Purpose: In image-guided radiotherapy, an artifact typically seen in axial slices of x-ray cone-beam computed tomography ͑CBCT͒ reconstructions is a dark region or "black hole" situated below the scan isocenter. The authors trace the cause of the artifact to scattered radiation produced by radiotherapy patient tabletops and show it is linked to the use of the offset-detector acquisition mode to enlarge the imaging field-of-view. The authors present a hybrid scatter kernel superposition ͑SKS͒ algorithm to correct for scatter from both the object-of-interest and the tabletop. Methods: Monte Carlo simulations and phantom experiments were first performed to identify the source of the black hole artifact. For correction, a SKS algorithm was developed that uses separate kernels to estimate scatter from the patient tabletop and the object-of-interest. Each projection is divided into two regions, one defined by the shadow cast by the tabletop on the imager and one defined by the unshadowed region. The region not shadowed by the tabletop is processed using the recently developed fast adaptive scatter kernel superposition ͑fASKS͒ method which employs asymmetric kernels that best model scatter transport through bodylike objects. The shadowed region is convolved with a combination of slab-derived symmetric SKS kernels and asymmetric fASKS kernels. The composition of the hybrid kernels is projection-angle-dependent. To test the algorithm, pelvis phantom and in vivo data were acquired using a CBCT test stand, a Varian Acuity simulator, and a Varian On-Board Imager, all of which have similar geometries and components. Artifact intensities and Hounsfield unit ͑HU͒ accuracies in the reconstructions were assessed before and after the correction. Results: The hybrid kernel algorithm provided effective correction and produced substantially better scatter estimates than the symmetric SKS or asymmetric fASKS methods alone. HU nonuniformities in the reconstructed pelvis phantom were reduced from 220 to 50 HU ͑i.e., 22%-5%͒. In the in vivo scans, the black hole artifact was reduced by up to 147 HU, a 73% improvement, and anatomical details in the prostate and rectum areas were made considerably more visible. Conclusions: Radiotherapy tabletops, which are generally flatter and larger than those used for diagnostic CT, can produce significant scatter-related artifacts. The proposed hybrid SKS algorithm accurately estimates scatter from both the object-of-interest and the patient tabletop, and resulting image uniformities and HU accuracies are greatly improved.

Országos Mentőszolgálat, Nyugat-dunántúli Régió Szentgotthárdi Mentőállomása, SzentgotthárdBevezetés: A megfelelő emelt szintű újraélesztési ismeretek elengedhetetlenek a sürgősségi ellátásban dolgozó szakemberek számára. Célkitűzés: A szerzők célja a magyarországi mentőtiszthallgatók felnőtt emelt szintű újraélesztési ismereteinek felmérése volt. Módszer: Felmérésüket a Pécsi Tudományegyetem Egészségtudományi Karának, a Semmelweis Egyetem Egészségtudományi Karának és a Debreceni Egyetem Egészségügyi Karának III. és IV. évfolyamos hallgatói körében végezték, saját szerkesztésű kérdőív segítségével. A mintába 97 fő hallgató került be (n = 97). Eredmények: A hallgatók átlagosan 67,79%-os eredménnyel teljesítettek a felmérésen. A férfiak és a nők összpontszá-mai között nem volt szignifikáns különbség (p = 0,725). Az alacsony életkor szignifikánsan javította az elért össz-pontszámokat (p = 0,003). A nappali tagozatosok szignifikánsan magasabb összpontszámot értek el, mint a levelező-sök (p = 0,004). Az egyes képzőintézmények hallgatóinak összpontszámai között szignifikáns különbség nem volt a felmérés során (p = 0,254). Következtetések: Célszerű lenne a mentőtisztképzésben a témával foglalkozó tantárgyak számát növelni, a számonkérések kritériumrendszerét szigorítani. A szerzők a jövőben indokoltnak tartanák a gyakorlati ismereteket vizsgáló felmérés elvégzését. Orv. Hetil., 2016, 157(37), 1476-1482. Kulcsszavak: újraélesztés, mentőtiszt, oktatás Adult advanced life support knowledge among ambulance officer/paramedic students in HungaryIntroduction: Resuscitation knowledge is necessery for emergency care workers. Aim: The aim of the authors was to investigate the advanced life support knowledge of paramedic students in Hungary. Method: The research has been executed at University of Pécs -Faculty of Health Sciences, Semmelweis University -Faculty of Health Sciences, and University of Debrecen -Faculty of Health Care. 97 students (n = 97) were involved in the study from third and fourth grades. Data were recorded with a self-fill-in questionnaire. Results: Average scores were 67.79%. There was no significant difference between women and men (p = 0.725). Younger age improved significantly scores (p = 0.003). Full-time students completed the test significantly better than part-time students (p = 0.004). There was no significant difference between the students from different locations (p = 0.254). Conclusions: It would be appropriate to increase the number of resuscitation courses and to tighten the exams. The authors propose that it would be reasonable to examine the students' practical skills.

Purpose: To characterize the CBCT performance of a new radiation therapy platform (Trilogy MX). Methods: An entirely new CBCT system has been developed for Trilogy MX. The new CBCT system differs from that of the On‐Board Imager® (OBI) in the use of a beam hardening filter, which reduces patient dose, and an improved reconstructor, which uses scatter correction algorithms to account for the x‐ray scatter caused by the cone‐beam geometry. Scans of Catphan® and electron density (Model 062A, CIRS) phantoms have been compared with OBI scans. Hounsfield unit (HU) accuracy was checked by changing the z scan length and the phantom diameters for pelvis (125kVp, 680mAs, 45cm dia.) acquisitions. The Catphan was imaged using doses ranging between 5–20mGy (CTDIw). Projections acquired using clinical OBI units were also reconstructed for comparison using the new reconstructor. Results: The new CBCT system has higher dose efficiency and higher HU accuracy. When the volume length is reduced from 160mm to 90mm or when the phantom diameter is reduced from 330mm to 180mm, the HU values measured for the same inserts differ by −190 to +80HU for OBI scans and by –60 to +50HU for Trilogy MX scans (for electron densities between 0.2 and 1.2). The contrast detectability of the 1% contrast objects in the Catphan phantom improves from 9mm to 4mm diameter when using the same CTDIw dose as OBI. Clinical images exhibit much better uniformity, elimination of streaks and better definition of the skin surface. Conclusions: The new reconstruction algorithm makes substantial improvements in CBCT image quality, reduces patient dose and increases HU accuracy. The new system produces CBCT images, which are much better suited to image guidance and which may be suitable for other tasks such as adaptive RT planning.

Purpose: An artifact typically seen in axial cone‐beam computed tomography (CBCT) reconstructions is a dark region or ‘black hole’ situated beneath the scan isocenter. We have traced the cause of the artifact to scattered radiation coming from the patient table. The artifact is most severe for offset‐detector scans and is especially significant in image‐guided radiotherapy (IGRT) where patient tables have flat tops and are larger than those used for diagnostic radiology. To address this problem, we have developed a hybrid scatter kernel superposition (SKS) method designed to correct for scatter from both the object‐of‐interest and the patient table. Method and Materials: The proposed algorithm uses separate kernels to estimate scatter from the patient table and the object‐of‐interest. For each projection image, the location of the shadow cast by the patient table on the imager is determined. The region not shadowed by the table is processed using asymmetric kernels that best model scatter transport through body‐like objects. The patient table region is processed using a combination of the asymmetric kernels and slab‐derived symmetric kernels. The composition of these hybrid kernels is projection‐angle dependent. To test the algorithm, pelvis phantom and patient data were acquired using the Varian On‐Board Imager (OBI) and processed. Artifact intensities and HU accuracies were assessed. Results: The hybrid kernel algorithm produced substantially better scatter estimates than previous SKS methods. HU non‐uniformities in the pelvis phantom were reduced from 97HU to 29HU. In the in vivo scan, the black hole artifact was reduced by 128HU and anatomical details were made more visible. Conclusions: Radiotherapy patient tables can produce significant scatter‐related artifacts. The proposed hybrid SKS algorithm effectively addresses this problem. Scatter from both the object‐of‐interest and the patient table was accurately estimated, and image uniformity and HU accuracy were greatly improved. Employees of Varian Medical Systems.

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