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A knowledge resource for patients and caregivers
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.
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.
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:
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.