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Hot topic - X-rays and cancer risk from radiation30 January 2004 - written by Bupa's Health Information Team A study into the risk of developing cancer from exposure to medical X-ray tests has estimated that 0.6% of all cancers diagnosed in the UK are due to medical X-rays. According to the researchers, this would account for roughly 700 of the 124,000 new cases of cancer in the UK each year. The work has been published in the 31 January 2004 issue of The Lancet medical journal. However, medical X-rays bring substantial benefits to health and the benefits usually outweigh any small risks associated with their use. In fact, X-rays are often used to diagnose life-threatening diseases and bring about large gains in health, quality of life and lifespan. Below Bupa explores how X-rays work, what they are used for, the risks associated with their use and how we can minimise our risk of exposure to X-ray radiation. What are X-rays?X-rays are a form of electromagnetic radiation, just like light waves and radiowaves. Because X-rays have higher energy than light waves, they can pass through the body. Just like other forms of high-energy radiation, X-rays can cause damage to cells in the body, which in turn can increase the risk of developing cancer. This increase in risk associated with each X-ray procedure is extremely low but does slowly increase with the increasing number of X-rays tests you have. This is the same principle as the way in which increased exposure to the sun increases skin cancer risk. How do X-ray tests work?Because of their high energy, X-rays can pass through the body. But the amount of X-rays that make it through to the other side is determined by the density of the tissues and bones in the body. Dense material such as tumours and bone absorb more X-rays. By using X-ray sensitive photographic film, pictures of the body can be taken. The photographic film is turned from white to black by X-rays, so the more X-rays that are absorbed by an area of the body, the whiter that area will appear. This is why bones appear white on X-ray photographs. What are X-rays used for?Normal X-ray testsSimple X-ray pictures - where a single snapshot is taken - are ideal for spotting major physical changes in the body. For example, a black line (representing a lack of material) within the white area of a bone clearly shows that the bone is broken or fractured. In the same way, a white area in the black area of the lungs show that material such as fluid or a tumour is present. However, X-ray techniques have been refined and there are now a number of other ways in which X-rays can be used to discover more sophisticated things about our bodies. FluoroscopyIn this technique, an X-ray dye is used to show the outline of a structure that the doctor is interested in. The dye is a material that absorbs X-rays and will appear as black on the X-ray screen. For example, when the workings of your gut need to be investigated you will be asked to drink a liquid "barium meal" - the barium absorbs the X-rays and shows up as black on the screen. By passing X-rays through the stomach and recording the X-ray images in real time on a TV screen, the passage of the meal through the stomach can be recorded. A similar technique is used when investigating whether or not an artery is blocked. This time the dye is injected into the bloodstream and its flow through the artery is then recorded on the TV screen. Computed tomography (CT) scanThis is a sophisticated use of X-rays. A large machine is used to take small X-ray picture slices of the body. These picture slices are then combined together using a computer to create 3-D images of the organs and bones in the body. This technique can give a very detailed view of the internal structures of the body. What is the risk of developing cancer from having X-ray tests?In the research published in The Lancet medical journal, the authors calculated that radiation from medical X-ray tests contributed approximately 14% of the annual exposure to radiation. The rest of a person's radiation exposure comes from other man-made sources and from the natural enviroment (known as background radiation). The researchers calculated that the additional radiation exposure (from medical X-ray tests) would increase a UK person's cumulative risk of developing cancer by the age of 75 by 0.6%. This is equivalent to around 700 of the 124,000 new cases of cancer diagnosed in the UK every year. Can we avoid being exposed to radiation?Perhaps surprisingly, radiation is a natural part of our environment. None of us can avoid being exposed to radiation. We are exposed to it all the time, everywhere we go. This naturally occuring radiation is known as "background radiation". In the UK, the majority of the background radiation we absorb comes from radon gas (roughly 58 per cent), which seeps out of the ground. Another 16 per cent comes directly from rocks in the ground, while 14 per cent streams down on us from cosmic rays and the final 12 per cent comes from the food we eat. To put the risks of radiation from X-rays into perspective: a four-hour airline flight will expose you to the same amount of radiation (from cosmic rays) as from a simple chest X-ray. This is the same as the amount of radiation we would be exposed to naturally (from background radiation) over 10 days. These days high-quality X-ray pictures can be produced from very small doses of radiation. This helps to minimise the risk of developing cancer as much as possible. Is the amount of radiation we receive from an X-ray test always the same?The amount of radiation we absorb from an X-ray test depends on two things: the type of X-ray test being performed and the area of the body being viewed. The area of the bodyDifferent tissues and organs have varying sensitivity to radiation exposure. This means that different doses of radiation are used depending on the area of the body being viewed. The type of X-ray testSince a simple X-ray is involves taking a single, brief snapshot of an organ or area of the body, the radiation dose is very low. Fluoroscopy involves passing X-rays through an area of the body over a period of time to allow the flow of a dye to be followed. Because of this the radiation dose is larger and depends on the length of time the dye is followed for. CT scanning involves the taking of many picture slices of the body using X-rays. Again the dose of radiation is dependent on the amount of slices that are taken. Another consideration is that newer CT machines don't need to take so many slices to obtain the same information. What is the radiation exposure for different X-ray procedures?
What are the benefits of having X-rays? Do they outweigh the radiation risks?All three forms of medical X-ray tests have brought about great advances in the diagnosis and treatments of a range of conditions. For example, the health benefit of diagnosing and fixing a broken arm far outweighs the few extra day's worth of radiation that the simple X-ray picture requires. In the UK, doctors and radiographers make every effort to ensure that the least amount of X-ray tests are taken and radiographers ensure that these are taken at the lowest X-ray dose possible. In all instances doctors will weigh up the benefits against any possible risks before asking for an X-ray test to be taken. If having a test is necessary to determine the best course of treatment then the risk to your health of not having the X-ray test is likely to be much higher than any possible radiation exposure. It is also worth noting that when CT and fluoroscopy tests (which involve higher doses of radiation) are needed, they are being used to diagnose more serious conditions which pose a far higher risk to health than the risk from the test's radiation. How can we minimise our risk from X-rays?
For more information on X-ray procedures in general and the risk of developing cancer from X-ray tests, please use the links below. Links for more information
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