Failure modes in stereotactic radiosurgery. A narrative review.

OBJECTIVES: Stereotactic radiosurgery (SRS) refers to an advanced radiotherapy technique that requires a high level of precision and accuracy and a flawless workflow. Failures within the SRS process can lead to serious consequences due to high doses delivered per treatment. This narrative review aimed to identify the riskiest failure modes (FMs) and the stages at which they occur in the SRS process, as well as the strategies applied to mitigate the risks. It was based on the analysis of published failure mode and effects analysis (FMEA) data. KEY FINDINGS: From the literature search in PubMed and Scopus, 7 articles met the eligibility criteria for inclusion in the qualitative synthesis. In total, 9 radiotherapy departments conducted FMEA in the SRS process. 4 of them were community hospitals and 5 were academic centers. Overall, 54 high-risk FMs were identified with treatment planning (FMs: 18), treatment delivery (FMs: 12), consultation and patient registration (FMs: 10) being the riskiest stages. 10 FMs were stereotactic specific, while the remaining 44 could be met in any radiotherapy technique. Failures associated with contouring, medical records review, target reirradiation, and patient positioning were mostly outlined. Risk mitigation strategies included timeouts, double-checks, checklists, training and changes in the working practice. CONCLUSION: Our review demonstrated that crucial FMs can occur in all SRS stages. Although generalisations were challenging, the FMs analysis provided a significant source of information about potential high risks and continuous improvement strategies that can be applied both in the SRS and other radiotherapy processes. IMPLICATIONS FOR PRACTICE: The results of this research will assist radiotherapy facilities in proactive risk management studies and will allow radiotherapy professionals to reflect on their practice and learn from others' experiences.

Characterization of breast calcification types using dual energy x-ray method.

Calcifications are products of mineralization whose presence is usually associated with pathological conditions. The minerals mostly seen in several diseases are calcium oxalate (CaC2O4), calcium carbonate (CaCO3) and hydroxyapatite (HAp). Up to date, there is no in vivo method that could discriminate between minerals. To this aim, a dual energy x-ray method was developed in the present study. An analytical model was implemented for the determination of the Calcium/Phosphorus mass ratio ([Formula: see text]). The simulation was carried out using monoenergetic and polyenergetic x-rays and various calcification thicknesses (100-1000 [Formula: see text]) and types (CaC2O4, CaCO3, HAp). The experimental evaluation of the method was performed using the optimized irradiation conditions obtained from the simulation study. X-ray tubes, combined with energy dispersive and energy integrating (imaging) detectors, were used for the determination of the [Formula: see text] in phantoms of different mineral types and thicknesses. Based on the results of the experimental procedure, statistical significant difference was observed between the different types of minerals when calcification thicknesses were 300 [Formula: see text] or higher.

The development of an exemplar e-module for the continuing professional development of European dentists.

AIM: To present the development of an exemplar e-module for dental continuing professional development (CPD) provided by dental schools and other dental educational providers. MATERIALS AND METHODS: The exemplar e-module covered the topic of 'Sterilisation and cross-infection control in the dental practice' as this is one of the most recommended topics for dental CPD in Europe. It was developed by a group of topic experts, adult learning and distance learning experts and a technical developer. Major concerns were pedagogy, interoperability, usability and cost reduction. Open-source material was used to reduce the cost of development. RESULTS: The e-module was pre-piloted in dental practitioners for usability and then evaluated by experts in the field and dental academics through an electronic questionnaire and an online presentation and discussion at the ADEE 2012 Special Interest Group on DentCPD-Lifelong learning. This facilitated refinement before final production. A Creative Commons License was implemented to ensure the developers' rights and facilitate wider distribution and access to CPD providers. DISCUSSION AND CONCLUSIONS: The e-module was developed according to well-defined pedagogical and technical guidelines for developing e-learning material for adult learners. It was structured to promote self-study by directing learners through their study, promoting interaction with the material, offering explanation and providing feedback. Content validity was ensured by extensive review by experts. The next step would be to expand the evaluation to practising dentists in various countries after relevant translations, and adaptations to local policies have been made.

Monte Carlo generated mammograms: development and validation.

We have developed a model using Monte Carlo methods to simulate x-ray mammography. All possible physical processes of interaction of x-rays with matter have been taken into account. A simplified geometry of the mammographic apparatus has been considered along with a software phantom of compressed breast. The phantom may contain inhomogeneities of various compositions and sizes. We have used this model to produce Monte Carlo mammograms under realistic conditions. The validation of the simulation includes both the modelling of physical processes and the production of Monte Carlo mammograms. The first part is accomplished by the demonstration of the coincidence between Monte Carlo and theoretical data, whereas the second is accomplished by the comparison of real mammograms, taken from irradiation of a simplified breast phantom that we have constructed, and Monte Carlo mammograms taken from simulation of the above phantom under the corresponding exposure conditions. The limitations of the model as well as the future use of Monte Carlo mammograms are discussed.

An experimental method to determine the effective luminescence efficiency of scintillator-photodetector combinations used in X-ray medical imaging systems.

The scintillator effective luminescence efficiency, which may be defined in terms of the scintillator's X-ray luminescence efficiency and the scintillator-photodetector spectral matching and geometrical configuration, was studied for various X-ray imaging applications. Four scintillator materials Gd2O2S:Tb, Y2O2S:Tb, ZnSCdS:Ag and CsI:Na were used to prepare test screens. They were evaluated in relation to various photodetectors used in X-ray imaging, such as radiographic films, photocathodes, and photodiodes. Effective luminescence efficiency was determined for a range of X-ray tube voltages (50-140 kVp) by measuring the light flux emitted per unit of incident exposure rate and the spectra of the light emitted by the four scintillators. Scintillator-photodetector combinations resulting in higher image brightness level were determined for different X-ray imaging systems. Findings indicate that CsI:Na is very efficient with orthochromatic radiographic films, Gd2O2S:Tb could be useful in conventional or digital fluoroscopy and in CT and ZnSCdS:Ag could be employed in some medium to low voltage digital radiography applications.

A computer model for the prediction of left epicardial coronary blood flow in normal, stenotic and bypassed coronary arteries, by single or sequential grafting.

This article describes a computer model for calculating left epicardial coronary blood pressure and flow waveforms of a right dominant coronary circulation. Using the geometry of 16 vascular branches and employing the one-dimensional Navier-Stokes equations the model allows for the prediction of blood pressure and flow patterns in normal and stenosed vessels. This model was also used to predict the haemodynamic changes observed after insertion of two single saphenous vein bypass grafts, as compared with the corresponding changes after insertion of a sequential (snake-like) saphenous graft. In normal vessels during systole and diastole, the pressure and the flow waveforms obtained showed patterns that correlate very well with the findings observed by other investigators using intracoronary flowmeter or Doppler velocimeter techniques. In coronary artery disease (90% stenoses in LAD and diagonal branch 1), the authors' main contribution is the reconfirmation of a previously described finding of systolic flow rises in stenotic segments. This finding seems to be an important compensatory mechanism, in contrast to normal coronary vessels, which maintain a mainly diastolic flow pattern. The introduction of single or sequential bypass grafts leads to pressure and flow restoration after graft revascularization. Besides this finding, the general concept of a diastolic flow restoration post-stenotically, in the previously decreased and systolic augmented flow areas, is also observed. The two revascularization methods were also compared with regard to their specific advantages, disadvantages and indications and were also extensively compared with several in vivo studies.

A model for image formation and image quality prediction in diagnostic radiology.

A computer program modelling the formation of radiological images and predicting values of physical quantities that determine diagnostic image quality has been developed. The quantities are the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) associated with signal to noise ratio (SNR). The program is based on mathematical models that describe the effects of x-ray interactions with the imaged object and the image detector as well as phenomena concerning the optical signal propagation within the detector. All data on x-ray effects necessary for computer calculations were derived from published work whereas optical data were determined in our laboratory using experimental techniques. Model predictions were compared with direct quality measurements performed after image formation, on the image itself.

Mitral valve replacement in a Jehovah's Witness with dextrocardia and situs solitus.

BACKGROUND AND AIMS OF THE STUDY: Dextrocardia with situs solitus and mitral valve insufficiency requiring surgical treatment is a rare presentation. Jehovah's Witnesses (JW), a specific religious group, deny any blood transfusion and for this reason the cardiac surgeon has to plan his operation well in advance, particularly in the case of adhesions from previous thoracic procedures. MATERIALS AND METHODS: A 50-year-old white female Jehovah's Witness with dextrocardia and situs solitus was referred for surgical treatment of massive mitral valve insufficiency of rheumatic etiology. Due to multiple adhesions from previous bilateral thoracotomies and the inverted position of the heart, cardiopulmonary bypass (CPB) was initiated with an aortic and a left common femoral vein cannulae. CPB was completed with an additional SVC cannula. The surgeon, having excellent exposure from the opposite side of the table, was able to perform a mitral valve replacement (MVR) with a 31 mm St. Jude Medical valve prosthesis, through a giant left atrium under moderate hypothermia and crystalloid cardioplegia. The operation was bloodless, with only two units of autotransfused blood being used with a postoperative hematocrit of 34%. RESULTS: The patient had an uneventful recovery and has been in NYHA class I for 24 months now. CONCLUSIONS: The case is presented for the safety of the approach, the excellent exposure from the left side in a dextrocardia case and the avoidance of blood transfusion in a Jehovah's patient.