Thickness accuracy of virtually designed patient-specific implants for large neurocranial defects.

The combination of computer-aided design (CAD) techniques based on computed tomography (CT) data to generate patient-specific implants is in use for decades. However, persisting disadvantages are complicated design procedures and rigid reconstruction protocols, for example, for tailored implants mimicking the patient-specific thickness distribution of missing cranial bone. In this study we used two different approaches, CAD- versus thin-plate spline (TPS)-based implants, to reconstruct extensive unilateral and bilateral cranial defects in three clinical cases. We used CT data of three complete human crania that were virtually damaged according to the missing regions in the clinical cases. In total, we carried out 132 virtual reconstructions and quantified accuracy from the original to the generated implant and deviations in the resulting implant thickness as root-mean-square error (RMSE). Reconstructions using TPS showed an RMSE of 0.08-0.18 mm in relation to geometric accuracy. CAD-based implants showed an RMSE of 0.50-1.25 mm. RMSE in relation to implant thickness was between 0.63 and 0.70 mm (TPS) while values for CAD-based implants were significantly higher (0.63-1.67 mm). While both approaches provide implants showing a high accuracy, the TPS-based approach additionally provides implants that accurately reproduce the patient-specific thickness distribution of the affected cranial region.

Radiation risk and protection of patients in clinical SPECT/CT.

Clinical studies have demonstrated that hybrid single photon emission computed tomography (SPECT)/CT for various diagnostic issues has an added value as compared to SPECT alone. However, the combined acquisition of functional and anatomical images can substantially increase radiation exposure to patients, in particular when using a hybrid system with diagnostic CT capabilities. It is, therefore, essential to carefully balance the diagnostic needs and radiation protection requirements. To this end, the evidence on health effects induced by ionizing radiation is outlined. In addition, the essential concepts for estimating radiation doses and lifetime attributable cancer risks associated with SPECT/CT examinations are presented taking into account both the new recommendations of the International Commission on Radiological Protection (ICRP) as well as the most recent radiation risk models. Representative values of effective dose and lifetime attributable risk are reported for ten frequently used SPECT radiopharmaceuticals and five fully diagnostic partial-body CT examinations. A diagnostic CT scan acquired as part of a combined SPECT/CT examination contributes considerably to, and for some applications even dominates, the total patient exposure. For the common SPECT and CT examinations considered in this study, the lifetime attributable risk of developing a radiation-related cancer is less than 0.27 %/0.37 % for men/women older than 16 years, respectively, and decreases markedly with increasing age at exposure. Since there is no clinical indication for a SPECT/CT examination unless an emission scan has been indicated, the issue on justification comes down to the question of whether it is necessary to additionally acquire a low-dose CT for attenuation correction and anatomical localization of tracer uptake or even a fully diagnostic CT. In any case, SPECT/CT studies have to be optimized, e.g. by adapting dose reduction measures from state-of-the-art CT practice, and exposure levels should not exceed the national diagnostic reference levels for standard situations.

Simulation study on the conversion between CT and CBCT dose quantities via the effective dose.

In recent years, cone-beam computed tomography (CBCT) has been used in many imaging tasks traditionally performed by computed tomography (CT). This has created challenges for dosimetry, as the dose quantities in CBCT and CT, i.e. the dose-area product (DAP) and dose-length product (DLP), are not mutually convertible. Convertibility would be desirable to compare doses in similar clinical studies performed using CT or CBCT and ultimately for the application of diagnostic reference levels (DRLs). In this work, the conversion of the DAP into the DLP and vice versa via the effective doseEis investigated with the aim of finding common diagnostic reference levels. The dose calculation was performed using Monte Carlo simulations for scan regions with imaging tasks, which can be carried out either with CT or CBCT scanners. Four regions in the head and four in the trunk were chosen. The calculations resulted in conversion coefficientsk=DAPDLPof 30(4) cm for the cranium, 22(4) cm for the facial bones, 24(2) cm for the paranasal sinuses, 18(2) cm for the cervical spine, 78(12) cm for the thorax, 85(13) cm for the upper abdomen, 57(6) cm for the lumbar spine and 70(12) cm for the pelvis.

Pediatric computed tomography doses in Germany from 2016 to 2018 based on large-scale data collection.

PURPOSE: Accumulating evidence from epidemiological studies that pediatric computed tomography (CT) examinations can be associated with a small but non-zero excess risk for developing leukemia or brain tumor highlights the need to optimize doses of pediatric CT procedures. Mandatory dose reference levels (DRL) can support reduction of collective dose from CT imaging. Regular surveys of applied dose-related parameters are instrumental to decide when technological advances and optimized protocol design allow lower doses without sacrificing image quality. Our aim was to collect dosimetric data to support adapting current DRL to changing clinical practice. METHOD: Dosimetric data and technical scan parameters from common pediatric CT examinations were retrospectively collected directly from Picture Archiving and Communication Systems (PACS), Dose Management Systems (DMS), and Radiological Information Systems (RIS). RESULTS: We collected data from 17 institutions on 7746 CT series from the years 2016 to 2018 from examinations of the head, thorax, abdomen, cervical spine, temporal bone, paranasal sinuses and knee in patients below 18 years of age. Most of the age-stratified parameter distributions were lower than distributions from previously-analyzed data from before 2010. Most of the third quartiles were lower than German DRL at the time of the survey. CONCLUSIONS: Directly interfacing PACS, DMS, and RIS installations allows large-scale data collection but relies on high data-quality at the documentation stage. Data should be validated by expert knowledge or guided questionnaires. Observed clinical practice in pediatric CT imaging suggests lowering some DRL in Germany is reasonable.

Handling of Incidents in the Clinical Application of Ionizing Radiation in Diagnostic and Interventional Radiology - a Multi-center Study. / Umgang mit unbeabsichtigten Expositionen bei medizinischen Anwendungen ionisierender Strahlung in der Röntgendiagnostik und interventionellen Radiologie ­ eine Multi-Center-Studie.

PURPOSE: According to the German legislation and regulation of radiation protection, i. e. Strahlenschutzgesetz und Strahlenschutzverordnung (StrlSchG and StrlSchV), which came into force on 31st December 2018, significant unintended or accidential exposures have to be reported to the competent authority. Furthermore, facilities have to implement measures to prevent and to recognize unintended or accidental exposures as well as to reduce their consequences. We developed a process to register incidents and tested its application in the framework of a multi-center-study. MATERIALS AND METHODS: Over a period of 12 months, 16 institutions for x-ray diagnostics and interventions, documented their incidents. Documentation of the incidents was conducted using the software CIRSrad, which was developed, released for testing purposes and implemented in the frame of the study. Reporting criteria of the project were selected to be more sensitive compared to the legal criteria specifying "significant incidents". Reported incidents were evaluated after four, eight, and twelve months. Finally, all participating institutions were interviewed on their experience with the software and the correlated effort. RESULTS: The rate of reported incidents varied between institutions as well as between modalities. The majority of incidents were reported in conventional x-ray imaging, followed by computed tomography and therapeutic interventions. Incidents were attributed to several different causes, amongst others to the technical setup and patient positioning (19 %) and patient movement or insufficient cooperativeness of the patient (18 %). Most incidents were below corresponding thresholds stated in StrlSchV. The workload for documenting the incidents was rated as appropriate. CONCLUSION: It is possible to monitor and handle incidents complient with legal requirements with an acceptable effort. The number of reported incidents can be increased by frequent trainings on the detection and the processing workflow, on the software and legal regulation as well as by a transparent error handling within the institution. KEY POINTS: · The software CIRSrad was developed to enable the present study and as prototype platform for a future radiological incident management system.. · 586 exceedances of thresholds were recorded by 16 facilities in a period of one year.. · Frequent trainings of all users increase the number of reported cases.. CITATION FORMAT: · Müller BS, Singer J, Stamm G et al. Handling of Incidents in the Clinical Application of Ionizing Radiation in Diagnostic and Interventional Radiology - a Multi-center Study. Fortschr Röntgenstr 2022; 194: 400 - 408.

[Prenatal Radiation Exposure in Nuclear Medicine]. / Pränatale Strahlenexposition aus nuklearmedizinischer Indikation.

Radiation exposure from nuclear medicine procedures during pregnancy may cause uncertainty among patients and medical professionals. In 2019, the German Society of Medical Physics (DGMP) and the German Society of Radiology (DRG) published a fully revised version of the report "Prenatal Radiation Exposure Arising from Medical Indication, Dose Calculation, Conclusions for Physicians and Pregnant Women". This report offers a basis for dose calculation and determination of radiation exposure to the unborn. This review summarizes the most notable general adaptions made in the report's newest version and specifically points out the changes relevant to the field of nuclear medicine.The DGMP report provides physicians and medical physicists with means to estimate prenatal radiation exposure to the unborn conservatively, in a prompt and comprehensible approach. The rapidly evolving field of indications in nuclear medicine and radiology gave rise to the initiative of profoundly revising the previous version of the report from 2002. It now accounts for the extended range of devices, nuclear medicine hybrid imaging and radiotracers recently introduced. The most extensive change is a shift from the former 3-step-concept for the dose calculation to a 2-step-concept. In diagnostic nuclear medicine the first step comprises a conservative approximation of radiation exposure on the basis of current diagnostic reference levels (DRL). If exposure is assessed to be below 20 mSv, risk to the unborn child is sufficiently low, no further approaches are considered necessary. If calculated doses exceed 20 mSv, for diagnostic studies without existing DRL or in case of radionuclide therapies step 2 requires dose calculation based on administered activity and the stage of pregnancy.The DGMP report on prenatal radiation exposure offers valuable guidance for physicians and medical physicists in the field of nuclear medicine. The calculation concept provides an important basis to estimate radiation exposure to the unborn. Its extensive revision in 2019 accounts for recent scientific and technical developments and a reform of the stepwise approach to dose estimation.

Prenatal radiation exposure in diagnostic and interventional radiology. / Pränatale Strahlenexposition in der diagnostischen und interventionellen Radiologie.

BACKGROUND: The exposure of a pregnant woman to X-rays is an event that can cause uncertainty for all concerned. This review provides guidance on how to assess such a situation and how to determine the dose to the unborn child. In general, the use of X-rays in pregnant women in radiology should be avoided. If possible, alternatives should be used, or examinations postponed to a time after the pregnancy. This review gives a summary of the procedure for determining the radiation exposure of a pregnant woman. METHOD: Based on the previous report of 2002 and the literature on prenatal radiation exposure published thereafter, the DGMP/DRG report on the procedure for the assessment of prenatal radiation exposure was adapted to the current state of science and technology. RESULTS: Typically, only relatively low radiation exposures of less than 20 mSv occur for the unborn child in X-ray diagnostics in the vast majority of cases. At these dose level the additional risk of damage to the embryo or fetus caused by the radiation is low and therefore only a rough conservative estimate using tabulated values are made. Only in a few types of examination (CT and interventional radiology) higher doses values might occur in the uterus. Instead of dose estimates (step 1 in the two-step model) in these cases the calculation of dose (step 2) are required and further action by the physician may be necessary. CONCLUSIONS: During the assessment, it is useful to initially use simple conservative estimation procedures to quickly determine whether a case falls into this large group less than 20 mSv, where there is a very low risk to the unborn child. If this is the case, the pregnant woman should be informed immediately by the doctor who performed the examination/treatment. This avoids a psychological burden on the patient. The DGMP/DRG report suggests a relatively simple, clearly structured procedure with advantages for all parties involved (physician, medical physics experts, MTRA and patient). KEY POINTS: · The DGMP/DRG report on prenatal radiation exposure describes the procedure for calculating radiation exposures and the associated risks for the unborn child.. · Using the two-step model, only a simple assessment based on the first step is necessary for most prenatal radiation exposures.. · With the given tables it is possible to estimate individual risks for the unborn child taking into account the radiation exposure.. · Only in the rare case that the first estimate results in a uterine dose larger 20 mSv a more accurate calculation is necessary.. CITATION FORMAT: · Fiebich M, Block A, Borowski M et al. Prenatal radiation exposure in diagnostic and interventional radiology. Fortschr Röntgenstr 2021; 193: 778 - 786.

Considerations concerning the use of counting active personal dosimeters in pulsed fields of ionising radiation.

Active personal electronic dosimeters (APDs) exhibit limitations in pulsed radiation fields, which cannot be overcome without the use of new detection technology. As an interim solution, this paper proposes a method by which some conventional dosimeters can be operated in a way such that, based on the basic knowledge about the pulsed radiation field, any dosimetric failure of the dosimeter is signalised by the instrument itself. This method is not applicable to all combinations of APD and pulsed radiation field. The necessary requirements for the APD and for the parameters of the pulsed radiation field are given in the paper. Up to now, all such requirements for APDs have not been tested or verified in a type test. The suitability of the method is verified for the use of one APD used in two clinical pulsed fields.