12FICHE BACKGROUND Dosimetry: individual measurements and methods of evaluating the received dose Determining the received dose on the basis of the clinical examination and/or the methods presented in this sheet is essential for evaluating the consequences of cases of exposure to ionising radiation and for determining the action to take with respect to the exposed persons. Irradiation SHEET Reading dosimeters In the event of an irradiation accident involving a person who is habitually monitored for the risk of exposure to ionising radiation, the received dose can be rapidly evaluated by reading the dose displayed on the active dosimeter or by sending the passive personal dosimeter by urgent delivery to the dosimetry agency for immediate reading. Biological dosimetry Biological dosimetry is indicated for persons who might have received doses exceeding 0.1 Gy. The analyses must be carried out as soon as possible. Two analyses are essential: the Complete Blood Count (CBC) and the search for chromosomal aberrations. People likely to have received the highest level of radiation (proximity to the site of the event and clinical signs) are analysed in priority. COMPLETE BLOOD COUNT Lymphocytes figure among the most radiosensitive cells With a subject suspected of having received a significant level of radiation, performing a blood count as early as possible is therefore very important. The downward trend in the number of lymphocytes is directly proportional to the received dose: the level of irradiation is determined according to the dosage carried out as early as possible after the accident, then again at 24 hours and 48 hours SEE SHEET 15 SEARCH FOR CHROMOSOMAL ABERRATIONS The search for chromosomal aberrations is the most sensitive biological dosimetry examination and the most specific for irradiation. It provides an accurate retrospective estimate of the received dose as from 0.1 Gy. • Taking a sample in the first hours enables a rapid estimate of the dose to be obtained when necessary, particularly if there is any doubt about the interpretation of the CBC. It takes a minimum of 72 hours to obtain the result. • In the other cases, the sample can be taken later, because there is no technical urgency for performing this analysis: The reliability of the examination remains the same whether the sampling is done on the same day or several weeks after exposure. SEE SHEET 15 OTHER EXAMINATIONS The prescribing of other examinations must be discussed according to the type and severity of the accident, seeking the expertise of the Institute of Radiation Protection and Nuclear Safety (IRSN) if necessary. Possible examinations: HLA I and II typing, phenotyping of the red blood cells, measurement of amylase level, level of follicle stimulating hormone (FSH) in plasma, measurement of phosphorous-32 in the skin appendages or sodium-24 by whole-body radiation measurement or in the blood. The characteristics and indications are described in SHEET 15 BACKGROUND MEDICAL RESPONSE IN NUCLEAR OR RADIOLOGICAL EMERGENCY 43
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