For many people, the concept of radiation is somewhat of a mystery. Maybe you know that doctors use radiation for diagnostic and treatment purposes, but you don't have a clear understanding of how it works. Or maybe you're concerned about the safety and risks associated with radiation.

"Radiation has gotten a bad rap, in large part because people associate the word 'radiation' with nuclear power plant accidents or the atomic bomb, which have been linked to cancer and birth defects," says Dr. Benjamin King, a radiation oncologist at Cedars-Sinai. "But those were uncontrolled, high-dose exposures—either accidental or designed to cause harm. The kind of radiation we use in medicine is precisely controlled and delivered at the lowest possible dose to achieve the desired outcome."

We talked with Dr. King for answers to patients' most pressing questions about radiation.

Dr. Benjamin King: Radiation is energy that travels in the form of energy waves or high-speed particles. There are two broad categories of radiation: non-ionizing and ionizing. Non-ionizing radiation includes everyday exposures, such as radio waves, cellphones, microwaves and visible light. Ionizing radiation includes radiation from the sun, radon, X-rays and gamma rays.

In medicine, we use radiation for two things:

1. Diagnostic imaging, through exams such as X-rays, CT and PET scans
2. Treatment, usually with targeted high-energy radiation
   

BK: Radiation is part of everyday life—it's all around us. A key source of radiation exposure is the sun. So, if you live in a high-elevation area, or when you're traveling in an airplane, the atmosphere is thinner. Without the atmosphere as a shield, you'll naturally be exposed to more radiation.

Radioactive substances also occur naturally in the ground, soil and water. Even eating a banana exposes you to some radiation. The good news: Our bodies are designed to manage low levels of radiation. However, too much exposure can damage tissues and cause long-term health problems, including cancer.

BK: Doctors always use radiation with the utmost caution—and only when the benefit outweighs the risk. With diagnostic radiation, we use the lowest possible dose and the lowest energy required to get the needed image. For cancer treatment, the radiation oncologist personalizes therapy to ensure the precise amount of radiation is delivered to the intended target while sparing healthy tissue.

Whether we're using radiation for diagnostic or treatment purposes, we always use masks, molds and casts to shield other parts of the body—and ask patients to remain still during treatment—to minimize unintended radiation exposure. In the event that surrounding tissues receive small amounts of radiation, it's rare for long-term damage to occur as a result of medical exposures.

BK: No test is completely risk-free, but the benefit of the test outweighs the absolute risk. The area of the body being screened or treated also plays a role in its potential for adverse effects. So, an X-ray of a broken arm, for example, carries less risk than a CT scan of the chest, which is a higher dose of radiation to a larger part of the body.

With every potential exposure, it's important to weigh the risks of radiation versus the benefits. Children, for example, may be more susceptible to the negative effects of radiation exposure than adults. But even among children, the risk of radiation-induced cancer is very low.

BK: Radiation is remarkably effective at destroying cancer cells and shrinking tumors. With targeted therapy, high-dose radiation creates small breaks inside the DNA of cancer cells, which can prevent the cells from growing, spreading and thriving.

The ultimate goal of radiation is to kill cancerous cells while sparing normal tissues—and it's most often used for patients who have solid tumors. In fact, more than half of people who are diagnosed with cancer receive radiation therapy as part of their treatment plan that may include chemotherapy, surgery and novel treatments. In some cases, radiation alone can obliterate tumors, and other times it is used in combination with chemotherapy and/or surgery.

BK: External-beam radiation—the most common type—does not make you radioactive. Therapy is delivered in precise amounts and is only present when the beam is operating. However, if your treatment plan calls for internal radiation, like radioactive iodine, you may emit radioactive substances through body fluids, such as saliva, urine and sweat.

In these cases, patients usually go on a sort of quarantine for several days and limit contact with other people, especially young children. In every case, it's important to talk to your healthcare provider about the risks inherent in your particular treatment regimen.

BK: A lot of people think radiation comes with the same side effects as chemotherapy. They worry about losing their hair, or that the effects of radiation will affect their whole body. But radiation only affects the part of the body that's being treated, and only those organs are vulnerable to its side effects.