What Is Radiation?

Editor's Choice
Main Category: Radiology / Nuclear Medicine
Also Included In: MRI / PET / Ultrasound;  Cancer / Oncology;  Medical Devices / Diagnostics
Article Date: 16 Jul 2009 - 10:00 PDT

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In general, radiation is a process where energy emitted by one body travels in a straight line through a medium or through space. Radiation comes from the sun, nuclear reactors, microwave ovens, radio antennas, X-ray machines, and power lines, to name a few.

Radiation can be classified as either ionizing or non-ionizing. Non-ionizing radiation is lower energy radiation that comes from the lower part of the electromagnetic spectrum. It is called non-ionizing because it does not have enough energy to completely remove an electron from an atom or molecule. Examples include visible light, infrared light, microwave radiation, radio waves, and longwave (low frequency) radiation.

Ionizing radiation has enough energy to detach electrons from atoms or molecules - the process of ionization. It comes from both subatomic particles and the shorter wavelength portion of the electromagnetic spectrum. Examples include ultraviolet, X-rays, and gamma rays from the electromagnetic spectrum and subatomic particles such as alpha particles, beta particles, and neutrons. Subatomic particles are usually emitted as an atom decays and loses protons, neutrons, electrons, or their antiparticles.

How is radiation measured?

Measuring radiation is complex and utilizes several different units. Scientists measure the amount of radiation being emitted in the conventional unit called the curie (Ci) or the SI unit called the becquerel (Bq). These units express the number of disintegrations (or breakdowns in the nucleus of an element) per second as the element tries to reach a stable or nonradioactive state. One Bq is equal to one disintegration per second and one Ci is equal to 37 billion Bq.

When measuring the amount of radiation that a person is exposed to or the amount of energy absorbed by the body's tissues, two units are used: the conventional Roentgen (or radiated) absorbed dose (rad) and the SI gray (Gy). One Gy is equal to 100 rad.

If a scientist is measuring a person's biological risk of suffering health effects of radiation, the units of measurement are the conventional Roentgen equivalent man (rem) or the SI sievert (Sv). One Sv is equal to 100 rem.

Scientists suggest that a form of vitamin D could be one of our body's main protections against damage from low levels of radiation.

To put some of these values into perspective, consider the following examples:

• Light radiation sickness tends to begin at about 50-100 rad (or 0.5-1 Gy, 0.5-1 Sv, 50-100 rem, 50,000-100,000 mrem).


• Exposure to cosmic rays during a roundtrip airplane flight from New York to Los Angeles results in 3 mrem (1 millirem = 1/1000th of a rem) or 0.03 mSv of absorbed radiation.


• One dental X-ray is 4 - 15 mrem or 0.04 - 0.15 mSv, one chest X-rays 10 mrem 0.1 mSv, and one mammogram is 70 mrem or 0.7 mSv.


• One year of exposure to natural radiation (from soil, cosmic rays, etc.) is about 300 mrem or 3 mSv.

The risk of developing cancer among radiation workers increases with the dose of ionising radiation they are exposed to, a British study found. The same study also reported that overall mortality in the UK's 175,000 radiation workers is lower than that in the general population

How is radiation used in medical imaging?

There is a branch of medicine called radiology that focuses on diagnosing and treating diseases using imaging technologies based on radiation. Common imaging techniques include:

• Projectional Radiography - X-ray radiation is directed through part of the body, which absorbs some of the radiation. Hard tissue such as bone absorbs more than soft tissue such as muscle. The X-rays that are not absorbed pass through the body and expose photographic film on the other side of the body, creating a shadow effect. Different X-ray strengths are employed depending on the part of the body that is being studied. Common projections include a chest X-ray, breast X-ray (mammography), dental X-ray (dental radiograph), and abdominal X-ray.


• Fluoroscopy (angiography, gastrointestinal fluoroscopy) - These are X-rays that use a contrast (usually iodine- or barium-based) in order to provide moving projections or images of movement inside the body. Angiography is used to view the cardiovascular system and gastrointestinal fluoroscopy is used to view the gastrointestinal tract.


• Computed Tomography (CT) - a CT scan uses X-rays and computers to create images that show slices of soft and hard tissues. Contrast agents are often used during CT scans, and the result is a 3D reconstruction of the part of the body being imaged. Widespread screening for the buildup of calcium in the arteries using computed tomography scans would lead to an estimated 42 additional radiation-induced cancer cases per 100,000 men and 62 cases per 100,000 women, a study revealed.


• Ultrasound - Ultrasound uses high-frequency sound waves to see soft tissues inside the body. Since the test uses sound waves, no ionizing or potentially damaging radiation is absorbed by the body. Ultrasounds can show images in real time, but they cannot be used to image bones, lungs, bowel loops, or other air-filled body parts.


• Magnetic Resonance Imaging (MRI) - An MRI uses strong magnetic fields and a radio signal to take high quality 3D images of the body. Although an MRI requires a patient to lie very still in a noisy tube for a long period of time, the scan provided excellent visualizations of soft tissue. MRIs do not use any damaging ionizing radiation, only strong magnetic fields and non-ionizing radio frequencies.


• Dual energy X-ray absorptiometry (DEXA or bone densitometry) - Commonly used to test for osteoporosis, DEXA scans use two narrow X-ray beams to collect information on the density of the bone. No images of the bone are created, and so this scan is not considered projectional radiography.


• Positron Emission Tomography (PET) - A PET scan is a nuclear medicine imaging technique that uses a radioactive contrast agent that is injected into the body. This tracer eventually begins to radioactively decay and emits positron particles that are picked up by the PET scanner. A computer is used to reconstruct 3D images.

How is radiation used in medical treatment?

Many of the radiological imaging techniques described above are used during diagnosis and treatment. For example, ultrasounds and X-rays may be used to guide biopsy procedures, and ultrasounds are used to break up kidney stones, making them easier to pass. The branch of medicine that focuses on the use of radiation for treatment (and imaging) is called nuclear medicine. Nuclear medicine uses special pharmaceuticals called radiopharmaceuticals that have as a component radionuclides - atoms with an unstable nucleus. Radiotherapy is the practice of using these radioactive particles for the treatment of diseases.

Radiotherapy uses ionizing radiation to treat diseases such as cancer, coronary artery disease, trigeminal neuralgia, severe thyroid eye disease, and pterygium and to prepare the body for bone marrow transplants.

Sometimes radiation can effectively help cancer patients who are not eligible for surgery. A system called stereotactic body radiation therapy may be effective in treating early-stage lung cancer, scientists from the University of Kentucky's Markey Cancer Center found.

When a cure is not possible, radiotherapy or radiation treatment may be used for palliative care, or the management of symptoms.

In treating many types of cancer, radiation therapy aims to damage the DNA of the cancer cells so that they will commit suicide. A beam of radiation (photon, electron, proton, neutron, or ion, but usually gamma rays from the Cobalt-60 isotope) is carefully directed towards the malignant cancer cells with the goal of ionizing or damaging the atoms that make up the DNA chain. This kills the cancer cells and/or slows down their growth. Radiation treatments can result in the absorption of several sieverts (Sv). Although radiotherapy is a painless procedure, it carries side effects as the body absorbs this ionizing radiation.

Common side effects include skin damage, swelling, infertility, fibrosis, hair loss, fatigue, cancer (radiation both causes and cures cancer), and dryness of the salivary and sweat glands. The Society of Nuclear Medicine reports that the benefits of medical imaging far outweigh the radiation risks.

Other types of radiation tThe reatment involve swallowing a radioactive isotope as a liquid or a capsule (Iodine-131 for thyroid cancer) or injecting radioactive isotopes into the spaces near the damaged body part.

Written by Peter Crosta M.A.
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today

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