No abstract

Objectives To provide direct estimates of risk of cancer after protracted low doses of ionising radiation and to strengthen the scientific basis of radiation protection standards for environmental, occupational, and medical diagnostic exposures. Design Multinational retrospective cohort study of cancer mortality. Setting Cohorts of workers in the nuclear industry in 15 countries. Participants 407 391 workers individually monitored for external radiation with a total follow-up of 5.2 million person years. Main outcome measurements Estimates of excess relative risks per sievert (Sv) of radiation dose for mortality from cancers other than leukaemia and from leukaemia excluding chronic lymphocytic leukaemia, the main causes of death considered by radiation protection authorities. Results The excess relative risk for cancers other than leukaemia was 0.97 per Sv, 95% confidence interval 0.14 to 1.97. Analyses of causes of death related or unrelated to smoking indicate that, although confounding by smoking may be present, it is unlikely to explain all of this increased risk. The excess relative risk for leukaemia excluding chronic lymphocytic leukaemia was 1.93 per Sv ( < 0 to 8.47). On the basis of these estimates, 1-2% of deaths from cancer among workers in this cohort may be attributable to radiation. Conclusions These estimates, from the largest study of nuclear workers ever conducted, are higher than, but statistically compatible with, the risk estimates used for current radiation protection standards. The results suggest that there is a small excess risk of cancer, even at the low doses and dose rates typically received by nuclear workers in this study.

The mortality of nuclear workers from contracting companies is very low compared to French national mortality.

The assessment and management of risks associated with exposures to ionising radiation are defined by the general radiological protection system, proposed by the International Commission on Radiological Protection (ICRP). This system is regarded by a large majority of users as a robust system although there are a number of dissenting voices, claiming that it is not suitable for estimating the risks resulting from internal exposures. One of the specific issues of internal exposure involves short-range radiations such as Auger and beta particles. Auger- and beta-emitting radionuclides can be distributed preferentially in certain tissue structures and even in certain cellular organelles, according to their chemical nature and the vector with which they are associated. Given the limited range of the low-energy electrons in biological matter, this heterogeneous distribution can generate highly localised energy depositions and exacerbate radiotoxic responses at cellular level. These particularities in energy distribution and cellular responses are not taken into account by the conventional methods for the assessment of risk.Alternative systems have been proposed, based on dosimetry conducted at the cellular or even molecular level, whose purpose is to determine the energy deposition occurring within the DNA molecule. However, calculation of absorbed doses at the molecular level is not sufficient to ensure a better assessment of the risks incurred. Favouring such a microdosimetric approach for the risk assessments would require a comprehensive knowledge of the biological targets of radiation, the dose-response relationships at the various levels of organisation, and the mechanisms leading from cellular energy deposition to the appearance of a health detriment. The required knowledge is not fully available today and it is not yet possible to link an intracellular energy deposition to a probability of occurrence of health effects or to use methods based on cellular dosimetry directly.The imperfections of the alternative approaches proposed so far should not discourage efforts. Protection against exposure to Auger and low-energy beta emitters would benefit from mechanistic studies, dedicated to the study of energy depositions of the radionuclides in various cellular structures, but also from radiotoxicological studies to define the relative biological effectiveness of the various Auger emitters used in medicine and of certain low-energy beta emitters, whose behaviour may depend greatly on their chemical form during intake. The scientific expertise, as well as the human and physical resources needed to conduct these studies, is available. They could be now mobilised into international low-dose research programmes, in order to ultimately improve the protection of people exposed to these specific radionuclides.

Le concept de niveau de référence diagnostique (NRD) introduit dans la ClPR 73 < Protection et sûreté radiologique en médecine n est spécifique aux expositions médicales. Dans ce domaine, en effet, l'un des trois principes de la radioprotection, la limitation réglementaire des doses, ne peut s'appliquer comme pour les expositions professionnelles et publiques. Les niveaux de référence ne sont ni des << limites de dose », ni des < doses optimales », ce sont des outils pour l'optimisation. Ils sont établis pour des examens standardisés et des patients types, et ne devraient pas être dépassés sans justification, pour des procédures courantes. Les NRD sont des indicateurs dosimétriques de la qualité des pratiques destinés à identifier les situations nécessitant une action corrective. Dans le cadre de la transposition de la directive 97/43 Euratom, le directeur générai de la santé a confié à I'OPRI', en 1999, une mission spécifique pour la mise en oeuvre des niveaux de référence, en concertation avec les sociétés savantes et professionnelles concernées. La méthode recommandée par la Commission européenne, dite du 75e percentile, basée sur le traitement statistique d'enquêtes dosimétriques représentatives, est a l'heure actuelle inopérante en France en raison de l'insuffisance des données. Une démarche spécifique a donc été définie. Dans un premier temps, un travail de standardisation des procédures radiologiques avec adoption des niveaux de référence européens comme point de départ a été effectué. Dans un second temps, une campagne nationale de mesures de doses co-pilotée par I'OPRI (actuellement I'IRSN et la DGSNR)3, la SFR3 et la SFPM' est en cours de réalisation pour établir des NRD français. RÉSUMÉABSTRACT Diagnostic reference levels for diagnostic radiology : French implementation methods.ICRP publication 73 (Radiological Protection and Safeîy in Medicine) introduced the concept of "diagnostic reference levels" (DRL), for medical exposures specifcally. Because dose limits should not be applied for diagnostic or therapeutic irradiation, the approach to radiological protection is slightly different from that in occupational or public exposures.