Radiation accidents: lessons learnt for future radiological protection.

PURPOSE: To review major radiation accidents that have occurred over a 50 year period. To identify common factors, since feedback may prevent recurrence. METHODS: Accidents are classified according to the difficulties involved in their management and to the delay between their occurrence and their recognition. RESULTS: The rate of severe accidents increases with time, especially those involving the public, and accidents are not always immediately recognized. The real number of serious unrecognized accidents is unknown. Human factors, such as lack of elementary safety rules and inadequate training, play a major role in most of the accidents occurring in industry and in the medical field. CONCLUSIONS: Common sense could have prevented many severe accidents that resulted in deaths and serious injuries. Delay in the identification of accidents results in severe consequences. Pre-planning is essential and may minimize the severity and the deterioration of the situation. Research efforts in the field of medical handling of severely radiation-injured victims should be maintained.

[Therapeutic approaches of hematopoietic syndrome following accidental total whole body irradiation]. / Approches thérapeutiques du syndrome hématopoïétique après irradiation globale accidentelle grave.

Since the first radiation accidents which resulted in severe health effects in the workforce or the population, great progress has been made in the fields of diagnosis, prognosis and treatment of accidentally overexposed victims. Since then, progress has also been made in the medical management of diseases such as aplasia. Because of the relative scarcity of radiation accidents, there is a need for complementary researches, in order to take advantage of new techniques and medical approaches. After whole body overexposure, the key issue is the therapeutic decision, ie, the choice between bone marrow transplantation and other strategies. The indications of bone marrow transplantation cover only a short range of doses, provided the exposure is distributed uniformly within the body. The last accidental overexposures which happened in the world have demonstrated the possible efficiency of haematopoietic growth factors, most of them being still under clinical trials. Actions based on these various approaches are summarized, as well as the lessons which have been learned.

Haematopoietic growth factors in the treatment of therapeutic and accidental irradiation-induced bone marrow aplasia.

Bone marrow aplasia is one of the main syndromes following a high dose accidental exposure of ionizing radiation. Although both transfusion and bone marrow transplantation have been used with some success since the first treatments of patients, other therapeutic strategies are needed. The strategies involving haematopoietic growth factors for the treatment of radiation victims have been explored in vivo mainly in animal models and it is hoped that new therapeutic regimens will be elucidated from such approaches. The growth factors stimulate proliferation and/or differentiation of haematopoietic progenitor cells and possible stem cells. Furthermore, they act on the functions of mature cells. They now have specific uses in haematology, related to their role in the regulation of growth and differentiation of haematopoietic progenitor cells. The results of the clinical trials, performed with numerous patients and often randomized bring important clues about what to expect from growth factor therapy. Other factors are only entering the preclinical or clinical trials now. Although numerous in vitro or in vivo experiments suggest a benefit from their effects, their possible uses in therapy are still questionable. Some growth factors have already been used for the treatment of accidental radiation-induced aplasia and lessons have been learned from their medical management and follow-up.

Overview of the radiological accidents in the world, updated December 1989.

Radiological accidents can be divided into two categories, depending on whether the accident involves large groups of the population with relatively low doses or a few individuals with high doses resulting in acute health effects. The accidents involving large groups are related to the dispersion of radioactive materials in the environment; although they may have different causes, the source is always very important. Most of the accidents which have occurred originated in civilian installations; two reactor accidents can be considered without any human consequences: the accidents in the UK (Windscale) in 1957 and in the USA (TMI) in 1979. The Chernobyl accident (USSR) in 1986 resulted in extensive contamination of the environment, with non-negligible doses to the population around the plant and large collective doses in the northern hemisphere; in addition, the Chernobyl accident caused the deaths of 31 workers and firemen who intervened to bring the installation back under control. Violations of the most elementary safety rules for the operation of medical sources were at the origin of two severe environmental contaminations with human consequences: in Mexico (1983-4) and Brazil (1987), with sources of 60Co and 137Cs, respectively. The accidents concerning only a few individuals are not always known with the same documented accuracy. Between the 1940s and 1960s six critical accidents caused eight deaths; since then only one has occurred, in Argentina in 1983. The fatal radiation accidents are due to high-energy radiation sources, such as 60Co, 137Cs, and 192Ir. The total number of deaths which has been registered is 28. The accidents related to internal exposure are not exceptional, but result very rarely in health consequences.

Medical and surgical management for localized radiation injuries.

Whereas the pathological effects of radiation to the skin are well known, it is often difficult to assess quickly and with accuracy the level of severity, because of the delay between exposure and appearance of the lesions and because of the hidden lesions in underlying tissues. The severity depends mainly on the nature of the radiation, high-energy penetrating radiation causing much more irreversible damage than low-energy lightly penetrating radiation. Therefore, besides the clinical observation, diagnosis and prognosis should be based on many various parameters such as dosimetry, reconstruction of the accident, thermography, scintigraphy, etc. Pain is the first difficult problem to solve. It starts quickly, is constant at all stages and rapidly dominates the clinical picture. It raises the problem of the use of toxic drugs, with the risk of addiction. Medical treatment deals with inflammation, moist desquamation and ulceration. The major problem is the risk of infection. Surgical treatment deals with deep ulceration and necrosis; the requirement varies, according to the nature and energy of the radiation, the localization of the injury and its severity. The two main methods are excision and grafting; the most favourable time for intervention is difficult to specify, and should be neither too early before the establishment of the clinical picture nor too late. The combination of radiation burns with an acute radiation syndrome raises many questions, many of which are not completely solved.

Bases biomedicales de l'intervention en cas d'accident grave

Les principes de la protection de public en cas dïaccident sont bien définis. Lïétablissement des niveaux de référence, relatifs a chaquemesure de protection, quel que soit le systeme de référence choisi, nécessite la meilleure connaissance possible des effets qui risquent dïapparaitre dans la population susceptible dïetre exposée. Les effects non stochastiques concernent des organes ou tissus bien déterminés: moelle osseuse, poumon, thyroide, peau ainsi que le foetus dans le cas dïexposition de femmes enceintes. Les formes de relations doseeffet concernant la plupart de ces organes sont en général suffisamment connues ainsi que les seuils auxquel les effets apparaissent. Cependant, lïincertitude sur les doses-seuils, les doses responsables de 50

et de 100

des effets, est, dans certains cas, du meme ordre de grandeur que lïintervalle DL0-DL100. Ces différences rendent dificile un pronostic quantifié des chances de survie dïune population éventuellement exposée dans la gamme de doses proposées pour la DL 50/60. En fait, les données nécessaires pour une prise de décision correcte nïont sans doute pas besoin dïetre affinées ni de recouvrir lïensemble des connaissances concernant la pathologie dïun organe ou dïun systeme. Il faut avant tout connaitre les niveaux de dose au-dessous desquels, dans une population normale, la probabilité dïapparition dïeffets non stochastiques est partiquement nulle. Cïest sur la base de ces doses-seuils que les autorités décideront du choix des niveaux de référence pour la mise en oeuvre de mesures de protection. (AU)

[The relationship between radiation doses and their effects]. / Relations entre les doses de rayonnements et leurs effets.

Dose-effect relationships have been developed both for the biological effects studied by Radiobiology and the long-term pathological effects (malignant diseases) studied by Radiation Protection. The former approach chiefly considers the primary biological injuries at the cellular level, and the relationship between the dependent variable characteristic of the effect and the dose--an independent variable--has an explanatory meaning. The parameters associated to the independent variable have a biophysical signification and fit into a model of the action of ionizing radiations. In the latter approach, the relationship is pragmatic and the previous parameters are just the result of a curve-fitting procedure realized on experimental or human data. The biophysical models have led to a general formulation associating a linear term to a quadratic term both of them weighted by an exponential term describing cellular killing at the highest doses. To a certain extent the curves obtained for leukemias, bronchopulmonary and breast cancers prove the validity of the pragmatic model.

[Radiations and public health (author's transl)]. / Rayonnements et santé publique

A short review is made of the general characteristics of electromagnetic and corpuscular radiations to which man can be exposed. Following some considerations on the action of ionizing radiations and the radiobiological factors governing their effects on health, the overall characteristics of pathological effects differentiating stochastic from non-stochastic effects are summarized. The uncertainties remaining as to low-level exposures are stated as well as the cautious assumptions usually madein this field. The various sources of exposure to which the population is submitted are considered, i.e. exposures from natural, medical, domestic, industrial sources or from fallout from nuclear weapon tests; the present or predictable levels of exposure and their variations are given for each source. But for medical irradiation, all the exposures connected to human activities are much lower than natural exposure variations; such exposures should modify the incidence of certain affections but quite insignificantly as compared with the regional or local variations observed.

Metabolic and dosimetric studies after inhalation of 227Th in rats with regard to the risk of lung and bone tumors.

227Th (alpha-emitter, half-life 18.7 days) was inhaled by rats from solution in nitrate form. Organ doses were calculated after whole body measurements and measuring of activity concentrations in the organs over a longer incorporation period. An initial deposition of 100 nCi 227Th in the lung resulted in mean total doses of 150 rad in lung and 36 rad in bone. The data for kidney and liver were 2 rad and 0.1 rad, respectively. For long-term experiments two dosages were applied to two groups of animals with mean values of 900 rad and 300 rad in the lung. The consequences for lung and bone tumor induction are discussed.