ASN Report 2018

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. 1.3.1  –  Radiosensitivity The effects of ionising radiation on personal health vary from one individual to the next. Since it was stated for the first time by Bergonié and Tribondeau in 1906, it is for example known that the same dose does not have the same effect when received by a growing child or by an adult. Furthermore, the variability in individual radiosensitivity to high doses of ionising radiation has been extensively documented by radiotherapists and radiobiologists. High levels of radiosensitivity have been observed in persons suffering from genetic diseases affecting the repair of DNA and cellular signalling; in these individuals they can lead to “radiological burns”. At low doses, there is both cell radiosensitivity and individual radiosensitivity, which could concern about 5 to 10% of the population. Thanks to the lowering of detection thresholds, recent methods of immunofluorescence of molecular targets for signalling and repairing DNA damage enable the effects of ionising radiation at low doses to be better documented. The biochemical and molecular effects of a simple X-ray examination then become visible and measurable. The results of the research work conducted using these new investigation methods must still be confirmed in the clinical environment before being integrated into medical practices. The monitoring of individual radiosensitivity in a medical treatment context through validated tests is not yet fully operational despite the progress of ongoing research. Several advances were made in 2018 concerning the variability of individual responses to ionising radiation: ∙ ∙ a growing number of publications on this subject, focusing as much on the clinical aspects in which this variability is seen, such as complications in radiotherapy due to increased radiosensitivity or the early appearance of cancers due to increased radiosensivity of the early appearance of cancers due to increased radiosusceptibility, as on the subjacent cellular and tissular mechanisms; ∙ ∙ the holding of an international seminar dedicated to the subject by the European research group MELODI in Malta in May 2018, the work of which is currently being published; ∙ ∙ the creation in October 2018 by the ICRP of a working group (TG111) dedicated to this subject with the aim of producing radiation protection recommendations based on acquired knowledge. The individual response to ionising radiation is thus gradually being recognised as an important subject of research and application in radiobiology and radiation protection. 1.3.2  –  Effects of low doses • The Linear No-Threshold (LNT) relationship The hypothesis of this relationship, adopted to model the effects of low doses on health (see point 1.2), albeit practical from the regulatory standpoint and albeit conservative from the health standpoint, is not as scientifically well-grounded as might be hoped for. Some feel that the effects of low doses could be higher, while others believe that these doses could have no effect below a certain threshold, and some others even assert that low doses have a beneficial effect. Research in molecular and cellular biology is progressing, as are epidemiological surveys of large cohorts. But faced with the complexity of the DNA repair and mutation phenomena, and the methodological limitations of epidemiology, uncertainties remain and the public authorities must exercise caution. • Dose, dose rate and duration of exposure The epidemiological studies performed on individuals exposed to the Hiroshima and Nagasaki bombings have given a clearer picture of the effects of radiation on health, concerning exposure due to external irradiation (external exposure) received in a few fractions of a second at high dose and high dose rate. The studies carried out in the countries most affected by the Chernobyl accident (Belorussia, Ukraine and Russia) were also able to improve our understanding of the effects of radiation on health caused by exposure through internal contamination (internal exposure), more specifically through radioactive iodine. Studies on nuclear workers have given a clearer picture of the risk associated with chronic exposures at low doses established over many years, whether as a result of external exposure or internal contamination. • Hereditary effects The appearance of possible hereditary effects from ionising radiation in humans remains uncertain. Such effects have not been observed among the survivors of the Hiroshima and Nagasaki bombings. However, hereditary effects have been documented in experimental work on animals: mutations induced by ionising radiation in embryonic germ cells can be transmitted to descendants. The recessive mutation of one gene on one chromosome will produce no clinical or biological indications as long as the same gene carried by the other counterpart chromosome is not affected. Although it cannot be absolutely ruled out, the probability of this type of event nonetheless remains low. • Environmental Protection The purpose of radiation protection is to prevent or mitigate the harmful effects of ionising radiation on individuals, directly or indirectly, including in situations of environmental contamination. Over and beyond environmental protection aiming at the protection of humans and present or future generations, the protection of non-human species as such forms part of the environmental protection prescribed in the French Pairs of chromosomes have characteristic bands of colouring (Inserm) ASN report on the state of nuclear safety and radiation protection in France in 2018  93 01 – NUCLEAR ACTIVITIES: IONISING RADIATION AND HEALTH AND ENVIRONMENTAL RISKS 01