With typical reported workloads, radiation doses to eye lenses may exceed the threshold for deterministic effects (ie, lens opacities or cataracts) after several years of work if radiation protection tools are not used.
This report describes occupational radiation doses of interventional cardiologists over 15 years and assesses action undertaken to optimize radiation protection. Personal dosimetry records of nine staff cardiologists and eight interventional cardiology fellows were recorded using personal dosemeters worn over and under their lead aprons. The hospital in which this study was conducted currently performs 5000 cardiology procedures per year. The hospital has improved its facilities since 1989, when it had two old-fashioned theatres, to include four rooms with more advanced and safer equipment. Intensive radiation protection training was also implemented since 1989. Initially, some individual dose values in the range of 100-300 mSv month(-1), which risked exceeding some regulatory dose limits, were measured over the lead apron. Several doses in the range of 5-11 mSv month(-1) were recorded under the apron (mean = 10.2 mSv year(-1)). During the last 5 years of the study, after the implementation of the radiation protection actions and a programme of patient-dose optimization, the mean dose under the apron was reduced to 1.2 mSv year(-1). Current mean occupational doses recorded under the lead apron are 14% of those recorded during 1989-1992 and those recorded over the apron are 14-fold less than those recorded during 1989-1992. The regulatory dose limits and the threshold for lens injuries might have been exceeded if radiation protection facilities had not been used systematically. The most effective actions involved in reducing the radiation risk were training in radiation protection, a programme of patient-dose reduction and the systematic use of radiation protection facilities, specifically ceiling-suspended protective screens.
The aim of this work has been to determine typical occupational dose levels in interventional radiology and cardiology installations and to relate doses to patient and occupational dosimetry through the dose-area product. An experimental correlation between environmental dosimetric records and dose-area products in the centres studied was established. The study covered a sample of 83 procedures performed by 10 specialists in six laboratories. The radiologists and cardiologists monitored wore nine thermoluminescent chips next to eyes, forehead, neck, hands, left shoulder, left forearm and left arm during each single procedure. In addition, direct reading electronic devices for environmental dosimetry were placed in the C-arm of the X-ray system, to estimate roughly the occupational radiation risk level. Typical shoulder doses derived from electronic dosimetry range between 300 and 500 muSv per procedure, assuming no lead protective screens were used. Using these values and patient dose-area data from two laboratories, averaged ratios of 84 and 120 muSv per 1000 cGy cm2 are obtained for cardiology procedures. Finally, occupational dose reductions of approximately 20% when using highly filtered X-ray beams with automatic tube potential (kV) reduction (available in some facilities), and by a factor of about three when using ceiling mounted screens, have been found.
The prediction of liquefaction and resulting displacements is a major concern for earth structures located in regions of moderate to high seismicity. Conventional procedures used to assess liquefaction commonly predict the triggering of liquefaction to depths of 50 m or more. Remediation to prevent or curtail liquefaction at these depths can be very expensive. Field experience during past earthquakes indicates that liquefaction has mainly occurred at depths less than about 15 m, and some recent dynamic centrifuge model testing initially appeared to confirm a depth or confining-stress limitation on the occurrence of liquefaction. Such a limitation on liquefaction could greatly reduce remediation costs. In this paper an effective stress numerical modeling procedure is used to assess these centrifuge tests. The results indicate that a lack of complete saturation and densification at depth arising from the application of the high-acceleration field are largely responsible for the apparent limitation on liquefaction at depth observed in some centrifuge tests.Key words: liquefaction, dynamic centrifuge modeling, numerical modeling, depth limitation.
Coronary angiography and percutaneous transluminal coronary angioplasty procedures performed in four different facilities were monitored in the present study by measuring maximum skin dose, dose-area product and other operational parameters. Radiographic slow film, thermoluminescent dosemeters and transmission ion chambers were used to measure dose related quantities. Values of 107-711 mGy for maximum skin dose and 27.3-370.6 Gy cm2 for dose-area product were found, together with cumulative skin dose estimates of 110-3706 mGy. A discussion of the relationship of measured dose-area product and skin dose values is made using a field concentration factor defined as a way to interpret the findings. No general correlation was observed between dose-area product and maximum skin dose. Cumulative skin dose estimates throughout a procedure should be discarded as a realistic method for assessing deterministic risk in cardiology procedures. Slow film in addition to thermoluminescent dosemeters for measurement of maximum skin dose is a good alternative, especially for complex interventional procedures. For repeated procedures, combining film and dose-area product monitoring favours optimization of radiation protection for the patient.
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