What is radiation?

Electromagnetic radiation is a type of energy that can move through empty space. Types of radiation include light, radio waves, ultra-violet and x-rays.

The type of radiation depends on the "wavelength". The longer the wave length, the less energy it carries. Radio waves have long wavelengths and low energies, and pass through us all the time without any noticeable effect. Gamma rays have very short wavelengths and high energies, and are a different matter.

What is ionising radiation?

High energy electromagnetic radiation is called "ionising radiation". X-rays are a form of ionising radiation.

Ionising radiation has many benefits, including medical imaging and sterilisation of food and medical equipment.

But ionising radiation can potentially cause harm as it can break molecules, causing damage to organisms depending on the type of radiation, the organ involved, and the intensity and duration of exposure.

How is radiation dose measured?

The different measuring systems are complex, but the usual standard is the "millisievert" or mSv, which is a measure of absorbed radiation in the body.

What are the effects of ionising radiation?

There are effects where the injury increases in severity with increasing dose. There is a threshold of several thousand mSv for these effects to occur, meaning that very high doses of radiation are needed to cause an effect, but that below a certain value, no effect occurs. Radiation burns are an example.

There are other effects where the injury is random and independent of the dose received. It is assumed there is no threshold, and the potential for causing damage is difficult to quantify. Tumours, leukaemia and genetic effects are examples. As there is no threshold, the dose of radiation should be reduced to a value as low as possible.

How do I get exposed to ionising radiation?

Unfortunately, just by living. There is "natural" or "background" radiation all around us for all our lives.

• It comes from below us because of the decay of elements like uranium and thorium.
• It comes from around us due to radon gas, which is in the atmosphere and collects in buildings.
• It comes from above us in the form of cosmic radiation.

How much radiation am I exposed to?

Typical values (in mSv) for exposure are:

• Natural background: 0.5–2.5
• Aircraft crew additional annual exposure: 2
• Astronaut in space for one month: 15
• Recommended annual occupational limit: 20
• Chest x-ray (NHMRC survey for Australian x-ray practices 1985): 0.01–15.5
• Chest x-ray (Mater Imaging): <0.01
• Mammography (NHMRC 1985): 4
• Mammography (Mater Radiology): 1.3
• DXA (bone mineral density): 0.005
• Radiotherapy dose to treat prostate cancer: 60000–70000

So how safe is medical radiation?

There have been many studies on the effect of ionising radiation. The major source of data is from the result of the atomic bombing of Hiroshima and Nagasaki in 1945. Many people were irradiated with very high doses of ionising radiation. It has been assumed, but never proven, that there is a proportional effect of radiation for small doses. That is, if a lot of radiation causes damage to a high proportion of people, then a very small amount of radiation may cause damage to a small proportion of people. This argument assumes there is no "safe" threshold below which ionising radiation will not cause any ill effects. Medical diagnostic irradiation is relatively low dose as can be seen from the numbers above.

The BEIR (Biological Effects of Ionising Radiation) V Report 1990 "Health Effects of Exposure to Low Levels of Ionising Radiation", found that the potential to cause cancer "was observed at relatively high doses and usually at high dose rates". The report also found that "... genetic risks were not of great importance in considering the safety of medical radiation exposures. This committee believes that adequate control of the carcinogenic hazard will adequately handle the risk of genetic damage ... x-rays and other medical treatments involving radiation clearly remain appropriate when benefits outweigh the risks."

How does Mater Imaging reduce any risk?

It is important to keep the radiation dose as low as is possible. In practice this is called ALARA (as low as reasonably achievable). This is a fundamental principle of Mater Imaging.

You should also be aware that it is in our own interest to reduce radiation, as all the doctors and staff may be exposed to part of the radiation that each person gets, by a process called "scatter".

Mater Imaging has spent a great deal of time and money in obtaining the most modern equipment. Outdated x-ray equipment is dangerous, as doses to patients are higher. Modern materials and breakthrough technologies such as those employed in the Toshiba Aquilion CT scanner ensure the radiation dose you receive is as low as reasonably achievable, while still obtaining the highest quality images.

All our equipment is regularly and routinely serviced. Checks are made of the radiation each machine generates, and tests performed to make sure there are no radiation leaks.

All radiographers are trained to perform as few x-ray exposures as possible to achieve optimum imaging.

What about radiation and pregnancy?

"... radiation exposure of the lower abdomen and pelvis of women of reproductive capacity should be kept to a minimum and during pregnancy, radiation exposure to these regions should only occur if the radiological examination cannot be postponed because of the urgent nature of the investigation.

"In such cases, greater than usual care should be taken to minimise the number of views and to minimise the absorbed dose per view. However, these alterations of technique should not be done to the undue detriment of the diagnostic value of the examination."
Recommendations for Minimising Radiological Hazards to Patients
– National Health and Medical Research Council, 1985

"The International Commission on Radiological Protection recommendations for inadvertent exposure to radionuclides from diagnostic testing states that, based on relative risk increment, foetal radiation exposure from a diagnostic procedure rarely justifies termination of a pregnancy. This principle can be extended to diagnostic x-ray examinations as well.

"There is a relatively high prevalence of congenital defects in humans (approximately 5%); therefore, it is impossible to ascertain scientifically whether any given exposure will produce a congenital birth defect. There is even conjecture by some that genetic mutations from irradiation do not occur in humans or at least are not detectable from the dose ranges used in diagnostic studies".

See: Smart, R.C. "What are the risks of diagnostic medical radiation?"
Medical Journal of Australia Volume 166, 2 June 1997