The internationally established public health objectives of radiation protection aim to prevent the appearance of deterministic effects and to reduce the probability of development of radiation-induced cancers; the results of the studies as a whole seem to indicate that radiation-induced cancers represent the predominant health risk associated with exposure to ionising radiation. 1.2 ASSESSMENT OF THE RISKS ASSOCIATED WITH IONISING RADIATION The monitoring of cancer epidemiology in France is based on disease registries, on the monitoring of causes of death and also, more recently, on the utilisation of data from the Medicalised Programme for Information Systems of healthcare facilities and the Long-Term Disease notifications. The registries are structures that provide “a continuous and exhaustive collection of nominative data concerning one or more health events in a geographically defined population, for purposes of research and public health, managed by a team with the appropriate skills”. Some are “general registers”, concerning all types of cancer and covering one département or more; others are “specialised registers”, focusing on a particular type of cancer. Their geographical perimeter can vary (town, département, region, or even nationwide). Of the three national registers, one concerns pleural mesothelioma, primarily in the context of exposure to asbestos fibres, while the other two cover all the cancerous pathologies in the child and adolescent up to 18 years of age (source: INCa). The aim of the register for a given area is to highlight differences in spatial distribution, to reveal changes over time in terms of increased or reduced rate of incidence in the different cancer locations, or to identify clusters of cases. Some registers, depending on the quality of their population database and their age, are used in numerous studies exploring cancer risk factors (including environmental risks). Epidemiological investigation is complementary to monitoring. Its purpose is to highlight an association between a risk factor and the occurrence of a disease, between a possible cause and an effect, or at least to enable such a causal relation to be asserted with a very high degree of probability. The intrinsic difficulty in conducting these surveys or in reaching a convincing conclusion when the illness is slow to appear or when the expected number of cases is low, which is the case with low exposure levels of a few tens of millisieverts (mSv) for example, must be borne in mind. Cohorts such as those of Hiroshima and Nagasaki have clearly shown an excess of cancers for an average exposure of about 200 mSv. Due to insufficient data on the impact of low doses on the occurrence of a cancer, estimates are provided by making linear no-threshold extrapolations of the observed effects described for high doses. These models give estimations of the risks run during exposure to low doses of ionising radiation, which nevertheless remain scientifically controversial. Studies are currently being conducted on very large populations to better characterise these risks. Recent epidemiological studies on nuclear industry workers(2) and on children and adolescents exposed to ionising radiation during computed tomography examinations(3) find an increase in the risk of cancer that is proportional to the dose received which remains significant, including when the studied interval is limited to low cumulative doses of less than 100 milligrays (mGy), thereby underpinning what until then was simply a hypothesis. 2. Source: Inworks study – IRSN, Information notice of 3 October 2023, irsn.fr. 3. Source: EPI CT study – IRSN, irsn.fr. 4. Radon is a natural radioactive gas, a progeny product of uranium and thorium, an emitter of alpha particles and has been classified as a known human pulmonary carcinogen by the International Agency for Research on Cancer (IARC) since 1987. These results consolidate knowledge on the impact of ionising radiation at low doses and confirm the importance of the principles of optimisation and justification for the radiological protection of exposed populations, whatever the cause of exposure (natural radiation, medical exposure, nuclear industry, etc.). On the basis of the scientific syntheses of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the International Commission on Radiological Protection (ICRP) has published the risk coefficients for death by cancer due to ionising radiation, i.e. 4.1% excess risk per sievert (Sv) for workers and 5.5% per sievert for the general public (see ICRP publication 103). The evaluation of the risk of lung cancer due to radon(4) is based on a large number of epidemiological studies conducted directly in the home, in France and internationally. These studies have shown a linear relationship, even at low exposure levels (200 becquerels per cubic metre – Bq/m3) over a period of twenty to thirty years. In 2009, the World Health Organisation (WHO) recommended a reference level of 100 Bq/m3, and whatever the case to remain below 300 Bq/m3. ICRP publication 115 compared the risks of lung cancer observed through studies on uranium miners with those observed in the overall population and concluded that there was a very good correlation between the risks observed in these two conditions of exposure to radon. The ICRP recommendations consolidate those issued by the WHO which considers that radon constitutes the second-highest risk factor in lung cancer, coming far behind tobacco. Furthermore, for given levels of exposure to radon, the risk of lung cancer is much higher in smokers: three quarters of the deaths by lung cancer that can be attributed to radon reportedly occur in smokers. In metropolitan France, about 12 million people spread over some 7,000 municipalities are potentially exposed to high radon concentrations. According to the French Public Health Agency (2018), an estimated 4,000 new cases of lung cancer are caused by radon in metropolitan France each year, far behind the number due to tobacco (the estimated number of new cases of lung cancer in Metropolitan France in 2018 was 46,000). A Radon National Action Plan has been implemented since 2004 on the initiative of ASN. It is updated periodically. The 4th plan (2020-2024) was published in early 2021 (see point 3.2.2). 1.3 SCIENTIFIC UNCERTAINTIES AND VIGILANCE The action taken in the fields of nuclear safety and radiation protection to prevent accidents and limit detrimental effects has led to a reduction in doses, whether, for example, in terms of the doses received by workers or those associated with discharges from BNIs. Many uncertainties persist; they induce ASN to remain attentive to the results of scientific work in progress in radiobiology and radiopathology for example, with possible consequences for radiation protection, particularly with regard to management of risks associated with low doses. One can mention, for example, several areas of uncertainty concerning radiosensitivity, the effects of low doses according to age, the existence of signatures (specific mutations of DNA) that could be observed in radiation-induced cancers and certain non-cancerous diseases observed after radiotherapy. ASN Report on the state of nuclear safety and radiation protection in France in 2023 101 • 01 • Nuclear activities: ionising radiation and health and environmental risks 01 05 15 08 11 04 14 06 07 13 AP 03 10 02 09 12
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