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Facts about Radiation

X-rays: Are they harmful?
There is a lot of unjustified fear and alarm about radiation from medical procedures. These notes should put the subject into perspective.

What is radiation dose?
We see images on an x-ray film because your body absorbs some of the x-ray beam, producing shadows. "Dose" is the amount of energy absorbed from radiation, adjusted for the particular area of the body. It is measured in Sieverts (Sv) or milliSieverts (mSv).

What does it do?
X-rays can trigger chemical reactions. We use this property to make an image on a film, or to destroy tumours in the body. Such reactions can also harm healthy tissue, so we are careful to ensure that the benefit of medical x-rays outweighs any harm that they might do.

Background dose: is energy that we absorb from cosmic rays, and radioactive elements in the earth's crust, the atmosphere, and our food. The average dose is about 2.6mSv per year in the UK, more in Scotland and the West, less in South and East England. Over 99% of background radiation is natural.

What is the risk associated with radiation dose?
Background radiation has been fairly constant during the evolution of life, so our bodies naturally repair damage caused by small doses. There is no evidence of any health risk associated with normal background doses in the UK. We know (mostly from studying industrial accidents and radiotherapy treatments) that a sudden dose of 1000mSv can overwhelm our capacity for repair, so we keep medical doses to the minimum needed for accurate diagnosis and treatment.

What dose will I receive from an x-ray examination?
This table shows some useful comparisons with exposure to natural background radiation.

Note that these figures are based on the UK population average, and most people live in the south-east of England, where the natural background is lowest.
A dose of 6mSv would be equivalent to living in Cornwall or the Scottish Highlands for a year - not a prospect that would worry a Londoner!


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