The assessment and management of risks associated with exposures to short-range Auger- and beta-emitting radionuclides. State of the art and proposals for lines of research.

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.

[Secondary recurrent hepatitis in ventricular arrhythmia]. / Hépatite récurrente secondaire à une arythmie ventriculaire.

INTRODUCTION: A major episode of hepatic cytolysis, rapidly regressive and occasionally recurrent, evokes a bilary or toxic pathology. We report an exceptional case in which several episodes of cytolysis were secondary to a paroxystic cardiac rhythm disorder. OBSERVATION: A 44 year-old woman was hospitalized 3 times during 4 months for episodes of asthenia and rapidly regressive cytolysis. Lithiasic, viral, metabolic, autoimmune and toxic causes were eliminated. A cardiac rhythm disorder was revealed during the last two episodes and diagnosis was made of intermittent and asymptomatic ventricular tachycardia, secondary to arryhthmogenic right ventricular dysplasia, and was confirmed on the electrocardiogram, cardiac scan and magnetic resonance imaging. Treatment of the cardiac rhythm led to the absence of further relapse. COMMENTS: In our patient, the clinical and chronological imputability appeared highly probable. The responsibility of perturbed cardiac rhythm in the genesis of an ischemic hepatopathy is classical, but little documented. Our observation confirms that severe unexplained cytolysis requires systematic search for a cardiac rhythm disorder, even in the absence of a known or symptomatic cardiopathy.

[From knowledge about risk to the regulation of exposures to ionizing radiation]. / De la connaissance des risques à la réglementation des expositions aux rayonnements ionisants.

Implementation of radiological protection principles has been introduced in French law in several ordinances during the last thirty years. They take in consideration: protection of the workers, including dose limitation, radiological quality control, individual dosimetry practices and features of medical survey; protection of the members of the public, including dose limitation, authorized levels of radioactive effluents from nuclear plants and reference levels for radioactive sources in the environment. Patients exposure is considered through several administrative recommendations taken from European Directive 84/466 from EURATOM. Future generations are not considered explicitely, up to now. Following a reappraisal of risk assessment by different scientific bodies new recommendations and new operational concepts have been provided by International Commission of Radiological Protection. They were directly transposed in European Directives. Implementation of European Directives 96/29 and 97/43 in national law will modify greatly the general architecture of French nuclear legislation which has been built up layer after layer without taking its roots in the bases of administrative, penal and civil laws.

[Carotid dissection. Study of 28 cases. Contribution of Doppler exploration, ultrasonic diagnosis and Doppler color echography]. / Les dissections carotidiennes. Etude de 28 cas. Apports de l'exploration Doppler, de l'echotomographie et de l'écho-Doppler couleur.

Carotid dissections often go undetected or are confused with an arteriosclerotic cause; in fact, they rarely require surgical treatment. Twenty-eight extracranial carotid dissections (in 25 patients) without direct cervical traumatism were explored successively by pulsed and duplex Doppler ultrasonography complemented in 10 cases by color Doppler flow imaging and secondarily in all cases by arteriography. Pulsed Doppler (DMS Angiodop 481 with 4 and 8 MHz probes) found severe hemodynamic signs in 93% of cases: 6 occlusions, 11 generally extensive or high tight stenoses and 9 significant slowdowns in carotid and ophthalmic artery circulation. For the same internal carotid artery, duplex Doppler (Ultramark 4 or Sonedap 40 with 5, 7.5 and 10 MHz probes) initially showed 5 occlusions and 2 stenoses (4 with fusiform features), 2 double canal images, 8 internal carotid arteries with tubular features (internal caliber less than or equal to 2 mm) and 2 segmental ectasias. There were only 3 other lesions with arteriosclerotic features, 2 of which were minor. Duplex imaging was thus suggestive in 57% of cases. Color Doppler flow imaging enabled precise visualization of these features, better analysis of occlusions and clear detection of 2 other false canal images. After 2 years of follow-up, Doppler ultrasound showed recanalization in 47% of cases with no anticoagulant complications. These combined ultrasonic explorations would thus appear to be useful for early diagnosis of carotid dissections, for guiding arteriography and for facilitating the monitoring of patients under anticoagulant.