Ionising and non-ionising radiation

:: Ionising and non-ionising radiation

Ionising radiation at high doses causes cancer in humans: only a few cancer types have never been related to ionising radiation. This has been known for decades, and excellent summaries of the scientific literature are available. The International Agency for Research on Cancer (IARC) recently classified X-rays, g-rays and neutrons as carcinogenic to humans (Group 1). This is irrespective of the different patterns of energy release and penetrating power of the different types of ionising radiation. Energy at high levels may lead to cellular and DNA damage followed by cell killing, whereas at lower doses it may lead to mutations increasing the risk of cancer. The International Commission on Radiological Protection (ICRP) issues recommendations for radiological protection based on the existing scientific literature.

High-dose ionising radiation is used in medicine to treat cancer. These types of exposures are at present outside the scope of the European Code Against Cancer. However, much of our evidence on the effects of ionising radiation on humans is derived from such uses, and from the atomic bomb survivors at Hiroshima and Nagasaki. The main source of radiation to the human population comes from the natural background, both terrestrial and cosmic, whilst the man-made sources, such as atmospheric nuclear testing, nuclear accidents (e.g. Chernobyl) and nuclear power production, which cause the most public concern, cause only very little exposure (Table 9).

The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) estimates the population risk of dying from cancer after an acute dose of 1000 mSv is about 9% for men and 13% for women. The estimates could be reduced by 50% for chronic exposures. The worldwide average annual effective dose is 2.4 mSv. The lifetime exposure of the population to all sources of ionising radiation was estimated by the National Radiological Protection Board to account for 1% of all fatal cancers in the UK.( risk.htm – 22 November 2002). Only 1% of this risk is ascribed to the small doses from man-made radiation.

For the purpose of the European Code Against Cancer, this review concentrates on the possible effects of the natural background radiation, terrestrial (in the form of radon gas) and cosmic radiation, as it is possible to control exposure to both. Furthermore, we assess the cancer risk related to the Chernobyl accident and that among nuclear workers and people living near nuclear installations. Diagnostic radiation is of concern for the population groups undergoing examinations, be it screening of healthy individuals with mammography or computed tomography (CT) scans for lung cancer or when there is a suspicion of thyroid disease. Screening with low-dose CT for lung cancer is reported to give an effective dose of between 0.2 and 1 mSv. Using the risk factor of 5% per 1 Sv (ICRP 60), this would imply one to five radiation induced fatal cancers per 100.000 examinations. Mammography screening for breast cancer typically gives an absorbed average glandular dose of 3 mGy. It has been estimated in Sweden that among women aged 50–69 years, with a reduction in breast cancer mortality due to a mammographic screening programme of 25%, that 560 deaths from breast cancer would be avoided. It is estimated that the effect of the radiation would be to induce between 1 and 5 fatal breast cancers per 100.000 examinations. Although the collective dose from diagnostics to the population is small relative to natural radiation, benefit analyses should be performed to avoid unnecessary exposure.

Non-ionising radiation from sources such as power lines, electrical equipment, mobile phones and solar radiation raise public concern as to a possible carcinogenic effect. The ICNIRP (International Commission on Non-ionising Radiation Protection) issues guidelines for limiting exposure, and the German “Stralenschutzkommission” and the UK NRPB recently published reviews assessing the health risks. The evidence on power lines and mobile phones are dealt with in this section, whereas solar radiation is dealt with separately.