There is a national drive towards establishing reference doses for radiological procedures with the aim of optimizing patient doses. Furthermore, the establishment of diagnostic reference level doses became a legal requirement for all hospitals on 13 May 2000. However, to date there are little published data on patient radiation doses from fluoroscopic procedures during orthopaedic surgery. Data relating to patient dose for 492 patients undergoing fluoroscopic examinations during a range of surgical orthopaedic procedures in 1997-1998 have been analysed. Median dose-area product (DAP) readings and interquartile ranges for a variety of common fluoroscopic orthopaedic procedures are presented. In general, the median DAP for procedures on limbs and extremities was quite low (0.04-1.62 Gy cm2), with screening times in the range 0.2-2.0 min, whilst for procedures involving the hips and spine the median DAP was considerably higher (0.4-10.2 Gy cm2), although overall screening times were similar, in the range 0.2-1.4 min. Approximate effective doses have been estimated. For procedures involving the limbs and extremities, the effective dose was generally less than 10 microSv, and for procedures involving the hips and spine it was found that the effective dose could rise to about 1 mSv. Collective doses for each procedure have been calculated to inform prioritization of procedures for local dose reduction strategies.
Dose-area product (DAP) measurements were made for 21 patients undergoing a modified barium swallow. The procedures were performed by a radiologist and speech and language therapist, to characterize swallowing disorders in patients with head or spinal injury, stroke, other neurological conditions or simple globus symptoms, in order to inform feeding strategies. The DAP values were used to estimate effective dose to the patient, in order to provide a measure of the radiation risk associated with the procedure. Whole body doses to operators, together with equivalent doses to extremities and eyes were also measured to inform the employer's risk assessment. Median DAP for the series was 3.5 (3.1-5.2) Gycm(2) with a corresponding effective dose to the patient of 0.85 (0.76-1.3) mSv, and a low associated risk, mainly of cancer induction, of about 1 in 16 000. The organ receiving the greatest dose was the thyroid, with a calculated median equivalent dose of 13.9 (12.3-20.7) mSv. Median screening time was 3.7 (2.5-4.3) min. Mean operator doses were 0.5 mSv equivalent dose (eyes), 0.9 mSv (extremities), and less than 0.3 mSv whole body dose. Extrapolating for an annual workload of 50 patients per year, this work will lead to annual operator doses of less than 0.6 mSv whole body dose, and approximately 1 mSv equivalent dose (eyes) and 1.8 mSv (extremities), against corresponding legal dose limits of 20 mSv, 150 mSv and 500 mSv, respectively.
The effects of prostheses on radiotherapy treatment planning are discussed. The compositions of commonly used materials are tabulated. Sample plots show the size of perturbations produced by typical absorbers at 8 MV. A technique for estimating the density of a prosthesis in a patient is demonstrated and the effects of prostheses on representative radiotherapy plans are illustrated.
CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures. It contributed an estimated 20% to the collective effective dose to the UK population from medical X-rays in 1990, rising to an estimated 40% in 1999. Tremendous national effort has been expended in reducing patient doses from other radiological procedures with considerable success, but much of the collective dose reduction achieved has been offset by a corresponding increase in the collective dose from CT. Over a period of about 2 years, following the installation of a helical CT scanner, CT scan parameters in this hospital have been adjusted with the aim of working towards optimization of image quality and patient dose. A 33% reduction in annual collective effective dose has been achieved, from about 16.5 manSv to 11 manSv. However, despite this dose reduction, the annual collective effective dose to our sub-population is 2.8 times the value 9 years ago. The increase is almost entirely the result of an increased application of CT; 6149 examinations per annum in 1999 compared with 2210 in 1991. The crucial importance of reducing patient doses from this modality is discussed. Indicative effective doses and image noise values are presented for examination protocols approaching optimization.
Calibration of patient dose monitoring devices in diagnostic radiology has become increasingly important in the light of new legislation that requires monitoring of patient dose against local and national diagnostic reference levels. An investigation was conducted into the long-term stability of 41 dose-area product (DAP) meters over a period of approximately 5 years, to assess the suitability of an annual calibration regimen. For DAP meters fitted to overcouch X-ray tubes, 77% of calibrations were within 10%, whilst for undercouch tubes only 50% of calibrations were within 10%. These findings suggest that annual calibration may be too infrequent. Suitable calibration frequencies for different clinical workloads are discussed.
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