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FAQ’s

What is radiation?

Radiation can simply be described as energy moving through space. It can take many forms, including visible light, x-rays, gamma-rays, microwaves and radio waves. This site specifically addresses high energy or ionizing radiation, which includes x-rays. Ionizing radiation has many uses, including sterilization of food and medical equipment, creation of medical images, and is even used in the treatment of certain types of cancer.

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Where does radiation come from?

Radiation is all around us. Currently, two main sources of ionizing radiation are from natural background radiation and medical exposure (CT scans and x-rays).  Natural background radiation comes from the Sun (cosmic radiation), the Earth (mostly Radon gas) and from naturally radioactive substances in our body.  Natural background radiation exposure accounts for an average of 3.1 mSv/yr with variations depending on where you live.

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What are x-rays?

X-rays are a type of radiation that are created using large amounts of electricity. X-rays are used in medical imaging much like a camera uses visible light to create an image. X-rays pass through the body and create an image on film based on how many x-rays get absorbed and how many pass through. These films are commonly referred to as “x-rays,” but x-rays are actually the type of radiation that is used to produce the image. Studies that use x-rays include plain films, fluoroscopy and computed tomography (CT scans).

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How do x-rays increase your risk for cancer?

When x-rays, or any ionizing radiation, pass through the body they cause electrons to be ejected from atoms, leaving behind positive ions. These positive ions, or free radicals, can cause damage to DNA. DNA can also be damaged directly by radiation. If DNA is damaged, there are three possible outcomes:

1. The cell dies (only occurs with very high doses).
2. The cell repairs itself perfectly (most common result).
3. The cell repairs itself with mistakes (rare).

The inaccurate repair of DNA is rare, but can cause a cell to act wildly or grow into a cancer. Oftentimes it takes decades for cancer to be detected following radiation exposure.

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Why isn’t there a study directly linking medical imaging and cancer?

There are no studies that directly link cancer to the low dose radiation used in current medical imaging. To scientifically prove a connection would require nearly one million patients followed closely over decades to detect the small increased risk with any confidence.

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Isn’t radiation used to treat cancer?

Radiation is very successful at treating some cancers. An entire field of medicine (Radiation Oncology) is devoted to this practice. Radiation treatment doses are much higher than doses used for medical imaging. High dose radiation causes cell death, specifically the cells which are growing the fastest including cancer cells, hair cells and gastrointestinal tract lining.

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If I have cancer, can radiation from medical imaging make it worse?

No. Low dose radiation from medical imaging does not affect known cancer. In fact, high dose radiation is used to treat cancer. Low dose exposure increases the risk of developing new cancer decades after exposure, which is the focus of this site. The information gained from imaging patients with cancer most likely outweighs the small risk of cancer induction many years in the future.

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Why is the average risk of developing cancer so high?

Regardless of radiation exposure, the average overall lifetime risk of developing an invasive cancer is 37.5% for women and 44.9% for men.⁶ These statistics are averages and do not predict what is going to happen to you. They do not take into consideration individual risk factors including lifestyle (smoking, diet, exercise, etc.), family history (genetics) or radiation exposure. The majority of cancers occur later in life and the average lifetime risk of dying from cancer is 25%.⁶

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Why does age and gender matter when calculating cancer risk?

Pediatric patients are at the greatest risk of developing cancer from radiation exposure. There are two theories why. First, rapidly dividing or growing cells are at greater risk of damage from ionizing radiation. Second, children have a long life ahead of them, therefore the chance of detecting a slow growing cancer is higher when compared to someone exposed later in life. With this in mind, most institutions make adjustments in the way they take images of pediatric patients, using lower doses or shielding sensitive organs.

In general, women are at slightly higher risk of developing cancer when compared to men exposed to the same dose of radiation. This is based on high dose exposure data from survivors of atomic bombs, nuclear accidents and the early use of x-rays. Men and women also have different average risks for developing cancer.

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If I am pregnant, what is the risk to the fetus?

Much like the risk estimates in adults, fetal risk estimates are not proven with any certainty, but are taken very seriously. We know that children are more sensitive than adults, so we assume the fetus is at even higher risk. If there is any chance you may be pregnant, you must inform your doctor as well as the staff that is performing your study. There are precautions that can be taken to limit risk or there may be alternative imaging modalities, such as MRI and Ultrasound. The estimates provided by this website are not designed to estimate fetal risk.

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If x-rays increase my risk of cancer, why should I get a Mammogram to screen for cancer?

Carefully evaluating the risks and benefits of screening studies (like mammograms) is an important part of medicine.  Screening mammograms have been proven to decrease mortality from breast cancer by approximately 30%.  Simply put, early detection of breast cancer using mammograms saves lives.  Therefore, the American Cancer Society recommends an annual screening mammogram for women over age 40.  The risk of getting cancer from the mammogram itself is negligible.  Women at high risk for breast cancer should discuss imaging options with their doctor.  

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Does MRI or Ultrasound cause cancer?

MRI uses strong magnetic fields and radio waves to obtain images, which have not been associated with an increased risk of cancer. Ultrasound uses sound waves to produce images. There is no exposure to ionizing radiation with MRI or Ultrasound.

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How does the risk from medical radiation compare to background radiation exposure?

Natural background radiation exposure accounts for an average of 3.1 mSv/yr with variations depending on where you live. In the US, the average person is exposed to an additional 3.0 mSv/yr from medical sources (predominantly CT scans). Of course, some people receive no radiation and others much, much more. The average US total radiation exposure (all sources) is 6.2 mSv/yr which is an increase from 20 years ago (3.6 mSv/year) when CT scans were much less common. For comparison, the dose for a standard Chest CT is 7 mSv. A standard Chest x-ray is 0.1 mSv. There are fundamental differences between a continuous dose over a year (background radiation) and a dose that occurs over a few seconds like in CT, but these are helpful comparisons.

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How does airline travel expose me to radiation?

A seven hour airplane trip exposes passengers to 0.02 mSv of radiation, which is a fraction of the exposure of a standard Chest x-ray (0.1 mSv). Domestic airline pilots are exposed to an additional 2.2 mSv per year, about the same dose as a brain CT.

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How do I protect myself from radiation exposure?

For the most part, background radiation is unavoidable. To limit your radiation exposure from medical sources, it is important to talk to your doctor about your imaging choices. Using a shield to cover part of the body that is not needed for an exam is an effective and easy way to decrease your exposure. You may remember your dentist doing this when you have dental x-rays taken. It is important to realize that in a properly performed individual exam, the potential health benefits almost always outweigh the potential risks of radiation exposure. Simply put, patients should not hesitate having a study if it is medically indicated.

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Does the US Government regulate radiation exposure?

Yes, there are limits to the amount of radiation a radiation worker (x-ray technician, radiologist, etc) can be exposed to. This is set by the Nuclear Regulatory Commission (NRC). This is separate from patients in which limits are not really defined, but they should follow the ALARA Principle (As Low as Reasonable Achievable). Radiation workers are limited to a total body dose of 50 mSv/yr (≈7 chest CTs) with averages ranging between 2-5 mSv/yr. Pregnant workers are limited to 5 mSv during pregnancy (≈7 abdominal x-rays). Workers are monitored closely with radiation badges that are collected monthly.

How much radiation do airport security whole body scanners use?

There are two types of whole body security scanners at airports which are very different than the baggage scanners. Millimeter Wave Scanners use radio waves which are not ionizing (i.e. do not induce cancer). Backscatter Wave Scanners use very weak x-rays at a dose of less than 10 microrem per scan (0.001 mSv). For comparison it would take;

ACR Statement on Airport Full-body Scanners and Radiation, January 2010. (http://acr.org/MainMenuCategories/media_room/FeaturedCategories/PressReleases/StatementonAirportFullbodyScanners.aspx)

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