Radiation has always been here. It is a form of energy traveling through space. We have been exposed to radiation from natural sources since the dawn of time. The sources include the sun, the air we breathe, the food we eat, the natural elements in the earth, the solar system on the whole and even the natural radioactive elements in our bodies. All these contribute to the natural background radiation we receive every moment of our life. Natural background radiation contributes about 88% of the annual dose to the population and medical procedures most of the remaining 12%.

Sunshine is one of the most familiar forms of radiation. Sunshine consists of radiation in a range of wavelengths from long-wave infrared to the shorter wavelength ultraviolet. The spectrum of the whole range of radiation energy is shown below.

X-rays and gamma rays are used widely in radiological procedures. These have greater penetrating power than sunlight and can pass through the human body. Thick barriers of concrete or lead are used as protection from them.

Radiation can also come from the atoms. Most atoms are stable, for example, an oxygen-16 atom remains an oxygen-16 atom forever; but certain atoms eventually decay into a totally new atom. These atoms are said to be unstable or radioactive. A radioactive atom gives off some of its excess energy as radiation in the form of gamma rays, alpha particles or beta particles.

Higher energy radiation on the left of the spectrum (gamma rays, X-rays, and ultraviolet) is called ionising radiation as it causes ionisation. Ionisation removes electrons from atoms or molecules, forming ions or charged atoms or molecules. The ions formed then go on to react with other atoms or molecules, causing damage. Ionising radiation has the ability to affect molecules of living cells and cause changes, which are biologically important. An example of this would be if a gammy 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 everyday from natural background radiation, the cells repair the damage rapidly. At higher doses (not encountered during a diagnostic radiological procedure), the cells might not be able to repair the damage, and they may either be changed permanently or die. Cells that are changed permanently may go on to produce abnormal cells when they divide and these cells may become cancerous. This is how cancer due to excessive radiation exposure begins.

Typical levels of patient doses from common X-ray examinations, expressed in terms of the equivalent number of Chest X-rays and also the equivalent period of natural background radiation are summarised above. The table should not be taken seriously since they vary considerably from one radiology department to another. Of course, large patients will need more radiation than small patients.

For X-ray examinations we only receive less than one year of natural background radiation (which is unavoidable). We must balance the risks with the benefits. It is something we do often. We accept the risks of driving for the benefit of getting to somewhere. We want to eat fattening food; therefore we will have to accept the risks of developing heart disease. Many things potentially of great benefit to humanity have associated risks when used. Radiation falls into this category. Research has shown that if is a very small risk (much smaller than the many risks we take everyday) compared to the tremendous benefits of improved diagnosis leading to a better quality of life.

Another point to keep in mind is that some radiological procedures, such as magnetic resonance imaging (MRI) and ultrasound, do not even use ionising radiation. Magnetic field and ultrasound energy used by these procedures have not been shown to cause significant health hazards.

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Last Updated:
Thursday, 21 August, 2003