What do the sun, nuclear reactors, microwave ovens, radio antennas, X-ray machines, and power lines all have in common? They all produce radiation.

While radiation can be lethal at higher levels and concentrations, radiation has been vital to the development of modern medicine. Doctors use it for everything from diagnosing a broken toe to treating cancer.

In this article, we explore the different types of radiation and their uses in medicine before taking a closer look at radiation as a part of cancer treatment.

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Radiation forms an important part of modern medicine, including imaging scans and radiation therapy.

Radiation occurs when an object or body gives off energy that travels in a straight line through a material or through space.

This energy moves in waves, which form a spectrum of longer to shorter waves. The shorter the wave is, the higher the energy becomes.

Cell phone signals, radio waves, and television broadcast all operate using low-spectrum radiation.

Doctors and scientists measure the absorption of radiation by human tissue in grays (Gy). This absorption is a dose.

When assessing the risk of exposure to radiation, they use millisieverts (mSv). These units help medical professionals keep radiation within safe limits while using them to assess and treat health problems.

Radiation is either ionizing or non-ionizing.


Non-ionizing radiation is lower-energy radiation that comes from the lower part of the electromagnetic spectrum.

The term “non-ionizing” comes from the radiation not having enough energy to completely remove an electron from an atom or molecule.

Examples of non-ionizing radiation include:

  • visible light
  • infrared light
  • microwave radiation
  • radio waves
  • longwave, or low frequency, radiation


Ionizing radiation has enough energy to carry out ionization. This means it can detach electrons from atoms or molecules.

This type of radiation comes from both subatomic particles and the shorter wavelength portion of the electromagnetic spectrum.

Examples include:

  • ultraviolet (UV) radiation
  • X-rays
  • gamma rays
  • subatomic particles, such as alpha particles, beta particles, and neutrons

Atoms usually give off subatomic particles as they decay. They lose protons, neutrons, electrons, or their antiparticles.

The more focused radiation, which forms the basis of CT scans and X-rays, is ionized radiation.

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Radiation carries a cancer risk.

High levels of radiation can be dangerous for people. However, low levels of radiation occur throughout the environment and do not affect human health.

Ionizing radiation is more hazardous than non-ionizing radiation.

Overexposure to ionizing radiation can cause:

  • skin redness
  • radiation burns
  • tissue and organ damage
  • hair loss
  • acute radiation syndrome, which is a series of highly dangerous conditions that occur in people who receive very high exposure in a short timespan and stops function in deep tissue and organ systems
  • cancers, even from low-level exposure over a long timespan

Rocks, soil, water, and air all give off ionizing radiation but at such low levels that they do not pose a health risk.

Around 80 percent of the radiation a person absorbs throughout the year is from these natural sources. Some areas have higher radiation than others. Higher altitude places a location closer to cosmic rays, which can increase radiation levels.

Being near or using manmade sources of radiation can increase the risk of radiation poisoning. These include nuclear power plants and medical equipment, such as CT scanners.

Medical devices are the most common manmade sources of radiation.

The more ionizing radiation people have exposure to, the more dangerous it becomes.

Health authorities, such as the International Organization for Medical Physicists (IOMP), advise that a dose of less than 100 mSv produces no observable effects on the human body.

To put 100 mSv in perspective, a dental X-ray has a biological risk of 0.04–0.15 mSv. A chest X-ray runs at 0.1 mSv and a mammography at 0.7 mSv.

A year of exposure to natural radiation in the environment amounts to 3 mSv.

While radiation might produce some dangerous effects and increase a long-term risk of cancer above certain levels, the levels at which people will normally receive a dose of radiation is a tiny fraction of any amount that could cause harm.

In healthcare, medical professionals use radiology to diagnose diseases using radiation-based imaging technologies.

Projectional radiography provides an image of a body part. These techniques include:


The radiologist, or X-ray technician, directs the ray a part of the body, which absorbs some of the radiation.

Hard tissue, such as bone, absorbs more radiation than soft tissues, including muscle and cartilage. The remaining X-rays pass through the body and expose photographic film on the other side, creating a shadow effect.

Different parts of the body require different strengths of X-ray. Doctors commonly use X-ray for examining the chest, in mammography, and on limb fractures.


Fluoroscopy uses X-rays and a contrast material, usually iodine or barium, to get a moving image of what is happening inside the body.

Examples include angiography, for viewing the heart and blood vessels, and gastrointestinal fluoroscopy, which lets physicians see the gastrointestinal tract.

CT scan

A CT scan uses X-rays and computers to show slices of soft and hard tissues.

They will often incorporate contrast agents, or dyes that make the image clearer. CT scans provide a 3D reconstruction of a part of the body.

Uses of CT scans include looking for a bleed in the brain and checking for appendicitis in the abdomen, among many others.


Ultrasound uses high-frequency sound waves to see soft tissues inside the body. Sound waves do not produce ionizing or potentially damaging radiation that the body can absorb.

Ultrasound scans can show images in real time and its use is gradually expanding. They can provide people with an image of their child during pregnancy or guide surgical procedures for improved accuracy.

Doctors use ultrasound increasingly often at the bedside to assist with a range of procedures, such as removing fluid from the lungs, known as pleural effusion, or evaluating for a tear in the rotator cuff of the shoulder.

Magnetic resonance imaging (MRI)

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An MRI machine uses non-ionizing radiation to produce high-quality images.

Magnetic resonance imaging (MRI) uses strong magnetic fields and a radio signal to take high-quality 3D images of the body.

The individual has to lie very still in a mildly noisy tube for a long period of time, and this experience can be uncomfortable. However, the scan provides excellent images of soft tissue.

MRIs do not use any damaging ionizing radiation, only strong magnetic fields and non-ionizing radio frequencies. MRI provides high-quality images of muscles, tendons, and ligaments.

In the brain, an MRI can identify the difference between a tumor and an aneurysm.

DEXA scan

Doctors use dual-energy X-ray absorptiometry (DEXA), or bone densitometry, to test for osteoporosis.

DEXA scans use two narrow X-ray beams to measure the density of the bone. They do not produce images, so this scan is not a type of projectional radiography.

PET scan

A positron emission tomography (PET) scan is a nuclear medicine imaging technique that requires the injection of a radioactive contrast agent, or tracer, into the body.

This tracer radioactively decays in the body and emits positron particles. The PET scanner picks up these particles, and the doctor or technician then uses a computer to reconstruct 3D images.

A PET scan detects chemical activity in the body, and it is useful in the surveillance of a variety of cancers. It can also highlight blood flow in the heart, and it can give information about neurological conditions such as Alzheimer’s and seizures.

Many of the imaging techniques we have just seen are used in treatment as well as diagnosis.

Ultrasounds and X-rays may be used to guide biopsy procedures, and ultrasound is used to break up kidney stones, making them easier to pass.

Radiation therapy

Healthcare professionals use the term nuclear medicine to describe the use of radiation in treatment and imaging nuclear medicine. Radiation therapy involves using targeted blasts of radiation to treat a range of health problems.

Radiation therapy uses special pharmaceuticals called radiopharmaceuticals.

These radiopharmaceuticals have atoms with unstable nuclei, meaning they can emit radiation.

In radiation therapy, doctors use these radioactive particles to treat many diseases, including:

Radiation in cancer therapy

Sometimes, radiation can help cancer patients who are not able to have surgery. Doctors can administer radiation therapy alongside surgery, or it can help people manage symptoms.

Radiation therapy works by damaging the DNA of the cancer cells so that they die and cannot reproduce. This can shrink tumors.

The healthcare professional carefully directs a beam of radiation at the area with malignant cancer cells. The goal is to ionize or damage the atoms that make up the DNA chain.

This kills cancer cells or slows down their growth.

Radiation therapy is painless, but the body might absorb radiation during the treatment.

This can cause side effects, which commonly include:

  • skin damage
  • hair loss
  • dryness of the salivary and sweat glands
  • swelling
  • fatigue
  • infertility
  • fibrosis
  • secondary cancers

What to expect from radiation therapy

An individual’s experience of radiation will depend on a number of factors, including the type and location of the cancer. Radiation treatment for esopheageal cancer, for example, can make eating difficult due to its effects on the food pipe.

Sit down with the treating doctor and look over all the options available.

Other types of radiation therapy involve swallowing a radioactive isotope as a liquid or a capsule, such as when treating thyroid cancer.

Alternatively, a doctor may inject radioactive isotopes into the spaces near the damaged body part. Radioactive iodine often plays a role in thyroid cancer treatment.

Researchers are looking into ways of improving radiation therapy. In particular, they are investigating more selective treatments that can specifically damage cancer cells while sparing healthy cells.


Can an X-ray harm me?


A single x-ray typically uses a very small amount of radiation to create an image of a part of your body.

Exposure to the x-ray itself is unlikely to have any short-term side effects, though if you have to ingest or inject a contrast for a scan, you might have a reaction to it. X-rays are generally safe for most people.

However, ask your doctor if you have any concerns about getting an X-ray.

People who are pregnant should also consult a doctor to find out what type of imaging test is best for them.

Yamini Ranchod, PhD, MS Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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