Development of a triage monitoring programme for the intake of radionuclides at CERN

Professionals working with unsealed radioactive sources and/or in the presence of contaminated materials are at risk of incorporation of radionuclides. In 2018, this risk has increased for some workers at the European Organization for Nuclear Research (CERN) with the commissioning of the CERN-MEDICIS facility. This facility produces novel radioisotopes to be used in medical research. The workers of the facility handle high activities of these short-lived and exotic radionuclides for which internal monitoring strategies are not yet defined by international standards and guidelines. This results in the need to review the internal monitoring programme at CERN. The purpose of this PhD project was to develop an in vivo internal monitoring programme for the CERN workers that is inspired by the Swiss radiation protection regulation and that aims to ensure the detection of intakes leading to an annual committed effective dose E50 > 1 mSv. The Swiss internal monitoring approach consists in rapid and simple screening measurements that aim to assess whether an intake requiring further evaluation has taken place. If a radionuclide-specific threshold is exceeded during a screening measurement, the worker must then undergo an incorporation measurement to quantify the incorporated activity and thus the E50. The first part of the project aimed to determine if and how the Swiss approach could be adapted to perform in vivo screening measurements of CERN workers. A procedure was elaborated to help the local Radiation Protection Officers (RPO) determine whether conventional radiation protection instruments would be suitable to perform screening measurements. Seven instruments widely used at CERN were characterised according to this procedure. The results were used to elaborate screening measurement protocols for some radionuclides of interest by taking into account CERN specific constraints. In the second part of the project, the existing procedure was extended to two portable gamma spectrometers that, as opposed to conventional radiation protection instruments, allow to identify the incorporated radionuclides. The feasibility of the monitoring with these portable spectrometers was determined for a selection of 21 exotic and conventional radionuclides. Finally, the influence of the measuring geometry on the minimum detectable activity associated to an in vivo measurement was numerically investigated with the help of Monte Carlo simulations. This was done by adopting a graded approach and considering four different phantoms: a simplified and easily reproducible torso phantom, a commercial anthropomorphic whole body phantom and two numerical phantoms (male and female). This work demonstrates that the Swiss internal monitoring approach can be successfully adapted to CERN requirements. The methodology developed during this project paved the way to the setting up of the new internal monitoring programme for the CERN workers, which can be adapted to other research centres, industries and hospitals where exotic radionuclides may be handled. -- Les professionnels travaillant avec des sources radioactives non scellées et/ou en présence de matériel contaminé courent le risque d’incorporer des substances radioactives. Ce risque a significativement augmenté en 2018 pour certains travailleurs de l’Organisation Européenne pour la Recherche Nucléaire (CERN), avec la mise en service de l’installation CERN-MEDICIS. Cette installation produit des radioisotopes exotiques (i.e. non conventionnels) à des fins de recherche médicale. Les travailleurs manipulent de hautes activités de ces radionucléides, pour lesquels des approches de surveillance de la contamination interne ne sont pas encore définies par des normes et directives internationales. Une mise à jour du programme de surveillance de la contamination interne du CERN est donc nécessaire. Le but de ce projet de doctorat était de développer un programme pour la surveillance de la contamination interne pour les travailleurs du CERN par des mesures in vivo. Ce programme s’inspire de la règlementation suisse en matière de radioprotection et vise à assurer la détection de toute incorporation pouvant mener à une dose efficace engagée E50 > 1 mSv/an. En Suisse, la surveillance de l’incorporation se base sur des mesures de tri simples et rapides, dont le résultat détermine si des analyses supplémentaires sont nécessaires. Si un seuil spécifique à chaque radionucléide est dépassé lors de la mesure de tri, le travailleur doit se soumettre à une mesure d’incorporation, qui permettra de quantifier l’activité incorporée et ainsi la valeur de E50. La première partie de ce projet visait à déterminer si et comment l’approche suisse pouvait être adaptée pour effectuer des mesures de tri in vivo pour les travailleurs du CERN. Une procédure a été élaborée afin de permettre aux experts de radioprotection locaux de déterminer quels instruments de radioprotection étaient adaptés pour effectuer ces mesures de tri. Sept instruments communément utilisés au CERN ont été caractérisés en suivant cette procédure. Les résultats de l’étude ont été utilisés pour établir des propositions de mesures de tri selon les exigences des experts locaux, en tenant compte des contraintes particulières du CERN. Dans la deuxième partie de ce projet, la procédure existante a été étendue à deux spectromètres gamma portables qui, contrairement aux instruments de radioprotection conventionnels, permettent l’identification des radionucléides potentiellement incorporés. La faisabilité d’une surveillance à l’aide de ces spectromètres portables a été étudiée pour une sélection de 21 radionucléides exotiques et conventionnels. Pour finir, l’impact de la géométrie de mesure dans l’évaluation de l’activité minimale détectable lors d’une mesure in vivo a été investigué à l’aide de simulations Monte Carlo. Pour ce faire, quatre fantômes différents ont été considérés en adoptant une approche graduée: un fantôme simplifié et facilement reproductible représentant un tronc humain, un fantôme anthropomorphe disponible sur le marché et deux fantômes numériques (homme et femme). Ce travail démontre que l’approche suisse pour la surveillance de la contamination interne peut être efficacement adaptée aux exigences du CERN. La méthodologie développée pendant ce projet pose les bases de l’établissement du nouveau programme de surveillance pour les travailleurs du CERN. Ce programme peut également être adapté aux besoins d’autres centres de recherche, industries et hôpitaux où des radionucléides exotiques pourraient être manipulés. -- Les professionnels travaillant avec des sources radioactives et/ou avec des objets contaminés par de la radioactivité courent le risque d’incorporer des substances radioactives. Par exemple, si un travailleur doit percer un tel objet dans le cadre d’un travail de maintenance, il pourrait inhaler des poussières radioactives s’il n’utilise pas de masque de protection adéquat. Lorsqu’une substance radioactive est incorporée à l’intérieur du corps, on parle de contamination interne. Les programmes de surveillance de la contamination interne visent à vérifier que les travailleurs soient efficacement protégés contre le risque d’incorporation et que cette protection respecte certaines exigences légales (limites à ne pas dépasser). Pour réaliser ces programmes de surveillance individuelle, on effectue des mesures directement sur les travailleurs avec des appareils de mesure de radiations. Les mesures permettent de détecter la présence d’une contamination interne, de déterminer la quantité de radiations re¸cues par le travailleur et, quand c’est possible, d’agir afin de réduire leurs effets nocifs. Il existe deux types de mesure qui dépendent de la nature du rayonnement émis par la source incorporée: (1) mesures in vivo, qui détectent directement les radiations qui sortent du corps ou (2) mesures in vitro, qui se basent sur des analyses d’échantillons biologiques du travailleur, tels que l’urine ou les selles. Le risque de contamination interne pour certains travailleurs de l’Organisation Européenne pour la Recherche Nucléaire (CERN) a significativement augmenté en 2018, avec la mise en service de l’installation CERN-MEDICIS. Cette installation vise à produire de nouvelles substances radioactives pour le diagnostic et la thérapie en médecine. Les programmes de surveillance de la contamination interne des travailleurs qui manipulent ces sources ne sont pas encore définis. Le but de ce projet de doctorat était donc de développer un programme de surveillance de la contamination interne pour ces travailleurs. Ce programme se base sur des mesures in vivo et vise à déterminer si et comment l’approche de surveillance en vigueur en Suisse peut être adaptée pour effectuer la surveillance interne des travailleurs au CERN. Les instruments les plus adaptés pour effectuer ces mesures ont été identifiés. Puis, différents instruments communément utilisés au CERN ont été testés face à des sources simulant la géométrie du corps du travailleur. Ces résultats ont été utilisés pour établir des protocoles de mesure pour les nouvelles substances produites au CERN. Ce travail démontre que l’approche suisse pour la surveillance de la contamination interne peut être efficacement adaptée aux exigences du CERN. La méthodologie développée pendant ce projet peut également être utilisée dans d’autres centres de recherche, industries et hôpitaux où des nouvelles substances radioactives pourraient être manipulées. -- Il personale che svolge la sua attività in contatto con delle sorgenti radioattive e/o con del materiale contaminato corre il rischio di incorporare delle sostanze radioattive. Ad esempio, un’incorporazione di polveri radioattive pùo avere luogo eseguendo la foratura di un materiale contaminato in assenza di una protezione respiratoria adeguata. Il termine “contaminazione interna” si riferisce alla presenza anormale di una sostanza radioattiva all’interno del corpo. Un programma di sorveglianza della contaminazione interna mira a verificare che i lavoratori siano protetti in modo efficace contro il rischio di un’incorporazione e che questa protezione rispetti determinate esigenze legali (quali i limiti di esposizione del personale). I programmi di sorveglianza individuali consistono in misure effettuate sul personale stesso. Queste misure permettono di rilevare la presenza di una contaminazione interna, di calcolare la quantità di radiazioni ricevute e, quando possibile, di contrastare i loro effetti nocivi. Due tipologie di misure possono essere effettuate a seconda della radiazione emessa dalla sostanza incorporata: (1) delle misure in vivo che hanno quale scopo quello di rilevare le radiazioni emesse all’esterno del corpo o (2) delle misure in vitro, che consistono in analisi di laboratorio su campioni biologici, quali l’urina o le feci. Il rischio di contaminazione interna per i lavoratori dell’Organizzazione Europea per la Ricerca Nucleare (CERN) è aumentato in modo significativo nel 2018, in seguito all’inaugurazione dell’installazione CERN-MEDICIS. Lo scopo di questa infrastruttura è quello di produrre delle sostanze radioattive innovative (non convenzionali) che trovano la loro applicazione nel campo della medicina nucleare. Per queste sostanze, dei programmi di sorveglianza della contaminazione interna non sono attualmente definiti. Lo scopo di questo progetto di tesi era quello di sviluppare un programma per la sorveglianza della contaminazione interna per questi lavoratori. Il programma si basa su misure in vivo e mira a stabilire se e come l’approccio svizzero per la sorveglianza della contaminazione pùo essere adattato per effettuare delle misure di sorveglianza al CERN. Una procedura è stata elaborata al fine di identificare gli strumenti più adatti per effettuare le misure. Degli strumenti comunemente impiegati al CERN sono stati testati usando vari modelli che mirano a riprodurre il corpo umano. I risultati sono stati utilizzati per redigere dei protocolli di misura per le sostanze innovative prodotte al CERN. Questo studio dimostra che l’approccio per la sorveglianza della contaminazione interna attualmente in vigore in Svizzera pùo essere adattato con successo per soddisfare le esigenze del CERN. Il metodo sviluppato durante questo progetto pùo ugualmente essere applicato in altri centri di ricerca, industrie e ospedali dove ha luogo la manipolazione di sostanze radioattive non convenzionali

Use of portable gamma spectrometers for triage monitoring following the intake of conventional and novel radionuclides

Current internal dosimetry monitoring programmes generally feature periodic measurements that are defined for the most commonly-encountered radionuclides. These programmes are not directly applicable to research centres that produce novel and short-lived radionuclides which are then used for the manufacture of radiopharmaceuticals, such as the CERN-MEDICIS facility hosted at CERN. This work presents an in vivo internal dosimetry programme based on the concept of triage monitoring. The programme allows to comply with the annual committed effective dose limit of E50=1 mSv by performing rapid gamma-spectroscopy screening measurements. Two portable spectrometers (HPGe- and NaI-based) were characterised using two different phantoms: a simplified model of the human torso and an anthropomorphic phantom allowing for customised source-filling geometries. The efficiencies of the spectrometers were determined using both phantoms and the minimum detectable activities were computed as a function of the measuring time for a selection of 21 among novel and conventional radionuclides. The minimum detectable activity was then used to calculate the minimum committed effective dose associated to each measurement for a realistic intake scenario. For a single screening measurement of 30 s performed at the end of the working day, the minimum detectable committed effective dose resulting from a radionuclide inhalation ranged between few uSv and hundreds of uSv for the majority of the considered radionuclides. The suggested approach allows to set up pragmatic in vivo measurements to monitor the workers’ internal contamination in research centres and industries where unsealed conventional and/or novel radionuclides may be handled

Impact of the phantom geometry on the evaluation of the minimum detectable activity following a radionuclide intake: From physical to numerical phantoms

The establishment of an in vivo internal monitoring programme requires the use of phantoms to represent an activity distribution of an incorporated radionuclide within the body. The aim of this study was to quantify the impact of the phantom geometry on the minimum detectable activity (MDA) of an incorporated radionuclide. The MDA was assessed for two instruments: a conventional radiation protection instrument and a portable gamma spectrometer. Four phantoms were considered: two physical phantoms, a simplified torso phantom and a commercial whole body phantom, as well as two numerical phantoms, the reference adult male and female voxel phantoms published by the International Commission on Radiological Protection (ICRP). The phantoms were loaded with activity at the level of the thorax and abdomen using reference sources of Co-57, Ba-133, Cs-137, Co-60 and Eu-152. The MDA for both instruments was experimentally assessed using the two physical phantoms. The experimental setup was modelled in GEANT4 and the simulated instrument responses were validated by the experimental data. The Monte Carlo model was then used to compute the instruments response and corresponding MDA when using the ICRP voxel phantoms. The simplified torso phantom provided one of the highest MDA estimates, up to a factor of 5 higher than the ones obtained with the voxel phantoms when considering a Co-57 source. Depending on the considered source distribution within the phantoms, physical phantoms may lead to an underestimation of the MDA when compared to more complex and anatomically accurate numerical phantoms. This work presents a quantitative comparison between the MDA obtained with different phantoms and radionuclide distributions

Monte Carlo simulations of the whole-body counter at Spiez Laboratory Switzerland: Impact of phantom size and biokinetic model

Whole-body counters (WBC) are used to detect potential intake of radioisotopes in the human body. To achieve a precise measurement of an incorporated activity, a WBC needs to be properly characterized and calibrated. However, due to technical limitations, not every geometry can be calibrated using adequate physical phantoms. To extend the use of a standard calibration to other geometries, we performed GEANT4 Monte Carlo (MC) simulations characterizing the WBC at the Spiez Laboratory, Switzerland. The aim of our project was threefold: (1) to validate our MC model against an experimental model, (2) to study the impact of a person's size on the detection efficiency of the WBC and (3) to study the impact of intake scenarios on the estimation of whole-body activity. First, we simulated the calibration of the WBC with the IGOR phantoms. Then, we computed the detection efficiency of the WBC for homogenous whole-body contamination using ICRP adult voxel phantoms scaled to sizes. We computed the bias of the activity that would be measured by the WBC relative to the activity contained in the body in case of inhalation, modeled by the ICRP biokinetic models. Our computed detection efficiency obtained with the IGOR phantoms agreed within 5% with the calibration measurements. We found that WBC efficiency depends on the weight over height ratio (w/h). We proposed a criterion for the calibration curve selection adequate for any person, and we validated this criterion using ICRP pediatric phantoms. We estimated that the precision of a whole-body activity measurement in the case of a homogeneous activity distribution is at the level of 20%. Finally, for a non-homogenous contamination of the body by inhalation, we showed that the WBC measurements can overestimate intake up to 40–80% depending on the absorption type of the substance into the blood, and the size of the scanned person. In conclusion, our study confirms the need of using phantoms with different sizes to calibrate a WBC and shows that in case of a highly non-homogenous distribution of the radioisotope in the body, the WBC may significantly overestimate the whole-body activity. To limit this bias, we recommend scanning the entire body with the detectors instead of setting them at fixed positions or increasing the distance between the detectors and the phantom. •The whole-body counter (WBC) of the Labor Spiez was characterised with GEANT4 Monte Carlo simulations.•The WBC efficiency was computed using ICRP adult voxel phantoms scaled to sizes.•The WBC efficiency depends on the size of the measured persons quantified by the weight over height ratio.•For a non-homogenous contamination of the body by inhalation, the WBC can overestimate the intake by up to 40–80%