to natural background radiation? What is the lifetime risk of cancer death from one exposure to this radiation source?

 

table-radiation-dose-and-risk

 †Dose is based on a normal effective dose for that type of scan.  Actual doses used for a specified scan vary widely depending on the medical institution, the individual, and other factors.59

‡Natural background radiation is equal to about 3mSv per year.60

§ Risk of developing cancer is based on EPA cancer risk estimates: “…health physicists currently estimate that overall, if each person in a group of 10,000 people exposed to 1 rem [10mSv] of ionizing radiation, in small doses over a life time, we would expect 5 or 6 more people to die of cancer than would otherwise.”[33]

§§ “In this group of 10,000 people, we can expect about 2,000 to die of cancer from all non-radiation causes. The accumulated exposure to 1 rem [10 mSv] of radiation, would increase that number to about 2005 or 2006.”[33]

 

 

 

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  33. Smith-Bindman R, Lipson J, Marcus R, et al. (December 2009). Radiation Dose Associated with Common Computed Tomography Examinations and the Associated Lifetime Attributable Cancer Risk. Archives of Internal Medicine, 169(22): 2078-2086.  
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