Patient and staff dose in fluoroscopically-guided interventions: Exploring new optimisation strategies

Au cours des dernières décennies, la fluoroscopie est devenue une technique d'imagerie à rayons X diagnostique et thérapeutique largement utilisée pour de nombreuses interventions médicales, grâce à sa capacité à visualiser des phénomènes dynamiques dans le corps humain en temps réel et à un caractère minimalement invasif. En raison de la présence obligatoire de personnel médical dans la proximité immédiate du patient, ces interventions posent un problème unique pour la radioprotection, impliquant que les radiologues et cardiologues interventionnels sont parmi les travailleurs professionnellement exposés aux rayonnements ionisants qui reçoivent les doses efficaces les plus élevées. En outre, de nombreuses autres spécialités médicales ont repris la fluoroscopie comme principal outil de travail. En conséquence, le manque de connaissances et d’une formation spécifique à l’utilisation des rayonnements ionisants est un défi qui peut être difficile à résoudre au niveau institutionnel. En outre, de nombreuses innovations technologiques ont été introduites afin de surveiller les doses délivrées aux patients (p. ex. des logiciels de collecte automatiques des doses), afficher l'exposition du personnel en temps réel, ou encore réduire la dose au patient en appliquant de fortes filtrations du faisceau primaire et en améliorant simultanément la « qualité d'image » en appliquant des traitements d’image en ligne, comme c'est le cas pour la reconstruction itérative des images en tomodensitométrie. Pour la qualité de l'image, il n'y a par conséquent plus de lien direct entre l'exposition du patient et la qualité de l'image – sans parler de l’absence-même de définition adéquate de la qualité d’image. Ainsi, les mesures physiques traditionnellement utilisées pour sa mesure, déjà peu appropriées pour une optimisation clinique pertinente, ne sont plus applicables. Durant cette recherche, nous avons testé plusieurs de ces innovations et tenté d’en déterminer les forces et faiblesses. Tout d'abord, nous avons effectué une revue de la littérature afin de résumer l'actuel état de l'art dans les procédures sous guidage fluoroscopique. Deuxièmement, nous avons décrit les moyens d'évaluer la dose au patient et le risque radiologique associé, ainsi que la façon de corriger les indicateurs dosimétriques en fonction de la corpulence du patient, et avons effectué une analyse spécifique de la prise en charge de la patiente enceinte. Troisièmement, nous avons décrit l'exposition et les risques du personnel médical, principalement en nous concentrant plus avant sur l’irradiation du cristallin et du cerveau (deux organes généralement pas protégés au cours de l’intervention, et pour lesquels plusieurs études récentes ont montré que le risque radiologique avait été sous-estimé), ainsi qu'une description précise de l'efficacité des lunettes plombées. Quatrièmement, nous avons proposé que la qualité d'image devienne la pierre angulaire de l'optimisation clinique. Pour cela, nous avons réalisé une étude de faisabilité de l'utilisation d'un modèle d’observateur mathématique dans des conditions d’acquisition statiques et dynamiques, visant à qualifier la qualité d'image sur la base d'une tâche de détection binaire pertinente d’un point de vue clinique. Enfin, notre conclusion souligne les limites actuelles de notre approche et propose une série de questions à développer, dont la résolution pourrait avoir un impact significatif sur la gestion globale de la dose et de la qualité de l'image. = Over the last decades, fluoroscopy has become a widely-used diagnostic and therapeutic X-ray imaging technique for numerous medical procedures thanks to its capability of displaying dynamic phenomena in the human body in real time and minimally-invasive nature. Due to the customary presence of medical staff in the immediate vicinity of the patient, interventional procedures pose a unique radiation protection problem, implying that interventional radiologists and cardiologists are among the professionally-exposed to ionising radiation workers who receive the highest effective doses. In addition, many other medical specialties have taken up fluoroscopy as a central working tool. As a consequence, the lack of radiation awareness and specific training is a challenge that may be difficult to solve at the institutional level. Furthermore, many technical innovations have been introduced to either monitor patient doses (such as automatic dose-collection software solutions), display staff exposure in real time, or reduce patient dose by applying heavy beam filtrations and simultaneously enhancing “image quality” through on-line image post-processing, as is the case for iterative image reconstruction in computed tomography. For image quality, the consequence is that there is no straightforward link anymore between patient exposure and image quality – and not even a proper definition of image quality. Therefore, the physical metrics classically used for quality measurement, already flawed for pertinent clinical optimisation, are no longer applicable. For this research, we tested several of these innovations, and tried to pinpoint their strengths and weaknesses. First, we performed a literature review to summarise the current state-of-the-art in fluoroscopic procedure guidance. Secondly, we described the ways of assessing patient dose and radiological risk, as well as how to correct the dose indicators based on patient body habitus, and performed a dedicated analysis of the management of the pregnant patient. Thirdly, we described the exposure and risks of the medical staff during interventional procedures, mainly by concentrating more thoroughly on eye lens and brain dose (two organs that are usually not protected during interventional procedures, and for which several recent studies have shown that the risk had been previously underestimated), as well as a precise description of the efficiency of leaded glasses. Fourthly, we proposed that the image quality becomes the cornerstone of clinical optimisation. For this purpose, we performed a feasibility study of the use of a mathematical model observer in static and dynamic imaging conditions, aiming at grading image quality on the basis of a clinically relevant binary detection task. Finally, we concluded by pointing out the current limitations of our approach, and proposed a series of follow-up questions whose resolution may have a significant impact on the overall management of patient and staff dose and image quality

Combined Ramp and Squeeze at the Large Hadron Collider

In the first two years of operation of the CERN Large Hadron Collider (LHC), the betatron squeeze has been carried out at constant flat top energy of 3.5 TeV. Squeeze setting functions are separated from the energy ramp functions. This ensured a maximum flexibility during commissioning because stopping at all intermediate optics for detailed measurements was possible. In order to then improve the efficiency of the operational cycle, combining the ramp and squeeze has been considered. In this paper, the various possibilities for this scheme are reviewed, and proposals of optimized operational cycles with combined ramp and squeeze are presented for different energies. Results of beam tests are also discussed

Medical physicists' implication in radiological diagnostic procedures: results after 1 y of experience

Since January 2008—de facto 2012—medical physics experts (MPEs) are, by law, to be involved in the optimisation process of radiological diagnostic procedures in Switzerland. Computed tomography, fluoroscopy and nuclear medicine imaging units have been assessed for patient exposure and image quality. Large spreads in clinical practice have been observed. For example, the number of scans per abdominal CT examination went from 1 to 9. Fluoroscopy units showed, for the same device settings, dose rate variations up to a factor of 3 to 7. Quantitative image quality for positron emission tomography (PET)/CT examinations varied significantly depending on the local image reconstruction algorithms. Future work will be focused on promoting team cooperation between MPEs, radiologists and radiographers and on implementing task-oriented objective image quality indicator

PATIENT EXPOSURE OPTIMISATION THROUGH TASK-BASED ASSESSMENT OF A NEW MODEL-BASED ITERATIVE RECONSTRUCTION TECHNIQUE

The goal of the present work was to report and investigate the performances of a new iterative reconstruction algorithm, using a model observer. For that, a dedicated low-contrast phantom containing different targets was scanned at four volume computed tomography dose index (CTDIvol) levels on a Siemens SOMATOM Force computed tomography (CT). The acquired images were reconstructed using the ADMIRE algorithm and were then assessed by three human observers who performed alternative forced choice experiments. Next, a channelised hotelling observer model was applied on the same set of images. The comparison between the two was performed using the percentage correct as a figure of merit. The results indicated a strong agreement between human and model observer as well as an improvement in the low-contrast detection when switching from an ADMIRE strength of 1-3. Good results were also observed even in situations where the target was hard to detect, suggesting that patient dose could be further reduced and optimised

Combined energy ramp and beta star squeeze at the Large Hadron Collider

In 2011, the LHC has exceeded expectations by producing a massive amount of data for the experiments. The turnaround time being a bottleneck in terms of operational efficiency, its duration has to be minimized. This is done by combining two already optimized steps, the energy ramp and the betatron squeeze. The aim of this feasibility study will be to generate a set of power converter settings combining both steps and validate them using dry-runs and beam tests