Biomedical subjects
Publications and source records attributed to B F Wall.
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Digital fluorography offers several advantages over conventional radiographic systems. The general expectation of digital equipment has been of a lower radiation dose to the patient. A series of dose-area product measurements on two digital sets during barium meal and barium enema examinations has shown that this expectation is not necessarily correct, particularly when the dose from the fluoroscopic part of the examination is considered. Users of digital fluorography sets are advised to check the performance of their equipment by suitable dose measurements.
The International Commission on Radiological Protection has recommended the use of a new dose quantity "effective dose". The doses to 22 organs of the human body are required for a formal calculation of this quantity. This paper shows that a quick estimate of the effective dose received by a patient from a barium meal or a barium enema can be made by multiplying the measured dose-area product for the complete examination by an appropriate conversion coefficient. Despite the varied techniques used for barium examinations, such an estimate is unlikely to be in error by more than 25%.
Data relating to patient dose have been acquired for enteroclysis examinations (small bowel enemas) performed at the John Radcliffe Hospital, Oxford, on 23 adult patients. Dose-area products, fluoroscopy times and the number of radiographs taken are used to compare the examination procedure at the John Radcliffe Hospital with enteroclysis and barium follow-throughs performed elsewhere. The mean dose-area product for the 23 examinations was 6.8 Gy cm2 and the mean effective dose was estimated to be 1.5 mSv. These doses are intermediate between those arising from barium meals and barium enemas performed in the same room.
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Surveys have been conducted in Britain, France and Italy, using essentially the same techniques, to establish the level of provision of diagnostic radiology services, the frequency of X-ray examinations and examples of the radiation doses delivered to patients in each country. Different national strategies for conducting some types of X-ray examination and marked differences in the general availability of this aspect of health care indicate that the justification and optimization of medical exposures is not interpreted in the same way in these countries.
A collaborative survey between the National Radiological Protection Board and the Hospital Physicists' Association has been conducted to ascertain current levels of exposure for patients undergoing 10 routine types of X-ray examination in England. The main part of this study consisted of measurements on nearly 3200 patients attending 20 randomly selected English hospitals. The energy imparted to each patient was determined from a measurement of the total exposure-area product for the examination. In addition, thermoluminescent dosemeters were attached to the patient's skin to enable the derivation of doses to the major radiosensitive organs, either directly or using appropriate conversion factors calculated for a mathematical phantom by a Monte Carlo technique. Histograms are presented showing the wide distributions often observed in the doses for each type of examination. Mean values of exposure-area product, energy imparted to the patient, entrance skin dose per film and organ dose are reported, together with coefficients of variation. Comparison of the results with those from similar surveys in the UK and abroad is complicated by inconsistencies in the reporting of such data, but substantial differences are sometimes apparent, particularly for the estimates of organ doses. The present measurements will provide a useful baseline for future measurements and will be used to evaluate the collective dose to the population from medical exposures and the radiation risks from the various radiological procedures.
A survey of the extent of diagnostic and therapeutic nuclear medicine procedures in the UK has been conducted, and information collected on the types of imaging equipment employed and the typical activities of radiopharmaceuticals administered to patients. A total of 380,000 administrations took place in 1982, corresponding to approximately 6.8 per thousand head of population. 84% were imaging investigations, 13% were non-imaging diagnostic procedures and about 3% were for therapy. Bone scans accounted for 25% of all procedures and 99Tcm was the radionuclide of choice for 75% of investigations. Gamma cameras are superseding rectilinear scanners and most are being purchased together with dedicated image processing computers. Their average annual workload is 922 patients per year. There was considerable variation between the typical administered activities reported by different hospitals for the same procedure, and in some cases the figures reported exceeded the maximum usual activities recommended by the Administration of Radioactive Substances Advisory Committee.
The mean energy imparted to the patient has been proposed as a practical quantity which may be useful for assessing somatic risk in X-ray diagnostic radiology. A technique is described for estimating energy imparted during most common X-ray examinations of the trunk or complete head from a measurement of exposure-area product conveniently provided by the Diamentor transmission ionisation chamber. The necessary energy imparted calibration for the Diamentor has been deduced from consideration of incident spectral energy fluence and Monte Carlo calculations of the fraction of total beam energy imparted to mathematical phantoms representing the patient. The relationship between energy imparted and exposure-area product depends primarily on the applied potential and total filtration of the X-ray beam, and to a lesser extent on voltage waveform and X-ray target angle. Direct measurements of energy imparted to an Alderson Rando phantom for a range of irradiation conditions provided an excellent verification of the technique developed. Using the energy imparted per exposure-area product factors presented, overall uncertainties of less than +/- 15% and +/- 20% should be possible for measurements of energy imparted during examinations of the trunk and head respectively using the Diamentor.
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The continued expansion of dental radiology in Britain up to the end of 1981 is demonstrated, with a rate of increase much in excess of that seen for general medical radiography. Of the total of 7.8 X 10(6) dental X-ray examinations undertaken in 1981 approximately 6.7 X 10(6) were intra-oral, 1.5 X 10(5) were extra-oral and 9.1 X 10(5) were pantomographic. Weighted dose equivalents for typical examinations in each of these categories were calculated using specific weighting factors for the important "remainder" organs. Values of 20 muSv, 30 muSv and 80 muSv were obtained for intra-oral, extra-oral and pantomographic techniques, respectively, corresponding to risks of fatal malignancy of 0.33, 0.5 and 1.3 per million. The estimated collective weighted dose equivalent of 212 man Sv to the population of Britain from the current level of dental radiology is predicted to result in no more than about three extra cases of fatal cancer when the age- and sex-related opportunity for manifestation of radiation-induced cancers is taken into account.
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The thermoluminescence properties of three different preparations of lithium borate have been studied with specific reference to their use in medical dosimetry. The properties of lithium borate powder doped with copper make it more attractive for low dose measurements than the more conventional phosphor doped with manganese. However, the energy response of the copper-doped material was not quite so suitable as that of the manganese-doped material for measuring doses to tissue at photon energies below 100 keV. It also exhibited appreciable light induced fading.
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