Search

International audience; Purpose The use of small photon fields is now an established practice in stereotactic radiosurgery and radiotherapy. However, due to a lack of lateral electron equilibrium and high dose gradients, it is difficult to accurately measure the dosimetric quantities required for the commissioning of such systems. Moreover, there is still no metrological dosimetric reference for this kind of beam today. In this context, the first objective of this work was to determine and to compare small fields output factors (OF) measured with different types of active detectors and passive dosimeters for three types of facilities a CyberKnife® system, a dedicated medical linear accelerator (Novalis) equipped with m3 microMLC and circular cones, and an adaptive medical linear accelerator (Clinac 2100) equipped with an additional m3 microMLC. The second one was to determine the kQclin,Q msrfclin,fmsr correction factors introduced in a recently proposed small field dosimetry formalism for different active detectors. Methods Small field sizes were defined either by microMLC down to 6 × 6 mm2 or by circular cones down to 4 mm in diameter. OF measurements were performed with several commercially available active detectors dedicated to measurements in small fields (high resolution diodes IBA SFD, Sun Nuclear EDGE, PTW 60016, PTW 60017; ionizing chambers PTW 31014 PinPoint chamber, PTW 31018 microLion liquid chamber, and PTW 60003 natural diamond). Two types of passive dosimeters were used LiF microcubes and EBT2 radiochromic films. Results Significant differences between the results obtained by several dosimetric systems were observed, particularly for the smallest field size for which the difference in the measured OF reaches more than 20%. For passive dosimeters, an excellent agreement was observed (better than 2%) between EBT2 and LiF microcubes for all OF measurements. Moreover, it has been shown that these passive dosimeters do not require correction factors and can then be used as reference dosimeters. Correction factors for the active detectors have then been determined from the mean experimental OF measured by the passive dosimeters. Conclusions Four sets of correction factors needed to apply the new small field dosimetry formalism are provided for several active detectors. A protocol for small photon beams OF determination based on passive dosimeters measurements has been recently proposed to French radiotherapy treatment centers. © 2013 American Association of Physicists in Medicine.

The medical staff performing interventional cardiology and radiology (IC/IR) procedures stand close to the patient and thus close to the primary radiation beam. Although they wear a lead apron and thyroid collar, their hands, legs and eyes are not protected. Therefore, these parts could receive significantly high doses. Moreover, thedose ranges for the same kind of procedures vary a lot, as many factors affect extremity and eye lens doses. Additionally, there is evidence that eye lens doses can be high in IR/IC, and cases of cataract have been reported in recent years. A lack of an appropriate eye lens dosemeter as well as an appropriate calibration procedure has been identified. Medical staff in IR/IC could benefit from the use of active personal dosemeters (APDs) as optimisation tool. However, a lack of appropriate APDs is identified for typical fields in IR and IC. Very few devices can detect low energy fields, and none of them are really designed for working in pulsed radiation fields. In the field of nuclear medicine (NM) the extremity doses to the technologists are also known to be very high. One can highlight the difficulties in estimating the dose distribution across the hands, and the need for greater knowledge of doses received during the main tasks of a nuclear medicine department, especially using unsealed sources. The ORAMED project, (www.oramed-fp7.eu) was set up to optimize the working procedures in these medical fields with respect to radiation protection. ORAMED wasstructured in 5 work packages: - Extremity and eye lens dosimetry in IR and IC - Development of practical eye lens dosimetry - Optimization of the use of APDs in IR and IC - Extremity dosimetry in NM - Training and dissemination A coordinated measurement program in European hospitals was organised both in IR/IC and NM departments. Moreover, simulations of the most representative workplaces/procedures were performed to determine the main parameters that influence the extremity and eye lens doses. Some dedicated studies on improving the eye lens dosimetry and active personal dosimetry were conducted. Based on the measurement and simulation results, a series of practical guidelines and training packages were developed. The influence of the different radiation protection measures (like shields)in IR/IChave been quantified, and clear monitoring requirements have been formulated for a series of medical procedures. A formalism for the use of the operational quantity for eye lens dose measurements have been worked out (calibration phantom, conversion coefficients, type test procedures, ...). A dedicated eye lens dosemeter has been developed that can be used in routine monitoring. The different existing APDs have been tested in fields that are representative for hospital fields (like pulsed fields), and a series of guidelines for the use of these APDs in hospitals have been made. Also, an improved APD device specifically for IR/IC fields has been developed.The extensive measurement and simulation campaign for extremity doses in NM lead to a systematic evaluation of the different radiation protection measures. These are condensed in a series of practical guidelines to be used. The dose distribution across the hands of the technologists was characterised, and recommendations for routine monitoring have been formulated. The outcome of the ORAMED project will improve the radiation protection standards for medical staff. The systematic measurements and simulations are the new standards that will be used for many years to come. The practical guidelines that have been developed can be used in the hospitals by the medical staff. In particular, the developments on the eye-lens dosimetry and the active personal dosemeters will result in an improvement of the practical measurement capabilities in the field.

The work package 3 of the ORAMED project, Collaborative Project (2008-11) supported by the European Commission within its seventh Framework Programme, is focused on the optimisation of the use of active personal dosemeters (APDs) in interventional radiology and cardiology (IR/IC). Indeed, a lack of appropriate APD devices is identified for these specific fields. Few devices can detect low-energy X rays (20-100 keV), and none of them are specifically designed for working in pulsed radiation fields. The work presented in this paper consists in studying the behaviour of some selected APDs deemed suitable for application in IR/IC. For this purpose, measurements under laboratory conditions, both with continuous and pulsed X-ray beams, and tests in real conditions on site in different European hospitals were performed. This study highlights the limitations of APDs for this application and the need of improving the APD technology so as to fulfil all needs in the IR/IC field.

In 2000, abnormally high ray fluxes have been detected on some beaches of Camargue. Then, sands of these beaches have been studied from a radiological point of view, showing on the one hand mean levels of uranium-238 and thorium-232 activity about some tens of Bq kg-1, and on the other hand some hot spots with more of 1000 Bq kg-1; and even more on two beaches: one to the east of the Beauduc lighthouse, the other to the east of Espiguette lighthouse. This radioactivity, of natural origin, is responsible of exposure of the public frequenting these two secluded beaches, but nevertheless open to everybody. The Institute for radiological protection and nuclear safety has carried out a dose assessment for people likely to frequent these beaches, taking into account local measurements and samples, in establishing the solubility of sands in the gastric and intestinal fluids, and with assumptions for site frequentation (scenarios). The maximal annual effective dose is about 0.8 mSv for adults and about 0.5 mSv for children; very wise values, in which external exposure widely predominates. © 2008 EDP Sciences.; En 2000, des flux de rayonnement anormalement élevés ont été détectés sur certaines plages du littoral camarguais. Les sables du littoral camarguais ont alors fait l’objet d’une caractérisation radiologique montrant des activités moyennes de quelques dizaines de Bq kg-1 en uranium-238 et thorium-232 d’une part, et l’existence de points chauds à plus de 1000 Bq kg-1 d’autre part ; voire plus sur deux plages : l’une située à l’Est du phare de Beauduc, l’autre située à l’Est du phare de l’Espiguette. Cette radioactivité, d’origine naturelle, est responsable de l’exposition des personnes fréquentant ces deux dernières plages relativement isolées, mais néanmoins accessibles à tout public. L’Institut de radioprotection et de sûreté nucléaire a réalisé une évaluation des doses susceptibles d’être reçues par des personnes fréquentant ces deux dernières plages, en se basant sur des mesures et des prélèvements effectués in situ, en établissant expérimentalement la solubilité des sables dans les fluides gastrique et intestinal, et en formulant des hypothèses sur la fréquentation des lieux (scénarios). La dose annuelle maximale ainsi évaluée est de l’ordre de 0,8 mSv pour des adultes et 0,5 mSv pour les enfants ; valeurs vraisemblablement très prudentes dans lesquelles la dose par exposition externe prédomine largement.

Following a radiological accident caused by a gammagraphy source in Chile in December 2005 involving one victim, IRSN was contacted to perform the dosimetric reconstruction of the accident using numerical simulation. Tools developed in the laboratory, associating anthropomorphic mathematic or voxel phantoms with the Monte Carlo calculation code mcnpx, were used in order to determine the dose distribution on the left buttock and absorbed doses to critical organs. The dosimetric mapping show that the absorbed at the skin surface is very high (1900 Gy) but drops rapidly at deep. At a depth of 5 cm, it is 20 Gy. Calculations performed with a mathematical phantom indicate that average doses to the critical organs are relatively low. Moreover, possible bone marrow sites for puncture are identified. Based on the dosimetric mapping, an excision measuring 5 cm in depth by 10 cm in diameter was performed on the left buttock of the victim. © 2007 EDP Sciences.; À la suite d’un accident radiologique dû à une source de gammagraphie survenu au Chili en décembre 2005 et impliquant une victime, l’IRSN a été sollicité pour réaliser la reconstitution dosimétrique par calcul Monte Carlo. Des outils, développés au laboratoire, associant des fantômes anthropomorphes mathématiques et voxélisés au code de calcul Monte Carlo mcnpx ont été mis en œuvre afin de déterminer la distribution de dose au niveau de la fesse gauche de la victime et la dose aux organes critiques. La cartographie dosimétrique réalisée au niveau de la fesse gauche montre que la dose à la surface est importante (1900 Gy) et chute rapidement pour atteindre 20 Gy à 5 cm de profondeur. Les calculs réalisés avec un fantôme mathématique indiquent que les doses moyennes aux organes critiques sont faibles et permettent d’identifier de possibles sites de prélèvement de moelle osseuse. S’appuyant sur la cartographie dosimétrique, une exérèse de 5 cm de profondeur et de 10 cm de diamètre a été pratiquée au niveau de la fesse gauche de la victime.

Professional practices involving ionizing radiation are evolving and require an adequate individual monitoring of workers. Dosimetric techniques are also in constant development with, for example, new electronic personal dosimeters, particularly for neutrons, and a larger choice of available techniques (TLD, OSL, RPL) for passive dosimeters. The dosimetric workplace study is now mandatory. Among its objectives, it is aimed at to choosing passive and electronic techniques from the determination of the characteristics of the encountered radiation fields. The passive dosimeters distributed by the approved dosimetric services are satisfactory overall. Moreover, many different models, covering almost all needs, of electronic personal dosimeters are commercialised. To ensure the correct implementation of passive dosimetric techniques by the approved dosimetric services, it is important to organise intecomparisons. National and international intercomparisons are carried out regularly in order to account for new developments, evolution of practices and situations. © 2007 EDP Sciences.; Les activités utilisant des rayonnements ionisants évoluent et nécessitent une surveillance dosimétrique adaptée. Dans le même temps, les techniques dosimétriques ont également évolué offrant notamment un choix de dosimètres électroniques plus important en particulier pour les neutrons ainsi qu’une diversification des techniques utilisables (TLD, OSL, RPL) pour la dosimétrie passive de routine. L’étude de poste est devenue incontournable afin de déterminer la façon la plus réaliste les caractéristiques de l’exposition dont résulte, entre autres, le choix des techniques passives et opérationnelles. Les différents dosimètres passifs aujourd’hui proposés par les laboratoires agréés présentent des performances globalement satisfaisantes. Par ailleurs, il existe sur le marché de multiples modèles de dosimètres électroniques susceptibles de couvrir les besoins associés à la dosimétrie opérationnelle. L’organisation d’intercomparaisons constitue un élément important du dispositif de contrôle de la bonne mise en œuvre des techniques de dosimétrie passive par les laboratoires agréés et des performances des dosimètres actifs dans des conditions réalistes d’utilisation. De telles intercomparaisons sont réalisées périodiquement, tant à un niveau national qu’international, afin de prendre en compte les évolutions des matériels, des pratiques et du plus grand nombre de situations possibles.