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According to the IRSN, medical exposure accounts for more than one third of the average annual exposure of an individual. More than 90% of this is due to radiological acts. According to the decree of 6 December 2011 on training and missions of the medical physicist, one of the main missions of medical physicists is “the estimation of the dose to the patient during diagnostic procedures”. This is part of an approach to optimize the doses delivered. The purpose of this presentation is to define the different methods of measurement and calculation of dose in three domains: conventional radiology, interventional radiology and CT. In each area, the various available dosimetric indicators are presented as well as their interests in practice. Estimates of the dose by analytical methods (accessible to physicists) are compared with those carried out by the measurement (according to the detectors most widely used in practice). In conventional radiology and in CT, the principles and practical interests of the various software for the calculation of the effective dose and organ doses are presented. In interventional radiology, the principles and practical interests of the different software for evaluating the maximum dose to the skin are also presented and compared with Gafchromic film.

Introduction Interventional radiology is constantly evolving. During these last years, acts performed under radiological guidance have significantly increased. However, doses delivered to patients may be significant and result in deterministic effects. Therefore, it is necessary to set up tools for monitoring the dose to the patient's skin. Materials and methods Interventional Reference Levels (IRL) peculiar to the department are generated by applying 75th percentile method. They allow creating warning thresholds in real time. At the same time as the use of the indicators, Nanodot® pastilles marketed by the company Landauer are used. These dosimeters with deferred reading are based on OSL technology (Optically Stimulated Luminescence) and are analyzed on-site by reader Microstar®. Dose delivered to patients is determined a posteriori and then compared to the indicators estimated by the local IRL. Results A retrospective collection of dosimetric quantities (DAP in cGy cm2 and DLP in mGy cm) has been performed for different types of practiced examinations. This review allowed determining local reference levels such they already exist in conventional radiology. They are intended to alert and warn operators when exceeding a threshold during an examination. OSL calibration for 0,010 to 10 Gy dose range is currently in process and will allow the putting in clinical routine of the in vivo dosimetry for acts of interventional radiology the most irradiant. Conclusion The complementarity of these dosimetric assessments will allow us to ensure dosimetric patients monitoring. We hope to obtain a better control on doses delivered by taking greater account of the radiation risk. Patients who will receive a significant dose (dose in the skin superior to 3 Gy) will be informed by the radiologist. They will receive information relative to the surveillance of the exposed zone and the involved risks as well as specific medical care if necessary.

Objectives Concerning Diagnostic reference levels (DRLs), IRSN's task is to analyse the data transmitted by the professionals of medical imaging, in order to update: the list of the relevant examinations, the dosimetric quantities and the numerical reference values. So, the collected data is representative of the national practices concerning the most common or radiation exposing examinations, taking into account technological developments and clinical practice. Materials and methods On the basis of the data collected between 2004 and 2008, the regulation was updated in 2011 (Decree of 24/ 10/2011). In 2009 and 2010 the dosimetric data analysis allows IRSN to strengthen and sometimes to complete the previous results, as well as to measure the evolution of: the regulation implementation, the clinical practices and the technologies implemented in conventional radiology, CT, and nuclear medicine. Results The DRL data transmission rate is heterogeneous and depends on the considered field of activity. With 67% of services having transmitted dosimetric evaluation in 2010, against 40% for CT and 20% for conventional radiology, nuclear medicine is the most assiduous. Nevertheless the annual periodicity is not followed by all services, regardless of the field of activity. For some exams, notable and recurring dosimetric differences between clinical practice and DRL are highlighted. On the other hand, it appears necessary that the DRL take into account new technologies affecting the delivered dose to the patient (CT of the PET-CT, iterative reconstruction in diagnostic CT) as well as the most radiation exposing procedures (diagnostic interventional radiology). Conclusions Following the analysis of data transmitted in 2009 and 2010, in addition to the update of the numerical values of the DRL for some examinations, the IRSN recommends to extend the scope of the NRD to the CT part of PET-CT examinations, even SPECT, and diagnostic interventional radiology. The reasons why, for certain exams, the average value is significantly higher than the DRL, with significant dispersion around this value, should also be investigated.