Where does radiation code from?

Radiation occurs every day naturally or in man-made forms.We are exposed to radiation from natural sources all the time. The average person in the U.S. receives an effective dose of about 3 millisievert (mSv) per year from naturally occurring radioactive materials and cosmic radiation from outer space. These natural "background" doses vary throughout the country.In 1992, the average dose received by nuclear power workers in the United States was 300 millirem (mrem) whole body equivalents in addition to their background dose.

People living in the plateaus of Colorado or New Mexico receive about 1.5 mSv more per year than those living near sea level. The added dose from cosmic rays during a coast-to-coast round trip flight in a commercial airplane is about 0.03 mSv. Altitude plays a big role, but the largest source of background radiation comes from radon gas in our homes (about 2 mSv per year). Like other sources of background radiation, exposure to radon varies widely from one part of the country to another.

How is radiation exposure measured?

The scientific unit of measurement for radiation dose, commonly referred to as effective dose, is millisievert (or mSv). Other radiation dose measurement units include rad, rem, Roentgen, Sievert, and Gray. Because different tissues and organs have varying sensitivity to radiation exposure, the actual radiation risk to different parts of the body from an x-ray procedure varies. The term effective dose is used when referring to the radiation risk averaged over the entire body.

The effective dose accounts for the relative sensitivities of the different tissues exposed. More importantly, it allows for quantification of risk and comparison to more familiar sources of exposure that range from natural background radiation to radiographic medical procedures.

What is the effect of radiation exposure?

Radiation causes ionizations in the molecules of living cells. These ionizations result in the removal of electrons from the atoms, forming ions or charged atoms. The ions formed then can go on to react with other atoms in the cell, causing damage. An example of this would be if a gamma ray passes through a cell, the water molecules near the DNA might be ionized and the ions might react with the DNA causing it to break. At low doses, such as what we receive every day from background radiation, the cells repair the damage rapidly.

At higher doses (up to 100 rem), the cells might not be able to repair the damage, and the cells may either be changed permanently or die. Most cells that die are of little consequence, the body can just replace them. Cells changed permanently may go on to produce abnormal cells when they divide. In the right circumstance, these cells may become cancerous. This is the origin of our increased risk in cancer, as a result of radiation exposure.

General Tips for Safe Imaging

The decision to have an x-ray or gamma ray exam is a medical one, based on the likelihood of benefit from the exam and the potential risk from radiation. If you have had frequent x-ray exams and change healthcare providers, it is a good idea to keep a record of your x-ray history for yourself. This can help your doctor make an informed decision.

You can reduce your radiation risks and contribute to your successful examination or procedure by:

• Keeping a medical x-ray history with the names of your radiological exams or procedures, the dates and places where you had them, and the physicians who referred you for those exams;
• Making your current healthcare providers aware of your medical x-ray history;
• Asking your healthcare provider about whether or not alternatives to x-ray exams would allow the provider to make a good assessment or provide appropriate treatment for your medical situation;
• Providing interpreting physicians and referring physicians with recent x-ray images and radiology reports;
• Informing radiologists or x-ray technologists in advance if you are pregnant or think you may be pregnant.

Children/Pediatric Imaging Tips

Children are considerably more sensitive to radiation exposure than adults, as demonstrated by epidemiologic studies of exposed populations. Since children have a longer life expectancy than adults, they have a larger window of opportunity for expressing radiation damage, most notably the development of cancer. As a result, the risk for developing a radiation-related cancer can be several times higher for a young child compared with an adult exposed to an identical CT scan. A study published in the Lancet on June 7, 2012 described a clear dose-response relationship for both brain tumors and leukemia. The study found that the amount of radiation exposure from an estimated 2 to 3 head CT scans given to a child can triple the risk of brain cancer, and an estimated 5 to 10 head scans can triple the risk of leukemia. Major national and international organizations responsible for evaluating radiation risks agree that no amount of radiation should be considered absolutely safe and that only necessary CT examinations should be performed.

You can reduce radiation risk to your child by:

• Talking with your child's physician. He or she will know or can find out if the imaging center to which they refer uses appropriate pediatric CT scanning techniques, and if a non-radiation imaging test might be as useful for your child's situation.
• Being your child's advocate. Learn about ways health care professionals can lower and limit radiation dose in the CT imaging of children without compromising diagnostic quality. Ask questions.
• Being sure that the imaging facility is using appropriate reduced radiation techniques. You may not know unless you ask, and it is reasonable and within your rights to do so.
• Checking credentials. Ask whether the facility has American College of Radiology accreditation, whether the CT technologists have the proper credentials, and if the person interpreting the studies is a board-certified radiologist or pediatric radiologist.

Radiation Dosage in Select Imaging Procedures