The Method validation step of biological dosimetry accreditation process

Titre du congrès :IRPA 2006 2nd European IRPA Congress on Radiation Protection Ville du congrès :Paris Date du congrès :15/05/2006

One of the missions of the Laboratory of Biological Dosimetry (LDB) of the Institute for Radiation and Nuclear Safety (IRSN) is to assess the radiological dose after an accidental overexposure suspicion to ionising radiation, by using radio-induced changes of some biological parameters. The "gold standard" is the yield of dicentrics observed in patient's lymphocytes, and this yield is converted in dose using dose effect relationships. This method is complementary to clinical and physical dosimetry, for medical team in charge of the patients. To obtain a formal recognition of its operational activity, the laboratory decided three years ago, to require an accreditation, by following the recommendations of both 17025 General Requirements for the Competence of Testing and Calibration Laboratories and 19238 Performance criteria for service laboratories performing biological dosimetry by cytogenetics. Diagnostics, risks analysis were realized to control the whole analysis process leading to documents writing. Purchases, personnel department, vocational trainings were also included in the quality system. Audits were very helpful to improve the quality system. One specificity of this technique is that it is not normalized therefore apart from quality management aspects, several technical points needed some validations. An inventory of potentially influent factors was carried out. To estimate their real effect on the yield of dicentrics, a Placket-Burman experimental design was conducted. The effect of seven parameters was tested: the BUdr, PHA and colcemid concentration, the culture duration, the incubator temperature, the blood volume and the medium volume. The chosen values were calculated according to the uncertainties on the way they were measured i.e. pipettes, thermometers, test tubes... None of the factors has a significant impact on the yield of dicentrics. Therefore the uncertainty linked to their use was considered as nil. The main difficulty of the quality program set up in the laboratory was to convince people working in the laboratory of the interest of such a project and to change their way of work. The laboratory is almost ready to request for accreditation. The establishment of quality system resulted in some practice changes that were positive for the laboratory and improved the results quality.