Benefits and Risks of Ionizing Radiation

The effect of ionizing radiation on our bodies differs according to its type and energy. Scientists have known for more than 80 years that large doses of ionizing radiation can damage human tissues. As more was learned, experts became increasingly concerned about the potentially damaging effects that exposure to large doses of radiation can cause. As a result of the need to regulate exposure to radiation, a number of bodies were formed such as the International Commission on Radiological Protection (ICRP)1 and the UN Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)2, to consider what should be done.

A consistent approach to radiation protection has been taken internationally since 1928 by the International Commission on Radiological Protection (ICRP). Today the ICRP recommends that any exposure above the natural background radiation should be kept as low as reasonably achievable and below the individual dose limits. The individual dose limit for members of the general public is 1 mSv per year. These dose limits are based on a cautious approach by assuming that any level of exposure can have a negative effect. This means that there is an increase in risk of a health effect proportionate to any additional dose.

At What Level Is Radiation Harmful?

Fig. 1: Chart comparing typical effective doses of medical examinations with the average natural background radiation.

Fig. 1: Chart comparing typical effective doses of medical examinations with the average natural background radiation.

As mentioned previously, the unit of measurement used for the biological effect of radiation on the human body is the millisievert (mSv). The average global exposure to natural radiation is 2.4 mSv per year. We know that very large doses of over 5,000 mSv, received by the entire body over a short time, result in death within a few days. We know, however, that some of the effects of exposure to radiation do not appear unless a certain large dose has been absorbed. Doses over 100 mSv can have a harmful effect on humans, such as a higher incidence of developing cancer.

At even lower doses of radiation, below 100 mSv, there is a lot of uncertainty about the overall effects. What we do know is that the risk of adverse effects in this dose range is very low. To be on the safe side, we assume that there is a risk even in this low dose range and this risk is proportional to the dose by the same amount as in the high dose ranges.

Risks of Ionizing Radiation from X-rays

Statistically, everyone has a one in three chance of developing cancer at some point in their life.3 In order to put the risk of cell damage caused by radiation exposure in medical imaging into some perspective, the UK Health Protection Agency (HPA)4 has calculated that:

  • an X-ray of your chest, teeth, arms or feet is the equivalent to a few days’ worth of background radiation and has a less than one in a million chance of causing cancer,
  • an X-ray of your skull or neck is the equivalent to a few weeks’ worth of background radiation and has 1 in 100,000 to 1,000,000 chance of causing cancer,
  •  an X-ray of your breasts (mammogram), hip, spine, abdomen or pelvis is the equivalent of a few months’ to a year’s worth of background radiation and has a 1 in 10,000 to 100,000 chance of causing cancer, and
  • an X-ray that uses a contrast fluid, such as a barium meal, is the equivalent of a few years’ worth of background radiation and has a 1 in 1,000 to 10,000 chance of causing cancer.

X-rays and Pregnancy

While the level of radiation used in X-rays is not thought to be a risk to an unborn baby during pregnancy, X-rays are not usually recommended as a precaution, unless there is a clear clinical need. Sometimes, an alternative method that does not involve radiation, such as an ultrasound scan, may be recommended instead.

1. (Last visited: Jul 27, 2011)
2. (Last visited: Jul 27, 2011)
3. Sasieni PD, Shelton J, Ormiston-Smith N, Thomson CS, Silcocks PB What is the lifetime risk of developing cancer?: The effect of adjusting for multiple primaries. Br J Cancer, 2011. 105(3): p. 460-5
4. (Last visited: Jul 27, 2011)

Last updated: Mar 1, 2012

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